Factors of Poor Fruit Set in New Peach Cultivar ‘Shimizu Hakuto RS’ Developed by Radiation Breeding

Abstract

A mutant peach (Prunus persica Batsch) cultivar 'Shimizu Hakuto RS', developed by radiation breeding, shows the same quality as the original cultivar, 'Shimizu Hakuto'. However, it shows poorer fruit set than the parent strains. The fruit set of this cultivar only reaches 20 to 30% of the total numbers of flower; whereas the original one reached 50 to 70%. As a result of morphological observation, the higher ratio of morphological abnormalities in pistils, slowing degeneration or incomplete development of the ovary and embryo sac, causes poor fruit set. Furthermore, the numbers of normal pollen per anther were smaller in 'Shimizu Hakuto RS' than in the parent strains. We suggest that this number reduces the probability of pollination and thus results in lower percentages of ovule fertilization. Nevertheless, the poor fruit set did not cause lower fruit productivity. We find it is a very labor-saving variety because the labor hours for flower or fruit thinning from March to May were remarkably reduced.