Effect of fruit crop load on peach root growth

Field experiments were conducted on mature, late-maturing peach trees ('O' Henry') to study the influence of assimilate availability on root growth. Crop load was used to vary assimilate availability by imposing three different fruit thinning treatments: thinned to commercial fruit loads, unthinned and completely defruited. Seven trees were used for each treatment, and four ingrowth root bags were buried per tree during four different periods of the growing season (corresponding to the three fruit growth stages and after fruit harvest). The bags were collected one month after burial and the root growth into each bag was determined from dry weight of all newly developed roots in a bag. Root growth values varied depending on crop load and fruit growth stage. During the first stage of fruit growth there was no effect of crop load on root growth. Root growth in all thinning treatments increased compared to the first stage and was significantly higher for the defruited trees. The root growth was minimal during the third stage of fruit growth in all the treatments. After harvest, root growth increased again in all the treatments. These experiments clearly demonstrated that there are seasonal patterns to root growth activity in peach trees and that crop load clearly influences the extent of that activity primarily during the late spring when the fruits are in the second stage of fruit growth.