Effects of a Peach Antisense ACC Oxidase Gene on Plum Fruit Quality

Stone fruit are harvested while still firm in order to be marketed in acceptable condition. A goal of our program is to determine if delaying the production of ethylene in ripening fruit will result in fruit that remain firm while developing tree-ripened flavors. Plum hypocotyls were transformed with an antisense construct of a peach ACC oxidase gene (responsible for the last step in ethylene formation) under the control of the 35S promoter. Eighteen lines were derived from four genetically different hypocotyls from 'Bluebyrd' and three from 'Stanley'. DNA blot data indicated that the majority of these lines had single insertions of the peach antisense ACO gene. Wound ethylene responses were measured on the seedlings in the greenhouse and after one year of growth in the field. Several of the transgenic lines had consistently reduced ethylene responses while a few had increased ethylene responses. Fruit quality data, consisting of firmness, color, date of ripening, brix, and size as well as ethylene production rates were measured for two years on the fruiting lines. Analyses of the data suggested that in some transgenic lines, ethylene production was delayed relative to the 'Bluebyrd' parental line and that softening was also delayed. Sugar levels were on the average lower in most of those lines as well.