Assessing the impacts of aminoethoxyvinylglycine and 1methylcyclopropene on fruit drop, cracking, quality and related transcript accumulation in 'Ambrosia' and 'Fuji' apples during on-the-tree ripening

Macarena Farcuh^*Emily Johnson

• University of Maryland, College Park, College Park, United States

Preharvest fruit drop, cracking, and advanced ripening prior to fruit harvest can promote significant losses in important apple cultivars such as 'Ambrosia' and 'Fuji' grown in the mid-Atlantic. These losses result from environmental factors, delays in harvest due to lack of red skin color development, cultivar-specific characteristics, among others. Aminoethoxyvinylglicine (AVG) and 1methylcyclopropene (1-MCP) are ethylene inhibiting plant growth regulators (PGRs) that can alter preharvest fruit drop, cracking, maturity and quality by impeding ethylene biosynthesis and perception, respectively. However, there is a knowledge gap on understanding the impacts of specific timings and dosages of such PGR treatments in 'Ambrosia' and 'Fuji' under mid-Atlantic environmental conditions. The objective of this work was to characterize and compare the impacts of specific rates of preharvest ethylene inhibiting PGRs on fruit drop and cracking, ethylene production, physicochemical properties, skin color, and associated gene expression in 'Ambrosia' and 'Fuji' apples during ripening on-the-tree. Multivariate statistical methods for identifying meaningful correlations among the measured variables were applied. 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 gene expression 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 gene expression 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 50% red blush coverage one week later than all other treatments in both cultivars. Correlations amongst the assessed features were also identified.This work specifies a framework for the use of ethylene inhibiting PGRs under mid-Atlantic environmental conditions.