2017 ASHS Annual Conference

Fruit size is one of the most coveted traits in fruit breeding and marketing. Peach fruit size is influenced by the genetic potential of a cultivar and the effects of different cultural practices on fruit development. Effects of early thinning of peach flowers and fruits on the fruit cell number and size, and associated differences in gene expression were investigated in four peach cultivars: Carored, Summerprince, Scarletprince and Redhaven. Trees of each cultivar were thinned either one or four weeks after petal fall to test the influence of crop load on peach fruit growth in 2014 and 2015. Fruitlets from each tree were sampled every 5 days from week 2 to week 5 post-bloom for histological and gene expression analyses. Cross-sections of each fruitlet were measured for average cell size, cell count, and overall fruit size. Early thinning of all cultivars positively correlated with increased mesocarp cell number, cell size, and fruit size compared to the late-thinned trees. A late spring freeze in 2015 compromised the control treatment and therefore no positive effect of early thinning on cell size, cell count and fruit size was observed. Expression level of five growth-regulatory genes, FW2.2, CNR12, TAGL1, SIM, and ANT, in fruitlets sampled in 2014 revealed differential expression between early thinned trees and controls. The global biochemical and genetic mechanisms through which time of thinning influences fruit development are being investigated using RNA-Seq, and will be discussed.