Fruit Set in Avocado: Pollen Limitation, Pollen Load Size, and Selective Fruit Abortion

Avocado is a woody perennial fruit crop originating in Central America and Mexico domesticated and cultivated in the Americas since pre-Columbian times, currently cultivated in subtropical, tropical, and Mediterranean climates worldwide, with increasing importance in international trade. Avocado shows an exuberant flower production that, however, results in a very low fruit set reflected in a massive abscission of flowers and fruitlets. Several factors are involved in this behavior, and, in this work, we have focused on pollination limitation. The results obtained show that pollen deposition takes place at the female and male stages during the avocado flowering season and that the percentage of flowers with pollen on the stigma varies along the flowering season, probably due to changes in temperature that affect not only the floral behavior but also pollinator activity. However, no embryo or endosperm development took place when pollination occurred during the male flowering phase. Thus, the low number of pollen grains landing on the stigmas of female stage flowers observed under natural pollination conditions might not be enough to ensure a good yield. The production of an excess of flowers and subsequent flower drop of most of the flowers provides the opportunity of a selective fruitlet drop depending on the genotype of the embryo since fruits derived from outcrossing showed higher chances of reaching maturity. Moreover, an important competition for resources occurs among developing fruits and new vegetative growth, conferring importance to the time of flower fertilization for effective fruit set.

Evaluation of Ethanol Extract of Moringa oleifera Lam. as Acaricide against Oligonychus punicae Hirst (Trombidiformes: Tetranychidae)

Tetranychidae family is a major group of mites causing serious damage in agricultural, vegetable and ornamental crops. Avocado bronze mite (ABM), Oligonychus punicae Hirst (Acari: Tetranychidae) causes major crop damage, defoliation and fruit abortion. At present, the control of this mite depends mainly on agrochemicals. Therefore it is necessary to find alternatives to synthetic pesticides that can help minimize environmental impact and health risks for the consumers. The aim of this research was to assess the effect of different concentrations (0.1, 0.5, 1, 5, 10, 15 and 20% (v/v)) of ethanolic extract of Moringa oleifera leaves against adult ABM females. Mites treated with 0.1 and 20% (v/v) of the extract showed mortality of 0.00% and 46.67%, 6.67% and 86.67%, 13.70% and 96.67%, at 24, 48 and 72 h, as compared to the control treatment, respectively. The number of eggs laid and hatch, as well as ABM feeding rates, depended on the extract concentration, which led to a reduction in the growth rate. M. oleifera leaf ethanolic extract has potential to control O. punicae.

Effect of Fruit Bagging on Eggplant Fruit and Shoot Borer for Quality Eggplant Production

The study was tested the technical feasibility of bagging eggplant fruits during production to protect them against Eggplant fruit and shoot borer (EFSB) following randomized complete block with 6 treatments. Highest number of marketable fruits per plant was produced by imported white bag (12.33), which was followed by butter paper bag (10.67). Maximum aborted fruit was obtained from the imported brown bag (23.33%) and HDPE bag (20.00%). The highest average fruit weight (363.33 g) was obtained from fruits bagged with Imported white, while maximum fruit length and fruit diameter was also produced from imported white bag (15.27 cm and 11.23 cm, respectively). Zero percent damage by eggplant fruit and shoot borer was produced by imported brown bag, imported white bag and butter paper bag, while higher infection was observed in open fruit (control) (17.70 %), HDPE bag (11.70 %). Bagging eggplant fruit produced 38.78 to 58.20 t/ha, while open fruit (control) produced only 35.66 t/ha. The highest calculated fruit yield 58.20 tons/ha was estimated from imported white bag and other bagging fruits were local brown bag (46.74 t/ha), HDPE bag (45.00 t/ha), butter paper bag (43.23 t/ha). The bagging of eggplant fruits with imported white bag and butter paper bag were more effective in reducing damage by eggplant fruit and shoot borer than the other bagging treatments and the control. These two treatments produced higher number of consumers preferred fruit, without negative effects on the color of the skin, fresh weight and fruit abortion, thus resulting in higher economic gains.

Reduced expression of a subunit gene of sucrose non-fermenting 1 related kinase, PpSnRK1βγ, confers flat fruit abortion in peach by regulating sugar and starch metabolism

Background Fruit abortion is a major limiting factor for fruit production. In flat peach, fruit abortion is present in the whole tree of some accessions during early fruit development. However, the physiological factors and genetic mechanism underlying flat fruit abortion remain largely elusive. Results In this study, we have revealed that the fertilization process was accomplished and the reduction of sucrose and starch contents might result in flat fruit abortion. By combining association and gene expression analysis, a key candidate gene, PpSnRK1βγ, was identified. A 1.67-Mb inversion co-segregated with flat fruit shape altered the promoter activity of PpSnRK1βγ, resulting in much lower expression in aborting flat peach. Ectopic transformation in tomato and transient overexpression in peach fruit have shown that PpSnRK1βγ could increase sugar and starch contents. Comparative transcriptome analysis further confirmed that PpSnRK1βγ participated in carbohydrate metabolism. Subcellular localization found that PpSnRK1βγ was located in nucleus. Conclusions This study provides a possible reason for flat fruit abortion and identified a critical candidate gene, PpSnRK1βγ, that might be responsible for flat fruit abortion in peach. The results will provide great help in peach breeding and facilitate gene identification for fruit abortion in other plant species.

A subunit gene of sucrose non-fermenting 1 related kinase, PpSnRK1γ, confers flat fruit abortion in peach by regulating sugar and starch metabolism

Background: Fruit abortion is a major limiting factor for fruit production. In flat peach, fruit abortion is present in the whole tree of some accessions during early fruit development. However, the physiological factors and genetic mechanism underlying flat fruit abortion remain largely elusive. Results: In this study, we have revealed that the fertilization process was accomplished and the reduction of sucrose and starch contents might result in flat fruit abortion. By combining association and gene expression analysis, a key candidate gene, PpSnRK1γ, was identified. A 1.67-Mb inversion co-segregated with flat fruit shape altered the promoter activity of PpSnRK1γ, resulting in much lower expression in aborting flat peach. Ectopic transformation in tomato and transient overexpression in peach fruit have shown that PpSnRK1γ could increase sugar and starch contents. Comparative transcriptome analysis further confirmed that PpSnRK1γ participated in carbohydrate metabolism. Subcellular localization found that PpSnRK1γ was located in nucleus. Conclusions: This study clarified the reason for flat fruit abortion and identified a critical candidate gene, PpSnRK1γ, responsible for fruit abortion in peach. The results would provide great help in peach breeding and facilitate gene identification for fruit abortion in other plant species.

Assessing New Tools for Management of the Pepper Weevil (Coleoptera: Curculionidae) in Greenhouse and Field Pepper Crops

The pepper weevil, Anthonomus eugenii Cano, is an economically important pest of field and greenhouse pepper crops in North America. In this study, a series of insecticides covering a broad-spectrum of insecticidal modes of action were assessed for their potential in managing the pepper weevil under laboratory and greenhouse conditions. To accomplish this, laboratory mini-spray tower and greenhouse cage trials were conducted that evaluated the efficacy of 16 conventional, reduced-risk, and microbial insecticides. In laboratory trials, adult weevils were sprayed with insecticides, placed on treated leaves within a cup cage, and were monitored for their survival over 10 d. Of the 16 insecticides tested, 8 provided greater than 60% weevil control, a threshold considered necessary for including products in further greenhouse testing. In greenhouse trials, adult weevil mortality, bud and foliar damage, bud and fruit abortion, and subsequent weevil offspring emergence were measured following each of three weekly insecticide applications. The most efficacious insecticides included kaolin clay and mineral oil, which performed as well as the thiamethoxam-positive control, and incurred 70 and 55% of adult weevil mortality, respectively. Additionally, kaolin clay and mineral oil reduced offspring weevil emergence by 59 and 54%, respectively, compared with untreated controls. Despite the clear challenge that controlling this pest represents, this study has identified useful new tools for the integrated management of the pepper weevil, which may accelerate the rate at which these become available for use in greenhouse and field pepper production.

Extreme summer heat and drought acts as an environmental veto for fruit production in European beech

<p>European beech is known to be a masting species, i.e. fruit production does not occur every year. It is thought to be a species which is flowering controlled, i.e. that after successful pollination, fruits and seeds would be produced. In the last two decades, years with high fruit production occurred every two to three years in Middle Europe, which may be indication for an inherent biennial cycle. However, successful fruit production can be hampered by disadvantageous weather conditions, such as frost events, during the pollination season.</p><p>In Switzerland, after high beech pollen concentration was measured in spring of 2018, high fruit production was expected. However, during the extremely hot and dry European summer of 2018, beech produced no, or only small amounts of beechnuts in two of three long-term monitoring beech stands in Switzerland, which are part of the Swiss Long-Term Forest Ecosystem Research Programme. We observed that beechnuts were aborted in early summer already. Over the last decades, we found similar examples of mast failure and fruit abortion in years with hot and dry summer conditions. These extreme conditions can thus act as an “environmental veto”, similar to frost events during flowering. In years with fruit abortion, summer mean temperatures were 1.2°C higher, and precipitation sums were 45% lower than the long-term average. Our findings are evidence for a biennial masting cycle in European beech, which can be interrupted by extreme weather conditions such as extreme summer heat and drought or frost during flowering.</p>

A Review of the Biology, Ecology, and Management of Plum Curculio (Coleoptera: Curculionidae)

The plum curculio, Conotrachelus nenuphar Herbst (Coleoptera: Curculionidae), is an insect native to the Americas that is a serious pest of stone and pome fruits in the United States and Canada. Failure to effectively manage this insect may result in up to 85% damaged fruit at harvest, as well as early season fruit abortion. Conotrachelus nenuphar is oligophagous, feeding and ovipositing on many Rosaceous plants, including apple, peach, plum, cherry, quince, and pear. Additionally, C. nenuphar in limited geographic ranges utilizes alternate hosts such as highbush blueberry (Ericaceae) and Muscadine grape (Vitaceae). Despite its long history as a pest, integrated pest management (IPM) lags behind similarly damaging native fruit pests. Although significant progress has been made on the identification of attractive lures for monitoring C. nenuphar adults, development of behaviorally based management strategies, and biological control with entomopathogenic nematodes, growers continue to rely heavily on top-down chemical inputs to manage this pest. Most of the research to date comes from studies done in apples where alternative management practices for C. nenuphar have, to some extent, been adopted; however, less IPM-based information is available for other susceptible crops. In this review, we summarize the history, biology, ecology, behavior, and control of C. nenuphar and future directions for IPM research.