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Ethylene, a key plant hormone, regulates various fruit ripening traits, including pre-harvest fruit drop (PFD) and color development. In commercially valuable apple cultivars like ‘Honeycrisp,’ excessive fruit drop before the commercial harvest date poses a significant challenge, leading to substantial crop losses. While ethylene inhibitors such as aminoethoxyvinylglycine (AVG) effectively reduce PFD, they can also hinder fruit coloration. To address this trade-off, we evaluated various plant growth regulators (PGRs), such as Accede (1-aminocyclopropane-1-carboxylic acid (ACC)-10%), Motivate (ethephon-21.7%), and ReTain (AVG-15%), in ‘Honeycrisp’ apples over two consecutive years (2023–2024). Our study found that ACC, alone or combined with AVG, promoted chlorophyll degradation and intensified red coloration at the normal harvest date and two weeks after the normal harvest date (WAH). ACC, ethephon, and AVG + ACC increased anthocyanin accumulation on apple fruit peel in both growing seasons. For fruit drop control, AVG and its combination with ACC significantly reduced PFD compared to the untreated control. Notably, AVG + ACC was the most effective treatment in reducing PFD by 27.05–46.30% while simultaneously enhancing red color. The anthocyanin content of AVG + ACC-treated apples was significantly greater than that of the control, correlating with the upregulation of anthocyanin biosynthetic genes such as MdCHS , MdCHI and MdDFR . No significant differences were observed in other fruit quality traits, e.g. fruit firmness, brix, and starch index, between AVG + ACC-treated and untreated fruits at any time point. Our results indicate that the AVG + ACC combination is a promising strategy for mitigating pre-harvest fruit drop while improving fruit color in apples.

Background Prunus sibirica L. is one of the most pivotal eco-economic tree species in China’s arid and semi-arid areas. The phenomenon of physiological fruit drop in P. sibirica L. is severe, and understanding fruit growth patterns and drop characteristics is crucial for high-quality cultivar production. However, there are few reports on P. sibirica fruit development and physiological fruit drop. Results In this study, we investigated the characteristics of fruit development, vegetative bud outgrowth, and fruit abscission, and explored the dynamic features of sugar metabolism in different tissues during physiological fruit drop and its relationship with fruit drop. The results showed that the fruit and vegetative bud outgrowth of the “Shanxing No. 1” variety exhibited an S-shaped growth pattern with three physiological stages. The flower and fruit drop of “Shanxing No. 1” lasted for about 70 days with an 89.73% total drop rate and three abscission peaks, which could be divided into the flower abscission stage mainly caused by pistil abortion, rapid fruitlet abscission stage, mainly caused by carbohydrate competition between the fruit and vegetative bud outgrowth; and slow fruit abscission stage mostly related to seed abortion. The perspective of the vegetative buds removal experiment further proved the competition between fruitlet and vegetative bud outgrowth simultaneously. During physiological fruit drop, the sugar contents and activities of sucrose metabolism enzymes in different tissues showed regular changes, corresponding to the dynamic law of fruit drop. Sucrose metabolism was mainly dominated by decomposition, and the enzymes involved in sucrose decomposition played a significant role. Acid invertase and sucrose synthase (decomposition direction) were the key enzymes regulating fruit abscission in P. sibirica L. Conclusions These results laid a foundation for revealing the physiological characteristics and physiological mechanism of P. sibirica L. fruit development, and also provided a theoretical basis for high-quality and high-yield cultivation of P. sibirica L.

Plant growth regulators (PGR's) are considered potential substances which lessen the abiotic stresses and help in delaying the pre-mature fruit drop (PFD). Therefore, a two-year (2021 and 2022) multi-locational study was designed to assess the effects of three different PGR's (NAA, 2, 4-D, GA 3 ) on PFD and postharvest quality of selected apple varieties ('Kashmir Amri', 'Red Delicious', 'Star Crimson') grown at three different locations (Bagh, Dheerkot, Rawalakot) of Azad Jammu and Kashmir (AJK). All PGR's were applied through foliar spray using a low pressure hand sprayer before the flowering period at the same concentration (25 ppm), while apple trees without any treatment application served as control. Apple trees sprayed with 25 ppm GA 3 showed 44.56% less PFD at Dheerkot location as compared to control. Moreover, 25 ppm GA 3 treated fruits showed better fruit size, fruit weight, and overall yield as well. In terms of postharvest quality parameters, a significantly high amount of strife index (5.60%), titratable acidity (2.58%), total soluble solids (13.81%), crude fiber (1.44%), total ash content (0.51%), total phenolics (136.3 mg GAE/100g FW), total flavonoids (14.83 mg/100g FW) and antioxidant activity (97.0 µg/100g FW) was found in apple trees sprayed with 25 ppm GA 3 as compared with other treatments. Among apple varieties, 'Star Crimson' while among locations, Dheerkot showed promising results. Thus, the overall results of this study revealed that PFD could be potentially minimized and postharvest quality could be enhanced with 25 ppm GA 3 spray, while Dheerkot is the most suitable location for growing apples.

Citrus post-bloom fruit drop (PFD) is caused by Colletotrichum acutatum and C. gloeosporioides species complexes and frequently occurs in São Paulo (SP) state, Brazil. The environmental requirements for conidial germination and appressorium formation have been already determined in vitro; however, the environmental conditions for infection in citrus flowers remain unknown. C. acutatum is considered the main species complex causing PFD in citrus, but a survey of the pathogen’s prevalence has never been performed in SP state. The aims of this study were to assess the influence of different temperatures and wetness periods on infection of flowers by C. acutatum and C. gloeosporioides in potted citrus trees, and to determine the prevalence of both pathogens in different SP regions and sweet orange varieties. Environmental requirement trials were conducted in 2- to 3-year-old potted sweet orange trees. Flowers at different development stages (R2, R4 and R5) were inoculated with C. acutatum and C. gloeosporioides, and the trees were incubated at 18 or 24 °C for wetness periods of 6, 8, 12, 16 or 24 h. The percentages of inoculated flowers with PFD lesions and persistent calyces were calculated. The prevalence of both pathogens in SP regions was assessed in samples of diseased flowers collected at 16 commercial orchards of ‘Natal’, ‘Valencia’ and ‘Pera’ sweet oranges. The species complex was confirmed by isolation and PCR with species complex-specific primers. Blossom blight and persistent calyx incidences were higher in flowers inoculated with C. acutatum than in those inoculated with C. gloeosporioides. Incubation periods ranged from 2 to 5 days, and from 5 to 6 days for C. acutatum and C. gloeosporioides, respectively. In SP, irrespective of the region and sweet orange variety, C. acutatum was isolated from more than 80% of symptomatic flowers. We concluded that C. acutatum is not only more aggressive than C. gloeosporioides for causing PFD but also more prevalent in SP orchards.

Colletotrichum abscissum and C. gloeosporioides are the causal agents of citrus Postbloom Fruit Drop (PFD), a major disease in several countries of the American continent. These pathogens infect only floral structures; however, in the absence of floral tissue, they survive asymptomatically on the leaf tissue. Thus, detecting and quantifying pathogens on leaves are critical for epidemiological studies. Colletotrichum species are detected through isolation, serological methods and conventional PCR, but these techniques are not effective for accurate detection of PFD agents. This study aimed to develop specific, more sensitive, faster and less laborious techniques than the traditional ones routinely used. We developed, standardized and validated a multiplex real-time PCR with high sensitivity (98–99.3%) and specificity (94.3–97.1%) for the detection and quantification of both pathogens. This technique was 1000 and 10,000 times more sensitive than Nested-PCR and PCR, respectively for the detection of C. abscissum. Similarly, the multiplex qPCR was 100 and 1000 times more sensitive than Nested-PCR and PCR, respectively for the detection of C. gloeosporioides. The diagnostic parameters used to validate the multiplex qPCR showed a high positive (17–35) and low negative (0.006–0.95) likelihood ratios, low percentage of false positives (2.8–5.6%) and false negatives (0.6–1.9%), good agreement between the results generated between qPCR and multiplex qPCR, revealed by the Kappa index (0.91–0.98) and coincidental results (95–99%). All parameters indicated that the multiplex qPCR was effectively validated to detect and quantify the causal agents of PFD.

The genus Colletotrichum comprises a group of important fungal pathogens that can infect a wide variety of host plants worldwide. Postbloom fruit drop (PFD) of citrus plants is responsible for extensive crop losses annually, and is particularly detrimental to Brazilian citrus production. The disease was first associated with Colletotrichum gloeosporioides and subsequently linked to Colletotrichum acutatum . However, a new species, C. abscissum , was described in 2015 as the causative agent of PFD in Brazil. The species description used a small number of strains and the distribution of the pathogen remains unclear. The proportion of PFD caused by this species is also unclear, because both C. abscissum and C. gloeosporioides are associated with the disease as well. By analyzing sequences of the GAPDH intron region, we identified 227 isolates of Colletotrichum associated with PFD in orchards of São Paulo state, 172 isolates were identified as C. abscissum and 55 as C. gloeosporioides . Morphological characters and multilocus sequencing confirmed species C. abscissum was the only species in the C. acutatum complex associated with PFD disease in Brazil. Although described as sensitive to benzimidazole-based fungicides, 20% of C. gloeosporioides isolates were found in regions with high use of this class of fungicide. Evaluated strains exhibited resistance to this fungicide in vitro. Because previously described primers differentiate between C. acutatum and C. gloeosporioides complexes, but not the particular species associated with PFD, we proposed and validated primers for a single multiplex PCR that specifically distinguished the C. abscissum and C. gloeosporioides sensu stricto.

Typhoons, which are a common natural disaster in Korea, have seen a rapid increase in annual economic losses over the past decade. The objective of this study was to utilize historical crop insurance records to predict fruit drop rates caused by typhoons from 2016 to 2021. A total of 1848 datasets for the fruit drop rate were generated based on the impact of 24 typhoons on 77 cities with typhoon damage histories. Three different types of measures—the average value, the maximum or minimum value, and the value at a specific point during the typhoon—were applied to four meteorological factors, yielding a total of twelve variables used as model inputs. The predictive performance of the proposed models was compared using five evaluation metrics, and SHAP analysis was employed to assess the contribution of predictor variables to the model output. The most significant variable in explaining the vulnerability to typhoons was found to be the maximum wind speed. The categorical boosting model outperformed the other models in all evaluation metrics, except for the mean absolute error. The proposed model will assist in estimating the potential crop loss caused by typhoons, thereby aiding in the establishment of mitigation strategies for the main crop-producing areas.

Preharvest fruit-drop is a challenge to bayberry production. 2,4-D sodium as a commonly used anti-fruit-drop hormone on bayberry can reduce the yield loss caused by preharvest fruit-drop. The persistence and risk assessment of 2,4-D sodium after applying on bayberries were investigated. A method for determining 2,4-D sodium in bayberry was established based on LC-MS-MS. The average recoveries of 2,4-D sodium were at the range of 93.7–95.8% with relative standard deviations (RSDs) ranging from 0.9 to 2.8%. The dissipation rates of 2,4-D sodium were described using first-order kinetics, and its half-life ranged from 11.2 to 13.8 days. A bayberry consumption survey was carried out for Chinese adults for the first time. The safety assessments of 2,4-D sodium were conducted by using field trail data as well as monitoring data. Results showed that the chronic risk quotient and the acute risk quotient were calculated to be 0.23–0.59 and 0.02–0.05%, respectively, for Chinese adults, indicating low dietary risk for adults and children. In the end, the household cleaning steps were compared, and results showed that water rinsing for 1 min can remove 49.9% 2,4-D sodium residue, which provides pesticide removal suggestion for consumers.

Postbloom fruit drop (PFD), an important disease caused by Colletotrichum spp., affects citrus yields in Brazil. PFD is characterised by the presence of necrotic lesions on the petals and stigmas of citrus flowers and by the subsequent abscission of young fruit. PFD epidemics have high disease progress rates, which is unusual for a pathogen that produces acervuli and is dispersed by rain. It is possible that other dispersal agents, such as insects and pollen, are involved in the spread of this disease. The objective of this work was to test whether citrus pollen grains can be colonised by Colletotrichum acutatum. Studies using light and electron microscopy showed that the pollen of Citrus sinensis can be infected by C. acutatum. This pathogen can penetrate and colonise citrus pollen grains 24 h after inoculation with the pathogen. The germ tube of conidia either penetrates the pollen sporodermis directly or passes through pollen germ pores. A single hypha can colonise more than one pollen grain. On the surface of the stigma, conidium formation can be observed. This study shows that Citrus sinensis pollen may, in fact, play a role in the spread of C. acutatum in citrus orchards.

A mechanistic overview of abscission signaling is presented to provide an easy entry point into the exciting field of research on how plants control shedding of organs. Abstract Abscission is a process in plants for shedding unwanted organs such as leaves, flowers, fruits, or floral organs. Shedding of leaves in the fall is the most visually obvious display of abscission in nature. The very shape plants take is forged by the processes of growth and abscission. Mankind manipulates abscission in modern agriculture to do things such as prevent pre-harvest fruit drop prior to mechanical harvesting in orchards. Abscission occurs specifically at abscission zones that are laid down as the organ that will one day abscise is developed. A sophisticated signaling network initiates abscission when it is time to shed the unwanted organ. In this article, we review recent advances in understanding the signaling mechanisms that activate abscission. Physiological advances and roles for hormones in abscission are also addressed. Finally, we discuss current avenues for basic abscission research and potentially lucrative future directions for its application to modern agriculture.