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The physiological and molecular markers were evaluated for defining leaf pruning line in bearing status of date palm (Phoenix dactylifera cv. Mazafati). Our results showed that the higher expression of the chlorophyllase (Chlase) gene was concomitant with lower expression of chlorophyll synthase (ChlG) and oxygen-evolving enhancer protein (PSBO) genes in the 6-year-old leaf line. In addition, the 6-year-old leaf line resulted in a lower Hill reaction rate, chlorophyll a/b ratio, photosystem Ⅱ quantum efficiency, and photosynthesis rate. Also, lower expression and activities of catalase (CAT), ascorbate peroxidase (APX), and glutathione peroxidase (GPX) was associated with higher malondialdehyde (MDA) and hydrogen peroxide (H2O2) accumulation in 6-year-old leaf line. These results suggested that the physiological maturity termination, senescence stage initiation, and source to sink transition could occur in 6-year-old leaves. Furthermore, delayed 5-year-old leaf pruning line adjustment in consecutive years could increase quantitative and qualitative yield loss, decrease water use efficiency, and promote alternate bearing and fruit abscission, which is considered a common problem of date growing areas. Further, the senescence-related markers in the alternate bearing trees pruned in pruning line 5 showed a tendency to normal trees. The five-year-old pruning line also resulted in the balance of bunching and loading the alternate bearing trees.

Table grape (Vitis vinifera L.) is one of the most popular berries in the world but easy to decay due to gray mold infiltration during storage. Sulfur dioxide (SO2) treatment is by far the most efficient way of for controlling gray mold development and long-term preserving table grape fruit. However, SO2 treatment causes severe abscission of berry from fruit cluster. In this study, two edible coatings (1.5% chitosan and 1.0% poly-e- lysine) were selected to prevent the berry from SO2-induced abscission in ‘Kyoho’ table grapes (Vitis vinifera L. x V. Labrusca) during room temperature (20 ℃) storage. Results indicated that both 1.5% chitosan and 1.0% poly-e- lysine treatments remarkably inhibited the SO2-induced abscission in ‘Kyoho’ fruits, and the abscission rates of both coating treated-groups were significantly lower even than the blank control (without SO2 treatment) after 6 d of storage. Meanwhile, both edible coating treatments significantly decreased fruit weight loss and inhibited the increase of the cell-wall-degrading enzyme activities. Overall, these two edible coating treatments maintained other fruit qualities such as, total soluble solids (TSS), titratable acids (TA), and content of vitamin C. Thus, the edible coating 1.5% chitosan or 1.0% poly-e- lysine provide potential effective ways to control SO2-induced fruit abscission and quality deterioration in table grape, and they may be of great commercial value during postharvest handling of table grape.

Pistachio is of high sensitivity to such physiological disorders as fruit abscission, endocarp lesion nut, blank, deformed, early split and non-split nuts. However, little research has been carried out on the physiological disorders in pistachio. In this study, the effects of organic manure, gypsum and boric acid treatments with their combination were studied on physiological disorders in ‘Kaleh-Ghoochi’ Pistachio. The treatments were done in autumn as soil application and physiological disorders as well as tree vegetative growth; in addition, biochemical traits including catalase (CAT), poly phenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonilyase (PAL) enzymes activities, total phenol content and proline content were measured throughout the growth. Results showed that organic manure and gypsum treatments alone or in combination reduced the physiological disorders and improved split nut percent and vegetative growth in pistachio as compared to control; however, combination treatments were more effective than each treatment lonely in reducing physiological disorders and increasing split nuts and vegetative growth. Effective treatments also reduced CAT, PPO, POD and PAL enzymes activities and total phenol and proline contents in the nuts. Generally, an increase in physiological disorders was concomitant with an increase in the enzyme activities and total phenol and proline contents in pistachio. The boric acid has not been effective alone or in the combined treatment in this study.

Fruit detachment can occur due to natural causes or be mechanically performed by a combination of mechanical stresses that cause tissue breakage in the plant. Forced abscission should not coincide with natural abscission zones (AZ). Abscission zones are very important in citrus harvesting both in terms of the destination market and of the possible damage caused to the tree or fruit. The objective of this study is to determine the abscission pattern of sweet oranges with a canopy shaker and compare it with other detachment systems. Five plots of Valencia oranges were tested during the 2017 and 2018 harvesting seasons, using a commercial tractor-drawn canopy shaker. The diameter, weight and breakage type were evaluated in the cases of natural fall, snap method, mechanical harvesting with canopy shaker, and pull test. Breakage type AZ-C predominated in natural fall (89.0%) and the snap method (79.5%). Similarly, AZ-A predominated for the canopy shaker (58.8%) and pull test (45.3%). Mechanical action on the fruit produced peel tear by breaking the flavedo, which reached highest frequency in the snap method (7.6%). Peel tear breakage required a mean fruit detachment force value of 99.3 N, higher than the average abscission values for AZ-C (88.7 N) and AZ-A (66.6 N). The fruit that remained on the tree after canopy shaker harvesting showed lower mean values of fruit detachment force (16.3%) than the pre-harvest fruit. The frequency of fruit with calyx with the canopy shaker and snap methods was similar, with a mean value of 36%.

The objective of this study was to investigate the response of leaf nutrients concentration, growth and yield of pistachio trees affected by changes in soil moisture and temperature as a result of different mulching. The experiment was conducted in a randomized complete block design with five replications in Feyzabad, Khorasan Razavi, Iran, for two years in 2014 (‘off’ year) and 2015 (‘on’ year). Treatments included sub-soil plastic (SPM1 and SPM2), up-soil plastic (UPM), woodchips (WM), barley residue (BM) mulches and control (CK). Treatment of SPM2 recorded the highest shoot growth and nut splitting, and lowest bud abscission in ‘off’ year. However, in ‘on’ year, maximum bud abscission was found in SPM2. Treatments of BM and WM were effective in decreasing flower bud and fruit abscission than other treatments during ‘on’ year. Mulching affected leaf P concentration in ‘off’ year and N, P and Mg in ‘on’ year, with the highest rate of these nutrients recording in BM treatment. Yield variations were not significantly affected by treatments in ‘off’ year, but in ‘on’ year, SPM2, WM, BM and SPM1 treatments increased yield by 29.2%, 28.7%, 19.8% and 10.5% compared to CK, respectively. Unlike other treatments, UPM had negative effect on leaf N concentration, and yield during ‘on’ year. This difference is attributed to high soil temperature in this treatment, so that yield reduced in soil temperature ranges over 36–37 °C in mean depth of 20–60 cm. In general, sub-soil plastic mulches, despite increasing yield in ‘on’ year, could not control flower bud abscission in that year. Thus, due to the increase of leaf nutrient concentration, regulation of alternate bearing phenomenon and improvement of yield, organic mulches are better options in arid and semi-arid regions with traditional irrigation methods.

Sapindus mukorossi Gaertn. (soapberry) is currently one of the most widely used biodiesel feedstocks in China. The canopy architecture of plants has significant impacts on microclimate, transpiration, and carbon acquisition and allocation, which can lead to plant disease and low yield. To solve low yield problems in soapberry and evaluate the relationship between light distribution and the canopy, crown architecture manipulation was carried out in this study to provide an ideotype to decrease leaf and fruit abscission. Canopy characteristics (LAI and CGfr), light characteristics (light ratio and PPFD) and photosynthetic characteristics (Pn, Tr, Gs and Ci) in different soapberry tree architectures were measured for 2 years to analyze light distribution, light interception and photosynthetic ability. This study also evaluated a two-factor interaction between scaffold branch angle (A30°, A45°, A60°, and A90°) and scaffold branch number (N3, N4, N5, and SC). Controlling the scaffold branch angle influenced light distribution, and branch angles of 60° and 90° increased light absorbance by 2–3 times in the vertical layers and decreased the disparity between inner and outer light ratios in the horizontal layers. Light interception ability was positively correlated (R2 = 0.785) with LAI from May to October, and the A90°N3 canopy architecture, which had 16% higher light interception ability than the other treatments and maintained the highest cumulative LAI (19.57) during the growing season, was the most suitable for preserving leaves in August and October. Light interception ability had no correlation with LAI in April (the month before blooming) but was positively correlated (R2 = 0.485) with the number of inflorescences, which indicated that higher light interception in April increased the number of inflorescences. Controlling the scaffold branch number significantly influenced Pn, Tr and Gs, and in particular, architectures with 3 scaffold branches provided 1–2 times higher photosynthetic ability than did the other architectures, with A60°N3 increasing Pn to 30 μmol CO2·m−2·s−1 and Gs to 0.26 mol H2O·m−2·s−1. The number of inflorescences was not directly correlated with yield, but yield in November was positively correlated (R2 = 0.5) with the photosynthetic rate*LAI in August. The highest yield, 0.3 kg·m−2 (projection area of crown), occurred in A60°N3 and A90°N3; the former was positively correlated with the photosynthetic rate in August, and the latter was influenced by high LAI and high light interception. Overall, high light interception ability could solve the problem of leaf abscission, and high photosynthetic ability could decrease fruit abscission in soapberry trees. A60°N3 and A90°N3 are the current ideotypes. These findings reveal the major factors influenced by canopy architecture and lay a foundation for further study of photosynthetic product distribution in different light environments. The selection of ideal architectural types will provide a mode and direction for further creative research into 3-dimensional visual structures, which will lead to additional theoretical and technical support for tree architecture planning.

Fruit abscission is largely governed by carbohydrate supply, and carbohydrate shortage intensifies fruit abscission. Understanding cues from the starving fruit that activate the abscission zone (AZ) is an intriguing research subject and important for control fruit abscission. In this study, starvation stress generated by girdling and defoliating the bearing shoots was used to explore the cues from the starving fruit that triggers abscission in longan. The starving fruit abscised quickly within 5 days. However, removing the starving fruit induced even faster AZ activation with greater ethylene production in the pedicel. Abscission of the defruited pedicel was strongly suppressed by IAA, slightly by ethylene action inhibitor, silver thiosulfate (STS), but not by GA3 or zeatin. Both IAA and ABA concentrations in the starving fruit and the pedicel were significantly reduced compared with the control. IAA exudation from the starving fruit was significantly lower, while IAA oxidase activity in the fruit was higher. The activity of plasma membrane H+-ATPase (PM H+-ATPase) in the fruit and the pedicel was not significantly affected by carbohydrate starvation, while that of PM Ca2+-ATPase in both organs was significantly reduced by starvation. The results suggested that the starving fruit seems not send abscission-promoting signal e.g. ABA or ethylene, but sends weakened abscission-suppressing signal, IAA, to the AZ. The weakened capacity of starving fruit to export IAA is related to increase in IAA deactivation and reduction in PM Ca2+-ATPase activity. The reduced IAA in the AZ leads to increased sensitivity to ethylene synthesized in situ in the pedicel, which activates the AZ under starvation.

Due to the high fruit abscission characterizing avocado, protocols for immature embryo rescue are an important tool in breeding programs based on hybridization of elite genotypes. The objective of this investigation was to evaluate the effect of in vitro desiccation under high relative humidity conditions on immature avocado embryo germination. The duration of the desiccation treatment significantly affected embryo germination, with optimum results achieved after a 14-day treatment (66.7% in desiccated embryos versus 15% in control, non-treated embryos). Other traits, such as recovery of complete plants and quality of the obtained plants, were also improved following desiccation. Trying to reproduce the final stages of avocado zygotic embryogenesis, the effects of desiccation after an in vitro maturation treatment was also evaluated. Results obtained revealed a significant effect of maturation stage, desiccation and the interaction between both factors; e.g., while desiccation significantly improved germination after in vivo maturation, a slight decline was observed in in vitro matured embryos, probably due to differences in embryo water status. However, recovery of complete plants and length of the structures formed were only significantly affected by maturation stage. Nevertheless, in embryos directly coming from trees, in vitro drying significantly improved rescue in all cases, independently of embryo developmental stage. Therefore, desiccation under high relative humidity conditions can be considered a valuable tool to be used in protocols for avocado embryo rescue. However, its use in conjunction with in vitro maturation treatments is not recommended.

Field experiments were conducted to study the effect of Boron (B) and Putrescine (PUT) on fruit drop percentage and quality of ‘Zebda’ mango during 2013 and 2014 seasons. Results indicated the beneficial effect of high concentration of B (0.3%) and PUT (0.45 mM) in decreasing the percentage of fruit drop and improving fruit quality. Fruit yield was increased by 19.2 and 16.2 kg tree−1 under B (0.3%) compared to the control in the first and second seasons, respectively. The reduction in fruit abscission was correlated with high activity of antioxidant enzymes (peroxidase, superoxide dismutase and catalase) in fruit petiole (FP). Also FP treated with B and PUT showed high contents of reducing sugars, free auxin, phosphorous and potassium as well as low contents of free amino acids, free phenolics and nitrogen. For fruit quality, total chlorophyll concentration in fruit peel was increased and ‘L’, ‘a’ and ‘b’ color values were affected by PUT (0.45 mM) and B (0.3%) treatments. Both treatments increased pulp (%), TSS (%) and TSS/TA ratio and decreased fruit firmness. It could be concluded that application of boron (0.3%) or Putrescine (0.45 mM) to ‘Zebda’ mango trees three times was effective in increasing fruit setting and yield in addition to improving fruit quality parameters.

Preharvest fruit drop is a challenge to apple production, in which fruit abscise from the tree prior to horticultural maturity. Depending on the growing season and the cultivar, yield losses of up to 30% are common by the beginning of harvest and worsen with any delay in harvest. This apple fruit abscission is influenced by developmental and environmental cues. Perception of metabolic changes leads to regulatory changes that promote cell wall degradation, involving the hydrolytic enzymes polygalacturonase and cellulase. Ethylene has a clear association with abscission promotion; whereas, the role of other plant hormones is unclear. The study of plant bioregulators has identified that apple abscission is managed by the ethylene biosynthesis inhibitor, aminoethoxyvinylglycine, and the competitive antagonist for ethylene receptors, 1-methylcyclopropene. This review examines recent progress in understanding preharvest fruit drop of apples, discusses horticultural practices that may alleviate preharvest fruit drop, and provides suggestions for future research.

[EN] While the ethylene-auxin interactions are well documented in model dicots such as tomato (climacteric fruit) during mature fruit abscission, the process is not clearly understood in citrus (non-climacteric fruit). The mature fruit produces very little ethylene but is sensitive to ethylene treatments to induce abscission. By contrast, auxin treatments delay fruit abscission, but the particular role of auxin in the process is unknown. Since the IDA-HAE/HSL2 ethylene-independent pathway seem to regulate organ abscission in both model and crop species, we proposed that auxin treatment delays citrus fruit abscission by reactivating the basipetal auxin flux and reducing CitIDA3 expression, without modifying ethylene synthesis. Comparing orange (C. sinensis) genotypes which differ in their abscission rate, 'Navelate' vs. 'Valencia Late', we found that the force needed to detach the fruit from the tree (FDF) declines in parallel with 1) an increase of ethylene synthesis and CitIDA3 gene expression, and 2) a reduction of PIN1-like (auxin transporter) gene expresion. Further, auxin (2,4-D) treatment maintains a higher force in the abscission zone upregulating PIN1-like and AUX1-like (auxin transporter) gene expression, and downregulating CitIDA3 gene expression, but without modifying ethylene production. We conclude that the 2,4-D treatment delays citrus mature fruit abscission through an ethylene-independent pathway., We thank Dr. D. Westall for her help in editing the manuscript. We thank FMC Corp. for partially funding this study, and, particularly, Dr. Pedro Espinosa (FMC Corp.) for his enthusiasm and confidence. We thank Mr. F. Zarzo for technical assistance.

Snap bean is a salt sensitive plant and suffers from losses in yield and pod quality with any little increase of salt concentration in irrigation water. In order to study the effect of salicylic acid (SA), spermidine (Spd), and glycine betaine (GB) as phytoprotectants on enhancing growth, yield and pod quality of snap bean under different levels of NaCl salinity, an outdoor pot experiment was conducted in 2012 and 2013 seasons. Salinity was applied as NaCl form at 0 and 2000 ppm. The concentrations of foliar treatments were two levels for each treatment; the first level was 0 mM which served as control, and the second level was 1 mM SA, 0.5 mM Spd and 5 mM GB, in addition to their combinations. NaCl salinity at 2000 ppm reduced most of vegetative growth parameters such as plant f.w., leaf area ratio and leaf area index, which in turn reflected on the reduction of pods no./plant and yield f.w./plant and an increase in the fruit abscission percentage. Pod moisture % decreased under 2000 ppm NaCl which reduced pod f.w., and increased pod curvature %. Under 2000 ppm NaCl, GB at 5 mM and all its combinations increased membrane stability index, total soluble sugars and total soluble proteins concentration, while reducing free amino acids concentration, which were concomitant with decreasing pod curvature %. Meanwhile, application of SA at 1 mM, GB at 5 mM, and GB5 + SA1 + Spd0.5 increased leaves and pods no./plant, pod moisture %, and pod f.w., which reflected on increasing green pod yield.

‘Hass’ avocado (Persea americana Mill.) is characterized by distinct periods of excessive flower and fruit drop. Determining the cause(s) of these abscission events is critical for the development of strategies to increase fruit set and yield. Therefore, the objectives of this research were to determine pollination and fertilization rates of abscising flowers and to quantify the viability of developing ovules (seeds) and hormone concentrations of abscising versus persisting fruit through early and June drop of ‘Hass’ avocado. Experiments were conducted during sequential off- and on-crop years. Pollination, pollen germination, pollen tube growth and ovule viability of abscising flowers were determined by microscopic analysis. During early and June drop, cellular deterioration of developing ovules of abscising and persisting fruit was visualized with Evan’s blue stain. Abscisic acid (ABA), indole-3-acetic acid (IAA), and isopentenyladenine (IPA) concentrations were determined by radio-immuno assay (RIA) during the on-crop year only. On average ≥ 70% of abscising ‘Hass’ flowers were pollinated but due to the failure of the pollen grains to germinate and produce pollen tubes, fertilization never occurred and the ovule deteriorated. Fruit abscission during early and June drop was also due primarily to a lack of fertilization. Fruit abscission was associated initially with deterioration of the nucellus within the developing ovule in early drop, and subsequently with deterioration of the integument (seed coat) in June drop; both occurred more frequently in abscising than persisting fruit. Abscising fruit had greater ABA concentrations during early drop, June drop and fall fruit drop compared to persisting fruit; IAA and IPA were greater in abscising fruit during June drop, but not early drop or fall fruit drop. Only 25% of the total number of fruit that abscised per crop year were fertilized. Taken together, these results provide strong evidence that the majority of flowers and fruit of ‘Hass’ avocado abscise due to a lack of pollen germination and subsequent fertilization. In addition, the results suggest that ABA accumulation is related to ovule (seed) abortion and reduced fruit growth in abscising fruit.

Growth and reproductive structure retention in cotton (Gossypium hirsutum) is dependent on light intensity, which is often irregular in tropical environments due to shading from cloudiness associated with the monsoon. The objective of this study was to evaluate the potential effects that cloudiness-induced reproductive organ abscission and compensatory responses might have on cotton growth, partitioning and conversion of radiation to biomass (radiation use efficiency RUE) as this was unknown for the monsoon tropics. Cotton cultivars representing different morphology were sown in field experiments at closely timed intervals during the early monsoon over 5 seasons to expose crops to varying amounts of cloud-related shading, creating a matrix of crop responses. In paper I, final boll number was strongly linked with lint yield, and boll retention on the early and late flowering sympodia and yield were correlated with the radiation environment during flowering. Grouping sowing time treatments that had a similar intra-canopy distribution of bolls at maturity provided a mechanism to compare yield recovery post boll loss and consider causal factors. Maximum crop biomass ranged from 1232−1933 g m−2. Lint yield was correlated with the fraction of total biomass present as bolls (P Differences in biomass partitioning between cultivars were minor. When cloud cover abated, extended concurrent vegetative and reproductive growth enabled yield recovery. Greater LAI was a consequence of compensatory processes following fruit loss. Faster development of LAI in response to the monsoon during early flowering could further shade lower canopy fruiting sites, exacerbating fruit abscission and impacting yield compensation. RUEg (glucose equivalent) of 2.35 & 2.63 g MJ−1 PAR was comparable with cotton grown in temperate environments but declined when lower canopy fruit abscission followed by extended concurrent growth altered the ratio of vegetative vs reproductive biomass partitioning. Cloudiness poses a dichotomy of challenges for crop management during the tropical monsoon season. After cloudiness-induced fruit loss, extended concurrent growth when the radiation environment improves must be encouraged to enable the initiation of new fruiting sites for yield recovery. However, expansionary canopy growth in response to cloud and fruit loss may exacerbate detrimental shading of the lower canopy and detract from later yield recovery. Therefore management tactics including the use of irrigation, nutrient and growth regulant inputs must achieve an appropriate balance between vegetative and reproductive components during compensatory growth.

Growth and reproductive structure development in cotton (Gossypium hirsutum) is dependent on light intensity, which is often irregular in tropical environments due to shading from cloudiness associated with the monsoon. The objective of this study was to evaluate the effects of cloudiness on reproductive organ abscission and how subsequent compensatory organ replacement, with the provision of irrigation, might recover yield in the semi-arid monsoon tropics. Cotton cultivars representing different morphology were sown in field experiments at closely timed intervals during the early monsoon over five seasons to expose crops to varying amounts of cloud-related shading, creating a matrix of crop responses. A wide range for lint yield (1099 to 2900 kg ha−1) was symptomatic of the treatments’ exposure to highly varied environmental conditions. Lint yield was moderately correlated (P The clustering of sowing times into groups according to similarities in the number and final distribution of bolls within the crop canopy provided a mechanism to identify sowing time treatments that shared similar compensation responses. The highest group yields occurred when minimal cloudiness during flowering allowed uninterrupted boll accumulation or alternatively when moderate boll losses from the lower canopy were compensated via additional later set bolls when radiation improved. Yield recovery was restricted for groups where cloudiness was ongoing or increased during late flowering or when canopy factors detracted from efficient use of available radiation. Extrapolation of the linear relationship between boll number and incident radiation showed boll retention was maximised at a mean daily value of 24.2 MJ m−2 (Rmax). Quantification of Rmax was a key finding as it could be applied to calculate a cumulative radiation deficit (RD) = ∑ (if daily radiation is Yield compensation from cloud induced fruit abscission in the semi-arid tropics will be assisted by management that can extend flowering to create new fruiting sites whilst balancing the partitioning of canopy growth.

The quality of tree nuts can be influenced by their harvest time, cultivar and seasonal growing conditions. Some macadamia cultivars retain mature nuts in the tree for several months before fruit abscission and this can result in variations in harvest time. It is not known how the variations in harvest time affect the quality and shelf life of macadamia cultivars. We investigated how harvest time and cultivar influence the quality and shelf life of macadamia kernels. We tested the shelf life of kernels using two techniques: (1) a long-term shelf-life method; and (2) a short-term accelerated-aging method that assessed oxidative stability based on hexanal concentrations. Cultivars HAES 344 (344) and Hidden Valley A16 (A16) were harvested in May and late-abscising nuts of cultivar A16 were also harvested in September. Peroxide values, free fatty acid levels and fatty acid composition of kernels in the long-term experiment were measured after 0, 6, 12, 15 and 18 months of storage at 25 °C. Kernels in the short-term accelerated aging experiment were incubated at 45 °C, and hexanal concentrations were measured before incubation and after 6, 12 and 18 days. Kernels from late-abscising nuts (September) had much higher free fatty acid levels after 18 months of storage than kernels from early-harvested nuts (May). Cultivar A16 (September) kernels had significantly higher hexanal concentrations than cultivar 344 (May) and A16 (September) kernels at 12 and 18 days of incubation. The accelerated aging technique could detect differences in oxidative stability between different batches. Nuts harvested in September had shorter shelf life by about 3–6 months than those harvested in May, based on both predicted shelf life and actual time taken to reach acceptable-quality limits. Therefore, we recommend harvesting macadamia nuts as soon as possible after maturity to minimise quality losses.

As Huanglongbing (HLB) becomes epidemic throughout Florida, there is a sharp rise in mature fruit drop prior to harvest in affected citrus, leading to a substantial reduction in yield. To investigate how HLB increases mature fruit abscission, this research evaluated the drop rate and compared the global gene expression using RNA sequencing in HLB-susceptible ‘Hamlin’ sweet orange (Citrus sinensis) versus HLB-tolerant ‘LB8-9’ mandarin {‘Clementine’ mandarin (C. reticulata) and ‘Minneola’ tangelo [hybrid of ‘Duncan’ grapefruit (C. paradisi) and ‘Dancy’ tangerine (C. reticulata)]}. Consistent with their susceptibility to HLB documented in the literature, the drop rate of mature fruit was significantly higher in ‘Hamlin’ sweet orange than ‘LB8-9’ mandarin. Between the two citrus, there were 368 differentially expressed genes (DEGs); 310 and 58 were upregulated and downregulated, respectively, in the abscission zone (AZ) of ‘Hamlin’ sweet orange compared to ‘LB8-9’ mandarin fruit. Although at the time of collection, fruits of both citrus were still attached to the tree branch (fruit detachment force > 6 kgf), upregulation of the DEGs related to cell wall loosening in ‘Hamlin’ sweet orange indicates that the process of abscission was already initiated in the AZ of this citrus. The pattern of DEGs related to the metabolism and signal transduction of hormones, specifically ethylene, auxin, cytokinin, abscisic acid, and gibberellic acid, also suggests that HLB likely brings about changes in endogenous hormone balance that promote mature fruit abscission. Interestingly, DEGs encoding antioxidants were upregulated, suggesting a demand for detoxification mechanisms against oxidative stress in the AZ of ‘Hamlin’ sweet orange fruit. Additionally, gene ontology (GO) terms for cell death and senescence, two of consequences of oxidative stress, were highly enriched. Together, the results of transcriptome analysis presented herein provide evidence that for HLB-susceptible ‘Hamlin’ sweet orange, oxidative stress caused by the pathogen infection likely results in cell wall modification, leading to cell separation and eventually fruit abscission. The results further suggest that ‘LB8-9’ mandarin may have an advanced antioxidant system to mitigate the pathogen-induced oxidative stress, thereby contributing to its tolerance to HLB.

The common marsh macrophyte Cladium jamaicense (sawgrass) has high levels of fruit abortion. We investigated the phenology of post-fertilization fruit development and of fruit drop in southern Florida, USA, to determine the timing of fruit abortion in relation to fruit shedding. Fruits at two sites were harvested at 2-week intervals, weighed individually and examined for potential viability (PV) to document changes in fruit biomass, morphology, and abortion rate. Fruits shed into 1/4 m 2 traps placed in sawgrass patches at two sites were counted and assayed for PV every one or two weeks in summer 2009 and 2010. Sawgrass sheds fruits from mid-July to September with peak fruit drop in late July to mid-August, 2–2.5 months after flowering. Sawgrass fruits had high rates of abortion that differed among plants and between sites and increased from mid-July through August. One-third to one-half of all fruits shed by a plant over the summer were aborted. Sawgrass plants had late fruit abortion that occurred prior to shedding but after investment in fruit development, producing persistent aborted fruits. A model for the effect of these fruits on seed bank viability predicted levels of 2% seed viability in the seed bank for 50% fruit abortion, similar to values for seed bank germination from the literature. The low percent of viable sawgrass seeds reported here provides a baseline population parameter for Everglades and other Caribbean marsh restoration and indicates the need to determine the input of viable fruits when studying seed banks and/or germination.

Prolonged drought stress in Palestine is one of the major limiting factors in the production and yield of the fruit of the olive tree, as this directly affects crop load, oil production per tree, oil quality and alternate bearing. The objective of the present study was to investigate the use of limited amounts of water as complementary irrigation to improve olive fruit growth and yield at harvest. Field-grown adult olive trees (Olea europaea L. cv. Nabali Baladi) were selected in three villages on the northern West Bank, and they were subjected to different complementary irrigation regimes from June to September, 2010. They were thus supplied with 1, 3, 6 m3 water irrigation per tree over this entire period, corresponding to 2.4%, 7.1%, 14.2% of the whole seasonal water requirement per tree (42 m3 water), respectively. Additional five rain-fed trees per site were used as controls. In one of the three villages, an additional treatment with 15 m3 (35.6% of the total need) water irrigation per tree, was also applied. The results showed that the fruit size, pulp-to-pit ratio (on a fresh and dry weight basis) and 1-year-old mixed shoots were not affected by these water irrigation regimes. Total fruit yield per tree increased as the water irrigation increased, with the greatest effects for the highest water irrigation treatment, due to a higher number of fruits per tree (apparently due to lower fruit abscission). This study demonstrates that complementary water irrigation of olive trees to 35% of the whole seasonal water requirement can produce positive effects on olive fruit production in Palestine.

Although oil synthesis in fruits of cv. Arbequina starts at the end of pit hardening (beginning of July in central Spain) most oil is synthesized from late summer (end August) until harvest (end October). An experiment was established in two nearby high-density olive orchards (C and L) trained in 4-m spaced hedgerows (2.3 m tall) and maintained over three successive seasons (2011–2013) to determine the effect of irrigation treatments during oil synthesis on stem water potential (Ψstem), fruit characteristics, production, water productivity (production per irrigation amount + effective rainfall), flowering and fruit-set and next-year growth. The control treatments (C1 and L1) were irrigated to maintain the “wetted” bulb near field capacity throughout the season. Three deficit-irrigation treatments were established in each orchard. In orchard C, treatments C2, C3 and C4 received 64, 38, 14% of the water applied to C1, while in orchard L, treatments L2, L3 and L4 received 71, 41, 18% of water applied to L1. The treatments produced significant differences in Ψstem that were lower in Orchard C (mean C4 value −4.91 MPa) than L (L4 −2.58 MPa) due to differences in soil depth and drip emitter spacing. At the two orchards, individually, the stressed trees were not significantly affected in terms of shoot length, flowering, fruit set, fruit abscission and consequently fruit number. While deficit irrigation significantly reduced size, oil and water content of fruit, and hence olive and oil production in Orchard C, there was no response in Orchard L. Analysis revealed that individual fruit parameters were maintained constant as Ψstem decreased during oil synthesis in response to treatment until a threshold value was reached. Oil content (% fresh weight-FW) was the least sensitive parameter (threshold −4.11 MPa) with a positive linear relationship between water and oil fruit content (R2 = 0.81). Olive production was more sensitive to Ψstem (threshold −1.82 MPa) than oil production (−2.21 MPa). Indicating that moderate stress can be applied during oil synthesis by irrigating such that Ψstem declines to the threshold value −2.21 MPa without reduction of oil production. This value corresponds to a water-stress integral of 130 MPa day−1. Maximum water productivity was achieved by irrigating at Ψstem −2.31 MPa with lower values obtained at higher or lower Ψstem. Our results indicate that Ψstem should be maintained higher than −2.21 MPa during oil synthesis for maximum production, but higher values of the water productivity will be achieved at −2.31 MPa.

In Australian macadamia ( Macadamia integrifolia Maiden and Betche, M . tetraphylla Johnson and hybrids) orchards, trees are generally side-hedged in early spring to maintain the inter-row for efficient orchard management. Hedging at this time increases fruit abscission and decreases yield due to competition for carbohydrates between fruit and post-pruning shoot growth, and to the loss of photosynthetic area. Girdling increases fruit set in many crops and the possibility that girdling might mitigate the effect of pruning on fruit abscission and yield was investigated in this study. Girdling was also investigated for its potential to control shoot growth and tree size. In the first experiment, in early spring around anthesis, trees were pruned (P), pruned and girdled (PG), or were left as unpruned and ungirdled control trees. Fruit per raceme over time, percent of racemes with fruit at 20 weeks post anthesis, fruit number per tree, nut weight, yield, and the shoot length and number of the post-pruning flush were measured. In a second experiment, trees were pruned (P) or pruned and girdled (PG) in autumn, and the shoot length and number of the post-pruning flush were measured. In a third experiment, trees were girdled at anthesis in 3 years over a 4-year period and shoot growth, tree height, yield, fruit number and nut weight were compared with ungirdled control trees. Girdling mitigated the effect of pruning on fruit abscission and yield but the mitigation was slight with PG trees producing 28% less yield than unpruned control trees. Girdling reduced shoot length and number but more so on unpruned branches (26% and 28%, respectively) than on pruned branches (10% and 14%, respectively). The tree height increment in girdled trees was around half that of ungirdled trees. In the 4-year study, girdling increased yield by around 10% in two out of four seasons, and decreased it in one season. Cumulative yields were similar for girdled and ungirdled trees. This study has shown that girdling was not useful in mitigating the effect of pruning on yield. However girdling was effective in controlling shoot growth and tree size, with no reduction in cumulative yield, and may be useful as a tree size control strategy. Further monitoring of long-term effects of repeat girdling is required to confirm this.

Abscission is an important postharvest factor for table grapes and cluster cherry tomatoes. There are methods to measure the individual fruit removal force but until now there has been no objective method to study the abscission at a whole cluster level. The working principle of the instrument is that a cluster is attached to a rod which is allowed to fall freely for a pre-determined distance; as the rod stops, the momentum of the berries is converted to detachment force applied to the abscission zone of each berry. The abscission potential can be evaluated as a percentage of fruit detached from cluster under given conditions. The instrument was constructed for robust and adjustable experimental use. It is shown that the abscission percentage for both table grapes and cluster cherry tomatoes was proportional to the free-fall distance. By using the instrument, we showed that the abscission potential of cluster cherry tomatoes was low during the first 2 weeks of storage and that it increased thereafter. Storage of cluster cherry tomatoes at 7 °C resulted in significantly less abscission than at 12 °C, as assessed either by manual shaking or by using the instrument. Treatment of grapes with the cytokinin-like compound forchlorfenthuron at 4 mg L −1 during the early stages of fruit development resulted in significant reduction in abscission potential. These results demonstrate that the method can be used as a reliable experimental tool for objective evaluation of abscission potential.

Chemical thinning of young apple ( Malus domestica , Borkh.) fruit has become standard agricultural practice worldwide. The general understanding about the mode of action of thinning substances is, however, still very limited. Benzyladenine (BA), one of the most promising newer thinning chemicals has been chosen as an example to study its “mode of action”. The following aspects were investigated: (1) the site of action, (2) effects on seed number and development, (3) fruit and vegetative growth, (4) photosynthesis and (5) polar indoleacetic acid transport (IAA PAT ). When BA was applied at 100 mg L −1 on three apple cultivars on whole trees or leaves-only, thinning effects were comparable to or even stronger than hand thinning. BA applied only on fruit showed insignificant thinning. At June drop the weight of abscising fruit was comparable or even higher when treated with BA. Growth of remaining fruit was not affected until harvest when only fruit were treated. However, when leaves-only or whole trees were treated remaining fruit showed a decreased fruit growth initially but surpassed control fruit thereafter. No direct correlations were found between thinning efficacy and seed number, shoot growth, photosynthesis and by indirect conclusion, assimilate allocation. Thus, these assessments provided no clear explanation for a possible mode of action of BA. Remarkably, a decrease in IAA PAT of lateral fruit was opposed to an increase in IAA PAT of bourse shoot tips after BA application. This was only observed when leaves/shoot tips but not fruit only were treated. Assuming a correlative IAA transport autoinhibition (ATA) of fruit by the IAA PAT of shoots, particularly of bourse shoot tips, may explain fruit abscission and the mode of action of BA applications in apple. The latter aspects are discussed in more detail.

Fruit thinning is an essential part of the commercial production of quality apples. A portion of the excessive fruitlets is abscised, or shed, physiologically as a self-regulatory mechanism; however, the degree of abscission varies depending on the environmental conditions and cultivars. The number of abscised fruitlets within a cluster is influenced by the number of leaves in the cluster. In some cultivars, the fewer leaves there are in a cluster, the larger the number of fruitlets undergo abscission is. Conversely, the growth rate of a fruit cluster is marginally influenced by the number of leaves in the cluster and appears constant for each cultivar. The constant growth rates of fruit clusters indicate the source strength, which supports the growth of individual fruitlets (sink organ) on the tree. The cultivar differences in the percentage of fruitlet abscission were highly correlated with the source strength of the cultivars, indicating that the rate of abscised fruitlets was determined by the source strength of the cultivars. The number of days between full bloom and diminishing growth of abscising fruitlets was also correlated with the source strength. Therefore, a cultivar with low source strength is prone to abscising many fruitlets at an early date compared with one with high source strength. The source strength of a cultivar, therefore, can be a useful index for selecting cultivars characterized by easy and early abscission.

Among melons, cantaloupes are most frequently implicated in outbreaks and surveillance-based recalls due to Salmonella enterica. There is limited but compelling evidence that associates irrigation water quality as a significant risk of preharvest contamination of melons. However, the potential for root uptake from water and soil and subsequent systemic transport of Salmonella into melon fruit is uncharacterized. The aim of this work was to determine whether root uptake of S. enterica results in systemic transport to fruit at high doses of applied inoculum through sub-surface drip and furrow irrigation during field production of melons. Cantaloupe and honeydew were grown under field conditions, in a silt clay loam soil using standard agronomic practices for California. An attenuated S. enterica sv. Typhimurium strain was applied during furrow irrigation and, in separate plots, buried drip-emitter lines delivered the inoculum directly into the established root zone. Contamination of the water resulted in soil contamination within furrows however Salmonella was not detected on top of the beds or around melon roots of furrow-irrigated rows demonstrating absence of detectable lateral transfer across the soil profile. In contrast, positive detection of the applied isolate occurred in soil and the rhizosphere in drip injected plots; survival of Salmonella was at least 41 days. Despite high populations of the applied bacteria in the rhizosphere, after surface disinfection, internalized Salmonella was not detected in mature melon fruit (n=485). Contamination of the applied Salmonella was detected on the rind surface of melons if fruit developed in contact with soil on the sides of the inoculated furrows. Following an unusual and heavy rain event during fruit maturation, melons collected from the central area of the beds, were shown to harbor the furrow-applied Salmonella. Delivery of Salmonella directly into the peduncle, after minor puncture wounding, resulted in detection of applied Salmonella in the sub-rind tissue below the fruit abscission zone. Results indicate that Salmonella internalization from soil and vascular systemic transport to fruit is unlikely to occur from irrigation water in CA production regions, even if substantially above normal presumptive levels of contamination. Although contaminated irrigation water and subsequently soil in contact with fruit remains a concern for contamination of the external rind, results suggest an acceptable microbial indicator threshold and critical limit for the presence of Salmonella in applied water may be possible by defining appropriate microbiological standards for melon irrigation in California and regions with similar climate, soil texture, and crop management practices.

a b s t r a c t Two experiments were conducted to assess the relationship between alternate bearing, flowering, fruit set, and fruit growth in mature ‘Hass’ avocado (Persea americana Mill.) in Irvine, California. In the first experiment, trees were grown on four clonal rootstocks (‘Thomas’, ‘Topa Topa’, ‘Duke 7’, or ‘D9’), and data collected on yield, number of fruit per tree, average fruit weight, and the timing and duration of flowering over five seasons. In the second experiment, ‘Hass’ trees were grown on ‘Duke 7’ rootstock and data collected on the rate of fruit retention and fruit volume growth over three years. In Experiment 1, the trees exhibited “on” and “off” years in most cropping cycles. Heavy yields were associated with a higher number of fruit per tree, lower average fruit weight, and early and longer periods of flowering. Although yield varied among rootstocks, especially in heavy crop load years, trees growing on different rootstocks had similar cropping patterns. In Experiment 2, fruit abscission varied over years, but rates of volume increase were similar over years. Low yields in ‘Hass’ avocado trees appear to be related to later and shorter flowering periods and fewer and larger fruit at harvest. © 2012 Elsevier B.V. All rights reserved.

Despite problems of low fruit set, small fruit size and alternate bearing, the Hass cultivar dominates commercial avocado production worldwide. To increase yield and fruit size, gibberellic acid (GA 3 ) (25 mg L −1 ) was applied at different stages of ‘Hass’ avocado tree phenology: ( i ) mid–late April (flower abscission), end of June–beginning of July (fruit abscission and beginning of the exponential phase of fruit growth), and mid-January (beginning of pre-harvest fruit drop); ( ii ) end of June–beginning of July; and ( iii ) mid-September (near the end of the major fruit abscission period; period of exponential fruit growth). In both years of the research, applications of GA 3 in April and June–July were within the periods of intense flower and fruit abscission, respectively; fruit abscission was low in September and January. Maximum air temperature was not related to flower or fruit abscission. In the on-crop year (391 fruit per untreated control tree), a single application of GA 3 at the end of June–beginning of July significantly increased total yield (kilograms only) and yield of commercially valuable fruit (178–325 g/fruit) (as kilograms and number per tree) compared with the control ( P 3 applied in September increased total yield (kilograms only) and yield of commercially valuable fruit (kilograms and number per tree) to values intermediate to and not significantly different from all other treatments, except trees receiving multiple applications of GA 3 . This treatment reduced total yield and yield of commercially valuable fruit (kilograms and number per tree) relative to all treatments ( P ≤ 0.0002). In contrast, during the off-crop year (32 fruit per control tree), no GA 3 treatment had a significant effect on yield or fruit size compared with the control and all other GA 3 treatments. For ‘Hass’ avocado, there was no negative effect from applying GA 3 at the end of June–beginning of July in both the off- and on-crop years; 2-year cumulative total yield and yield of commercially valuable fruit were increased by 27 kg (128 fruit) and 22 kg (101 fruit) per tree, respectively, above the yield of untreated control trees ( P

Worldwide, gibberellic acid (GA3) is used routinely to increase fruit number and size of seedless mandarins. The efficacy of seven combinations of GA3 concentrations and application times to maximize total yield and yield of commercially valuable fruit (diameter 57.2–76.2 mm) of ‘Nules’ Clementine mandarin (Citrus reticulata Blanco) was determined in a commercial orchard. GA3 applied during the period of intense flower abscission failed to reduce the total number of abscised flowers in both the light off- and heavy on-bloom years. No GA3 treatment reduced fruit abscission when trees were setting the low yield off-crop. However, all trees receiving GA3 in the high yield on-crop year had fewer abscised fruit than untreated control trees (P = 0.0188) and GA3 applied 10 days after 75% petal fall and in July increased the number of fruit retained on tagged branches >20% compared to control trees (P = 0.0005). Maximum air temperature was not related to flower or fruit abscission. In the off-crop year (548 fruit per untreated control tree), it was necessary to apply 15 or 25 mg L−1 GA3 at 60% bloom, 90% bloom, 75% petal fall and 10 days after 75% petal fall to significantly increase the number of fruit per tree and yield of commercially valuable fruit (kilograms and number per tree) (P

Pseudocercospora macadamiae causes husk spot of macadamia. Husk spot control would be improved by knowledge of the persistence of the pathogen in orchards between seasons, and by characterising macadamia cultivars for susceptibility to infection, premature fruit abscission, and spatial escape from inoculum sources. Field observation of seven macadamia cultivars found a significant exponential relationship between husk spot incidence and the prevalence of fruit pericarp that failed to abscise (sticktights) in the canopy. Viable conidia of P. macadamiae were readily (>100 conidia per fruit) produced on sticktights for 30 months. The incidence of husk spot was up to four times greater in trees with sticktights than trees without sticktights. Assessment of the propensity to form sticktights, husk spot incidence and fruit abscission after the insertion/removal of sticktights, demonstrated differences in macadamia cultivars; cv. A16 was susceptible to infection and formation of sticktights, but tolerant of premature abscission; cv. 246 was susceptible to infection, tolerant of premature abscission, and spatially escapes P. macadamiae inoculum due to a lack of sticktights; cv. A38 was susceptible to infection, premature abscission, and sticktight formation. Our findings suggest that disease could be reduced by removing sticktights from trees, and that fungicide inputs could be reduced in trees with naturally low numbers of sticktights. In addition we show that sticktights can be used as an inoculum source for field assays to better characterise macadamia cultivars for better informed cultivar selection, and as a tool in breeding programs to screen for germplasm with high levels of resistance.

Fruit abscission in water dropwort ( Oenanthe stolonifera DC.) was investigated by measuring fruit removal force (FRF) affected by fruit ages and plant hormones. FRF decreased rapidly 30 days after anthesis (DAA). Ethylene evolution increased rapidly at 35 DAA and ABA concentration increased gradually after 20 DAA. ACC and ethephon decreased the FRF of fruit explants and the promoting effect of ACC was delayed by silver thiosulphate and cycloheximide, but not by norbornadiene and actinomycin D. ABA enhanced fruit abscission without increasing ethylene evolution. However, the observation that CoCl 2 delayed abscission induced by ABA indicates possible involvement of ethylene in the ABA effect. Treatment with NAA, fenoprop and IAA had no effect on 30 DAA fruit explants, but IAA delayed abscission of 25 DAA explants. This suggests that the effect of auxins may differ with fruit age when used as control agents.

We tested the effect of extended drying of half the root system on fruit yield and fruit Ca concentration, an indirect measure of fruit quality, in avocado (Persea americana Mill. cv Hass). In a field experiment on a sandy soil, withholding irrigation and plastic sheeting was used to dry the root-zone beneath the whole canopy (DD) or half the canopy (WD), compared with well-watered trees (WW). The irrigation water contained added nutrients and was slightly saline. Yield, shoot growth, leaf conductance, leaf and fruit water status and mineral concentrations of leaves and fruit were studied. The responses of treated trees were assessed in the following season during which normal irrigation practices were restored. With respect to yield, the WD treatment behaved the same as the DD treatment. It reduced yield by more than half and proportionately more than the reduction in water supply thus reducing irrigation efficiency. Re-watering did not restore yield of WD or DD-trees in the next season. The WD and DD treatments had no effect on the concentration of Ca in the fruit mesocarp and so are unlikely to affect fruit quality. The main impact of reduced water supply on the trees was fruit abscission and this was linked to dry soil around the roots rather than the water status of the leaves or fruits. We conclude that extended drying of half of the root-zone in one season reduced irrigation efficiency for two seasons by promoting the abscission of developing fruit to the same extent as occurred when the whole root system was exposed to extended drying.

Postbloom fruit drop (PFD), caused by Colletotrichum acutatum, produces blossom blight, fruit abscission and persistent calyces. In groves of Pera-Rio and Natal sweet orange located in Santa Cruz do Rio Pardo and Rincao, Sao Paulo, Brazil, four experiments were carried out to evaluate the effectiveness of fungicides sprayed alone or as mixtures, at different flowering stages for the control of PFD of citrus. The number of symptomatic flowers, the percentage of fruit set (FS), and the relationship between persistent calyces and total fruit weight per plant were evaluated. The fungicides carbendazim and folpet were sprayed at 0.50 ml and 1.25 g a.i. l−1 of water, respectively, were superior by all the criteria to the other treatments. Carbendazim and folpet fungicides performed best when they were applied at the green bud through hollow ball stages. Difenoconazole, independent of application timing, was less effective by all criteria used. Application of mancozeb at 1.60 g a.i. l−1 at the green bud stage followed by application of mancozeb in a tank mix with carbendazim or folpet at 1.0 ml and 1.25 g a.i. l−1, respectively, during green bud bloom and hollow ball stages were effective for disease control. Carbendazim combined with 0.25% KNO3, reduced the number of persistent calyces and increased fruit production significantly. Applications must be made between green bud and hollow ball stages for best control. Applications only at hollow ball or open flower stages did not provide effective disease control.

The effect of temperature on the ability of 2-chloroethylphosphonic acid (ethephon), when applied at 20 mm stage of fruit development, to induce ethylene evolution of fruit and leaves and abscission of fruit and leaves was determined using 9-year-old root-bagged ‘Golden Delicious’/M.27 apple ( Malus domestica Borkh.) trees in environment-controlled growth rooms. Ethephon at 400 μL L −1 effectively thinned apples, and its thinning effect was not affected by increasing day/night temperature from 21.1/10 to 32.2/21.1 °C. Fruit ethylene evolution was enhanced by application of ethephon. Peak fruit ethylene evolution occurred 1 day after application of ethephon when day/night temperature was 32.2/21.1 °C whereas it occurred 2 days after application of ethephon at a day/night temperature of 21.1/10 or 26.7/15.6 °C. Ethephon increased leaf ethylene evolution drastically but it did not induce leaf abscission regardless of temperature.

Understanding the influence of reductions in solar radiation on crop physiology, growth and yield is important because of the widespread practice of protected cultivation under various light reducing covers. Parts of a commercial bearing grapefruit orchard (Citrus paradisi L.) were covered with aluminized reflective screens during three consecutive summers in southern Israel. Screens were installed shortly after fruit set and removed a week or 2 before harvest. Screens were of two types, 30 and 60% shade, erected horizontally over the rows. Shading reduced mid-day direct radiation reaching the trees and reduced exposed leaf temperatures, but increased their net CO2 uptake (A) and conductance (gl). The increased gl was reflected by decreases in carbon isotope ratios (δ13C) of leaves from under both shades and of fruit flavedo from the 60% shade. Final leaf area index (LAI), determined by gap fraction inversion, was 10% higher in 30% shade than in the control and canopy volume increased similarly. Trunk cross-section, total yield and size distribution of fruit were little affected by shade. During the second year, however, early shading presumably induced more than normal fruit abscission, leading to fewer but larger fruit. Fruit in the middle of the canopy of shaded trees were consistently heavier and also larger in the first 2 years, but peel width was not affected by shade. Juice content was reduced in the second and third years, but the ratio of sugar to acid was not affected. Mid-day leaf water potentials in August and September under 60% shade increased by 13%. Shading did not significantly reduce fruit yield.

Cherry tomatoes harvested as bunches are sensitive to abscission during storage and this is a significant commercial problem for this produce. We examined effect of methyl jasmonate (MJ), ethylene and the inhibitor of its action, 1-methlcyclopropane (1-MCP) on abscission during storage and on the expression of six tomato endo-1,4-β-glucanases (EGase). It is reported that exogenous methyl jasmonate (1 mM) enhanced abscission during storage, as did ethylene (50 μL L−1). Application of 100 nL L−1 of 1-MCP for 24 h inhibited fruit abscission but only partial effect was obtained when it was applied 3 h after supplying methyl jasmonate or ethylene. The effects 1-MCP, methyl jasmonate and ethylene on expression of tomato endo-1,4-β-glucanases, Cel1, Cel2, Cel3, Cel 5, Cel7 and Cel8 were examined in abscission zone tissue at five time points during storage. The expression of Cel1 and Cel5 increased during storage, further establishing their role in abscission. Both ethylene and methyl jasmonate enhanced the expression of tomato endo-1,4-β-glucanases whereas, 1-MCP blocked the expression of the genes. These results demonstrate the benefit of 1-MCP in preventing fruit abscission and provide a wide view on the role of endo-1,4-β-glucanases in abscission of cherry tomatoes during storage.

Longkong fruit abscission was found to be sensitive to external ethylene at concentrations as low as 0.05 μL L −1 . Ethylene induced fruit drop at the junction between the main peduncle and the calyx, at a clear abscission zone. Fruit drop at the junction between calyx and the fruit, however depended on an external force. There may or may not be an abscission zone at this site. Dipping longkong fruit in 200 μL L −1 NAA solution delayed fruit abscission and slightly reduced ethylene production. NAA application was also found to reduce the effect of external ethylene treatment. Applications of 1 μL L −1 1-MCP for 6 h minimized the effect of external ethylene and almost doubled storage life of longkong. The combination of NAA and 1-MCP treatment did not give a synergistic effect.

An adequate supply of boron (B) is critical for optimal cotton (Gossypium hirsutum L.) growth and yield development. A better understanding of the effect of B deficiency on plant physiology and metabolism will help refine the diagnosis of B deficiency and improve B fertilizer recommendations. Determining B distribution in plant tissues and change in the pattern during growth is fundamental for diagnosis of plant B deficiency. Growth chamber and field studies were conducted in 1999 and 2000 to determine the effects of B deficiency on cotton growth, leaf photosynthesis, and nonstructural carbohydrates. The chamber study mainly investigated changes in leaf blade nonstructural carbohydrate concentrations and plant tissue B content during the development of B deficiency. The field study determined whether soil or foliar supplements of B could improve plant growth, carbon assimilation and translocation, and lint yield. In the growth chamber, B deficiency during the early growth of cotton decreased leaf CO2 exchange rate, increased leaf blade nonstructural carbohydrate concentration, and depressed photosynthate export from leaves to fruits, resulting in increased fruit abscission. Among plant parts, leaf blades had highest B concentration. Leaf blade B content accounted for more than 75% of plant total accumulating B under favorable growth chamber conditions. The critical B level of uppermost fully expanded main-stem leaf blades, which affected plant growth and physiological processes, was about 17–20 mg kg−1 during squaring and fruiting. Under our field study conditions, cotton did not respond to either soil or foliar B application due to sufficient soil B for plant growth (0.2 and 0.3 mg B kg−1 at two study sites). These results will provide useful information for cotton plant B diagnosis and B fertilizer recommendations in cotton production.

Effects of ethephon on tabasco (Capsicum frutescens L.) pepper fruit ripening and abscission at the fruit–receptacle abscission zone (FR–AZ) were studied in two lines, ‘McIlhenny Select’ and ‘Hard Pick’. Fruit color development and changes in fruit detachment force (FDF) were correlated in both tabasco lines; FDF decreased significantly at color stages 3 and 4 in ‘McIlhenny Select’ fruit and at stages 5 and 6 in ‘Hard Pick’ fruit based on a scale of 0 for green-mature and 7 for red-mature. The two tabasco lines had different FDF at the FR-AZ; FDF was significantly lower in ‘McIlhenny Select’ than in ‘Hard Pick’ after color stage 3 and was 5-fold lower in ‘McIlhenny Select’ than in ‘Hard Pick’ at the red-mature stage. There were also differences between the two lines in the time for reduction of FDF, which occurred 40 and 42 days after anthesis (DAA) in water-treated ‘McIlhenny Select’ and ‘Hard Pick’ fruit, respectively. Ethephon treatment (1000 μl l−1) decreased FDF at 36 DAA in ‘McIlhenny Select’ and 38 DAA in ‘Hard Pick’. Ethephon applied at 29 and 32 DAA decreased the fruit development period by 3–7 days in both lines. Ethephon did not affect ‘McIlhenny Select’ fruit at 35 and 38 DAA, while treatment of ‘Hard Pick’ fruit of the same developmental stage shortened the developmental period.

Gibberellin accumulation in citrus ovaries has been proposed as an activating signal for fruit set in citrus. Our data under tropical conditions associate pollination-dependent fruiting of ‘Valencia’ orange with high ratios of growth promoters to inhibitors ( G / I ) in floral organs. Lower values of G / I were found in the parthenocarpic ‘Marsh Seedless’ grapefruit and ‘Ortanique’ tangor, the latter a self-incompatible, seedless hybrid. In all the varieties, two kind of fruitlets were identified at the early stages of fruit development: (1) normal developing fruits, with high peel chlorophyll content, firmly attached to the stem (2) non-growing fruits with lower peel chlorophyll content, prone to early abscission. G / I values of firmly attached fruitlets were higher than those of non-growing, early abscising fruits during the fruit set period. In addition, higher absicisic (ABA) and ABA-like inhibitor accumulation as well as lower growth promoting substances were found in proximal abscission zones of abscising fruits. Furthermore, higher contents of jasmonic acid-like compounds in floral organs and in developing fruits were found in the cultivars with stronger early fruit abscission, which suggest that ABA-like and jasmonic acid-like substances could play a shared role in fruit set and early fruit abscission.

The susceptibility of cotton fruiting forms (squares or bolls) to abscission is age dependent. After flower opening, abscission probability peaks and then decreases rapidly, suggesting the existence of a stage beyond which boll abscission does not occur. However, the timing and characterization of this stage need further refinement. This paper compares the susceptibility to abscission of fruiting forms with age according to sympodial position, and relates abscission probability of bolls to the time-course patterns of boll diameter, seed-cotton weight and water content. Square appearance, flower opening and abscission events were monitored in three experiments conducted with high inputs and in one experiment receiving no fertilizer. In the latter, the duration of fruiting and the appearance rates of fruiting forms were lower than in the high-input experiments. For a given age-class of fruiting form, the abscission rate increased from the innermost to the outermost position on the sympodium but the relative pattern of susceptibility with age did not change. Abscission followed a bimodal pattern with squares and bolls abscising most during early stages of development (≤80 Degree Days from appearance for squares, and ≤160 DD from flower opening for bolls). Applying a 60% light reduction for four or eight days during the late flowering period increased the abscission rate in proportion to the duration of shading. However, the frequency distribution of abscission with age was not affected by shading. In general, there was a consistent period at 200–240 DD after flower opening beyond which abscission ceased to occur. This period corresponded to a change in boll water content, which fell below 0.80 g g −1 , and in seed-cotton dry weight which started to increase linearly and rapidly. Boll diameter was found to be a convenient measure to delimit this transition period. In our experimental conditions a critical diameter of 30 mm marked the end of abscission sensitivity of bolls.

Stem-end rot (SER) caused by Diplodia natalensis is a major postharvest disease of fresh Florida citrus degreened with ethylene to enhance fruit appearance. Significant increase in disease incidence by the use of ethylene at concentrations above those needed for degreening may be related to the activity of the abscission enzymes, polygalacturonase (PG) and cellulase (CX). Quiescent mycelia of D. natalensis in necrotic tissue on the surface of the calyx and disk (button) at the stem-end of the fruit grow into the fruit upon separation of the button from the fruit during abscission. Activity of the abscission enzymes in oranges was enhanced by high ethylene (0.055 ml l−1), and a larger number of cells were degraded within the abscission layer by their activity than at lower (0.002 ml l−1) more typical degreening concentrations. Commercial enzymes or partially purified preparations of the abscission enzymes added to abscission areas of debuttoned oranges before inoculation with mycelia of D. natalensis caused a significant increase in SER. Fruit dipped in 2,4-dichlorophenoxyacetic acid (2,4-D) or silver thiosulfate (STS) before degreening were more resistant to SER when inoculated following degreening. Addition of these metabolic inhibitors or cycloheximide (CHI) to the fruit abscission zone after removal of the button during early stages of degreening (18 h) with high ethylene also caused a significant reduction in SER. The metabolic inhibitors had no affect on SER if applied at 60 h after terminating the ethylene treatment. Reductions in activity of PG and CX were obtained by applying 2,4-D or STS to fruit before degreening, and STS or CHI to fruit abscission zones at early stages of degreening (18 h).

Seasonal changes of sucrose, glucose and fructose were monitored in the bark (phloem) and xylem in Ponkan mandarin (Citrus reticulata Blanco cv. Yoshida). Sucrose was the most abundant sugar. A decline in bark sucrose content coincided with the major fruit abscission period. Stem girdling was carried out at anthesis (May), end of June drop (July), start of autumn (September) and in early winter (November). Girdling in July and September slightly increased leaf sugar content. At peak starch content (in winter), the September girdled treatment had the highest starch content. May girdling increased fruit set significantly and also improved fruit color. July and September girdling improved fruit size, but late girdling (November) had no effect on fruit size. Flowering and fruit set in the following year were closely related to starch content in the previous winter: they were highest in September girdled trees and lowest in May girdled trees.

Summary Soluble sugar, a-galactosidase (EC 3.2.1.22) and soluble acid invertase (EC 3.2.1.26) were determined in fruit tissues and peduncles of melon (Cucumis melo L. cv. Ranjadew) in the course of fruit development. Fruit development was followed from anthesis to fruit abscission (53-55 days after anthesis). At fruit maturity, the exo-mesocarp had the highest sugar content followed by endocarp and placenta, seeds and peduncles. Stachyose and raffinose were present in all fruit tissues and peduncles at all stages of development. Stachyose was the main sugar of the peduncles. In all other fruit tissues, sucrose and the hexoses prevailed. The sugar composition of phloem exudate collected from peduncles cut near stem or fruit was identical, indicating that translocate is conducted along the phloem of fruit peduncles unchanged. Acid invertase activity followed optimum curves, alkaline α-galactosidase activity declined and acid α-galactosidase slightly increased during fruit development, a-galactosidase and invertase activities are closely correlated with the distribution of raffinose oligosaccharides, sucrose and hexoses. Our data confirm a recent conclusion that raffinose oligosaccharides are translocated within the phloem into Cucurbit fruits and seeds and that oligosaccharides are effectively decomposed here by a-galactosidases.

Cotton (Gossypium hirsutum L.) growers are increasingly using growth regulators such as ethephon (2-chloroethyl-phosphonic acid) for crop management. Ethephon is widely used as crop terminator to facilitate early harvest. When applied on cotton, ethephon has been shown to have an effect on defoliation, boll opening, immature fruit abscission, and end-season growth. A process-level simulation model was developed using data collected under controlled-environment conditions over a range of temperatures and water regimes. Equations were developed for the physiological processes involved, i.e., rate of boll opening, immature fruit abscission, and defoliation. Stress parameters were also calculated to alter the growth of cotton after ethephon application. The ethephon model was tested and incorporated into the cotton management system GOSSYM/COMAX. The model simulations were compared with observed data over a range of climatic conditions.

Carbohydrate levels in fruitlets of control and defoliated trees of dwarf Citrus unshiu (cvs. Clausellina and Okitsu) were determined from bloom up to the end of fruit set. Full and partial (50%) defoliations were carried out at anthesis and at the beginning of the cell enlargement period. Carbohydrate reserves in woody storage tissues were also analyzed soon after defoliation. In control fruits, sucrose, glucose, fructose and starch showed a transient increase at anthesis and remained low during the cell division phase. Soluble sugars accumulated at the onset of the cell enlargement phase. Defoliation did not modify carbohydrate status in either fruits or woody tissues during the cell division period, although the first fruit abscission wave, which takes place at this stage, was increased. Fruit growth was not altered either. However, at the onset of the second phase of growth, soluble sugars were reduced in fruits and sucrose and starch were lower in woody tissues from defoliated plants. In these plants, fruit abscission at this stage (June drop) was also increased, while fruit growth was arrested or delayed. Once the June drop was overcome, fruits remaining on either defoliated or control plants were similar in size and contained analogous high levels of sugars. Taken together, the results suggest that developing fruitlets are utilization sinks during the cell division period and act as storage sinks during the cell enlargement stage. At this critical transition, sucrose levels correlated positively with fruit growth and negatively with fruit abscission. These results are compatible with the proposal that sucrose supply is a major factor of the regulatory mechanism for citrus fruit abscission during the June drop.

At four dates from autumn to harvest time, 4-year-old erect and inclined branches were selected at random from mature plantations of redcurrant (Ribes rubrum L.) cultivars ‘Red Dutch’ and ‘Rotes Wunder’. In November, the number of flower initials per bud was higher on erect than on inclined branches in both cultivars, and, compared with other shoot types, the lowest number of flower initials was usually found in buds of short shoots. In many buds flower initials aborted during the winter months, more on inclined than on erect branches. Due to abortions and premature fruit abscission, the crop potential of an average branch, near harvest time, was about one-quarter of that in the previous autumn. Based on examination by scanning electron microscopy, an improvement of Lenz's classification of the developmental stages of currant flower initials is proposed.

The abscission of young fruit occurring in apple trees was measured under various conditions in order to locate the possible source of the signal that induces fruit drop. The effect on fruit abscission of shading of leaves, girdling of conducting tissue, extracting seeds and defruiting pedicels was investigated. Complete shading of whole trees for 5 days, steam girdling of defoliated fruiting wood proximal to the abscission zone and removal of seeds from attached fruit resulted in 100% fruit drop when treatment was carried out prior to the June drop period. When the same treatment was applied after June drop no fruit abscised. However, fruit abscission took place before and after June drop when steam girdling was applied to the pedicel distal to the abscission zone. The same effect was observed in defruited pedicels, which always abscised after fruit removal throughout fruit development. The results show that during the pre-June drop period, abscission can be induced by treatments which reduce or block nutrient supply to the abscission zone of fruit. After that period the growing fruit becomes a sugar storage organ which is resistant to abscission. It is though likely that inhibition of abscission is related to the presence of stored carbohydrates already accumulated in the young fruit. An indication for the involvement of the sugar level, in particular glucose, in the control of the abscission process was provided by the results of measurements of individual sugar levels in conducting tissue distal and proximal to the abscission zone. It was found that during fruit development, glucose concentration in the pedicel was normally above the concentration found in fruiting wood proximal to the abscission zone. However, when abscission during the June drop period was induced, the glucose level dropped to a minimum in the pedicel, reaching the same value as in the fruiting wood. It is suggested that the glucose level in the pedicel of growing fruit may therefore be a factor in the control of the abscission process in young apple fruit, abscission occuring only in those fruit in which the glucose content in the pedicel is below a critical level. Fruit which remain on the tree have most likely reached a stage in their development at which sufficient amounts of sugar have accumulated to prevent abscission.

The ripe fruit of several red raspberry cultivars had a wide range of ethylene-producing capacities and fruit retention strengths (FRSs). With the exception of the cultivar ‘Phyllis King’, those fruits with the higher rates of ethylene (C2H4) production when ripe had lower FRS values. The initial decline in FRS appears independent of C2H4 production and may be the result of structural changes in the drupelets and receptacle. The receptacles of those cultivars with low FRSs when ripe were more advanced (having a smoother surface) than those with higher FRSs.

Reproductive efficiency was studied in 10 cultivars of cowpea, evaluated for 2 years. There were significant differences between the cultivars for total number of flowers produced, flower retention, pod drop and yield. Cultivar ‘TVX 3236’, which produced the highest number of flowers, was one of the cultivars that retained the highest number of flowers and its yield was not significantly different from the highest yielding cultivar. Positive correlations were found between total number of flowers produced and total number of pods harvested, and between percentage flower retention and number of pods harvested. Total number of flowers produced, percentage flower retention, number of pods produced and total number of pods harvested were positively correlated with yield. The implications of these findings in improving flower retention in otherwise outstanding cultivars and possible genetic causes of flower/pod abscission in cowpea are discussed.

Summary Apple fruits were collected in the period between 20 and 49 days after anthesis. The relation between histological structure and gibberellin content was investigated in ovules of control fruits (sample A), fruitdrop affected fruits not yet abscinded from the plant (sample B) and fruit-drop affected fruits already abscinded from the plant (sample C). The results of the histological analyses showed that: i) ovules from sample A generally contained a developing embryo, a dividing endosperm, and a conspicuous antipodal tissue; ii) ovules from sample B were degenerating. However, they contained a degraded embryo mainly in fruits collected 29 days post anthesis. No endosperm or antipodal cells were detected; iii) ovules from samples C also degenerated and had no recognizable structure. Gibberellins were determined in ovules isolated from the same three samples of fruits. The gibberellin content was very low in all samples and quantitative differences between sample A, on the one hand, and samples Band C on the other, were only detectable 49 days after anthesis. Moreover, biological activity appeared to be distributed in different Rf-zones in the TL chromatogram, suggesting the presence of various gibberellin-like substances. The differences observed were confirmed after HPLC purification. Further analyses by means of GC and GC - MS led to the identification of GA4 and GA63 as two of the GAs present in ovules from sample A. The results obtained are discussed in relation to fruit abscission heterogeneity.