MUTANTS OF GOLDEN DELICIOUS APPLE INDUCED BY IONIZING RADIATION

Abstract

The study of 300 selections of Golden Delicious apple from plant material irradiated with gamma rays from a 60Co source resulted in the final selection of two clones that represent an improvement of the original cultivar in reduced russetting in fruit stem cavity; greatly reduced tendency to biennial bearing; and slightly lowered fertility, an advantage in Golden Delicious which tends to overset. In a single-tree first trial, about 50% of the examined clones showed reduced pollen stainability; the majority of the semi-fertile mutants had 51 to 55% stainable pollen. The number of seeds per fruit was very closely related to pollen fertility. A close relationship was found among indicators of fruit maturity, that is, skin color, flesh color, soluble solids, and titratable acidity of fruit at harvest. More detailed measurements of 14 promising selections in a replicated second test revealed highly significant differences among clones in number of seeds per fruit, the incidence of russetting in the stem cavity, shape of fruit, skin color of fruit, flesh color of fruit, biennial bearing index, weight of fruit, and trunk cross-sectional area of the tree. Clonal differences were nonsignificant in yield ratings for a four-year period, and the yield for 1969 in kg per cm2 of trunk cross-sectional area.