Enhancing Anna Apples’ Productivity, Physico-Chemical Properties, and Marketability Using Sprays of Naphthalene Acetic Acid and Inhibitors of Ethylene for Alleviating Abiotic Stresses

Abstract

In order to improve the resistance of apples to stresses (abiotic stresses) during hot and dry summers to enhance their productivity and marketability, Anna apple trees were treated with aminoethoxyvinylglycine (AVG), 1-methlcyclopropene (1-MCP), and naphthalene acetic acid (NAA), alone, or in combination, in two successive seasons. All treatments significantly increased the yield per tree, the average fruit volume, fruit diameter, and fruit weight compared to the control (growing under hot and dry summers without any treatments). All treatments significantly reduced the apple size, total soluble solid (TSS) content, anthocyanin content, carotenoid content, total sugar solids, and sugar percentage, and they led to fruit softening, loss of fruit weight, firmness, breakdown percentage, as well as a decreased polyphenol oxidase and peroxidase activity at one-week post-harvest (except for 20-ppm NAA) in comparison with the control. Trees treated with 320-ppm 1-MCP + 250-ppm AVG exhibited maximum yield per tree, fruit firmness, and no-reducing sugars or starch. On the other hand, the 20-ppm NAA produced the maximum TSS content, total sugars, with a reduced sugar percentage, carotenoid and anthocyanin fruit content, and (TSS)/acidity ratio. The application of 320-ppm 1-MCP + 250-ppm AVG effectively delayed the harvest for 14 days compared to the control. Our results show that the sprays of NAA and inhibitors of ethylene had a significant effect on the productivity and marketability of Anna apples under abiotic stresses.