574 Nitrogen, Trunk Scoring, and AVG Treatments Influence Fruit Color and Quality of `Jonagold' Apple

Abstract

`Jonagold' apple often has problems of inadequate red blush development at harvest, and loss of firmness and skin “greasiness” after refrigerated storage. During two growing seasons we tested factorial combinations of three preharvest treatments for managing these problems: 1) N fertilization (no applied N, 34 kg N/ha in May, or 1% (w/w) foliar urea sprays in May and June); 2) mid-summer trunk scoring (girdling); and 3) aminoethoxyvinylglycine (AVG) applications 3 weeks prior to harvest. Fruit were harvested at four weekly intervals each year, and evaluated for size, blush, firmness, soluble solids, ethylene, and starch hydrolysis. Nitrogen delayed blush development in 1998, but not 1999, and there was no difference in fruit surface blush coverage between foliar urea and soil applied N. Nitrogen applications increased fruit size, decreased fruit firmness, and increased post-storage flesh breakdown in 1999. Trunk scoring increased blush coverage and intensity both years, and improved market-grade packouts. Blush increase after trunk scoring was not caused by advanced fruit maturity (based on ethylene and starch indices) in either year, although it did increase skin greasiness slightly. AVG treatments delayed maturity and blush development of `Jonagold' by 7 to 10 days both years, relative to untreated fruit. Flesh firmness increased and greasiness decreased in AVG treated fruit harvested on the same dates as controls. However, in AVG fruit harvested at comparable stages of maturity 7 to 10 days later, firmness and greasiness were equivalent to untreated fruit on the previous harvest date. Trunk scoring and no N fertilizer were effective for improving fruit blush coloration, and AVG for delaying harvest maturity.