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The timing of nitrogen (N) fertilizer application has a direct impact on fertilizer use efficiency of potato (Solanum tuberosum L.) and nitrate leaching. The objective of this study was to determine the effect of N fertilizer rate combined with application timing on soil mineral N availability, tuber yield and quality of crisp potato in northeast Florida. Trials were performed on three commercial farms in 2011 and repeated on two farms in 2012. N fertilizer was applied at three different timings: at pre-plant (Npre-pl), at plant emergence (Nemerg) and at tuber initiation (Ntuber init). All seven treatments received a total of 224 kg ha−1 of N, with each treatment differing in the proportion of N supplied at each application timing. N was applied at 0 or 56 kg ha−1 at Npre-pl followed by 0, 56, 112 or 168 kg ha−1 of N applied at Nemerg and 0, 56, 112 or 168 kg ha−1 of N applied at Ntuber init. Treatments were combined in fractional factorial arrangement in a randomized block design with four replicates. Tuber marketable yield ranged from 23.7 to 44.6 Mg ha−1. Total and marketable yields were unaffected by timing or N rate combinations on two out of three farms and tuber quality was mostly unaffected by application timing. Higher yields were obtained when 56 kg ha−1 of N was supplied at pre-plant compared to 0 kg ha−1 of N on only one farm in both years. On the same farm, regardless of the application of 0 or 56 kg ha−1 Npre-pl, the application of 168 kg ha-1 of Nemerg resulted in superior total yields than when 168 kg ha−1 was instead supplied later in the season at Ntuber init. Higher proportions of N at pre-plant and tuber initiation tended to decrease potato tuber size, and a high proportion of N supplied at tuber initiation resulted in lower yield and higher residual soil mineral N at the end of the season.

Knowledge of seasonal nutrient demand is necessary to maximize potato (Solanum tuberosum) yield and profitability while also minimizing the risk of excess fertilizer leaching into waterways. The objective of this study was to determine the effect of the N fertilizer rate and timing of application on the N use efficiency (NUE) and yield of chipping potato ‘FL1867’. This study was conducted with grower collaboration on three commercial farms for two years (2011 and 2012) using subirrigation on course textured soils in Florida. All treatments received 56 kg ha−1 of N as ammonium nitrate applied as a band approximately 40 days before planting (Npre-pl). Liquid urea ammonium nitrate was then band applied at 0, 56, 112, or 168 kg ha−1 at plant emergence (Nemerg) followed by 56 or 112 kg ha−1 applied as a side-dress at tuber initiation stage (Ntuber init). The treatments were arranged in a factorial design with four replicates. The total amount of N fertilizer applied ranged from 112 to 336 kg ha−1. Maximum daily N uptake by the potato crop occurred between 55 and 65 days after planting, coinciding with the onset of the tuber bulking stage. Heavy rainfall prior to planting the 2011 crop reduced soil N availability from pre-plant applied N fertilizer indicating the high susceptibility of that application timing to leaching. Average tuber yield ranged from 25.6 to 47.2 Mg ha −1, with the lowest yields occurring when heavy rainfall close to harvest increased yield loss to decay. While higher Nemerg rates increased soil inorganic N, tuber yield was either not affected by N application or responded quadratically peaking at Nemerg levels between 95 and 125 kg ha−1. N application rates above this range decreased yield and NUE while increasing soil residual N at the end of the season. Plant N uptake and tuber yield did not increase with Ntuber init rate above 56 kg ha−1 and it was associated with lower NUE and also higher residual soil N.

Optimum nitrogen fertilizer management is necessary to maintain sustainable and economical potato (Solanum tuberosum) production. The objective of this study was to determine the effect of N-fertilizer rate and timing of application on plant biomass, tuber marketable yield and quality of chipping potato irrigated by subirrigation. This study was conducted with grower collaboration on three farms for two consecutive years (2011 and 2012). All experimental plots received 56 kg ha−1 of N as ammonium nitrate approximately 40 days before planting, a common grower practice. Nitrogen fertilizer treatments were 0, 56, 112 or 168 kg ha−1 applied at plant emergence (Nemerg) combined with 56 or 112 kg ha−1 of N applied as a sidedress at tuber initiation (Ntuber init). The two years of this study were characterized by low rainfall conditions, reducing the risk of N leaching and runoff. Under these conditions, the N treatments rarely increased potato aboveground biomass. Mean marketable tuber yield across all sites ranged from 19.2 to 39.7 Mg ha−1 with the lowest yield when a large amount of rainfall occurred prior to harvest at one site. Marketable yield responded quadratically to increase N-fertilizer rates applied at plant emergence, with optimum yield calculated at Nemerg rate between 88 and 113 kg ha−1. Applying more than 56 kg ha−1 of N at tuber initiation did not increase marketable yield, tuber specific gravity or tuber quality on any farm in either year. Nitrogen rate treatments above 112 kg ha−1 at emergence, and 56 kg ha−1 at tuber initiation did not improve potato marketable yield or tuber quality. The contribution of 56 kg ha−1 applied at pre-plant to potato yield is still unknown, and may be more beneficial to move this application closer to planting.

The silverleaf whitefly, Bemisia tabaci biotype B (Gennadius) (Hemiptera: Aleyrodidae), is a key pest of tomato (Solanum lycopersicum L.) and other vegetable crops worldwide. To combat this pest, a non-crop banker plant system was evaluated that employs a parasitoid, Encarsia sophia (Girault & Dodd) (Hymenoptera: Aphelinidae) with whitefly, Trialeurodes variabilis (Quaintance) (Hemiptera: Aleyrodidae), as an alternative host for rearing and dispersal of the parasitoid to the target pest. (a) Multi-choice and no-choice greenhouse experiments were conducted to determine host specificity of T. variabilis to papaya (Carica papaya L.) and three vegetable crops including tomato, green bean (Phaseolus vulgaris L.), and cabbage (Brassica oleracea L.). The result showed that papaya was an excellent non-crop banker plant for supporting the non-pest alternative host, T. variabilis, whose adults had a strong specificity to papaya plants for feeding and oviposition in both multi-choice and no-choice tests. (b) The dispersal ability of E. sophia was investigated from papaya banker plants to tomato and green bean plants infested with B. tabaci, as well as to papaya control plants infested with T. variabilis; and (c) the percent parasitism by E. sophia on T. variabilis reared on papaya plants and on B. tabaci infested on tomato plants was also evaluated. These data proved that E. sophia was able to disperse at least 14.5 m away from papaya plants to target tomato, bean or papaya control plants within 48–96 h. Furthermore, E. sophia was a strong parasitoid of both T. variabilis and B. tabaci. There was no significant difference in percent parasitism by E. sophia on T. variabilis (36.2–47.4%) infested on papaya plants or B. tabaci (29–45.9%) on tomato plants. Thus, a novel banker plant system for the potential management of B. tabaci was established using papaya as a non-crop banker plant to support a non-pest alternative host, T. variabilis for maintaining the parasitoid to control B. tabaci. The established banker plant system should provide growers with a new option for long-term control of B. tabaci in greenhouse vegetable production. Ongoing studies on the papaya banker plant system are being performed in commercial greenhouses.

Carrot (Daucus carota L.) seed germination may be erratic or reduced under high temperatures (above 35 °C). Even in tropical genotypes (tolerant to high temperatures during crop development), the negative effects of high temperatures on carrot stand establishment have been observed, especially during summer. The objectives of this study were to characterize commercial carrot cultivars and accession lines for their ability to germinate at high temperature and determine the ethylene production during imbibition at high temperature. Seeds from 34 commercial cultivars and 125 carrot accessions from the North Central Regional Plant Introduction Station were germinated at 25 °C (optimal) and 35 ± 0.5 °C (high) in constant light. Ethylene production during seed imbibition at high temperature was evaluated in some genotypes. Many of the commercial cultivars had reduced germination at 35 °C. ‘XPC-3617’, ‘Alvorada’, ‘Brasilia’, and ‘Esplanada’ had the greatest germination at 35 °C. A greater number of accessions germinated at 35 °C than did the commercial genotypes. The accession PI 319858 germinated 95% at both temperatures and was considered thermotolerant. Six accessions (Ames 7665, Ames 7698, Ames 25031, PI 167082, PI 294637, and PI 319858) germinated above 80% at 35 °C and were also identified as potential sources of thermotolerance. Fifteen other accessions (Ames 7694, Ames 25031, Ames 25036, Ames 25049, Ames 25705, PI 167082, PI 179687, PI 180834, PI 261782, PI 269486, PI 273658, PI 277710, PI 288242, PI 294637, and PI 319858) had thermotolerance ratios of T35/T25 0.85 or greater (where T35 = germination at 35 °C and T25 = germination at 25 °C) and were identified for further testing. The identified thermotolerant genotypes might be useful for carrot seed germination mechanism studies as well as for breeding programs. Ethylene production during seed germination at high temperature was greater in thermotolerant genotypes than in thermosensitive genotypes. High correlations were observed between first germination count at 35 °C and ethylene production, total germination at 35 °C and ethylene production, and thermotolerance ratio and ethylene production.

Eight plant densities (8.8, 9.5, 10.4, 11.4, 17.6, 19.1, 20.8, and 22.9 plants m −2 ) in 2001–2002 and 12 plant densities (8.8, 9.5, 10.4, 11.4, 12.7, 14.3, 17.6, 19.1, 20.8, 22.9, 25.4, and 28.6 plants m −2 ) in 2002–2003 were evaluated on growth and fruit yield of ‘Sweet Charlie’ strawberry ( Fragaria × ananassa Duch.) grown in a passively ventilated greenhouse. Plant densities were derived by varying within-row plant spacings (PS) (17.5 and 35 cm) with between row spacings (RS) (40, 45, 50, 55, 60 and 65 cm). Plants were grown in Polygal ® ‘Hanging Bed-Pack’ troughs filled with pine bark and fertigated with a complete nutrient solution. In 2001–2002, total marketable yield (g plant −1 ) or (no. fruit plant −1 ) were not influenced by RS. In 2002–2003, total marketable yield (g plant −1 ) or (no. fruit plant −1 ) were reduced at 40 cm RS, the narrowest RS used in the experiment. Early (November through January) and total marketable yields (g plant −1 ), crown diameter, and leaf number of plants grown at 35 cm PS were significantly greater than those of plants grown at 17.5 cm RS in both experiments. Total and early marketable yield (kg m −2 ) increased linearly as plant density (plants m −2 ) increased in both experiments. Winter strawberry production in a greenhouse using high plant densities and soilless substrates may be a viable alternative to open-field with methyl bromide fumigation production system.

‘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.

Frequent fertigation of soilless-grown bell pepper (Capsicum annuum L.) can increase fruit production, but development of fruit disorders may offset the increase in yield of first-quality (blemish-free) fruit in greenhouses with minimal environmental control. Fruit yield and quality were studied as affected by water volumes and nutrient concentration levels, delivered with irrigation events initiated after determined cumulative solar radiation levels, in ‘HA3378’ bell pepper from October to May in north–central Florida. Irrigation events occurred after solar radiation integral levels (SRI; ±SD) 1.7 ± 0.42, 3.7 ± 0.42, 5.7 ± 0.42, 7.7 ± 0.42, and 9.7 ± 0.42 kW·min−1·m−2, which led to mean number of daily irrigation events of 61 ± 31, 26 ± 12, 17 ± 8, 12 ± 5, and 10 ± 4 respectively. In peat mix, perlite, and pine bark media, volume per irrigation event and concentration levels of the nutrient solution were, in the first experiment, 74 mL standard (74-s), and in a second concurrent experiment, 74 mL half-standard (74-½s) or 3) 37 mL standard (37-s). In both studies, combined marketable fruit yields of first quality and second quality (minor cracking patterns and yellow spots) increased linearly with decreasing SRI (increased events per day). First-quality fruit weight with 74-s was unaffected by media and, in a quadratic response to SRI, reached 5.4 kg·m−2 at 5.7 kW·min−1·m−2. First-quality weight with 74-½s and 37-s did not differ. Weight was unaffected by SRI in peat mix and perlite, and a quadratic response was recorded in pine bark, with yields of ≤3.6 kg·m−2. Fruit cracking incidence decreased with increased SRI, and was generally greater in pine bark. Incidence of yellow spots doubled with 74-½s compared with 37-s, and decreased linearly with increased SRI; the disorder was minor with 74-s. Compared with 37-s, 74-½s decreased fruit with blossom-end rot by 14%, increased marketable fruit weight by 10% in media with the lowest water-holding capacity (perlite, pine bark), and increased nutrient use efficiency. With any media used, the SRI set point of 5.7 kW·min−1·m−2 (daily mean of 17 irrigation events) and 74 mL, at standard nutrient concentration levels, appeared to produce greater blemish-free fruit yield than delivering 37 mL/event or half-concentrated 74 mL/event within the range of SRI means of 1.7 to 9.7 kW·min−1·m−2 (61–10 irrigation events/day). Disorder-tolerant pepper cultivars, better temperature control, and August plantings are additional suggestions for irrigation management to increase first-quality fruit yield.

'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.

In the spring of 2001 and 2002, different combinations of media (coarse perlite, medium perlite, and pine bark) and containers (polyethylene bags and plastic pots) were used for hydroponic production of `Galia' muskmelons (Cucumis melo L.) to determine their effect on fruit yield and quality, and their influence on costs of production. Marketable yields obtained for `Gal-152' in the spring 2001 and 2002 were 25.5 kg·m–2 and 39.0 kg·m–2 respectively. When data were combined for 2001 and 2002, fruit yield and fruit quality were unaffected by any combination of media and container. Average soluble solids content was generally greater than 10° Brix. It was determined that the use of pine bark media and plastic pots instead of perlite and bags would save $18,200 per year (two crops)—a feasible option for reducing costs of producing `Galia' muskmelons in greenhouses using soilless culture without loss of yield and fruit quality.

Lettuce (Lactuca sativa L.) `South Bay' transplant growth and development were evaluated at 0, 30, 60, 90, and 120 mg·L–1 N fertigated at frequencies of every 1, 2, 3, or 4 days in a floatation production system to produce plants with optimum roots and shoots which easily pull from trays. Greenhouse experiments (four) were conducted to evaluate root and shoot weight, percent transplant pulling success, and leaf N content, 28 days after sowing (DAS). Field trials, using transplants produced in Greenhouse experiments 2 and 4, were conducted to evaluated subsequent yield, head quality characteristics, and leaf N content. Generally, as N concentrations increased, dry shoot weight and leaf N concentration increased, and root:shoot ratios decreased linearly or quadratically. Lettuce transplants grown in a floatation irrigation system fertigated every second to third day with 60 to 90 mg·L–1 N resulted in transplants with optimum root systems to achieve the highest pulling success rate from flats. Subsequent yields and head quality were optimum for pretransplant production fertigation N concentration of 60 to 90 mg·L–1, regardless of irrigation frequency.

`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.

Laboratory assays were performed to determine the impact of three predators, the bigeyed bug, Geocoris punctipes Say, minute pirate bug, Orius insidiosus (Say), and the pink spotted lady beetle, Coleomegilla maculata fuscilabris (Mulsant), on two herbivores, the cotton aphid, Aphis gossypii Glover, and the twospotted spider mite (TSM), Tetranychus urticae Koch, using strawberry (Fragaria ananassa Duchesne) leaflets as a substrate. Both herbivores are considered important strawberry pests worldwide. Daily and hourly consumption of a single prey species studied were conducted as well as a preference for prey test. All stages of the bigeyed bug, minute pirate bug, and pink spotted lady beetle fed on the cotton aphid and TSM. The pink spotted lady beetle had a higher rate of consumption for both the cotton aphid and TSM, and therefore, may be a more effective predator of both prey species. The bigeyed bug and minute pirate bug (third instar and adult) prefer TSM over cotton aphids based on handling time. In contrast, the pink spotted lady beetle (third instar and adult) prefers aphids over mites. Results from these experiments indicated that the pink spotted lady beetle seems to be a good predator to incorporate into an existing biological control program for cotton aphid and TSM on strawberries. Better understanding of these three predators will lead to their more efficient use for biological control of aphids and TSM.

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.

Silverleaf whitefly (SLW) ( Bemisia argentifolii Bellows and Perring) feeding on tomato (Lycopersicon esculentumMill.) plants induces a disorder in the fruit known as irregular ripening. The effects of silverleaf whitefly feeding on ripening of tomato fruit both attached to and detached from the plant are described. ‘Florida Petite’ tomatoes free of SLW, attached to the plant, began an ethylene climacteric between 40 and 45 days after anthesis (DAA), coincident with a rapid increase in red color and loss of firmness. The ethylene climacteric began between 45 and 50 DAA in tomato fruit from plants infested with SLW, and the fruit developed less red color and softened less than did fruit from plants free of SLW. Fruit harvested 45 DAA from plants free of SLW reached the respiratory and ethylene climacteric peak 3 days after harvest, developed normal red color, and softened similar to fruit ripened on the plant. In contrast, fruit harvested 45, 50 or 55 DAA from SLW-infested plants showed no respiratory or ethylene climacteric, had poor color development, and did not soften to the same extent as did fruit from plants free of SLW. Published by Elsevier B.V.

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...

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.

Somatic embryos of Ipomoea batatas Lam. (sweet potato cv. ‘White Star’) were produced in an airlift bioreactor. This work describes the optimization of the embryogenic system on semisolid medium, followed by transfer of the system to liquid cultures and ultimately to the airlift bioreactor. The physiological age of embryogenic callus influenced the number and overall morphology of the embryo population in both semisolid and liquid medium. Maximum mature embryo production (35 embryos 10 mg-1 inoculum) was obtained from six-week-old callus at 30°C. Somatic embryogenesis occurred in liquid cultures containing 20 mM NH4NO3 and 30 mM KCl. Globular embryos formed and continued development in suspension producing viable, mature cotyledonary embryos by day 14. Embryo formation and development was limited in the bioreactor. Although shear stress was responsible for some embryogenic damage, the effect of purging the system with fresh air needed to be investigated. To isolate aeration effects from shear stress effects, atmospheric determinations were performed on shaker flask cultures. Initially the gas composition within the Erlenmeyer headspace was that of room air. Ethylene increased to a maximum of 6.4 ppm (day 16), maximum CO2, 21.2%, was also evident on day 16, and oxygen was depleted to a minimum of 8.1% by day 14. Purging the cultures with fresh air reduced the number of embryos formed; however, they were significantly longer than those formed in closed flasks. The gas response model of Ipomoea batatas will enable atmosphere replenishment in the bioreactor mimicking that of the shaker flask environment. Once the damaging effects of shear stress have been overcome, the regulation of bioreactor gasses should allow somatic embryo formation in the bioreactor comparable to that in shaker flasks.

This work has demonstrated the aseptic, automated harvest of somatic embryos from a bioreactor suspension culture. Machine vision, emulating the selection criteria of an experienced biologist, classified embryos as harvestable or non-harvestable as they flowed through a 3 mm glass conduit. Embryos classified as harvestable were separated in a sealed harvest chamber. The system harvested 60% of the embryos at a rate of 2.4 embryos/h and incorrectly harvested less than 1% of the non-harvest objects. The low harvest rate precludes the applicability of this technique to research and commercial tissue culture laboratories. The suspension feed-rate, culture population density and culture homogeneity were identified as the most important factors influencing embryo harvest rate. The performance of this technique on more densely populated cultures was projected using anticipated improvements in suspension feedrate. It was concluded that, under the conditions of this analysis, the harvester would be of limited value in a commercial propagation environment but could be beneficial to many research labs working with plant somatic embryos.

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.

A method for somatic embryo production of sweet potato ( Ipomoea batatas (L.) Lam.) has been developed. The first step of somatic embryogenesis was to obtain embryogenic callus from 0.2 mm apical domes with 1–2 leaf primordia on medium containing 10 M 2,4-dichlorophenoxyacetic acid (2,4D). Selective proliferation of embryogenic callus has been obtained on solid media containing 10 μM 2,4-D and 1 μM benzylaminopurine (BAP) and in liquid media containing 5 μM 2,4-D. The fraction of suspension cultures larger than 710 μM was commonly used to produce embryos. Cultures were recultured every 2 weeks in liquid media and every 6 weeks on agar media. The formation of embryos was triggered by transferring embryogenic calli or cell aggregates from nutrient media containing 2,4-D to fresh media without 2,4-D. Late torpedo and cotyledonary stage embryos had the highest potential for plant formation. The automated production of synthetic seed in combination with fluid drilling technology could render economically feasible the production of sweet potato for biomass.

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 suspension cultures of Ipomoea batatas Poir. contain heterogeneous populations of discrete cellular units. In order to optimize embryo production, a study was conducted to identify the embryogenic fraction of such cultures. Suspension cultures were fractionated with sieves of 1000, 710, 500, 355, 250, 180, 125, 90 and 63μm mesh openings and the composition of each fraction was determined. Cellular units larger than 355 μm were primarily calli and made up 75% of the total mass of cultures in the stationary phase of growth. These calli were composed of embryogenic and non-embryogenic subunits, and 98% of the embryogenic subunits measured 355–1000 μm. Calli and embryogenic calli subunits produced clusters of embryos at various stages of development upon transfer to liquid or solidified media without 2,4-D. The 125–355 μm fraction of suspension cultures was composed of cell aggregates of which 20% were embryogenic. The embryogenic cell aggregates produced single globular embryos upon transfer to liquid media containing 0 or 1 μM 2,4-D. The 63–125 μm fraction of suspension cultures contained only 2% of embryogenic cell aggregates. It can be inferred from our results that the embryogenic fraction of cultures was essentially represented in calli, and that proliferation of the embryogenic fraction occurred through the separation of embryogenic cell aggregates from larger calli when cultures approached their stationary growth phase.

High numbers of embryos are difficult to obtain in liquid cultures of sweet potato (Ipomoea batatas (L.) Lam.) because discrete cell aggregates, produced through calli fragmentation, do not support embryo growth. In an effort to demonstrate that embryo development is possible from discrete cell aggregates, we compared embryo formation from cell aggregates 250–355 μm in diameter cultured either in suspension in liquid medium, on agar solidified medium, or immobilized on alginate beads floated in liquid medium. Embryos were initiated but remained arrested in their globular stage on cell aggregates cultured in suspension. Embryos developed to the torpedo stage from cell aggregates cultured on solidified medium and from cell aggregates anchored on alginate beads. Thus, embryos continued to develop beyond the globular stage when a structural polarity, which led probably to the establishment of a physiological polarity, was created. The production of sweet potato embryos in liquid culture can be improved by using alginate beads or culture conditions and protocols leading to the release during calli fragmentation of polarized individual cell aggregates.

Embryogenic callus cultures of Ipomoea batatas Poir. produce fast growing non-embryogenic material which soon dominates the cultures. Our objective was to selectively enhance the proliferation of the embryogenic fraction. For this, the effect of BAP and 2,4-D concentrations on growth of embryogenic and non-embryogenic callus were studied and consequently, nutrient media for the production and indefinite maintenance of embryogenic callus without embryo formation were defined. Selective proliferation of embryogenic callus was obtained on solid media with 10 μM 2,4-D and 1 μM BAP and in liquid media with 5 μM 2,4-D. Selective proliferation of non-embryogenic callus occurred in liquid medium with 1 μM 2,4-D. In embryogenic liquid culture, embryos were produced with 0–2 μM 2,4-D. Increasing 2,4-D concentration from 0 to 2 μM in these cultures restricted embryo development.

The loss of flesh firmness during muskmelon (Cucumis melo var. reticulatus L. Naud. cv. Galia) fruit ripening was related temporally to modifications of pectic and hemicellulosic polysaccharides, and a net loss of non-cellulosic neutral sugars. An increase in solubility and a decrease in molecular size of polyuronides occurred during ripening; however, the decrease in molecular size was apparently not the result of polygalacturonase (EC 3.2.1.15) activity. Molecular size of hemicelluloses shifted from larger to smaller polymers during ripening, and this decrease was accompanied by changes in neutral sugar composition. Galactose, glucose, and xylose were the predominant neutral sugars in the hemicellulosic polymers. On a mol% basis there were decreases in galactose and glucose in large hemicellulosic polymers with ripening. Relative xylose content approximately doubled in the large polymers during ripening; xylose was the predominant neutral sugar in the small polymers and remained fairly constant.