Mutation frequency increase in apple cultivar ''Wealthy'' by gamma irradiation

The winter grafts of the ''Wealthy'' cultivar were twice subjected to acute gamma irradiation with doses from 3360 to 8400 rad. The taking rate was very low in the grafts that had been irradiated with doses higher than 5000 rad. The shoots from the irradiated grafts were further studied in four variants of different reproduction. In one of them, after blinding the buds, the growth was induced from deeper histogenic layers. The frequencies of 21 mutation types were determined according to repeated changes of fruits on the basis of the estimation of their proportions in the graft and their chimeric character. The radiation dose exerted the strongest influence on the mutation frequency. A dose increased by 840 rad produced a 25% increase of the number of mutations. Further, the frequency of mutations augmented markedly by later irradiation (at the beginning of vegetation) and by blinding the buds. As to the types of mutations, negative changes generally prevailed, particularly various degrees of fruit angularity and irregular distribution of the colour of the fruit. (author)