Comparative effects of gibberellin A3 , glycine betaine, and Si, Ca, and K fertilizers on physiological disorders and yield of pomegranate cv. Wonderful

BACKGROUND

Damage from cracking, russeting, and sunscalds causes significant yield losses in pomegranate worldwide and may result from stressful environmental conditions. Although foliar sprays with minerals or growth regulators could be an important orchard management, little is known on the effectiveness of glycine betaine, silicon (Si)-based fertilizers or the response of cv. Wonderful to gibberellin A₃ (GA₃ ).

RESULTS

During a 2-year study, foliar spraying with GA₃ at 75 or 150 mg L^-1 applied in July substantially reduced cracking, russeting, and sunscald symptoms and increased fruit size, yield, and 100-aril weight, without affecting the % edible portion or % juice, suggesting that arils and skin increased similarly. Nevertheless, they reduced the skin red coloration, especially at the higher dose. GA₃ at 75 mg L^-1 applied in September resulted in a low number of harvested fruit as a result of delayed maturation. Spraying with glycine betaine at seven repeated times at biweekly intervals starting in July, reduced sunscald symptoms, red coloration, and maturity index only in the year with high damage. Foliar sprays with calcium chloride or Si-based fertilizer containing potassium, applied as in the glycine betaine treatment, did not affect the occurrence of physiological disorders, whereas Si-based fertilizer containing potassium and calcium increased cracking and decreased sunscald only in the year with high damage.

CONCLUSION

Spraying with GA₃ at 75 mg L^-1 in July could have a significant impact on a grower's income by reducing damage from physiological disorders, improving yield with a minimum decrease in red skin coloration. The efficacy of nutrient-related fertilizers and glycine betaine were not constant, and this would be useful to evaluate at earlier application times and under stress conditions. © 2021 Society of Chemical Industry.

Physiological Disorders and Fruit Quality Attributes in Pomegranate: Effects of Meteorological Parameters, Canopy Position and Acetylsalicylic Acid Foliar Sprays

Meteorological parameters and occurrences of cracking (CR), russeting (RS), and sun scald (SS) symptoms were monitored in a pomegranate cv. "Wonderful" orchard planted in a W-E orientation, during a 3-year study. Moreover, the efficacy of preharvest foliar sprays with acetylsalicylic acid (ASA; 0.5 mM or 1.0 mM), applied biweekly four to six times, on yield and fruit quality attributes were evaluated in a 2-year study. Fruit from the N-side of the canopy had greater CR and RS, whereas SS symptoms were lower, compared with the S-exposed part of the canopy. The N-side of the canopy had also substantially lower fruit number and yield, suggesting for an important role of light on bisexual flower formation and/or fruit set. Following the occurrences in CR and RS during the fruit maturation period, it was found that temperature fluctuation was the main cause. The presence of RS damages may also be related with increased relative humidity and water movement as symptoms were higher in years with higher values, in the N-side of the canopy and often occurred in the exposed and stylar end of the fruit. The ASA treatment substantially reduced RS by up to 57%, improved the peel red coloration, while anthocyanin, antioxidant capacity, and soluble solid contents in juice were higher. Foliar sprays with ASA did not affect yield, but induced a trend of bigger-sized fruit. In conclusion, planting in a N-S row orientation and selecting an orchard plantation site with a minimum temperature fluctuation and low relative humidity during the fruit-ripening period are measures to control CR and RS in pomegranate. ASA foliar applications proved to have beneficial effects on juice antioxidant contents, but more importantly on fruit appearance.