ASSESSING THE EFFECT OF AMINOETHOXYVINYLGLYCINE AND 1- METHYLCYCLOPROPENE ON PREHARVEST FRUIT DROP AND CRACKING, QUALITY, AND RELATED GENE EXPRESSION OF ‘AMBROSIA’ AND ‘FUJI’ APPLES IN THE MID-ATLANTIC

Abstract

Preharvest fruit drop, cracking, and advanced maturity prior to commercial harvest can promote significant losses in important apple cultivars such as ‘Ambrosia’ and ‘Fuji’ grown in the mid- Atlantic. Aminoethoxyvinylglicine (AVG) and 1-methylcyclopropene (1-MCP) are ethylene inhibiting plant growth regulators (PGR) that can alter preharvest fruit drop, cracking, maturity and quality by impeding ethylene biosynthesis and perception, respectively. However, integrative studies examining the impacts of such PGR treatments in ‘Ambrosia’ and ‘Fuji’ are lacking in the mid-Atlantic region. The objectives of this work were to, first, characterize and compare the effects of different rates of preharvest ethylene inhibiting PGRs on fruit drop and cracking, ethylene production, physicochemical properties, skin color, and transcript accumulation of associated genes in 'Ambrosia' and ‘Fuji’ apples throughout ripening on-the- tree, and second, to use multivariate analysis to detect statistically significant correlations amongst evaluated variables. Our results show that both full-rate AVG (130 mg a.i. L−1) and 1-MCP (150 mg a.i. L−1) significantly reduced preharvest fruit cracking with respect to control fruit in ‘Ambrosia, but not in ‘Fuji’, suggesting a cultivar-specific effectiveness under mid-Atlantic conditions. Furthermore, amongst all treatments, full-rate AVG (130 mg a.i. L−1) displayed the lowest ethylene production and transcript accumulation of ethylene -related genes, ultimately delaying ripening. 1-MCP (150 mg a.i. L−1) and half-rate AVG (65 mg a.i. L−1) treatments exhibited an intermediate performance between full-rate AVG and control fruit, presenting a reduction in ethylene production and transcript accumulation of ethylene-related genes when compared to the latter. Regarding color, apple skin blush and anthocyanin-related gene expression was lowest in full-rate AVG (130 mg a.i. L−1) treated fruit, explaining why this fruit met the minimum requirement of 50% red blush coverage one week later than all other treatments in both assessed cultivars. Correlations amongst the assessed features were also identified. This work specifies a framework for the use of ethylene inhibiting plant growth regulators under mid-Atlantic environmental conditions.