Efficiency of exogenous zinc sulfate application reduced fruit drop and improved antioxidant activity of ‘Kinnow’ mandarin fruit

‘ Kinnow’ mandarin (Citrus nobilis L.× Citrus deliciosa T.) is an important marketable fruit of the world. It is mainstay of citrus industry in Pakistan, having great export potential. But out of total production of the country only 10% of the produce meets the international quality standard for export. Pre-harvest fruit drop and poor fruit quality could be associated with various issues including the plant nutrition. Most of the farmers do not pay attention to the supply of micro nutrients which are already deficient in the soil. Furthermore, their mobility within plants is also a question. Zinc (Zn) is amongst those micronutrients which affect the quality and postharvest life of the fruit and its deficiency in Pakistani soils is already reported by many researchers. Therefore, this study was carried out to evaluate the influence of pre-harvest applications of zinc sulfate (ZnSO4; 0, 0.4%, 0.6% or 0.8%) on pre-harvest fruit drop, yield and fruit quality of ‘Kinnow’ mandarin at harvest. The treatments were applied during the month of October i.e. 4 months prior to harvest. The applied Zn sprays had significant effect on yield and quality of the “Kinnow” fruit. Amongst different foliar applications of ZnSO4applied four months before harvest, 0.6% ZnSO4 significantly reduced pre-harvest fruit drop (10.08%) as compared to untreated control trees (46.45%). Similarly, the maximum number of fruits harvested per tree (627), fruit weight (192.9 g), juice percentage (42.2%), total soluble solids (9.5 °Brix), ascorbic acid content (35.5 mg 100 g-1) and sugar contents (17.4) were also found significantly higher with 0.6% ZnSO4 treatment as compared to rest of treatments and control. Foliar application of 0.6% ZnSO4 also significantly improved total antioxidants (TAO) and total phenolic contents (TPC) in fruit. In conclusion, foliar spray of ZnSO4 (0.6%) four months prior to harvest reduced pre-harvest fruit drop, increase yield with improved quality of ‘Kinnow’ mandarin fruit.

Reduction of Early Fruit Abscission by Main-branch-girdling in Macadamia Is Related to the Favorable Status of Carbohydrates and Endogenous Hormones

Fruit abscission occurring severely in the early fruit development affects macadamia yield. Developing effective methods to improve fruit retention is a priority for macadamia cultivation and production. Girdling is an important horticultural practice that has been widely used to increase fruit yield. Previous studies have shown that girdling fails to increase macadamia yield despite enhancing the early fruit set, but few have examined the effect of girdling on its related physiological mechanism. The objective of this study was to investigate the effects of main-branch girdling (MBG) on early fruit retention and also on the levels of carbohydrates and endogenous hormones in the leaves, bearing shoots and fruit of macadamia. Herein, MBG was performed at fruit set using a single-blade knife on 9-year-old macadamia trees (Macadamia integrifolia). Results showed that MBG significantly reduced young fruit drop, concurrent with significant increases in the contents of starch in both the leaves and the bearing shoots and in glucose, fructose, and sucrose levels in the husk and seed. It was suggested that the availability of carbohydrate for fruit retention was improved by MBG. Additionally, MBG increased indole-3-acetic acid (IAA), gibberellin (GA3), and zeatin-riboside (ZR, a type of cytokinin) concentrations and decreased abscisic acid (ABA) contents in the husk and the seed, indicating that MBG reduced the early fruit drop by modifying the balance of endogenous hormones. Therefore, a positive interplay between carbohydrates and endogenous hormones induced by MBG was involved in the reduction of early fruit abscission in macadamia.

Comparative Analysis of the Transcriptomes of Persisting and Abscised Fruitlets: Insights into Plant Hormone and Carbohydrate Metabolism Regulated Self-Thinning of Pecan Fruitlets during the Early Stage

Pecan is one of the most popular nut species in the world. The fruit drop rate of the pecan ‘Pawnee’ is more than 57%, with four fruit drop stages, which is very serious. In this study, we conducted transcriptomic profiling of persisting and abscised fruitlets in early fruit development by RNA-seq. A total of 11,976 differentially expressed genes (DEGs) were identified, 3012 upregulated and 8964 downregulated, in a comparison of abscised vs. persisting fruitlets at 35 days after anthesis (DAA). Our transcriptomic data suggest that gene subsets encoding elements involving the biosynthesis, metabolism, perception, signal transduction, and crosstalk of the plant hormones abscisic acid (ABA), auxin, cytokinin, ethylene, and gibberellin (GA) and plant growth regulators jasmonates, salicylic acid, and brassinosteroids were differentially expressed. In addition, the majority of transcriptionally activated genes involved in hormone signaling (except for ethylene and salicylic acid signaling) were downregulated in abscised fruitlets. The differential expression of transcripts coding for enzymes involved in sucrose, glucose, trehalose, starch, galactose, and galactinol metabolism shows that sucrose, galactinol, and glucose synthesis and starch content were reduced as starch biosynthesis was blocked, and retrogradation and degradation intensified. These results suggest that the abscised pecan fruitlets stopped growing and developing for some time before dropping, further indicating that their sugar supply was reduced or stopped. The transcriptome characterization described in this paper contributes to unravelling the molecular mechanisms and pathways involved in the physiological abscission of pecan fruits.

Effects of foliar Application with Zinc and Boron On fruitset and yield of Sweet cherry (Prunus avium L. var. Bing): تأثير الرش بالزنك والبورون في نسبة العقد والإنتاج للكرز الحلو (Prunus avium L. var. Bing)

The study aims to increase the fruitset percentage of sweet cherry trees, reduce their fall rate and increase fruit retention percentage that reaches the maturity stage. It was conducted during 2019/2020 years at Cherry orchard located in Sargaya- Al- Zabadani area in Rural Damascus, in Syria. the experiment included 4 foliar spray treatments (T1: Control, T2: Zn (100 ppm), T3: B (500 ppm), T4: (100 ppm Zn + 500 ppm B) on sweet cherry trees (Prunus Avium L.) cultivar (Bing) the fruitset percentage, fruit drop percentage, fruiting factor, and yield quantity were calculated for all treatments. The results showed that all treatments (T2, T3, T4) recorded higher fruitset percentage, compared to the control (T1) with no significant differences between (74.83, 76.35, 76.25%) respectively, while the control fruitset percentage (72.76%), and (T4) has achieved the highest percentage of fruiting factor (41.40%) with no significant differences between it and treatment (T3) (37.12%), and the highest yield (19.98 kg), as well as (T2, T3) treatments was (9.39, 10.80 kg/tree) respectively, while the control yield was (5.93 kg/tree). Therefore, it can be considered that treatment (T4) has succeeded in reducing Sweet cherry fruit drop, where the fruit drop percentage didn't exceed (70.27%), and in (T2, T3) treatments was (74.94, 72.99%) respectively, while it reached in the control treatment to (80.64%).

Soil temperature and horticultural traits as influenced by mulching materials and orchard floor management practices in ber (Zizypus mauritiana Lamk.)

Different type of mulches viz. paddy straw mulch (PSM), black polythene mulch (BPM), and white polythene mulch (WPM) were spreaded under the canopies of Indian ber (Zizypus mauritiana Lamk.) trees in second fortnight of October. The treatments of inter-cultivation (IC) and chemical weed management (CWM), and control trees were also kept for comparative analysis. The daily soil temperature recorded at 0900, 1200, 1400 and 1700 hours from October to April months during 2018-19 and 2019-20 revealed significant variations under different treatments. The respective soil temperature variation during 1st and 2nd year was minimum (9.2 and 9.9 oC) under PSM as compared to 16.5 oC in control plots throughout the investigation period. The soil temperature under PSM was higher during extreme winters whereas, it was comparatively lower during pre and post-winter season as compared to other treatments.The variations in intra-day average soil temperature during the months of October-November and again in March-April was higher than in December-February; the period of extreme winters. Significant reduction in physiological fruit drop was recorded under all the treatments with minimum fruit drop under PSM followed by BPM, while it was maximum in control trees. Likewise, fruit weight and fruit yield was also recorded highest under PSM followed by BPM treatments. The microbes in the rhizopshere of mulched trees with PSM followed by BPM exhibited highest and sustained activity from from Otober to April month under North-West Indian conditions.

Assessment of Fruit Drop in Different Cultivars of Litchi

Individual panicles produce hundreds of pistillate flowers but only a small proportion of these bear fruit and reach maturity. There are some stages of fruit drop during growth and development caused by different factors. An experimental trial was conducted in National Active Germplasm Site (NAGS) at ICAR-NRC on Litchi, Muzaffarpur, to assess the fruit drop due to different factors during 2014–2015. The result revealed that four factors viz., improper pollination and fertilization, embryo abortion, seed and fruit borer, and normal fruit abscission were associated with fruit drop in litchi and fruit drop varied from 23.53–77.54% with a maximum in Shahi and lowest in Elaichi during the first week of flowering. Fruit drop increased to 92.65–97.86% during the third week of flowering because of improper pollination and fertilization, and it reached a maximum level of 98.51–99.70% at the time of ripening stage with the lowest in Deshi. Embryo abortion was one primary cause of fruit drop during the 4th week whereas infestation of seed and fruit borer was the major factor for fruit drop during the 5–7th week. Such fruit drop can be controlled by managing the infestation of borer. Abscission due to ethylene production and heat stress during the maturity of fruit was yet another cause of fruit drop. This study will help to researcher to find out the time of infestation of seed and fruit borer which causes heavy fruit drop and it can be controlled with pest management option.

Haskap Preharvest Fruit Drop and Stop-drop Treatment Testing

Haskap (Lonicera caerulea), also known as honeyberry, is a relatively new fruit crop in North America. To date, most academic activity and research in North America involving haskap has focused on cultivar development and health benefits, with relatively few field experiments providing information to guide field planning and harvest management for the recently released cultivars. In 2020, we documented preharvest fruit drop (PHFD) rates for 15 haskap cultivars planted in a randomized block design at our research center in western Montana with the aim of preliminarily determining whether certain cultivars may be prone to this phenomenon. Additionally, we evaluated two plant growth regulators (PGRs) to reduce PHFD in two cultivars previously observed to have high rates of PHFD. Results suggest cultivar-specific variations in PHFD near berry maturation. Because haskap harvest indices are not well-defined and may be cultivar-specific, we share our 1-year study results as preliminary information and as a call for further research. Cultivars Aurora, Boreal Blizzard, Borealis, Indigo Gem, Kapu, and Tana all had PHFD rates less than 12% of yield, where yield is the weight of berries lost to PHFD plus marketable yield and marketable yield is fruit remaining on the shrub at harvest. Cultivars Chito, Kawai, and Taka had the highest rates of PHFD, although marketable yields were still relatively high, especially for Kawai. We note that ease of fruit detachment is an important consideration in mechanical harvest, and this characteristic could be advantageous if managed appropriately. The PGRs evaluated (1-napthaleneacetic acid and aminoethoxyvinylglycine) did not influence PHFD rates; however, our study was limited by the sample size and by the lack of information regarding haskap abscission physiology. In summary, the haskap cultivars evaluated exhibited variable PHFD rates in the year of the study, and further research is needed to understand haskap fruit maturation, harvest indices, and abscission.