Flower Abscission Research Articles

SHEDDING OF FRUITING STRUCTURES IN COTTON: FACTORS, COMPENSATION AND PREVENTION

<p>The fruiting potential of advanced cotton cultivars is not a limiting factor for achieving yield targets but retention of squares and flowers for successful maturation into bolls is major challenge. In this article, we focused on why shedding occurs, its mechanism, yield losses, plant self-compensation, effects on plant growth and possible management to ameliorate its adverse effects. We concluded that it is quite unfair to blame single factor, instead it is an integrated effect of plant and stress factors i.e., high temperature, drought, thick plant stand, insects and diseases etc. contribute to accelerate shedding which ranges about 40-50%. The stresses induce the excessive production of degrading enzymes like pectinase, cellulose and hydrolase, while ethylene and abscisic acid is produced excessively to hasten the degradation process for shedding. The physiological disturbance contributes 7-35 and 42-64% abscission of unopened flowers and bolls, respectively. The square and flower are more frequent to shedding at high temperature compared to immature bolls. The flowers and boll shedding up to 30% is tolerable limit because cotton can recover yield provided weather support the crop later in season. The self-regulated abscission of floral parts is not easy to control under field conditions, however, the adverse effects of stress mediated shedding can be ameliorated with girdling and avoiding pest and stressful conditions, application of plant growth regulator (PGR) to control vegetative growth and abscisic acid (abscission promoter) and ethylene inhibitors like naphthalene acetic acid, silver thiosulfate and 1-methylcyclopropene.</p>

Bypassing Negative Epistasis on Yield in Tomato Imposed by a Domestication Gene

Selection for inflorescence architecture with improved flower production and yield is common to many domesticated crops. However, tomato inflorescences resemble wild ancestors, and breeders avoided excessive branching because of low fertility. We found branched variants carry mutations in two related transcription factors that were selected independently. One founder mutation enlarged the leaf-like organs on fruits and was selected as fruit size increased during domestication. The other mutation eliminated the flower abscission zone, providing "jointless" fruit stems that reduced fruit dropping and facilitated mechanical harvesting. Stacking both beneficial traits caused undesirable branching and sterility due to epistasis, which breeders overcame with suppressors. However, this suppression restricted the opportunity for productivity gains from weak branching. Exploiting natural and engineered alleles for multiple family members, we achieved a continuum of inflorescence complexity that allowed breeding of higher-yielding hybrids. Characterizing and neutralizing similar cases of negative epistasis could improve productivity in many agricultural organisms. VIDEO ABSTRACT.

De novo Transcriptome Profiling of Flowers, Flower Pedicels and Pods of Lupinus luteus (Yellow Lupine) Reveals Complex Expression Changes during Organ Abscission.

Yellow lupine (Lupinus luteus L., Taper c.), a member of the legume family (Fabaceae L.), has an enormous practical importance. Its excessive flower and pod abscission represents an economic drawback, as proper flower and seed formation and development is crucial for the plant's productivity. Generative organ detachment takes place at the basis of the pedicels, within a specialized group of cells collectively known as the abscission zone (AZ). During plant growth these cells become competent to respond to specific signals that trigger separation and lead to the abolition of cell wall adhesion. Little is known about the molecular network controlling the yellow lupine organ abscission. The aim of our study was to establish the divergences and similarities in transcriptional networks in the pods, flowers and flower pedicels abscised or maintained on the plant, and to identify genes playing key roles in generative organ abscission in yellow lupine. Based on de novo transcriptome assembly, we identified 166,473 unigenes representing 219,514 assembled unique transcripts from flowers, flower pedicels and pods undergoing abscission and from control organs. Comparison of the cDNA libraries from dropped and control organs helped in identifying 1,343, 2,933 and 1,491 differentially expressed genes (DEGs) in the flowers, flower pedicels and pods, respectively. In DEG analyses, we focused on genes involved in phytohormonal regulation, cell wall functioning and metabolic pathways. Our results indicate that auxin, ethylene and gibberellins are some of the main factors engaged in generative organ abscission. Identified 28 DEGs common for all library comparisons are involved in cell wall functioning, protein metabolism, water homeostasis and stress response. Interestingly, among the common DEGs we also found an miR169 precursor, which is the first evidence of micro RNA engaged in abscission. A KEGG pathway enrichment analysis revealed that the identified DEGs were predominantly involved in carbohydrate and amino acid metabolism, but some other pathways were also targeted. This study represents the first comprehensive transcriptome-based characterization of organ abscission in L. luteus and provides a valuable data source not only for understanding the abscission signaling pathway in yellow lupine, but also for further research aimed at improving crop yields.

1-Aminocyclopropane-1-Carboxylate Oxidase Induction in Tomato Flower Pedicel Phloem and Abscission Related Processes Are Differentially Sensitive to Ethylene.

Ethylene has impact on several physiological plant processes, including abscission, during which plants shed both their vegetative and reproductive organs. Cell separation and programmed cell death are involved in abscission, and these have also been correlated with ethylene action. However, the detailed spatiotemporal pattern of the molecular events during abscission remains unknown. We examined the expression of two tomato ACO genes, LeACO1, and LeACO4 that encode the last enzyme in ethylene biosynthesis, 1-aminocyclopropane-1-carboxylate oxidase (ACO), together with the expression of other abscission-associated genes involved in cell separation and programmed cell death, during a period of 0–12 h after abscission induction in the tomato flower pedicel abscission zone and nearby tissues. In addition, we determined their localization in specific cell layers of the flower pedicel abscission zone and nearby tissues obtained by laser microdissection before and 8 h after abscission induction. The expression of both ACO genes was localized to the vascular tissues in the pedicel. While LeACO4 was more uniformly expressed in all examined cell layers, the main expression site of LeACO1 was in cell layers just outside the abscission zone in its proximal and distal part. We showed that after abscission induction, ACO1 protein was synthesized in phloem companion cells, in which it was localized mainly in the cytoplasm. Samples were additionally treated with 1-methylcyclopropene (1-MCP), a competitive inhibitor of ethylene actions, and analyzed 8 h after abscission induction. Cell-layer-specific changes in gene expression were observed together with the specific localization and ethylene sensitivity of the hallmarks of cell separation and programmed cell death. While treatment with 1-MCP prevented separation of cells through inhibition of the expression of polygalacturonases, which are the key enzymes involved in degradation of the middle lamella, this had less impact on the occurrence of different kinds of membrane vesicles and abscission-related programmed cell death. In the flower pedicel abscission zone, the physical progressions of cell separation and programmed cell death are perpendicular to each other and start in the vascular tissues.

Ethylene-dependent effects on generative organ abscission of Lupinus luteus

The abscission of certain organs from the plant is part of the fulfilment of its developmental programs. The separation process occurs in a specialized abscission zone usually formed at the base of detached organ. The changing level of phytohormones, particularly ethylene, is the element responsible for coordinating anatomical and physiological transformation that accompanies organ abscission. The application of ethylene (ET) on <em>Lupinus luteus</em> stimulates flower abortion. However, the treatment with 1-aminocyclopropane-1-carboxylic acid (ACC) – direct ET precursor – does not cause such a strong physiological response. In turn, when applied on the pedicels both ET biosynthesis (2-aminoethoxyvinylglycine; AVG) and action (norbornadiene; NBD) inhibitors reversed the stimulatory effect of ET on generative organ separation. In order to determine ET role in the flower abscission process in <em>L. luteus</em>, we identified the sequences coding for synthase (<em>LlACS</em>) and oxidase (<em>LlACO</em>) of ACC and measured their expression levels. Abscission zone activation is accompanied by a considerable increase both in <em>LlACS</em> and <em>LlACO</em> cDNAs and also ACC content, which is specifically localized in the dividing cells at the base of the flower being detached. Obtained results suggest that ET is a strong stimulator of flower abortion in <em>L. luteus</em>.

Investigation of the Fusarium virguliforme Transcriptomes Induced during Infection of Soybean Roots Suggests that Enzymes with Hydrolytic Activities Could Play a Major Role in Root Necrosis.

Sudden death syndrome (SDS) is caused by the fungal pathogen, Fusarium virguliforme, and is a major threat to soybean production in North America. There are two major components of this disease: (i) root necrosis and (ii) foliar SDS. Root symptoms consist of root necrosis with vascular discoloration. Foliar SDS is characterized by interveinal chlorosis and leaf necrosis, and in severe cases by flower and pod abscission. A major toxin involved in initiating foliar SDS has been identified. Nothing is known about how root necrosis develops. In order to unravel the mechanisms used by the pathogen to cause root necrosis, the transcriptome of the pathogen in infected soybean root tissues of a susceptible cultivar, ‘Essex’, was investigated. The transcriptomes of the germinating conidia and mycelia were also examined. Of the 14,845 predicted F. virguliforme genes, we observed that 12,017 (81%) were expressed in germinating conidia and 12,208 (82%) in mycelia and 10,626 (72%) in infected soybean roots. Of the 10,626 genes induced in infected roots, 224 were transcribed only following infection. Expression of several infection-induced genes encoding enzymes with oxidation-reduction properties suggests that degradation of antimicrobial compounds such as the phytoalexin, glyceollin, could be important in early stages of the root tissue infection. Enzymes with hydrolytic and catalytic activities could play an important role in establishing the necrotrophic phase. The expression of a large number of genes encoding enzymes with catalytic and hydrolytic activities during the late infection stages suggests that cell wall degradation could be involved in root necrosis and the establishment of the necrotrophic phase in this pathogen.

Phosphorous Nutritional Level, Carbohydrate Reserves and Flower Quality in Olives.

The olive tree is generally characterized by relatively low final fruit set consequential to a significant rate of undeveloped pistils, pistil abortion, and flower and fruitlet abscission. These processes are acknowledged to be governed by competition for resources between the developing vegetative and reproductive organs. To study the role of phosphorus (P) nutritional level on reproductive development, trees were grown under four levels of P for three years in large containers. Phosphorus nutritional level was positively related to rate of reproductive bud break, inflorescence weight, rate of hermaphrodite flowers, pistil weight, fruitlet persistence, fruit set and the consequential total number of fruits. The positive impact of P nutrition on the productivity parameters was not related to carbohydrate reserves or to carbohydrate transport to the developing inflorescence. Phosphorous deficient trees showed significant impairment of assimilation rate, and yet, carbohydrates were accumulated in inflorescences at levels comparable to or higher than trees receiving high P. In contrast to female reproductive organs, pollen viability was consistently higher in P deficient trees, possibly due to the enhanced carbohydrate availability. Overall, the positive effect of P on female reproductive development was found to be independent of the total carbohydrate availability. Hence, P is speculated to have a direct influence on reproductive processes.

Longevidade de inflorescências de Epidendrum ibaguense Kunth. tratadas com óxido nítrico

Nitric oxide (NO) acts as anti senescence substance, which may extend the postharvest life of fruits, vegetables and flowers when they are treated with micro molar concentrations of compounds like the donor sodium nitroprusside (SNP). This work aimed to evaluate the effect pulsing or spraying of NO on the longevity of cut Epidendrum ibaguense inflorescences. After harvested, the inflorescences were pulsed for 6, 24 or 48 hours with 5, 10, 50, 100 and 500 µM SNP or sprayed until run off with the same mentioned solutions. Controls were treated with distilled water. After the treatment, the flowers were placed in deionized water, which was changed every 2 days. No significant differences were observed on the longevity of flowers treated with 5, 10, 50 or 100 µM SNP, regardless of the mode of application. Inflorescences treated with 500 µM SNP had reduced longevity and increased flower abscission. In inflorescences kept in SNP solution, toxic symptoms such as darkening of the labellum resulting in reduced longevity compared with the control. The longevity of inflorescences sprayed with 500 µM SNP reduced from 6.8±0.57 to 5.1±0.82 days. Collectively, NO treatments were not able to extend the shelf life of E. ibaguense inflorescences and high concentrations of the NO donor compound in vase solution or spraying leads to toxicity symptoms on the flower labellum.

Identification and molecular characterization of an IDA-like gene from litchi, LcIDL1, whose ectopic expression promotes floral organ abscission in Arabidopsis.

Unexpected abscission of flowers or fruits is a major limiting factor for crop productivity. Key genes controlling abscission in plants, especially in popular fruit trees, are largely unknown. Here we identified a litchi (Litchi chinensis Sonn.) IDA-like (INFLORESCENCE DEFICIENT IN ABSCISSION-like) gene LcIDL1 as a potential key regulator of abscission. LcIDL1 encodes a peptide that shows the closest homology to Arabidopsis IDA, and is localized in cell membrane and cytoplasm. Real-time PCR analysis showed that the expression level of LcIDL1 accumulated gradually following flower abscission, and it was obviously induced by fruit abscission-promoting treatments. Transgenic plants expressing LcIDL1 in Arabidopsis revealed a role of LcIDL1 similar to IDA in promoting floral organ abscission. Moreover, ectopic expression of LcIDL1 in Arabidopsis activated the expression of abscission-related genes. Taken together, our findings provide evidence that LcIDL1 may act as a key regulator in control of abscission.

Evaluation of a Sprayable Formulation of 1-Methylcyclopropene in Floriculture

We conducted a series of studies to determine the efficacy of a sprayable formulation of 1-methylcyclopropene (1-MCP; AFxRD-038) to inhibit ethylene-mediated flower abscission in Impatiens walleriana. Exposing Impatiens plants to 1.0 μL·L−1 ethylene for 18 hours caused complete abscission of open flowers and most buds. Sprays of the novel 1-MCP formulation at concentrations >2.5 mg·L−1 protected plants from ethylene. At 5 and 10 mg·L−1, the efficacy of 1-MCP increased as spray volume increased from 102 mL·m−2 to 306 mL·m−2. 1-MCP was rainfast with no decrease in efficacy resulting from heavy overhead irrigation within 1–2 minutes of application. Prepared 1-MCP solutions (10 mg·L−1) remained effective up to 2 weeks after mixing if held in airtight containers. The sprayable 1-MCP formulation provided protection against exogenous ethylene for a maximum of 4 days and reduced stress-related abscission from 3 days of darkness (in the absence of exogenous ethylene) at 20 °C or 40 hours darkness at 28 °C.

Allele-Specific Interactions between CAST AWAY and NEVERSHED Control Abscission in Arabidopsis Flowers.

An advantage of analyzing abscission in genetically tractable model plants is the ability to make use of classic genetic tools such as suppression analysis. We have investigated the regulation of organ abscission by carrying out suppression analysis in Arabidopsis flowers. Plants carrying mutations in the NEVERSHED (NEV) gene, which encodes an ADP-ribosylation factor GTPase-activating protein, retain their outer floral organs after fertilization. Mutant alleles of CAST AWAY (CST), which encodes a receptor-like cytoplasmic kinase, were found to restore organ abscission in nev flowers in an allele-specific manner. To further explore the basis of the interactions between CST and NEV, we tested whether the site of a nev mutation is predictive of its ability to be suppressed. Our results suggest instead that the strength of a nev allele influences whether organ abscission can be rescued by a specific allele of CST.

The influence of abscisic acid on the ethylene biosynthesis pathway in the functioning of the flower abscission zone in Lupinus luteus

Flower abscission is a highly regulated developmental process activated in response to exogenous (e.g. changing environmental conditions) and endogenous stimuli (e.g. phytohormones). Ethylene (ET) and abscisic acid (ABA) are very effective stimulators of flower abortion in Lupinus luteus, which is a widely cultivated species in Poland, Australia and Mediterranean countries. In this paper, we show that artificial activation of abscission by flower removal caused an accumulation of ABA in the abscission zone (AZ). Moreover, the blocking of that phytohormone’s biosynthesis by NDGA (nordihydroguaiaretic acid) decreased the number of abscised flowers. However, the application of NBD – an inhibitor of ET action – reversed the stimulatory effect of ABA on flower abscission, indicating that ABA itself is not sufficient to turn on the organ separation. Our analysis revealed that exogenous ABA significantly accelerated the transcriptional activity of the ET biosynthesis genes ACC synthase (LlACS) and oxidase (LlACO), and moreover, strongly increased the level of 1-aminocyclopropane-1-carboxylic acid (ACC) – ET precursor, which was specifically localized within AZ cells. We cannot exclude the possibility that ABA mediates flower abscission processes by enhancing the ET biosynthesis rate. The findings of our study will contribute to the overall basic knowledge on the phytohormone-regulated generative organs abscission in L. luteus.

Does carbohydrate availability play a role in sweet cherry fruitlet abscission?

Fruitlet abscission is an issue impacting the profitability of the cherry industry, with particular cultivars showing enhanced susceptibility. This study examined the role of carbohydrate availability in fruitlet abscission in two sweet cherry cultivars, 'Kordia' and 'Lapins'. Starch and soluble sugar concentrations in branch, trunk and root tissue were measured regularly throughout the growing season of 2012/2013. Normal transport of carbohydrates was disrupted 5 weeks after full-bloom by applying trunk girdling and limb defoliation treatments, and the rate of flower and fruitlet abscission was monitored. In 'Lapins', trunk girdling decreased the rate of abscission, but abscission was unaffected by girdling in 'Kordia'. When fruit was assessed at commercial harvest, the fruit from the defoliated treatment was immature in both cultivars. The highest sugar concentration was found in fruit from the girdled trees in both 'Kordia' and 'Lapins'. Trunk starch concentrations ranged from 22.6 mg g-1 at the beginning of the season to 28.80 mg g-1 just after harvest in 'Lapins', and were higher in 'Kordia' with 42.02 mg g-1 at the beginning of the season to 39.13 mg g-1 just after harvest. Shoot starch concentrations were very similar to trunk in both cultivars, whereas root carbohydrate concentrations did not recover after the trunk girdling treatment in either cultivar, which is expected to have an impact on the following season's return bloom.

Increased hydrolase gene expression and hydrolase activity in the abscission zone involved in chilling-induced abscission of Dendrobium flowers

After 4days exposure to15°C and 5°C temperature, cut cv. Ear Sakul Dendrobium inflorescences were returned to 25°C.The exposure of open flowers and floral buds to 5°C induced more abscission than exposure to 15°C after transfer to 25°C. Ethylene production rates of floral buds and open flowers with and without 1-MCP treatment were comparatively low during exposure to to15°C and 5°C. Flower buds had a greater increase of ethylene production than open flowers after upon transfer to 25°C and flower buds stored at 5°C had a greater increase than that of flower buds stored at 15°C. 1-MCP treatment reduced significantly more ethylene production rates of floral buds stored at 5°C than those stored at 15°C compared with open flowers upon transfer to 25°C on the last 3days. The abscission zone (AZ) activities of pectin methylesterase (PME), polygalacturonase (PG), β-1,4 glucanase (cellulase, CEL) and β-galactosidase (β-GAL) increased after exposure to5°C, while β-GAL also increased after 15°C exposure. Treatment with 100nlL−1 1-MCP for 4h at 25°C, lower temperature exposure reduced abscission in both open flowers and floral buds. 1-MCP also prevented an increase in the activities of PME, PG, CEL and β-GAL in the AZ. Genes encoding a PME, a CEL, and a β-GAL were isolated from the AZ. In the absence of 1-MCP an early increase was found in the expression of the β-GAL and PME genes in the AZ, that was correlated with the abscission rates. An increase in the expression of the CEL gene was found later in abscission. 1-MCP prevented the increase in expression of the β-GAL, PME and CEL genes in the AZ. It was concluded that chilling-induced abscission was mediated by ethylene, that induced gene expression and increased the activity of cell wall hydrolases. The high correlation between abscission and gene expression of β-GAL and CEL suggests that they were involved relatively early and again in late stages of abscission. The role of PME and PG was less clear, but they were possibly involved in the abscission after the 5°C treatment.

Effect of Temperature on Flower and Pod Abscission and Yield of Three Soybean Genotypes

A pot experiment was conducted at Soil Science Division, Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh, during January to April 2014 to investigate the growth, abscission of flower and pod and yield performance of three soybean varieties (BINA Soybean-1, BINA Soybean-2, and Shohag) under three different temperature conditions. Flower abscission number and percentage were maximum in elevated temperature but the abscission of pods plant-1 was found to be the maximum in ambient temperature. In case of the performance of varieties, tallest plant and maximum node plant-1 were noted from the variety Shohag but number of nodules plant-1 , number of seeds pod-1, weight of 100 seed and seed yield was highest in BINA soybean–2 while BINA soybean–1 had maximum flowers plant-1 and pods plant-1. Abscission of flowers plant-1 was maximum in BINA soybean–1 under elevated temperature while similar variety grown under ambient temperature obtained the maximum abscission of pods plant-1 and the variety Shohag grown under elevated temperature noted the maximum abscission percentage of flower at all the data recording stages. These results suggested that ambient temperature and BINA soybean–2 singly or their interaction would be the most significant compared to others.J. Environ. Sci. & Natural Resources, 8(2): 89-92 2015

Shared and divergent pathways for flower abscission are triggered by gibberellic acid and carbon starvation in seedless Vitis vinifera L.

BackgroundAbscission is a highly coordinated developmental process by which plants control vegetative and reproductive organs load. Aiming at get new insights on flower abscission regulation, changes in the global transcriptome, metabolome and physiology were analyzed in ‘Thompson Seedless’ grapevine (Vitis vinifera L.) inflorescences, using gibberellic acid (GAc) spraying and shading as abscission stimuli, applied at bloom.ResultsNatural flower drop rates increased from 63.1 % in non-treated vines to 83 % and 99 % in response to GAc and shade treatments, respectively. Both treatments had a broad effect on inflorescences metabolism. Specific impacts from shade included photosynthesis inhibition, associated nutritional stress, carbon/nitrogen imbalance and cell division repression, whereas GAc spraying induced energetic metabolism simultaneously with induction of nucleotide biosynthesis and carbon metabolism, therefore, disclosing alternative mechanisms to regulate abscission. Regarding secondary metabolism, changes in flavonoid metabolism were the most represented metabolic pathways in the samples collected following GAc treatment while phenylpropanoid and stilbenoid related pathways were predominantly affected in the inflorescences by the shade treatment. However, both GAc and shade treated inflorescences revealed also shared pathways, that involved the regulation of putrescine catabolism, the repression of gibberellin biosynthesis, the induction of auxin biosynthesis and the activation of ethylene signaling pathways and antioxidant mechanisms, although often the quantitative changes occurred on specific transcripts and metabolites of the pathways.ConclusionsGlobally, the results suggest that chemical and environmental cues induced contrasting effects on inflorescence metabolism, triggering flower abscission by different mechanisms and pinpointing the participation of novel abscission regulators. Grapevine showed to be considered a valid model to study molecular pathways of flower abscission competence acquisition, noticeably responding to independent stimuli.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0722-7) contains supplementary material, which is available to authorized users.

Salinity Negatively Affects Pollen Tube Growth and Fruit Set in Grapevines and Is Not Mitigated by Silicon

Soil salinity impairs viticultural production by reducing vegetative growth and yield parameters such as bud fruitfulness, bunch number per cane, bunch weight, and berry weight. However, the effects of salinity on flower fertility, berry set, and berry development, and the resulting impacts on fruit yield are not well understood. The ability of silicon (Si) to enhance salt tolerance and yield performance has been well documented for some crops. Here, we investigated whether Si could improve grapevine reproductive performance, particularly under saline conditions. One-year-old Shiraz (<i>Vitis vinifera</i> L.) cuttings were grown in controlled conditions and treated with salt (35 mM NaCl) and/or Si (1.5 mM K₂SiO₃) from budburst to veraison. Salt stress reduced fruit set by increasing flower abscission and interrupting normal berry development, which resulted in more live green ovaries and seedless berries per bunch. In vitro and in vivo studies confirmed that poor berry development due to impaired fertilization was correlated with poor pollen tube growth in the style; pollen viability and stigma receptivity were not affected by salinity. Significantly more sodium (Na⁺) and chloride (Cl⁻) were present in leaves and flowers of plants in the salt treatments compared to control plants. Silicon did not prevent the accumulation of Na⁺ and Cl⁻ in reproductive organs or ameliorate the deleterious effects of salinity on reproductive capacity. However, Si-treated vines showed better instantaneous water use efficiency than control vines. This study suggests that fertilization is sensitive to salt accumulation and that salt exposure should be avoided to minimize negative effects of salinity on fruit yield.

Regulation of DTA-6 by Abscission Cellulase and GmAC Gene Expression in Flowers and Pods of Soybean

It is effective to regulate abscission of soybean flowers and pods by spraying plant growth regulators (PGRs). This study was carried out to determine the effect of DTA-6 on abscission cellulase (AC) activity, abscission cellulase gene (GmAC) expressive, abscission of flowers and pods, and yield in soybean. DTA-6 was foliage sprayed at R1 stage on three varieties of Suinong 28, Kenfeng 16, and Hefeng 50 in 2012 and 2013. The results demonstrated that DTA-6 treatment inhibited GmAC gene expression in abscission zone of flower and pod, with the maximum reduction of 51% among three varieties compared with the control. The abscission cellulase activity was periodically decreased by DTA-6, with different decrements among soybean culti- vars. DTA-6 significantly decreased (P<0.05) abscission rate of soybean flowers and pods, and significantly increased yield (P<0.05). The relative expression of abscission cellulase gene (GmAC) in abscission zone of flowers-pods was decreased and the AC activity was regulated by DTA-6, resulting in reduced abscission rate of soybean flowers and pods and promoted yield.

Impact of drought on flowering, yield and quality parameters in diverse genotypes of tomato (Solanum lycopersicum L.)

The effect of drought stress on flowering, yield and quality of tomato ( Solanum lycopersicum ) genotypes was investigated under field conditions in rainout shelter. The drought condition was imposed on the first day after trans-planting based on field capacity of soil. Experimentation was undertaken with ten genotypes adopting Factorial Randomized Block Design with three replications and two treatments viz., 1.0 IW/CPE and 0.5 IW/CPE field capacity. As the stress increased from 100% field capacity to 50% field capacity, reductions in chlorophyll index, soluble protein con-tent, days to flower initiation, sucrose phosphate synthase (SPS) activity, fruit volume, fruit diameter, yield and increased flower abscission percentage were noted. Significant increases in TSS and lycopene were observed under drought. The genotypes LE 118, LE 57 and LE 114 showed significantly less reduction in soluble protein content; SPS activ-ity and fruit yield during drought were considered as drought tolerant. Genotypes LE 1 and LE 125, which gave the lowest soluble protein content, SPS activity and ultimately poor yield, were considered as drought susceptible.

Physiological factors affecting flower and fruit abscission of ‘Hass’ avocado

‘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.