Fruit Abscission Research Articles

Amelioration of physiological disorders in pistachio nuts by organic manure and gypsum

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.

Chemical thinning of 'BRS Kampai' peach trees

Abstract: The objective of this work was to evaluate the effect of thinning with metamitron on the fruit yield and quality of 'BRS Kampai' peach (Prunus persica) trees. The experiment was carried out in the municipality of Eldorado do Sul, in the state of Rio Grande do Sul, Brazil, in the 2016 and 2017 crop years. Treatments consisted of the application of 100, 200, 300, and 400 mg L-1 metamitron and of hand thinning 40 days after full bloom, besides control plants. Fruit abscission, effective fructification, number of fruits, and fruit yield per plant were evaluated. Regarding fruit quality, fresh fruit biomass, epidermis color, pulp firmness, soluble solids, total phenolic compounds, and antioxidant activity were assessed; fruits were also classified into diameter classes. For fruit abscission, the effect of the application of 100 mg L-1 metamitron is similar to that of hand thinning. Fruit yield and mean mass in all treatments with metamitron are similar to those obtained by hand thinning. The application of metamitron does not affect the fruit quality of peach trees. Chemical thinning with metamitron may be an alternative to hand thinning in peach trees used for the production of fruits for fresh consumption.

Time of metamitron application and concentration in the chemical thinning of ‘Maciel’ peach

Abstract In the peach tree cultivation, the producer has the challenge of obtaining good quality fruits and maintaining production in a balanced way over the years. Thinning favors these parameters and reduces the fruit load on plants. Manual thinning commonly practiced on peach trees requires high labor and increases production costs. Chemical thinning as an alternative to manual thinning, which depending on the species, time and concentration, has demonstrated high efficiency. The aim of this study was to evaluate the effect of metamitron applied at different seasons and concentrations on the chemical thinning of peach trees in southern Brazil. Experiments were conducted in a commercial peach orchard (‘Maciel’ cultivar), in the municipality of Morro Redondo, Rio Grande do Sul, Brazil, during the 2015 and 2016 harvests. In experiment 1, metamitron at concentration of 200 mg L-1 was applied at 20, 30, 40, 50 and 60 days after full bloom and manual thinning performed at 40 days after full bloom. In experiment 2, metamitron was applied at concentrations of 100 mg L-1, 200 mg L-1, 300 mg L-1 and 400 mg L-1 and manual thinning at 40 days after full bloom, in addition to control plants. Fruit abscission, fruit set, total number of fruits per plant, yield per plant, average mass and fruit diameter were evaluated. Metamitron at concentration of 200 mg L-1 has thinning effect when applied before 40 days after full bloom. Metamitron concentration of 100 mg L-1 applied at 40 DAFB promoted fruit abscission superior to manual thinning. Therefore, the application of metamitron to ‘Maciel’ peach trees close to full bloom at concentration of 100 mg L-1 results in thinning practice similar to manual thinning.

Vesicular trafficking in abscission zone cells during ethylene-promoted fruit abscission in citrus

Vesicular trafficking in abscission zone cells during ethylene-promoted fruit abscission in citrus

Water status and productivity of 'Hass' avocado trees in response to supplemental irrigation during winter

Abstract: The objective of this work was to evaluate the effects of supplemental irrigation, during winter dry season, on the water status and productivity of 'Hass' avocado (Persea Americana) trees. The experiment was carried out on a clayey Oxisol from 2014 to 2016, when extreme climatic events were recorded in the state of São Paulo, Brazil. The rainfed regime was compared with two irrigation regimes, applied during the whole and half of the irrigation run time defined by the grower, corresponding to 5,091 and 2,545 m3 ha-1 water, respectively. The following variables were evaluated: soil water tension; leaf water potential, color, and chlorophyll content; leaf and fruit abscission rates; tree size; and fruit size and yield. Supplemental irrigation applied during half of the run time increased fruit yield by 18.2%. However, irrigation applied during a fixed-time period and the occurrence of unusual rainfall spells caused soil water logging, negatively affecting tree growth and water status.

Natural fruitlet abscission as related to apple tree carbon balance estimated with the MaluSim model

Apple trees produce many more flower clusters than needed for a full crop, but natural early season flower and fruitlet abscission drastically reduce the final fruit number. Natural fruit abscission varies significantly year to year. There have been attempts to try to model apple fruit abscission in the past. However, due to the great complexity of a perennial crop system in a dynamic environment with significant plant manipulations, regulatory processes and controlling environmental variables have been difficult to elucidate. In 1995, a field trial was planted at the New York State Agricultural Experiment Station in Geneva, New York with 3 apple cultivars (‘Delicious’, ‘Gala’, and ‘McIntosh’). Beginning in 2000 and for 18 years thereafter, we recorded the natural whole-season fruit abscission of untreated trees that received no chemical or hand thinning. We also estimated early season patterns of carbohydrate supply-to-demand each year with a carbon balance model. These data were used to correlate tree carbon balance status and other environmental variables with natural fruit abscission responses. In general terms, natural set, defined as final fruit/flower cluster, of ‘Gala’ averaged ˜1 fruit for each flower cluster (fruit set = 0.9), whereas fewer fruits were set on ‘Delicious’ and ‘McIntosh’ (fruit set = 0.7 and 0.6, respectively). Fruit set of ‘Gala’ was less variable than of ‘Delicious’ or ‘McIntosh’, and there was a clear pattern for decreasing fruit set when the number of initial flower clusters per tree increased. Fruit weight was less dependent on fruit number for ‘Delicious’ and ‘McIntosh’ than for ‘Gala’. Multiple regression models indicated that number of flower clusters per tree and average carbohydrate balance between 0–60 degree days (DD) after bloom and 300–360 DD after bloom were the main significant variables that explained 60–80% of the variability in natural fruit set or final fruit number. For ‘Delicious’, temperatures of the previous fall also explained a significant amount of variation in final fruit set and final fruit number. For ‘Gala’, carbon balance from bloom to shortly after petal fall and when fruits were about 18 mm were the two main periods, which were more sensible to carbohydrate deficiency triggering fruit abscission. A later susceptible period was also observed for ‘McIntosh’, suggesting a larger thinning window for this cultivar.

Vesicular trafficking in abscission zone cells during ethylene-promoted fruit abscission in citrus

Abscission is a cell separation process by which plants are able to shed aerial organs. This physiological process proceeds through a breakdown in adhesion between a group of specialized cells that usually differentiate in particular positions of the plant body named abscission zones (AZs). The occurrence of fruit abscission has special relevance in fruit tree crops such as citrus since it may have negative consequences on yield. To identify AZ-specifically expressed genes involved in citrus fruit abscission, we used a combined strategy of laser microdissection and microarray analysis to compare the global expression profiles of calyx abscission zone (AZ-C) cells of citrus fruits and adjacent fruit rind cells during ethylene-promoted fruit abscission. The comparison enabled to identify a set of potentially specific genes including those associated with vesicular transport and intracellular transport vesicles. The first ultrastructural observations on AZ-C cells during fruit abscission (Iwahori and van Steveninck, 1976) showed an increase in rough endoplasmic reticulum profiles and dictyosome stacks with associated vesicles that fused with the plasma membrane to release their contents to the cell wall. In this comparative transcriptomic survey, we highlighted specific over-expression in AZ-C cells of genes belonging to the major transport steps along the secretory and the endocytic pathways of vesicle trafficking. In particular, it is likely that some of the genes identified in this study would represent major candidate genes for further biotechnological approaches aimed at trying to solve or at least mitigate agronomic issues regarding citrus fruit abscission.

Vesicular trafficking in abscission zone cells during ethylene-promoted fruit abscission in citrus

Vesicular trafficking in abscission zone cells during ethylene-promoted fruit abscission in citrus

Sensitivity of potted ornamental peppers to ethylene

Many environmental factors affect the post-production shelf life of potted ornamental plants. Exposure to ethylene can reduce the quality of many species, inducing flower, fruit and leaf abscission and senescence. The present study identified ethylene-resistant pepper genotypes during post-production shelf life testing. Potted plants of eleven pepper cultivars were transferred o a 90-L sealed container when they had 30% of ripe fruits and treated with 10 μL L-1 of ethylene for 48 hours. Number of leaves and fruits were counted at the beginning of ethylene exposure and after 48, 96 and 144 hours. The experimental design was completely randomized, with five replicates of individual pots. The cultivars showed varied rates of foliar and fruit abscission. ‘Peloteira’ showed higher resistance to ethylene, with foliar abscission of 19%, after 144 hours. For fruit abscission, the cultivars ‘Peloteira’, ‘Jalapeño’, ‘Stromboli ornamental’, ‘Malagueta’ and ‘Rocoto Vermelha’ presented a lower percentage of leaf drop, varying between 9 and 34%, after 144 hours of exposure to ethylene. This study showed that ornamental peppers have high genetic diversity regarding ethylene sensitivity.

Effects of solar irradiation and night-time temperature on the thinning efficacy of metamitron (Brevis®) in apple

Trials with metamitron (Brevis®) were conducted at different phenological stages of apple fruit (7-18 mm fruit diameter) in the 2014-2016 seasons. Within each season, the same dosages were used at all application dates for all tested cultivars. On the basis of the obtained results a model was developed in order to estimate the efficacy of Brevis® at the established treatment. Metamitron causes a measurable reduction of electron transport in photosystem II for about 10 days, leading to a reduced photosynthetic output. In addition when elevated night-time temperatures (>10°C) occur a further fruit abscission can be enhanced.

EFFECT OF PREHARVEST APPLICATIONS OF CALCIUM, ANTI- ETHYLENE COMPOUNDS AND THEIR COMBINATIONS ON “CANINO” APRICOT FRUIT QUALITY AND STORABILITY

This study was conducted during two sequential seasons of 2015 and 2016 in a private orchard located in El-Khattaba District, Menoufia Governorate, Egypt to investigate the influence of calcium chloride (CaCl2) at 2%, anti-ethylene compounds namely Aminoethoxyvinylglycine (AVG) at 150 ppm and 1- Methylcyclopropene (1-MCP) at 25 ppm in addition to their combinations (CaCl2 plus AVG, CaCl2 plus 1- MCP, AVG plus 1-MCP and finally CaCl2 plus AVG and 1-MCP, at the same concentrations) on fruit drop at harvest and yield as well as firmness, jelly pulp and other quality parameters of “Canino” apricot fruits during cold storage at 0oC and 90- 95% RH for one month. During 2015 and 2016 seasons, apricot trees were sprayed three times starting after full bloom, fruit setting and finally ten days before harvest. Quality of sprayed fruits was evaluated at harvest and every ten days of cold storage. The results showed that external browning, internal browning, jelly pulp, fresh weight loss, total sugars, total soluble solids (TSS), TSS to acidity ratio, carotene content were increased, while firmness, electrolyte leakage, vitamin C, acidity, chlorophylls a and b contents were decreased with the progress of cold storage duration. Furthermore, the results revealed that all used treatments reduced external and internal browning symptoms in addition to jelly pulp formation and fruit fresh weight loss. Moreover, the treatments lessened electrolyte leakage of fruits, retarded the loss of fruit firmness and were effective on keeping the physical and chemical qualities relative to the control treatment. Finally, this study indicated that the addition of CaCl2 to anti- ethylene compounds was more effective than the individual application of each compound on reducing fruit abscission, increasing average fruit weight and yield/tree at harvest plus retarding the loss of firmness, other physical and chemical qualities and prolonging the storability of “Canino” apricots stored at 0oC, especially the combination of AVG and 1-MCP in the presence of CaCl2.

Hormonal control of parthenocarpic fruit set in ‘Rojo Brillante’ persimmon (Diospyros kaki Thunb.)

In persimmon (Diospyros kaki Thunb.), one to three waves of fruit abscission can occur. The parthenocarpic cv. Rojo Brillante may abscise close to 50% of flowers, which implies a major economic losses.In order to study this process, 700 flowers were labelled, 600 had the lobes of the calyx removed at three stages to promote abscission. Half of them were also treated with gibberellic acid (GA3; 10 mg l−1) to counteract the effect, and 100 were used as control. In the second year, GA3 (25 mg l−1) was applied to whole trees.Calyx lobe removal (CLR) reduced fruit growth rates and advanced and increased fruitlet abscission, whereas GA3 counteracted this effect. Furthermore, when GA3 was applied to the whole tree, fruit set was increased. The time-course of fruit abscission paralleled a decreased in hormonal and carbohydrate contents.Control fruit showed a peak of gibberellin (GA1 and GA4) and IAA concentration at anthesis. Hexose concentrations remained almost constant from flower bud to fruit set, whereas that of sucrose diminished with time.A peak in ethylene production occurred at anthesis, which increased when CLR was performed prior to or at anthesis, but not when performed at fruit set, when ethylene was markedly smaller. GA3 also counteracted it.Accordingly, we suggest that fruit set depends on the induction of gibberellin (GA) and IAA responses in the persimmon, and since there is no shortage of hormones or carbohydrates at anthesis, ethylene production at anthesis seems the most plausible cause of the physiological fruitlet abscission.

Effect of ethylene and temperature on physiological and biochemical changes during fruit drop of longkong postharvest

Longkong (Aglaia dookoo Griff.) is a popular tropical fruit that currently experiences around 99.37% domestic consumer demand. The main problem in terms of export is that longkong fruit drops from its bunch after harvesting. Therefore the objective of this research is to study the development of fruit drop in longkong bunches being harvested and stored at room temperature. Weight loss, fruit drop and polygalacturonase (PG) activity increased rapidly during storage time; while firmness, respiration rate and ethylene of longkong fruit bunches decreased after storage at room temperature. Activity of the enzymes pectinesterase (PE), cellulase (Cx) and peroxidase (POD) of longkong fruit slightly increased up to six days and then decreased until the end of storage. The effect of ethylene (at the concentration of 0, 200 and 400 ppm) on physiological and biochemical changes during fruit drop of longkong postharvest was evaluated. Dipping longkong in 200 and 400 ppm ethephon rapidly increased fruit abscission and respiration rate. The untreated fruit showed increased ethylene production and activity of enzymes PG, PE and Cx, and weight loss was delayed longer than longkong dipped in 200 and 400 ppm ethephon. Firmness and POD were not significantly different between the fruit treated with ethephon and those untreated. Effects of temperature (at 13 and 25°C) on physiological and biochemical change during fruit drop of harvested longkong bunches was also evaluated. The results indicate that storage at 13°C delayed the weight loss, fruit drop, firmness, respiration rate, ethylene production and activity of enzymes pectinesterase (PE), cellulase (Cx) and peroxidase (POD).

Effects of mulching on soil temperature and moisture variations, leaf nutrient status, growth and yield of pistachio trees (Pistacia vera.L)

Abstract 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.

Effect of chemical thinning using 6-benzyladenine (BA) on Maciel peach (Prunus persica L.)

High effective peach fruit set results in an excessive amount of fruits, requiring thinning accomplishment, which is a manual practice and demands specialized labor, raising production costs. In this sense, chemical thinning may be an alternative to improve the peach production chain. The objective of this work was to evaluate the efficiency of 6-benzyladenine (BA) on chemical thinning and the effect of different BA dosages on peach production and color characteristics of 'Maciel' fruits. Treatments consisted of plants without thinning (Control), sprayed BA at doses of 100 mg L-1, 200 mg L-1 and 400 mg L-1, applied 45 days after full bloom (DAPF) and hand thinning at 45 DAPF. The applications of different dosages were carried out by spraying, using backpack spraying equipment. Percentage of thinning abscission, number of fruits per plant, yield per plant, fruit mass, color and average fruit diameter were evaluated. The doses of 200 and 400 mg L-1 BA for thinning increased the percentage of fruit abscission and fruit mass. The doses of 400 mg L-1 BA presented lower yield per plant, but fruits with higher average mass. Increasing BA dose reduced the number of fruits per plant. Hand thinning and 400 mg L-1 BA resulted peach fruits with larger diameter. BA application to thin peaches did not alter the fruit skin color. Therefore, BA may be a chemical thinning alternative for 'Maciel' peach cultivar, because it reduces the time of thinning in plants when compared to manual thinning. For an efficient chemical thinning with BA the product dose must be taken into account, along with climatic conditions and the cultivar.

Canopy characteristics and light distribution in Sapindus mukorossi Gaertn. are influenced by crown architecture manipulation in the hilly terrain of Southeast China

Abstract 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.

Benzyl adenine is more effective than potassium silicate on decreasing the detrimental effects of heat stress in pepper (Capsicum annum cv. PS301)

ABSTRACT- Heat stress causes flower and fruit abscission in pepper. This study was conducted in the greenhouses of Isfahan University of Technology to evaluate the effect of foliar application of Benzyl adenine (BA) and potassium silicate (K2SiO3) under heat stress condition on bell pepper. Two factorial experiments based on completely randomized design with four concentrations of BA (0, 0.06, 0.6 and 6 ppm) and the second with two levels of K2SiO3 (0 and 5 Mm) both in two temperature treatments (25±2 (optimum) 35±2 (high temperature)) with six replicates were conducted. The results of the study indicated that the use of BA (especially 6 ppm) promoted growth parameters and increased proline, phenol and antioxidant content. Also, application of BA 6 ppm improved cell membrane stability assessed via decreasing electrolyte leakage (EL) and also reduced flower abscission in bell pepper. BA at 6 ppm increased plant height, shoot and root dry weight, proline and total phenol, root fresh weight, potassium (K) concentration and decreased flower abscission. Antioxidant content increased with heat stress in all BA levels. Results of the study indicated that fresh and dry weight of root and K concentration increased with 5 mM K2SiO3. Moreover, root fresh weight and K concentration and antioxidant content increased in 5 mM K2SiO3 under heat stress.

Brassinolides have a small effect on vegetative growth, and increase reproductive growth of pistachio trees Cv. Owhadi

ABSTRACTThe effects of different applications of 24-epi-brassinolideon the physiology and yield of ‘Owhadi’ pistachio trees was investigated in Iran over an off and on year. Plants were treated by 24-epi-brassinolide at 0, 0.25, 0.5, 0.75 and 1mgl−1at green tip and tight cluster of bud stage. Brassinolide decreased the incidence nut physiological disorders and increased yield. The sprays decreased the incidence of inflorescence bud abscission, fruit abscission, misshapen nuts, blank, early splitting and indehisced shell compared with the controls. In both on and off years, the effect of brassinolide was dependent on the time of application and concentration used. Application of this compound, especially at tight cluster stage of buds, increased indehisced shell and yield in both on and off years. Brassinolides appear to play a key role in the growth and development of pistachio.

Abundance across seasons and early impact of the florivorous weevil Anthonomus santacruzi (Curculionidae) on Solanum mauritianum (Solanaceae) in KwaZulu-Natal Province, South Africa

The florivorous weevil Anthonomus santacruzi Hustache (Coleoptera: Curculionidae) was first released in South Africa in 2009 to reduce fruiting by the invasive Solanum mauritianum Scopoli (Solanaceae). Additional releases during 2011–2014 achieved widespread establishment in KwaZulu-Natal Province, notably in its warmer coastal regions. The aims of this study were to determine whether A. santacruzi abundance: (i) varied monthly at coastal versus inland sites; (ii) was influenced by floral availability and the numbers of ants associated with S. mauritianum inflorescences and; (iii) negatively affected the weed’s fruit production. Sampling over a 12-month period indicated that A. santacruzi abundance varied seasonally across coastal and inland sites, with populations consistently peaking in the austral autumn months and declining during winter. Although A. santacruzi numbers were significantly positively correlated with floral availability in the previous month, <10% of available flower buds were infested monthly by weevil larvae. Significant negative correlations between weevil numbers and fruit set recorded two months later was likely caused by the abscission of ripe fruit, rather than feeding damage. While ant abundance on S. mauritianum inflorescences was positively linked with numbers of mature fruit, there was no evidence of any interference with adult A. santacruzi numbers. Given the weed’s reproductive phenology, substantially higher weevil numbers are needed throughout the year to achieve meaningful impact. However, since A. santacruzi has only recently become widely established in KwaZulu-Natal Province, and is still in the process of increasing its range, its impact on S. mauritianum fruiting may increase over time.

IMPACT OF THE INTERACTION BETWEEN AMINO ACIDS (AA), NAPHTHALENE ACETIC ACID (NAA) AND NAPHTHALENE ACETAMIDE (NAD) ON SANTA ROSA PLUM FRUIT ABSCISSION, YIELD AND QUALITY.

To decrease fruit abscission, increase yield and improve fruit quality of Santa Rosa (Prunus salicina Lindl.) plum; amino acids (AA), naphthalene acetic acid (NAA) and naphthalene acetamide (NAD) and a combination of them were applied at different concentrations; at full bloom stage and one week after fruit setting stage during 2015 and 2016, in a private orchard at Ashmoun, Monofia governorate, Egypt. Results indicated that fruit set percentage significantly increased by all AA, NAA and NAD treatments compared to the control. AA 0.25 ml/L+NAA 10 ppm + NAD at 10 ppm recorded the highest significant fruit set percentage and the lowest significant fruit drop percentage and gave the maximum yield (62- 64 Kg/ tree). With regard to fruit quality, the same treatment increased fruit weight, length, diameter, firmness, pulp/stone ratio, and total soluble solids content, but decreased titratable acidity in Santa Rosa plum. In addition, total carbohydrates, total nitrogen, and C/N ratio in leaves were higher in treated trees than the control ones. Anatomical studies indicated that inactive embryo development after ovule fertilization may be the major cause of young fruit drop observed in ‘Santa Rosa’ plum trees. Furthermore, there was a relationship between physiological fruit drop which occurred from the middle of Growth Stage 2 to the beginning of Growth Stage 3, and seed development which contains inactive endosperm. From this study, it can be concluded that the combination of AA, NAA, and NAD increased fruit set, reduced fruit abscission, enhanced C/N ratio in leaves, and improved fruit yield and quality of Santa Rosa plum. Thus, it may be recommended to spray AA 0.25 ml/l +NAA 10 ppm + NAD 10 ppm under similar conditions