Crop load and rootstock influence on dry matter partitioning in trees of early and late ripening peach cultivars

Effect of crop load on dry matter partitioning was studied on 3-year-old peach [(Prunus persica (L.) Batsch (Peach Group)] trees of the early ripening 'Early May Crest' (EMC) grafted on 'GF677' and Penta (Prunus domestica L.) rootstock and the late ripening 'Flaminia' grafted on 'GF677' rootstock [(Prunus persica x Prunus dulcis (Mill.) D. A. Webb] and grown outdoors in 230-L containers, for 2 years. Fruit thinning was carried out 10 days after fruit set to produce different crop loads. Trees were sampled destructively throughout two growing seasons and divided into above-ground and root components, for dry matter and carbohydrate analysis. At the end of the fruit development period, in the first year, total tree dry matter accumulation was related linearly to crop load even when the increase in crop load greatly decreased vegetative and root growth. Total dry matter accumulation was highest in EMC/'GF 677' at any specific crop load, and EMC trees on 'GF677' allocated relatively more dry matter than EMC/'Penta' trees to vegetative and root growth, even under increasing fruit sink demand. Two consecutive years of heavy crops resulted in an inverse relationship between crop load and dry matter accumulation of trees, due to a major reduction of vegetative, root, and fruit growth. The percentage of dry matter partitioned to fruit decreased with the vigor of the rootstock, and EMC/'Penta' trees had the lowest harvest index at each specific crop load. The early ripening EMC/'GF677' trees which had twice the harvest index of 'Flaminia'/'GF677' trees for any level of crop load. 'Flaminia'/'GF677' trees had the largest canopy size. Starch content in the roots was lowest for cropping trees and depended on the rootstock and on the length of the fruit development period, being highest for the late ripening 'Flaminia'/'GF677' trees. Individual fruit weight decreased with crop load, and the reduction of fruit size was related to rootstock and time of ripening.