‘Ambrosia’ is an emerging apple cultivar recently introduced from British Columbia and knowledge of ripening and preharvest physiology is limited in the mid-Atlantic region. ‘Ambrosia’ must meet minimum quality and color marketability standards in the US though it requires a high temperature differential for full color development and has a short harvest period. Plant growth regulators, such as aminoethoxyvinylglicine (AVG) and 1-methylcyclopropene (1-MCP), can alter preharvest fruit drop, maturity and quality by hindering ethylene biosynthesis and perception, respectively. AVG has historically been used at several rates by mid-Atlantic growers with variable cultivar specific impacts. The objective of this study was to characterize and compare the effects of AVG and 1-MCP on preharvest fruit drop and crack, ethylene production, fruit physicochemical parameters, skin color, and transcript accumulation of ethylene and anthocyanin-related genes in 'Ambrosia' apples throughout on-the-tree ripening over two production seasons. Four treatments were established and applied based on manufacturer’s recommendations: full-rate AVG (Retain), half-rate AVG (Retain), 1-MCP (Harvista) and a control. Fruits were harvested at three maturity stages: 1 week before the anticipated commercial harvest (1WBCH), at the anticipated commercial harvest (CH), and one week after CH (CH 1). Our results showed that both AVG and 1-MCP treatments significantly reduced preharvest fruit drop and crack with respect to control fruit. While full-rate AVG treatment showed the most significant decrease in ethylene production and exhibited the greatest downregulation of ethylene biosynthesis and perception-related gene expression, it also negatively impacted red color and anthocyanin biosynthesis related gene expression and reached minimum 50% skin blush one week later than the other treatments. Half-rate AVG and 1-MCP treatments displayed an intermediate behavior between full-rate AVG and control fruit, delaying fruit maturity and the associated gene expression when compared to control, but without sacrificing skin blush development. This study contributes to understand how preharvest ethylene regulator treatments influence ‘Ambrosia’ apples grown under the mid-Atlantic environmental conditions.
