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Datil hot pepper (Capsicum chinense) has potential for increased production due to its unique, spicy flavor and aroma. However, few reports have been published related to postharvest handling characteristics. The purpose of this study was to determine the effect of harvest maturity on fruit quality under simulated commercial storage conditions. ‘Wanda’ datil pepper plants were grown hydroponically under protected culture. Fruit were harvested at yellow and orange maturity stages, placed in vented clamshell containers, and stored at 2, 7, or 10 °C for 21 days. Peppers harvested at yellow stage maintained greater quality than orange peppers during storage at all temperatures. Marketable fruit after 21 days for peppers harvested at the yellow stage was 94% (2 °C), 88% (7 °C), and 91% (10 °C); that for orange-stage peppers was 68%, 74%, and 82% for the same respective temperatures. No chilling injury (CI) symptoms were observed in these tests. Initial pepper moisture content was 90%, decreasing only slightly during 21 days of storage; weight loss ranged from 2% to 8%. Soluble solids content (SSC) was greater for peppers harvested at the orange stage (9.5%) than for those at yellow stage (7.8%). Neither harvest maturity nor storage temperature affected total titratable acidity (TTA; 0.13%) or pH (5.3). Respiration rate varied with temperature but not by harvest maturity and ranged from 12 to 25 mg·kg−1 per hour after 8 days of storage. Peppers harvested orange contained double the amount of total carotenoids as yellow fruit. Carotenoid content for yellow and orange peppers was 58 and 122 µg·g−1, respectively. Capsaicinoid content ranged from 1810 to 4440 µg·g−1 and was slightly greater for orange-harvested peppers. Datil peppers harvested at the yellow stage and stored in vented clamshell containers had better quality than peppers harvested at the orange stage after 21 days at 2 °C.

Diagnostic structural features for competence to form shoots were tested among sweet potato embryos by combining morphological image capture (using a computer vision system) with anatomical analyses (using light microscopy). Five major morphological variants (`perfect', `near perfect', `limited/no meristematic activity', `disrupted internal anatomy', and `proliferating') were identified among torpedo- and cotyledonary-stage embryos. Among these, only the first two were found to be competent for conversion into plantlets. Lack of organized shoot development in somatic embryos of sweet potato was associated with the following abnormalities: lack of an organized apical meristem, sparcity of dividing cells in the apical region, flattened apical meristem, and multiple meristemoids and/or diffuse meristematic activity throughout the embryo. Diagnostic separation of most shoot-forming and non-shoot-forming torpedo and cotyledonary embryo variants was achieved.

Apical and axial shoot tips of sweet potato were cultured to produce somatic embryos that mature and develop into plants in basal nutrient medium. However, the lack of high regeneration efficiency is an impediment to the use of somatic embryos to produce synthetic seeds. Conversion experiments with mature embryos over a 20-day period revealed that 80-90% of the embryos formed roots but only 40-50% formed shoots. Using computer vision and canonical or Fisher discriminant function (CDA) analysis along with conversion results, it was possible to correctly classify competent embryos 40-50% of the time based on size features, 50-60% of the time based on shape features, and 55-60% of the time based on color features. Non-competent embryos were correctly classified 65-75%, 55-60%, and 70-75% of the time based on size, shape, and color, respectively. These results can be used effectively to identify and select competent embryos for improved regeneration efficiency.

Carrot (Daucus carota) seed germination can be erratic or reduced under temperatures above 35ºC. Priming circumvents seed thermoinhibition in several crops, including carrot. The involvement of ethylene in germination at supra-optimal temperatures has been reported in other species, but its role in carrot seed germination has not been examined. The objective of this study was to determine whether priming-mediated improvement in carrot seed germination at high temperature was associated with increased ethylene production. Seeds of two tropical carrot genotypes (Alvorada and Brasília) were incubated over a range of temperatures. 'Brasilia' seeds were primed for 72 hours in aerated PEG solution at 15ºC under light conditions and germination tested at 20 and 35ºC. Seeds of a thermosensitive genotype 'Arrowhead' were primed for 0, 4, 8 and 12 days in aerated PEG 6000 solutions at 15ºC under light conditions. Seeds were incubated at 20 and 35ºC, and ethylene production was measured immediately before visible primary root protrusion. Temperatures above 30ºC decreased seed germination percentage of 'Alvorada' and 'Brasilia'. Priming increased 'Brasilia' seed germination at 35ºC. 'Arrowhead' germinated 96% at 20ºC, and 13% at 35ºC. Seed germination and ethylene production of 'Arrowhead', a thermosensitive genotype, increased in response to increased duration of priming. The results suggest that seed priming circumvents thermoinhibition of carrot seed germination by increasing ethylene production at high temperatures.

To investigate thermotolerance in seeds of lettuce (Lactuca sativa L.), primed, nonprimed, or seeds matured at 20/10 and 30/20 °C (day/night on a 12-h photoperiod) were imbibed at 36 °C for various periods and then dissected. Structural changes in seed coverings in front of the radicle tip were observed during germination at high temperature. Thermotolerant genotypes, ‘Everglades’ and PI 251245, were compared with a thermosensitive cultivar, ‘Dark Green Boston’. In all seeds that germinated, regardless of seed maturation temperature or priming, a crack appeared on one side of the cap tissue (constriction of the endosperm membrane near the basal end of the seed) at the micropylar region and the endosperm separated from the integument in front of the radicle tip. Additional changes took place during imbibition in these seeds; the protein bodies in the vacuoles enlarged and gradually depleted, large empty vacuoles formed, the cytoplasm condensed, the endosperm shrank, the endosperm cell wall dissolved and ruptured, and then the radicle elongated toward this ruptured area. The findings suggested that the endosperm layer presented mechanical resistance to germination in seeds that could not germinate at 36 °C. Weakening of this layer was a prerequisite to radicle protrusion at high temperature. Seeds of ‘Dark Green Boston’, ‘Everglades’, and PI 251245 matured at 30/20 °C had greater thermotolerance than those matured at 20/10 °C. Results of the anatomical study indicated that the endosperm cell walls in front of the radicle of seeds matured at 30/20 °C were more readily disrupted and ruptured during imbibition than seeds matured at 20/10 °C, suggesting a reason why these seeds could germinate quickly at supraoptimal temperatures. Similar endosperm structural alterations also were observed in primed seeds. Priming led to rapid and uniform germination, circumventing the inhibitory effects of high temperatures. From anatomical studies conducted to identify and characterize thermotolerance in lettuce seed germination, we observed that genotype, seed maturation temperature, or seed priming had the ability to reduce physical resistance of the endosperm by weakening the cell wall and by depleting stored reserves leading to cell collapse.

The minute broad mite, Polyphagotarsonemus latus (Banks), can cause serious damage to peppers (Capsicum annuum) when infestations occur at early plant developmental stages. A first study was set to evaluate biological control strategies during seedling development. Timing of release of Neoseiulus californicus McGregor, a commercially reared predatory mite, was investigated in scenarios of pest and predator presence to simulate preventive and curative strategies of control. Undamaged seedlings were produced when two predators per seedling were released preventively. Curative control strategies were not effective for producing undamaged or broad mite-free transplants. Further studies were carried to evaluate the effectiveness of N. californicus on pepper seedlings that host a few broad mites and are transplanted into the production greenhouse. N. californicus released at different times and densities, and conventional control methods (micronized-sulfur sprays) were evaluated for pest control, plant damage, and fruit yield. Yields of red fruits from plants with four predators per plant released at any of the release times (a week before, at, or four days after transplanting) or with sulfur sprays were not significantly different from an uninfested control treatment. Releases of two predatory mites per plant led to yields similar to the uninfested control only when introductions were a week before transplanting, while later introductions led to serious plant damage and significantly lower yields. Early broad mite infestations in pepper crops grown in greenhouses might be effectively controlled with N. californicus released at early seedling developmental stages in the nursery and at transplanting in the fruit production greenhouse. INTRODUCTION Infestations of broad mite [Polyphagotarsonemus latus (Banks); (Acari: Tarsonemidae)] initiated at early developmental stages of pepper (Capsicum annuum) can lead to severe plant damage in greenhouses where transplants or fruit are produced (de Coss-Romero and Pena, 1998; Gerson, 1992; Weintraub et al., 2003). Seedlings will appear undamaged when they become infested with the minuscule mite a few days before transplanting but they carry the pest to crops transplanted in greenhouses. Biological control programs initiated at early pepper crop stages are disrupted by multiple sprays of the commonly used pesticides (e.g., sulfur, abamectin, and dicofol). Neoseiulus californicus McGregor (Acari: Phytoseiidae), a predaceous mite released on greenhousegrown vegetables for biological control of two-spotted spider mite [Tetranychus urticae Koch (Acari: Tetranychidae)], has been reported to feed on broad mites as well (Castagnoli and Falchini, 1993; Pena and Osborne, 1996). N. californicus can reproduce when feeding on broad mites (Castagnoli and Falchini, 1993). Preventive releases may provide effective pest management as the predator can remain on plants for short periods when prey is absent (de Courcy Williams et al., 2004). This manuscript presents selected results of research that evaluated the use of N. californicus as a broad mite management Proc. IV IS on Seed, Transplant and Stand Establishment

‘Galia’ (Cucumis melo var. reticulatus L. Naud. cv. Galia) fruit were harvested at the three-quarter slip stage and treated with 1 μL L−1 1-methylcyclopropene (1-MCP) at 20 °C for 24 h. The fruit were processed and stored as fresh-cut cubes and intact fruit for 10 d at 5 °C. Ethylene production of fresh-cut cubes was approximately 4–5-fold higher than intact fruit at day 1. Afterward, the ethylene production of fresh-cut cubes declined significantly whereas that of intact fruit remained relatively constant at about 0.69–1.04 ng kg−1 s−1. 1-MCP delayed mesocarp softening in both fresh-cut and intact fruit and the symptoms of watersoaking in fresh-cut fruit. Continuously stored fresh-cut cubes and cubes derived from intact fruit not treated with the ethylene antagonist softened 27% and 25.6%, respectively, during 10 d storage at 5 °C while cubes derived from 1-MCP-treated fruit softened 9% and 17%, respectively. Fresh-cut tissue from 1-MCP-treated fruit exhibited slightly reduced populations of both total aerobic organisms and Enterobacterium, although the differences did not appear to be sufficient to explain the differences in keeping quality between 1-MCP-treated and control fruit. Based primarily on firmness retention and reduced watersoaking, 1-MCP treatment deferred loss of physical deterioration of fresh-cut ‘Galia’ cubes at 5 °C by 2–3 d compared with controls.

'Galia' is a high-quality muskmelon cultivar that is grown in greenhouses or tunnels to maximize fruit quality and yield. 'Galia' has a short shelf life of 2-3 weeks due to rapid fruit softening. In vitro regeneration and transformation of 'Galia' melon parental lines with antisense technology, targeting enzymes involved in the ethylene biosynthesis pathway, is a feasible strategy that can be used to increase its fruit shelf-life. In this study, the male parental line of 'Galia' muskmelon was transformed with two different constructs: one plasmid was bearing the uidA (GUS) reporter gene and another the ACC oxidase gene (CMACO-1) in antisense orientation. Transgenic ACC oxidase antisense (TGM-AS), azygous (PCR negative), transgenic GUS (TGM-GUS) and wild type (WT) fruit, from plants grown in the greenhouse, were harvested at zero-, half-, and full-slip developmental stages. Fruit firmness of full-slip TGM-AS was almost twice that of wild type, azygous and TGM-GUS. Ethylene production and ACC oxidase in half-slip wild type, azygous and TGM-GUS fruit were greater than those from TGM-AS fruit. TGM-AS 'Galia' male parental melon fruit exhibited delayed softening compared to wild type fruit.

Ethylene synthesis and sensitivity, and their relation to germination at supraoptimal temperatures, were investigated in lettuce (Lactuca sativa L.) seeds matured at 30/20 °C [12-h day/night, high temperature matured (HTM)] or 20/10 °C [12-h day/night, low temperature matured (LTM)]. HTM seeds of both thermosensitive `Dark Green Boston' (DGB) and thermotolerant `Everglades' (EVE) had greater germination at a supraoptimal temperature (36 °C), in both light or dark, than LTM seeds of DGB and EVE. HTM seeds of DGB and EVE produced more ethylene during germination than LTM seeds, regardless of imbibition conditions. The ethylene action inhibitor, silver thiosulfate, led to reduced germination in both cultivars. The ethylene precursor, 1-aminocyclopropane-1-carboxylic acid at 10 mm increased germination of both cultivars at supraoptimal temperatures, whereas germination of HTM seeds was greater than that of LTM seeds. No differences in ethylene perception were detected between HTM and LTM germinating seeds using a triple response bioassay. This study demonstrated that at least one method through which seed maturation temperature influences lettuce germination is by affecting ethylene production.

`Galia' (Cucumis melo var. reticulatus L. Naud. `Galia') melons exhibit relatively short postharvest longevity, limited in large part by the rapid softening of this high quality melon. The present study was performed to characterize the physiological responses of `Galia' fruit harvested at green (preripe) and yellow (advanced ripening) stages and treated with 1-methylcyclopropene (1-MCP) before storage at 20 °C. Treatment with 1.5 μL·L-1 1-MCP before storage delayed the climacteric peaks of respiration and ethylene production of green fruit by 11 and 6 d, respectively, and also significantly suppressed respiration and ethylene production maxima. Softening of both green and yellow fruit was significantly delayed by 1-MCP. During the first 5 d at 20 °C, the firmness of green control fruit declined 66% while 1-MCP-treated fruit declined 46%. By day 11, firmness of control and 1-MCP-treated green fruit had declined about 90% and 75%, respectively. The firmness of control yellow fruit stored at 20 °C declined 70% within 5 d while 1-MCP-treated fruit declined 30%. The 1-MCP-induced firmness retention was accompanied by significant suppression of electrolyte leakage of mesocarp tissue, providing evidence that membrane dysfunction might contribute to softening of `Galia' melons. The mesocarp of fruit harvested green and treated with 1-MCP eventually ripened to acceptable quality; however, under the treatment conditions (1.5 μL·L-1 1-MCP, 24 h) used in this study, irreversible suppression of surface color development was noted. The disparity in ripening recovery between mesocarp versus epidermal tissue was considerably less evident for fruit harvested and treated with 1-MCP at an advanced stage of development. The commercial use of 1-MCP with `Galia'-type melons should prove of immense benefit in long-term storage and/or export situations, and allow for retention of quality and handling tolerance for fruit harvested at more advanced stages of ripening.

High temperatures during lettuce seed imbibition can delay or completely inhibit germination and the endosperm layer appears to restrict the radicle protrusion. The role of endo-beta-mannanase during lettuce seed germination at 35°C and the influence of ethylene in endo-beta-mannanase regulation were investigated. Seeds of 'Dark Green Boston' (DGB) and 'Everglades' (EVE) were germinated in water, or 10 mmol L-1 of 1-aminocyclopropane-1-carboxylic acid (ACC), or 10 mmol L-1 of aminoethoxyvinylglycine (AVG), or 20 mmol L-1 of silver thiosulphate (STS). Seeds were also primed in polyethylene glycol (PEG), or PEG + ACC, PEG + AVG, or PEG + STS. Untreated seeds germinated 100% at 20°C. At 35°C, EVE seeds germinated 100%, whereas DGB seeds germinated only 33%. Seed priming or adding ACC during incubation increased germination at 35°C. Higher ethylene evolution was detected in EVE than in DGB during germination at 35°C. AVG did not inhibit seed germination of DGB at 35°C, but STS did. Higher endo-beta-mannanase activity was observed in EVE compared with DGB seeds. Providing ACC either during priming or during germination increased endo-beta-mannanase activity, whereas AVG and STS led to decreased or no activity. Ethylene may overcome the inhibitory effect of high temperature in thermosensitive lettuce seeds due to increased endo-beta-mannanase, possibly leading to weakening of the endosperm. Altas temperaturas durante a embebição das sementes de alface podem atrasar ou inibir a germinação e o endosperma parece ser o responsável na restrição da protrusão da radícula. O envolvimento da enzima endo-beta-mananase durante a germinação de sementes de alface a 35°C e a influência do etileno na regulagem desta enzima foram estudados. Sementes das cultivares Dark Green Boston (DGB) e Everglades (EVE) foram germinadas em água ou em soluções de 10 mmol L-1 de 1-aminociclopropano-1-ácido carboxilico (ACC), 10 mmol L-1 de amino-etoxi-vinil-glicina (AVG), ou 20 mmol L-1 de tiossulfato de prata (STS). Sementes foram ainda osmoticamente condicionadas em soluções de polietilenoglicol (PEG), ou PEG + ACC, PEG + AVG, ou PEG + STS. Sementes não tratadas germinaram 100% a 20°C. A 35°C, EVE germinou 100%, enquanto DGB germinou somente 33%. A germinação a 35°C aumentou em sementes osmoticamente condicionadas ou sementes que receberam ACC durante a incubação. Maior evolução de etileno foi detectada em EVE do que em DGB durante a germinação a 35°C. AVG não inibiu a germinação de DGB a 35°C, enquanto que STS inibiu. Maior atividade de endo-beta-mananase nas sementes foi observada em EVE quando comparado com DGB. Fornecimento de ACC tanto durante o condicionamento osmótico como durante a germinação, aumentou a atividade de endo-beta-mananase, enquanto que AVG e STS proporcionaram um decréscimo ou ausência da atividade enzimática. O etileno pode minimizar o efeito inibitório de altas temperaturas na germinação de sementes de genótipos sensíveis de alface devido ao aumento da enzima endo-beta-mananase, possivelmente levando ao enfraquecimento do endosperma.

A physiological disorder in greenhouse-grown pepper (Capsicum annuum L.) plants was observed in Florida, wherein the base of the main stem becomes swollen below the cotyledonary node level and crack-like wounds develop at the base of the stem's epidermis. The disorder may predispose the plant to a localized rot and result in a sudden plant wilt. The effects of soilless media type, transplant depth, and amount of nutrient solution applied per day were studied to evaluate the development of what was termed “Elephant's Foot” disorder, on a greenhouse-grown bell pepper crop in Gainesville, Fla. The percentage of plants with epidermal wounds at the base of the stem was highest (83%) on plants transplanted at half of the cell height (3.8 cm), compared to plants transplanted to the cotyledonary node level (6%) and the second leaf node (0%). Salts were washed from the surface of basal stem epidermis and electrical conductivity measured in the washing solution was expressed per unit area of epidermal sample (ECA). The ECA in the solutions from plants transplanted at half of the cell height was higher than that from plants transplanted to the cotyledonary node level and to the second leaf node. There was a positive linear relationship (r = 0.81) between the percentage of plants with epidermal wounds and the ECA of the solution obtained from washing the epidermal tissues. Salts deposited on the epidermis beneath the cotyledonary node provoked a tissue injury that may predispose the plant to a Fusarium infection. Simple management practices, such as transplanting deep, using cultivars with lower susceptibility to salt damage, and gradually moving back the emitter from the base of the plant after transplanting (to reduce humid conditions near the base of the stem) would help reduce the appearance of this basal stem disorder in soilless-grown peppers.

High levels of 2,4-dichlorophenoxyacetic acid (2,4-D, 10 µM) and sucrose (3%) are required for both the induction and maintenance of callus for somatic embryogenesis in sweetpotato. Newly inducted embryogenic callus lines in sweetpotato cv. White Star produce competent embryos that convert readily into plantlets. With age, these embryogenic callus lines produce a greater proportion of incompetent embryos with poor conversion potential. One hypothesis for this change is that auxin- and/or sugar-responsiveness may be altered with aging. A comparison of two older embryogenic lines (K592 and M892) to two new lines (K1194 and K195) addressed the relationship between extent of embryo conversion and relative abundance of mRNAs hybridizing with heterologous auxin- or sugar-responsive gene probes. The respective cDNAs utilized were the auxin-responsive pJCW1 and pJCW2 and the sugar-responsive Ivr2 and Sh1. Embryos from new callus lines formed more shoots, roots, and viable plantlets than embryos from older callus lines. In addition, new callus lines had greater relative levels of mRNAs hybridizing to auxin-responsive cDNAs. These sweetpotato mRNAs were themselves found to be 2,4-D-responsive in dosage analyses. In contrast, differences between young and old cultures were not evident for mRNAs hybridized to sugar-regulated genes. Our results support the suggestion that desensitization of auxin-responsiveness is a central feature of reduced embryogenic competence in callus lines following prolonged exposure to 2,4-D and elevated sucrose levels.

Six transgenic 'South Bay' lettuce lines ( Lactuca sativa L.) with elevated levels of 5-enolpyruvyl shikimate-3- phosphate synthase (EPSPS) were evaluated for tolerance to the herbicide glyphosate. The six lines were selected from ≈150 independent transformation events using an Agrobacterium tumefaciens system. Three assay methods were used to identify gene expression with regard to glyphosate resistance. Leaf disks of the transgenic lines were cultured on media containing 0 to 1280 μM glyphosate. Leaf disks of the control had lower dry weight (DW) at 40 μM and greater glyphosate than all the transgenic lines. The transgenic lines continued to grow even at 1280 μM. Plants 21 days old were sprayed in the greenhouse with rates of glyphosate at 0 to 35.84 kg·ha -1 . DW of all the lines were similar to the control, with a few exceptions, at glyphosate concentrations from 0 to 0.56 kg·ha -1 . At 2.24 to 8.96 kg·ha -1 all of the transgenic lines had DW greater than the control, while at 17.92 and 35.84 kg·ha -1 only B-32, B-33, C-3, and C-14 had DW greater than the control. The resistant line from the greenhouse experiment, B-32, grew normally in field trials at the highest glyphosate rate, 17.92 kg·ha -1 , while control plants died at 0.56 kg·ha -1 glyphosate. Lines A-11 and C-3 had lower DW than B-32 at 2.24 kg·ha -1 glyphosate and greater. While leaf disk assays can identify potential transformed lines expressing the EPSPS and glyphosate oxidase (GOX) gene, and greenhouse screening can evaluate seedling vigor after glyphosate application, field trials are necessary to evaluate plant growth and yield through the growing season. Chemical name used: N-(phosphono-methyl) glycine (glyphosate). mature head after application of glyphosate. Selection of expressed tolerances can be affected by age of the plant material being tested. Different tests might result in different interpretations of herbicide tolerance based on the method performed. Gene number and position effect can all affect expression of the character under question, thus, potentially altering gene expression and/or normal plant growth. This paper reports results of laboratory, greenhouse, and field tests to determine glyphosate tolerance in several trans- genic lettuce lines.

Weakening of the endosperm tissue around the radicle tip before radicle protrusion and a potential role of endo-β-mannanase during germination of lettuce seeds (Lactuca sativa L.) at high temperature (35 °C) were investigated. Seeds from the thermotolerant genotypes 'Everglades' and PI 251245 had greater endo- β-mannanase activity before radicle protrusion at 35 °C than the thermosensitive genotypes 'Dark Green Boston', 'Valmaine' and 'Floricos 83'. Thermotolerant genotypes also generated more ethylene at high temperature. At 35 °C, germination of 'Dark Green Boston' and 'Everglades' seeds produced at days/nights of 20/10 °C was 10% and 32%, respectively, whereas germination of seeds produced at days/nights of 30/20 °C was 67% and 83%, respectively. Higher endo-β-mannanase activity was observed before radicle protrusion in 'Dark Green Boston' seeds produced at 30/20 °C compared with those produced at 20/10 °C. A relationship between seed germination at high temperature, ethylene production, and an increase in endo- β-mannanase activity before radicle protrusion was confirmed. and Opoku-Boateng, 1991). Lettuce seeds produced in hot cli- matic regions germinated better at high temperature (Damania, 1986; Harrington and Thompson, 1952) compared to seeds produced at lower temperature regimes. Under controlled condi- tions, Gray et al. (1988) verified that lettuce seeds produced at days/nights of 30/20 °C germinated better at 30 °C than seeds produced at 25/15 °C or 20/10 °C. In another study, Sung et al. (1998a) reported that lettuce seeds matured at 30/20 °C had a greater germination percentage at high temperature than those matured at lower temperatures. These authors concluded that the thermotolerance character in lettuce seed was regulated by an interaction between genotype and temperature during seed devel- opment.

The influence of municipal solid waste (MSW) and biosolids compost maturity on germination of several weed species seeds was evaluated. Ivyleaf morning glory (Ipomoea hederacea L.), barnyard grass (Echinochloa crus-galli L.), common purslane (Portulaca oleracea L.), and corn (Zea mays L.) were selected as plant indicators to determine the compost maturity stage with maximum germination inhibition. Extracts were prepared from immature (three day-old, four week-old, eight week-old), and mature (one year-old) composts. Extract from eight week-old compost decreased percentage germination, root growth, and germination index (a combination of germination percentage and root growth), and increased mean days to germination of each indicator specie. Extract from eight week-old compost was evaluated for effect on germination percentage of 14 economically important weed species. Extract from eight week-old compost inhibited germination of most weed species, except yellow nutsedge (Cyperus esculentus L.) for which tu...

Temperature is an important environmental factor that affects lettuce (Lactuca sativa L.) germination. The present research was conducted to determine the role of seed coverings on lettuce seed germination at high temperature. Five lettuce genotypes were primed in order to bypass thermoinhibitional effects on germination. During germination of primed and nonprimed seeds, imbibition followed a normal triphasic pattern. Primed seeds had higher final water content, a decreased imbibitional phase II, and germinated at 36 °C compared to nonprimed seeds of thermosensitive genotypes, which did not germinate at 36 °C. Puncture tests were conducted to determine the force required to penetrate the whole seed or endosperm of the five genotypes at 24 and 33 °C. `Dark Green Boston', a thermosensitive genotype, had the highest mean resistance (0.207 N) and PI 251245, a thermotolerant genotype, had the lowest (0.139 N). Resistance to penetration of the endopserm of the five genotypes was different at both temperatures. However, three thermotolerant genotypes had lower endosperm resistance than two thermosensitive types. At 36 °C, the penetration force for primed and nonprimed seeds was compared after the first hour of imbibition and 1 hour before radicle protrusion. The force required to penetrate the seed was affected by genotype, seed priming, and duration of imbibition. Puncture force decreased as imbibition time at 36 °C increased in primed and nonprimed seed of each thermotolerant genotype but not in the thermosensitive genotypes. Priming reduced the initial force necessary to penetrate the seed and endosperm in all genotypes. Thus, for radicle protrusion to occur, there must first be a decrease in the resistance of the endosperm layer as evidenced by priming or thermotolerant genotype. Then, the pericarp and integument are sufficiently weakened so that tissue resistance is lower than the turgor pressure of the expanding embryo, allowing germination to be completed.

Seed germination is a critical step to achieve economic success in a transplant operation. Total germination of a seed lot dictates total plant sales by the producer, while uniformity of germination dictates the quality of the transplant crop. Using high vigor seed will help to achieve uniform stands, as well as maximize stands, in the transplant house or field. In order to maintain the highest seed quality, transplant producers should store unused seeds at recommended temperature and relative humidity for the crop species. Methods to promote uniformity and optimum stands under a wide range of conditions include the use of seed priming, film coating with fungicides, and pelleting for ease of planting.

Lettuce (Lactuca sativa L.) seeds can fail to germinate at temperatures above 24 °C. The degree of thermotolerance is thought to be at least partly related to the environment under which the seed developed. In order to study the effects of temperature during seed development on subsequent germination, various lettuce genotypes were screened for their ability to germinate at temperatures ranging from 20 to 38 °C. Seeds of the selected genotypes `Dark Green Boston' and `Valmaine' (thermosensitive), `Floricos 83', `Everglades', and PI 251245 (thermotolerant) were produced at 20/10, 25/15, 30/20, and 35/25 °C day/night temperature regimes in plant growth chambers. Seeds were germinated on a thermogradient bar from 24 to 36 °C under 12 h light/dark cycles. As germination temperature increased, the number of seeds that failed to germinate increased. Above 27 °C, seeds matured at 20/10 or 25/15 °C exhibited a lower percent germination than seeds that matured at 30/20 or 35/25 °C. Seeds of `Dark Green Boston' and `Everglades' that matured at 30/20 °C exhibited improved thermotolerance over those that matured at lower temperatures. Seeds of `Valmaine' produced at 20/10 °C exhibited 40% germination at 30 °C, but seeds that matured at higher temperatures exhibited over 95% germination. Germination of `Valmaine' at temperatures above 30 °C was not affected by seed maturation temperature. The upper temperature limit for germination of lettuce seed could thus be modified by manipulating the temperature during seed production. The potential thermotolerance of seed thereby increased, wherein thermosensitive genotypes became thermotolerant and thermotolerant genotypes (e.g., PI251245) germinated fully at 36 °C. This information is useful for improving lettuce seed germination during periods of high soil temperature, and can be used to study the biology of thermotolerance in lettuce.

Carrot (Daucus carota L.) seeds vary greatly in maturity as a result of umbel order formation on the mother plants. The objectives of this study were to investigate the possibility of using chemical growth regulators as chemical pruning agents to modify seedstalk development in carrot plants, and to determine the effect of such modification on seed yield and quality. The number of days to primary umbel anthesis was unaffected by application of growth regulators. Seedstalk height was increased by GA3 and reduced by ancymidol or daminozide. The decrease in seedstalk height was linear with the increase of ancymidol concentrations from 25 to 100 ppm and quadratic when daminozide (1000 to 8000 ppm) was used. Ancymidol and daminozide were effective in reducing total number of branches per plant and were effective in reducing the number of tertiary umbels. Total seed yield was reduced by ancymidol and daminozide compared to the control. When compared to hand pruning, ancymidol and daminozide generally h...

The shrunken-2 (sh2) mutant of maize (Zea mays L.) increases sucrose and reduces starch in developing endosperm. An associated trait is poor seed and seedling vigor in seeds containing the mutation. The specific effects of sh2 mutant endosperm on embryo and seedling vigor were determined by analyzing seeds that contained either concordant wild-type or nonconcordant combinations of mutant and wild-type embryo and endosperm genotypes. The nonconcordant seed types that contained a wild-type embryo in association with a sh2 mutant endosperm or a sh2 mutant embryo in association with a wild-type endosperm were generated using the TB-3La translocation chromosome in which a wild-type Sh2 gene is attached to the centromeric portion of a B chromosome. Under stress conditions (complex stress vigor test), the seeds with mutant endosperm had lower germination, seedling fresh and dry weight, and index of conductivity than seeds with wild-type endosperm. Mutant endosperm and embryos excised from mutant endosperm imbibed more water than wild-type endosperm or embryos excised from wild-type endosperm. Because of the high concentration of osmotic solutes in the mutant endosperm, a rapid water uptake may induce a membrane disorganization. Leachate conductivities of seeds with mutant endosperm were higher than seeds with wild-type endosperm. In addition, a higher sucrose content and a lower raffinose to sucrose ratio were measured in the wild-type embryos associated with mutant endosperms than in the normal embryos excised from concordant wild-type seeds. These results suggest that a high rate of water uptake caused by the elevated concentration of osmotic solutes in seeds with mutant endosperms may affect membrane integrity during imbibition. Alternatively, the lower raffinose to sucrose ratio present in the mutant endosperm class might affect stabilization of cell membranes during seed desiccation. Embryos cultured in media containing 10% starch or no carbohydrate produced smaller seedlings than embryos cultured in 5% or 10% sucrose. Wild-type embryos excised from mutant endosperms exhibited lower germination in 0% and 5% sucrose media than embryos from concordant seed, indicating that reduced water uptake rates associated with lower external osmotic potential (10% sucrose) can improve vigor of embryos associated with sh2 mutant endosperm. The reduced vigor of embryos and seedlings that develop in association with sh2 mutant endosperm can be traced to the physiological and biochemical effects of the elevated sucrose levels present during seed formation and imbibition. reserves are noted changes in sh2 seeds, the direct effect of the mutation on germination and subsequent seedling vigor is not clearly understood. Increased seed leakage after imbibition has been associated with membrane damage in cotyledons of soybean (Schoettle and Leopold, 1984). Heat-killed embryos have greater water uptake due to changes in fluidity or ordering of the membranes (Murphy and Noland, 1982). Koster and Leopold (1988) proposed that raffinose may prevent crystallization of the sucrose during dehy- dration, improving membrane protection and stabilization. Seed vigor of maize embryos was correlated with raffinose concentra- tion (Bernal-Lugo and Leopold, 1992). A high raffinose to sucrose ratio in maize seeds was highly correlated with membrane stability during drying (Chen and Burris, 1990). The characteristics of the endosperm affect the embryo during germination and subsequent seedling growth. The structure and chemical composition of the endosperm may alter the quality and quantity of the metabolites available for the embryo, seed osmotic potential, and germination. The embryo is responsible for the initial growth of the axes and subsequent control of reserve mobilization (Bewley and Black, 1978). Poor germination and seedling vigor of sh2 seeds is an enigma. All current molecular and biochemical data show that the sh2 gene is expressed only in the endosperm. Although the embryo and seedling contain starch and have ADP-glucose pyrophosphorylase activity, this activity is independent of the sh2 mutation in seedlings. Clearly, seedling vigor is reduced as a consequence of the seed mutation. This may be explained by the association between the endosperm and embryo as discussed above. The question can be addressed by creating seeds that contain a mutant endosperm and wild-type embryo. If the poor germination of sh2 is due to endosperm, then the genetic constitution of the sh2 locus in the

The effect of temperature on seedstalk development, seed yield and quality in carrot ( Daucus carota L.) was investigated in growth chambers at constant day/night temperatures of 33/28, 28/23, 25/20, 23/18, 20/15, and 17/12 °C. Days to flowering, seedstalk height, number of umbels, and seed yield decreased linearly with increasing temperature from 17/12 to 33/28 °C. Continuous high temperature (33/28 °C) had a detrimental effect on germination as measured by a standard germination test and an accelerated aging test. Optimum germination of the progeny occurred at 20/15 °C; however, germination rate was faster when seeds matured at 23/18 °C. Seeds that developed at 33/28 °C produced seedlings with the lowest vigor, while those which developed at 20/15 °C produced seedlings with the highest vigor. Brief exposure of plants to 33/28 °C during anthesis or early seed development was as detrimental to seed yield as continuous exposure to 33/28 °C. Exposure to high temperature (33/28 °C) during late seed development had less effect on seed yield, and seed quality was improved. Progeny vigor was reduced greatly by seed development at continuous high temperature (33/28 °C), but was unaffected by brief exposure to 33/28 °C at anthesis, early, or late in seed development. These results suggest that high (33/28 °C) day/night temperatures during pollination, fertilization, or early stages of seed development can greatly reduce carrot seed yield and seed quality. The purpose of the present study was to investigate the effect of different growing temperatures on seedstalk development, seed yield, and seed quality in carrots.

Stable expression of foreign genes was achieved in sweet potato (Ipomoea batatas (L.) Lam) plants using anAgrobacterium tumefaciens mediated system. Embryogenic calluses produced from apical meristems of cultivar White Star were multiplied and cocultivated withA. tumefaciens strain EHA101 harboring a binary vector containing the β-glucuronidase (GUS) and neomycin phosphotransferase (NPT II) genes. The calluses were transferred to selective regeneration medium and kanamycin resistant embryos were recovered which developed into morphologically normal plants. Histochemical and fluorimetric GUS assays of plants developed from the kanamycin resistant embryos were positive. Amplified DNA fragments were produced in polymerase chain reactions using GUS-specific primers and DNA from these plants. Transformation was confirmed by Southern analysis of the GUS gene. With the developed method, transgenic sweet potato plants were obtained within 7 weeks. This method will allow genetic improvement of this crop by the introduction of agronomically important genes.

Mature seeds of strawberry (Fragaria x ananassa) were placed on Murashige and Skoog medium supplemented with 2.22 μM 6-benzyladenine. After four weeks of culture, and without an intervening callus phase, approximately 36% of the resulting seedling radicles had formed numerous adventitious buds near their tips. A few buds on each radicle developed into shoots, while others formed disorganized calli. Consequently, the seedlings exhibited shoot apices at both ends of the axis of polarity. Our overall results suggest that a considerable level of plasticity in organ determination occurs even in higher plants, and that exogenous growth regulators can cause a root primordium in the radicle to be converted to a shoot primordium.

Early plant growth, root quality, and yield from sweetpotato plants obtained from zygotic seed, somatic embryos, or cloned from stock plants (through micropropagation, rooted node explants, or nonrooted terminal vine cuttings) were compared in field plantings established in 1986, 1987, and 1988 in Gainesville and/or Homestead, Fla. At planting, transplants derived from somatic embryos had more nodes than the other propagules, while vine length per plant was greatest with nonrooted vine cuttings obtained from stock plants. The number of nodes (up to 253%) and vine growth (up to 517%) were greater when plants were derived from stock plants and zygotic embryos than from somatic embryos 4 weeks (1987) and 6 weeks (1988) after planting. Vegetative growth, larger-sized storage roots (>6 cm in diameter), and total yields (all root grades combined) were consistently reduced when plants were derived from somatic embryos compared with propagules of stock plant origin. Plants obtained from somatic embryos required more time for roots to bulk or size than the other propagule types. Root yield from plantlets derived from somatic embryos showed a 14-fold increase when harvest was delayed at least 53 more days. Root weight, regardless of harvest date, was greater when plants were derived from stock plants rather than from somatic embryos, while in most cases plants derived from somatic embryos yielded a greater number of roots than from stock plants. Plants obtained through somatic embryony and harvested at a later date typically had yields exceed 1.8 kg per plant. Morphology of plants obtained from somatic embryos was uniform and identical to plants derived from stock plants.

`Sunny' tomato (Lycopersicon esculentum Mill.) containerized transplants were grown with the standard or conventional systems (SS) and with recently developed flotation systems (FS). Standard system and FS transplants, and direct-seeding using coated seeds were evaluated in the field for root and shoot growth and yield at Parrish, Bradenton, and Naples during fall, winter, and spring plantings. Plant growth characteristics were measured weekly before, during, and after transplanting or sowing. In the Parrish and Bradenton Fall 1987 and Bradenton Spring 1988 experiments, SS transplants had greater leaf area, root volume, shoot dry weights, and shoot: root ratios than FS transplants. During early development, the FS transplants had more lateral root growth than SS transplants, but had similar total root growth and horizontal and vertical root distribution after transplanting in the field. Transplants and direct-seeded plants allocated 72% of the total root mass in the upper 0 to 10 cm of the soil. In Fall 1987, SS transplants had between 29% and 41% more fruit yield than FS transplants at Bradenton and Parrish, respectively. In the Naples Winter 1988 and Parrish and Bradenton Fall 1989 experiments, both transplant types had similar fruit yields, but more than direct-seeded plants. Transplants grown with the flotation system are recommended for use provided that seedlings are grown and maintained with minimum hardening before establishment in the field.

In a test to overcome poor seed germination and seedling vigor of sweet corn (Zea mays L.) seeds carrying the shrunken-2 (sh2) mutant endosperm, primed seeds of two sh2 sweet corn cultivars—Crisp N'Sweet 711 (CNS-711) and How Sweet It Is (HSII)—were redried at 15, 20, 30, or 40C and 25% relative humidity after solid matrix priming (SMP). The dehydration rate was significantly lower in `CNS-711' than `HSII' at all temperatures. In both cultivars, the drying temperature after SMP was critical for seed performance. Primed seeds with a higher dehydration rate (dried at 30 or 40C) had better seed vigor, greater field emergence and seedling vigor, lower leachate conductivity and imbibition rate, and a higher respiration rate and glutamic acid decarboxylase activity than primed seeds redried at the lower temperatures or control seeds. Increased incidence of pathogen growth was observed on seeds dried at 15 and 20C relative to those dried at 30 or 40C, probably as a consequence of greater leakage from the seeds at a lower redrying temperatures. Lack of tolerance to dehydration at 15 and 20C was another factor adversely affecting the seeds redried at low temperature. A more rapid dehydration rate at a higher temperature after priming sh2 sweet corn improved many of the physiological characteristics used to measure seed quality and the subsequent emergence and vigor of the seedlings under field conditions.

Knowledge of proper conditions for transplant preand postharvest handling and shipping are not understood clearly by many shippers and growers. In fact, few studies have dealt with improving transplant performance and early seedling growth via new shipping and handling technology. My purpose is to bring into focus some factors that directly or indirectly affect preand postharvest transplant quality, betterearly plant growth, and higher yield. Price and Zandstra (1988) reported that any cessation in plant growth caused adverse cropping response (i.e., seedstalk development), greater disease susceptibility, and, potentially, reduced yield. Thus, plant growth should never be interrupted, whether the crop is grown directly from seed or from a transplant. This is difficult in practice, especially when one considers that transplants might be shipped long distances in the United States (1800 km), and that growers may be forced to hold the plants for 7 or more days due to adverse environmental conditions (Orzolek, 1989; Wood, 1988). When this happens, transplants may survive well in the tray or even in the field, but subsequent growth may become slow and uneven, and may negate any beneficial reasons for transplant use (Wood, 1988). Several preand postharvest handling factors have been studied to a limited extent, and have been relatedto improved transplant quality. They include: 1) controlling plant growth (by varying seedling tray-cell size, fertilization, irrigation, and temperature), by mechanical root or shoot pruning, or using chemical growth retardants; 2) age of the transplant: and 3) conditions of the storage/handling procedures

Transgenic plants of lettuce cultivar (cv.) ‘South Bay’ were produced by using Agrobacterium tumefaciens vectors containing the β-glucuronidase (GUS) reporter gene and the NPT II gene for kanamycin resistance as a selectable marker. High frequency of transformation, based on kanamycin resistance and assays for GUS expression, was obtained with 24 to 72-h-old cotyledon explants cocultivated for 48 h with Agrobacterium tumefaciens. After the cocultivation period, the explants were placed in selection medium containing 50 or 100 mg l−1 of kanamycin, 100 mg l−1 cefotaxime and 500 mg l−1 carbenicillin for 10 days. Surviving explants were transferred every 14 days on shoot elongation medium. Progenies of R0 plants demonstrated linked monogenic segregation for kanamycin resistance and GUS activity.

Transplants produced with overhead or subirrigation and plants from direct seeding using primed or nontreated `Jupiter' bell pepper (Capsicum annuum L.) seeds were evaluated for growth and yield in the field for 3 years. Early in development, overhead-irrigated (01) transplants had more basal root elongation than subirrigated (SI) transplants; however, root growth differences caused by irrigation systems in the greenhouse were minimized during late ontogeny in the field. Basal, lateral, and taproot dry weights accounted for 81%, 15%, and 4% of the total for transplants and 25%, 57%, and 18% of the total for direct-seeded plants. Direct-seeded plants maintained a more-balanced root, stem, leaf, and fruit dry matter partitioning than transplants, which allocated more dry weight (per unit of root growth) to stems, leaves, and fruits. Over all seasons, transplants exhibited significantly higher and earlier yields than direct-seeded pepper plants, and total yields were similar between SI and OI transplants and between primed and nontreated seeds.

Embryogenic callus growth of sweetpotato (Ipomoea batatas (L.) Lam.) was selectively enhanced by subculture on basal callus proliferation medium modified to contain 15 m M NH4NO3. Embryogenic callus production was doubled on basal callus proliferation medium modified to contain 60 m M K+, while nonembryogenic callus production was reduced 40%. Additions of up to 40 mM NaCl to basal callus proliferation medium did not affect callus proliferation. The development of embryos from calli subculture to embryo production basal medium was unaffected by the KCl or NaCl treatments of the callus proliferation phase. However, embryo production was increased by subculturing callus from callus proliferation medium containing 20 m M to embryo production medium containing 10 m M Our results demonstrate that changes in mineral nutrition, in addition to growth regulator differences between callus proliferation and embryo production media, are important factors in sweetpotato somatic embryogenesis. Clonal propagation via somatic embryogenesis has been pro- posed by Cantliffe et al. (1988) for synthetic seed production of sweetpotato. Sweetpotato somatic embryo production is ac- complished in two stages (Chee and Cantliffe, 1988a). Embry- ogenic callus is continuously proliferated by subculture on media containing growth regulators; embryos are produced by trans- ferring embryogenic callus to media without growth regulators. Formation of embryogenic callus was enhanced by addition of 10 µM (2,4-dichlorophenoxy)acetic acid (2,4-D) and 1 µ M N- (phenylmethyl)-1 H- purine-6-amine (BA) (Chee and Cantliffe, 1988b). Further improvements in embryogenic callus growth and embryo production could be expected by optimizing in- organic salts in the basal medium. However, information on the mineral nutrition of embryogenic callus is insufficient (Ammir- ato, 1983; Vasil, 1984). Nitrogen is quantitatively the major mineral nutrient taken up during growth of plant tissues (Marschner, 1986). Supplying N in its reduced rather than oxidized form to tissue culture likely would be more efficient for growth, since NO3 reduction is energetically expensive (Clarkson and Hanson, 1980). How- ever, cultured cells were unable to grow on as the sole N source when media did not include organic acids as buffers, or without continuous titration of the medium (Chaleff, 1983; Dou- gall and Verma, 1978; Fukunaga et al., 1978; Gamborg and Shyluk; 1970; Martinet al., 1977). This result is to be expected since uptake is physiological ly acidic (Marschner, 1986). The relative and absolute amounts of also in- fluence embryogenesis in cell cultures (Tazawa and Reinert, 1969). Generally, it is thought that the ionic form of N affects growth and nutrient uptake by altering cation-anion balance, changing organic anion accumulation and ultimately affecting medium and cytosol pH values (Marschner, 1986; Poole, 1978

ABA and drought stress were evaluated on growth morphology and dry weight of pepper (Capsicum annuum L.) seedlings subjected to continuous watering (CV) or alternate watering (AW) subflotation irrigation. When ABA (10- 4 M) was sprayed on to leaves 28, 32, or 37 days after seeding (DAS), leaf growth was limited relative to the controls. Root dry weight, basal root count, and diameter decreased in AW compared with CW-treated seedlings. ABA did not influence root growth of the transplants or subsequent total fruit yield. When ABA was applied to leaves at 20,23, or 29 DAS, there was a transient inhibition of leaf weight increase, but root growth was unaffected. Exogenous ABA may have a practical application as a substitute for drought stress to control transplant growth in the nursery. Chemical name used: abscisic acid (ABA). The use 'of containerized transplants in pepper is important to improve plant growth and productivity (Leskovar et al., 1990). A subflotation recirculating system has recently been developed for growing transplants (Beirenger and Bostdorff, 1989). Fre- quent irrigations promote root growth that eventually might ex- teed the volume of the bottom of the cell. This response requires either mechanical or heated-air root pruning, thus disrupting the root-tip zone which is critical for axial root growth (Pilet and Saugy, 1987). ABA, synthesized in the root cap (Rivier et al., 1977), is

Rapid plantlet development is critical for successful direct-field sowing of somatic embryos. Sweet potato somatic embryos were placed in hydroxyethyl cellulose gel (2.5% w/v) that was amended with different sources and concentrations of nutrients and carbohydrates to optimize plant formation. Greater root, shoot, and plantlet formation occurred in gel amended with Murashige and Skoog's (MS) or Gamborg's salts compared with White's or Hoagland's salts. Murashige and Skoog's salt concentrations at one-half and full-strength resulted in 40% plantlet production, while at one-quarter-strength 80% of the somatic embryos produced roots but no shoots. Both the macronutrients and micronutrients of Murashige and Skoog were necessary for maximum plant conversion in the gel, while the addition of the MS vitamins resulted in no significant improvement. Plantlet formation was greatest in get amended with fructose, maltose or sucrose as a carbohydrate source. Embryos would not survive without these carbohydrates amended to the gel or with galactose. Concentrations of fructose or sucrose in the gel between 23 and 187 mmol resulted in the most rooting, while concentrations ranging from 23 to 93 mmol were best for plantlet formation. By amending a transfer gel for direct fluid sowing, over 90% of the somatic embryos commonly formed roots and up to 50% of the embryos formed normal plantlets.

Generally, sweet corn cultivars (Zea mays L.) carrying the shrunken-2 (sh2) gene have lower germination and seedling vigor than normal or sugary (su) cultivars. Seeds of sh2 'How Sweet It Is' (HSII) and 'Crisp N'Sweet 711' (CNS-711) were imbibed for 6 hours. Rapid water uptake, higher seed leakage, and fungal infection were found in HSII, the lower germinating cultivar. Imbibition rate and leakage conductivity were reduced in both cultivars during the first 5 hours at 5C as compared with 25C. Sodium hypochlorite was an effective seed disinfectant. When the seeds were primed with sodium hypochlorite via solid matrix priming (SMP), germination under stressful con- ditions (soilcold test) was significantly improved in both cultivars. Primed seeds had significantly lower imbibitional rates and leakage conductivity than nonprimed seeds. The superior germination measured in primed and disinfected seeds was possibly due to the lower imbibitional rate and reduced seed fungal infection. The incorporation of the mutant sh2 gene in sweet corn has greatly improved sweet corn eating quality (Garwood et al., 1976). The sh2 supersweet hybrids have high levels of sugar in the endosperm and excellent postharvest sugar retention (Laugh- nan, 1953). However, germination and seedling vigor are often poor, especially under stress conditions (Styer et al., 1980). Small endosperm (Warm, 1980), susceptibility to seed- and soil- borne diseases (Pieczarka et al., 1978), and dysfunction in re- serve mobilization (Styer and Cantliffe, 1983) have been re- ported as causes of reduced seed viability and seedling vigor. Imbibition, or seed hydration, is the first step in germination. Rapid water uptake can negatively affect germination (Powell and Mathews, 1978). If water absorption is reduced during the early stages of imbibition, tissues develop in an organized man- ner, allowing sufficient time for membrane rearrangement and thus possibly reducing imbibition injury (Woodstock and Tao, 1981). Throughout imbibition, seeds lose a wide variety of car- bohydrates, mineral nutrients, proteins, and organic acids (Nor- din, 1984). Leakage can provide essential nutritive substances for fungi to develop on and around the seed (Schroth and Cook, 1964). Berger and Wolf (1974) reported that poor stand in sh2 sweet corn was associated with seed rot and damping off. Fu- sarium moniliforme (Sheldon) penetrated sh2 corn kernels via small cracks in the pericarp, where the pathogen localized be- tween the pericarp and aleurone layer, and eventually moved into the endosperm and embryo (Styer and Cantliffe, 1983). Sodium hypochlorite has been used as a seed disinfectant in pepper (Fieldhouse and Sasser, 1975) and corn (Schoen and Kulik, 1977). Similarly, seedlings of 'Iochief' and 'Earlivee' sweet corn were less infected with F. moniliforme after sodium hypochlorite seed disinfection (Anderegg and Guthrie, 1981). Seed priming has been a successful presowing seed treatment to improve the rate and uniformity of seed emergence under stress conditions. SMP controls seed hydration by the physical and osmotic characteristic of a solid matrix carrier (Kubik et al., 1989). The biochemical mechanisms involved in osmotic priming treatments are not entirely understood (Bradford, 1986).

Studies were conducted to evaluate growth of tomato (Lycopersicon esculentum Mill.) transplants in the field in response to age of transplants in Spring and Fall 1989. Transplants were 2 (2W), 3 (3W), 4 (4W), 5 (SW), or 6 (6W) weeks old. Drip and subseepage irrigation were used. In spring, older transplants produced more shoot and root growth up to 2 (T2) weeks after transplanting. At 3 (T3) and 4 (T4) weeks after transplanting, there were no differences between 4W, 5W, and 6W transplants. These trends were independent of irrigation systems. Total yield and early yield were similar for all transplant ages. In fall, shoot growth increased linearly with increasing transplant age at TO, but not thereafter. Chlorophyll a + b increased over time, but no treatment differences were found at T4. At planting, 2W transplants had a higher Chl a: b ratio than older transplants. This difference was reduced at T1 and T2 and became insignificant at T4. These results indicate that no improvement in yields was obtained using the traditional older transplants. Younger transplants might be used to achieve rapid seedling establishment with-minimal transplant production costs.

Among Cucurbitaceae, Cucumis melo is one of the most important cultivated cucurbits. They are grown primarily for their fruit, which generally have a sweet aromatic flavor, with great diversity and size (50 g to 15 kg), flesh color (orange, green, white, and pink), rind color (green, yellow, white, orange, red, and gray), form (round, flat, and elongated), and dimension (4 to 200 cm). C. melo can be broken down into seven distinct types based on the previously discussed variations in the species. The melon fruits can be either climacteric or nonclimacteric, and as such, fruit can adhere to the stem or have an abscission layer where they will fall from the plant naturally at maturity. Traditional plant breeding of melons has been done for 100 years wherein plants were primarily developed as open-pollinated cultivars. More recently, in the past 30 years, melon improvement has been done by more traditional hybridization techniques. An improvement in germplasm is relatively slow and is limited by a restricted gene pool. Strong sexual incompatibility at the interspecific and intergeneric levels has restricted rapid development of new cultivars with high levels of disease resistance, insect resistance, flavor, and sweetness. In order to increase the rate and diversity of new traits in melon it would be advantageous to introduce new genes needed to enhance both melon productivity and melon fruit quality. This requires plant tissue and plant transformation techniques to introduce new or foreign genes into C. melo germplasm. In order to achieve a successful commercial application from biotechnology, a competent plant regeneration system of in vitro cultures for melon is required. More than 40 in vitro melon regeneration programs have been reported; however, regeneration of the various melon types has been highly variable and in some cases impossible. The reasons for this are still unknown, but this plays a heavy negative role on trying to use plant transformation technology to improve melon germplasm. In vitro manipulation of melon is difficult; genotypic responses to the culture method (i.e., organogenesis, somatic embryogenesis, etc.) as well as conditions for environmental and hormonal requirements for plant growth and regeneration continue to be poorly understood for developing simple in vitro procedures to culture and transform all C. melo genotypes. In many cases, this has to be done on an individual line basis. The present paper describes the various research findings related to successful approaches to plant regeneration and transgenic transformation of C. melo. It also describes potential improvement of melon to improve fruit quality characteristics and postharvest handling. Despite more than 140 transgenic melon field trials in the United States in 1996, there are still no commercial transgenic melon cultivars on the market. This may be a combination of technical or performance factors, intellectual property rights concerns, and, most likely, a lack of public acceptance. Regardless, the future for improvement of melon germplasm is bright when considering the knowledge base for both techniques and gene pools potentially useable for melon improvement.

The objectives of this work were to assess and describe pepper (Capsicum annuum L.) root distribution in the soil profile and to relate root to shoot growth. Plants were field-grown from transplants, produced with either top or bottom irrigation, or from direct seeding using either primed or raw seeds. Dry weights were determined every 2 weeks beginning at 30 days post-planting. Root growth was measured at two soil levels, 0–10 cm and 10–20 cm and in three 10-cm wide positions within each level. Transplants and direct seeded plants had 150 and 100%, respectively, greater root mass in the upper than in the lower soil level. Root growth increase over 56 days was linear for transplants while in direct seeded plants root growth had a lag phase of approximately 14 days, with a sharp increase thereafter. At the end of the growth period, fruit, stem, leaf and root dry weight accounted for 66, 11, 19 and 4% for transplants and 39, 16, 33 and 12% for direct seeded plants. The coordination of growth between root and shoot changed after fruit set only in transplants, which indicates that transplants exhibited a greater fruit sink demand and fruit production than seeded plants.

Embryogenic callus of sweetpotato ( Ipomoea batatas (L.) Lam.) disassociates in liquid medium to form a heterogeneous population of embryogenic and nonembry- ogenic cell aggregates of varying sizes. To improve embryo production, such cell ag- gregate populations were obtained by manually fragmenting calli 5 to 10 mm in size into liquid medium. The resulting suspensions were analyzed and the embryogenic fraction identified. The percentage of embryogenic aggregates and the percentage of aggregates forming embryos decreased with decreasing aggregate size. Thus, 76% of the 710- to 1000-µm-diame ter aggregates but only 14% of the 180- to 250-µm aggre- gates had embryogenic potential. However, only 20% of the 710- to 1000-µm aggregates and only 2% of the 180- to 250-µm aggregates actually formed embryos. Conversely, embryogenic callus and embryo production per milligram of cultured embryogenic callus increased quadratically with decreasing aggregate size. Individual torpedo-stage embryos were produced from cell aggregates 180 to 250 µm in size. Sweetpotato, a major food crop and po- tential biomass crop, is conventionall y prop- agated using stem cuttings. This propagation method is costly since intensive labor and large nurseries and storage facilities are re- quired. The lack of resistance to virus dis- eases further complicates the maintenance and multiplication of virus-free stocks. Mass production of disease-free plant material can be expected using tissue culture. The pro- duction of synthetic seed, through somatic embryogenesis, and direct seeding would re- duce the production cost of this vegetatively propagated crop. The application of somatic embryogenesis to synthetic seed production will require many

Shoot and root growth changes in response to handling and storage time in `Sunny' tomato (Lycopersicon esculentum Mill.) transplants were investigated. Transplants, 45 days old, were stored either in trays (nonpulled) or packed in boxes (pulled) for 0, 2, 4, 6, or 8 days at 5 and 15C. Also, 35-day-old nonpulled and pulled transplants were kept in darkness at 20/28C for 0, 1, 2, or 3 days. At SC, pulled transplants had longer and heavier stems, a higher shoot: root ratio, higher ethylene evolution, and lower root dry weight than nonpulled transplants. At 15C, pulled transplants had more shoot growth than nonpulled transplants. Nonpulled, initially 35-day-old transplants had heavier shoots and roots and higher (7.0 t·ha-1) yields of extra-large fruit than pulled transplants (4.1 t·ha-1), but there were no differences in the total yields of marketable fruits.

Plant formation from somatic embryos in response to BAP, NAA, and sucrose was studied in sweetpotato [Ipomoea batatas (L.) Lam.]. A maximum of 15% embryos at the torpedo stage of development formed plants of agar-solidified basal medium containing 3% sucrose and no growth regulators. The percentage of embryos forming shoots was increased to 53% by 4 μm BAP, but BAP reduced whole plant formation and promoted callusing at the root axis end of embryos. The frequency of plant development was increased to 38% by adding 0.1 μm NAA to the basal medium. Reducing sucrose concentration to 1.6% in basal medium increased the frequency of plant development to 32%. Chemical names used: 6-benzylaminopurine (BAP; α-naphthaleneacetic acid (NAA).

The role of endo-β-mannanase (EBM) during lettuce seed germination at 35°C and the influencele of ethylene in EBM regulation were investigated. Seeds of ‘Dark Green Boston’ (DGB) and ‘Everglades’ (EVE) were germinated in water, 1-aminocyclopropane-1-carboxylic acid (ACC), or aminoethoxyvinylglycine (AVG). Seeds were also primed in polyethylene glycol (PEG), or PEG + ACC, PEG + AVG. Untreated seeds germinated 100% at 20°C. At 35°C, EVE germinated 100%, whereas DGB germinated only 4%. Seed priming or adding ACC during incubation increased germination at 35°C. AVG inhibited seed germination of DGB at 35°C. Higher enzyme activity was observed in EVE compared with DGB seeds. Providing ACC either during priming or during germination increased EBM activity, whereas AVG decreased activity. Higher ethylene production was detected in EVE than DGB during germination at 35°C. The results suggest that ethylene overcomes the inhibitory effect of high temperature in thermosensitive lettuce seeds by weakening of endosperm due to increased EBM activity.

Synthetic seeds are functionally defined as somatic embryos engineered to be of use in commercial plant production (Gray 1990b). The actual form of synthetic seed (i.e., presence or absence of a synthetic seed coat, whether they are hydrated or dehydrated, quiescent or not, etc.) may vary depending on the specific crop application.

In many lettuce (Lactuca sativa L.) cultivars, temperatures above 30 °C can inhibit germination completely. Lettuce seeds imbibed at supraoptimal temperature for 72 hours or more will not germinate even when the temperature is returned to the optimal range. Sung et al. (1998) reported that thermosensitive `Dark Green Boston' and thermotolerant `Everglades' responded to temperature at seed maturation by being able to show greatly enhanced germination at 36 °C when seeds were matured at 30/20 °C. Abscisic acid (ABA) plays an important role relative to both dormancy and germination of many seeds and may contribute to lettuce seed thermodormancy. Therefore, sensitivity of `Everglades' and `Dark Green Boston' to ABA of seeds maturated at 30/20 °C and 20/10 °C in light and dark was determined. Seeds were germinated at 20 °C and 36 °C in light and dark. All seeds of `Dark Green Boston'and `Everglades' matured at 30/20 °C and 20/10 °C germinated similarly regardless of maturation temperature and light/dark condition at 20 °C. At 36 °C in dark, both genotypes matured at 30/20 °C germinated more than those matured at 20/10 °C. `Dark Green Boston' genotypes were more sensitive to ABA (0.5, 1, 10, 50, 100 μM) during germination at 36°C in dark. When ABA was added, seeds matured at 30/20 °C germinated better than those matured at 20/10 °C, regardless of genotype. At 36 °C in light, 40% of both genotypes were inhibited at 0.5 μM ABA. At 36 °C in dark, germination of all seeds but `Everglades' matured at 30/20 °C were completely inhibited at all ABA concentrations. Thus, seed maturation temperature has an influence on lettuce seed germination at high temperature and sensitivity to ABA.

Thermotolerance in lettuce seed at high temperature was investigated using primed and nonprimed seed or seeds matured at 20/10°C and 30/20°C. During seed germination at 36°C, the structural changes of the seed coverings in front of the radicle tip were observed in an anatomical study. In all seeds during imbibition, regardless of seed maturation temperature or priming, a crack appeared on one side of the cap tissue and the endosperm separated from the integument in front of the radicle tip. Additional changes took place during imbibition: the protein bodies in the vacuoles enlarged and were gradually depleted, large empty vacuoles formed, the cytoplasm condensed, the endosperm shrank, the endosperm cell wall dissolved and ruptured, then the radicle elongated toward this ruptured area. The findings suggested that the papery endosperm layer presented mechanical resistance to lettuce seed germination and the weakening of this layer was a prerequisite to radicle protrusion at high temperature. Seeds of `Dark Green Boston', `Everglades', and PI 251245 matured at 30/20°C had greater thermotolerance than those matured at 20/10°C. Results of the anatomical study indicated that the endosperm cell walls in front of the radicle of seeds matured at 30/20°C were more easily disrupted and ruptured during early imbibition than seeds matured at 20/10°C, suggesting that these seeds could germinate quickly at supra-optimal temperatures. From anatomical studies conducted to identify and characterize thermotolerance in lettuce seed germination, it was observed that genotype thermotolerance had the ability to reduce physical resistance of the endosperm by weakening the cell wall and by depleting stored reserves.

Pollen germination timing has a paramount role in fertilization of a flower. Rapid germination and outgrowth of a pollen tube that penetrates the stigma is required. Physical and biological factors can affect pollen germination timing. The objective of this study was to determine if ACC oxidase antisense gene expression could influence in vitro pollen germination and in vitro pollen tube length growth. A transgenic (ACC oxidase antisense) `Galia' male parental line had a reduced fruit set compared to its wild type. Likewise, embryo abortion and empty seeds after self-pollination in a `Galia' male parental line were observed. Wild type and transgenic `Galia' male parental line melon plants were grown in a greenhouse according to the practices of Rodriguez (2003). Male flowers were collected from these plants between 10 to 12 am; pollen was obtained by dipping the anther in germination medium (10.25% sucrose, 0.031% calcium nitrate, 0.015% boric acid, 0.0075% KNO3, and 0.016% MgSO4) at 25 °C and analyzed immediately, either for total percentage of germination after 5 minutes of incubation or to measure pollen tube growth rate every 5 minutes during 1 hour. Each flower provided an average of 250 pollen grains. Assays were conducted by using the “Hanging Drop Method” (Okay and Ayfer, 1994). Percentage of pollen germination in WT `Galia' male parental line was greater than the transgenic line. Likewise, in vitro pollen tube growth in wild type `Galia' melon was greater than pollen from the transgenic line. Possibly the ACC oxidase antisense gene expression in `Galia' male parental line may have had an influence on the reduced fruit set observed.

Embryo abortion and empty seeds after self-pollination occur in some transgenic (ACO antisense) `Galia' male parental lines. An embryo-rescue system in this melon was developed to save potential viable embryos. To obtain the best and reliable embryo-rescue technique, several parameters were used including an improved (five new supplements) nutrient medium (named E-21) from the E-20A basic medium (Sauton and Dumax de Vaulx, 1987), an inoculation system (removing the embryo from the seed or intact seed), and the use of different fruit harvesting dates of the wild type and a transgenic `Galia' male parental line. Fruits of wild type (WT) and transgenic (ACO gene in antisense orientation) `Galia' male parental line were harvested at 4, 10, 17, 24, and 30 days after pollination (DAP). Fruits were surface sterilized by dipping in a 20% commercial bleach solution for 30 minutes. Subsequently, seeds were removed from fruit under sterile conditions. These seeds were either used to dissect the embryos or placed directly with the hilum facing E-20A or E-21 medium. Seedlings from all treatments were transferred to E-21 elongation medium, incubated 4 weeks, and transferred to soil to evaluate growth. The efficiency of this technique was greater when the time after pollination (4, 10, 17, 24, and 30 DAP) to rescue the embryos was increased. Thus, 30 DAP was the best time to rescue the embryos. The number of rescued embryos using E-21 medium was greater than with E-20A. We did not find any significant differences in survival efficiency rate between WT and transgenic embryos. We have obtained a competent embryo-rescue technique for WT and transgenic `Galia' male parental line, which can be applied to rescue valuable GMO hybrid-melon embryos.

Pepper seedlings can be infested with broad mites prior to transplanting. Transplanted seedlings may not present visible mite damage symptoms and few microscopic mites will be undetected by growers. A rapid increase of the mite population can subsequently result in yield losses in greenhouse-grown crops. Control of broad mites based on biological (N. californicus) and conventional (sulfur) methods were evaluated after infested transplants were introduced into a production greenhouse. Seedlings were artificially infested with two broad mites, 3 days before they were transplanted in mid-September in a passively ventilated greenhouse in Florida. Plants had either two predatory mites released once [4 days after transplanting (DAT)], or twice (4 and 22 DAT), or were sprayed with sulfur (four weekly applications starting 13 DAT when first damage symptoms were noticed). Damage on plants was assessed by an injury scale transformed into percentage values, with 100% being total damage on untreated infested plants. Broad mites were absent in all plants 38 DAT but the damage caused to the plants at this time was negatively correlated (r= –0.95) with marketable yield at 90 DAT. Plants produced no marketable yield where broad mites were not controlled. One or two releases of predators led to respective damages of 56% and 45%, and fruit yields of 2.0 and 3.0 kg·m-2. Plants sprayed with sulfur had a damage of 7% after reaching a maximum of 74% at 18 DAT; however, yields were 4.3 kg·m-2, which was similar to the yield obtained in the uninfested control treatment (4.6 kg·m-2). Releases of predators prior to transplanting and/or higher predator release densities may be needed under similar conditions and will be evaluated in a subsequent experiment.

`Galia' is a high-quality muskmelon cultivar that is grown in green-houses or tunnels to maximize fruit yield and to help improve fruit quality. Maximum fruit quality and flavor are achieved when `Galia' are harvested at maturity. This however leads to reduced firmness and short shelf life. In vitro regeneration and transformation of `Galia' melon is a strategy that can be used to increase fruit shelf life. Melon cotyledons were transformed with the ACC oxidase gene in antisense orientation according to the protocol described by Nunez-Palenius et al. (2001, 2003). Experiments were conducted to compare fruit quality parameters between transgenic (TT) and wild type (WT) fruits from plants grown in greenhouse conditions. The melon plants were grown using commercial growing practices that included pruning and training to one vertical stem and the use of soilless media and drip fertigation. Wild type fruits were harvested at 37, 42, and 50 days after pollination (DAP), whereas transgenic fruits were harvested at 42, 50, and 56 DAP. TT fruits were harvested with that delaying period since their ripening process was slower than WT. Thirteen preharvest parameters were evaluated in transgenic and wild type fruits. Wild type and transgenic weight, lenght, width, soluble solids, tritatable acidity, pH, firmness, flesh thickness, seed cavity size and seed number parameters were not significantly different. Ethylene production and ACC oxidase from 42 DAP wild type fruits were greater than from transgenic fruits. Transgenic (ACC oxidase) galia melon fruits had a delayed fruit ripening process compared with wild type fruits.

Cell size and media density can modify plant quality of greenhouse grown transplants through variation in light competition among plants, water and nutrient retention and root growth volumes required to fill the cells Thus, `South Bay' lettuce (Lactuga sativa L.) seedlings were grown in the greenhouse during different seasons to investigate the effect of different cell size and media packing density on transplant quality and yield for lettuce grown on sand and muck soils at different latitudes. Four Speedling flat cell sizes (882, 392, 242, 124 cells/flat) and two media packing densities (unpacked and packed - 1.5 times in weight) were tested in all the trials. Few seedling data parameters had an interaction between cell size and media density at transplanting. The larger cell size (242, 124 cells/flat) and greater media density led to increase leaf area, leaf length, shoot and total dry weight, RGR and LWR Conversely, RWR and the root:shoot ratio had the opposite trend, reaching the greater values with smaller cell size and less media density. High root growth can improve the pulling of the plants from the tray at transplanting and quicker establishment in the field. The treatments did not affect yield of plants grown on organic soil. When plants were grown on sandy soil head weights were greater from plants grown in 392, 242, or 124 cells/flat compared to 882 cells/flat.

A physiological disorder, “Elephant's Foot”, can develop in greenhouse hydroponic sweet pepper (Capsicum annuum L.). In a plant with this disorder, the base of the stem becomes swollen below the cotyledon level and wounds develop at the base of the stem's epidermis, what might predispose it to a localized rot and result in a sudden permanent plant wilt. Salt accumulation at the base of the stem could be a possible cause of the epidermis wounds. The effects of soilless media type (perlite, coconut coir, pine bark, and peat–perlite–vermiculate mix), transplant depth, and amount of nutrient solution applied per day were studied to evaluate the development of “Elephant's Foot” on a summer–fall sweet pepper greenhouse crop in Gainesville, Fla. Seedlings grown in polyethylene containers were transplanted 29 June 1999 into 11.4-L pots at three transplant depths: a) at half of the cell height, discarding only the bottom of the container (TOP); b) at the cotyledon level (LEVEL), and c) at the second stem node (DEEP). Plants were irrigated with 2, 2.5, 3, 3.5, and 4 L/day per plant of solution. The percentage of plants with epidermis wounds at the base of the stem was highest (82.5%) on TOP plants, compared to LEVEL (5.8%) and DEEP plants (0%). TOP plants had higher values of electrical conductivity on the stem epidermis than LEVEL and DEEP plants. There was a positive linear relationship (r = 0.82) between the percentage of plants with epidermis wounds and the electrical conductivity. Early yield of extra large and large fruits was higher in DEEP (1.05 kg·m–2) than in TOP plants (0.82 kg·m–2). Transplanting sweet pepper with the cotyledonary node under the soilless media could minimize salt accumulation and epidermis damage at the base of the stem level.