POSITIONS OF MUTATED SECTORS IN SHOOTS FROM IRRADIATED BUDS OF BRAMLEY SEEDLING APPLE

A large population (over 5000 plants) of Bramley's Seedling apple trees that were the MV2 generation derived from 266 irradiated dormant buds was screened for mutants and 58 were found. These MV2 trees had been grown from all the buds of the MV1 shoots, and as the position of each bud on its stem had been recorded before it was used for propagation, a picture of the distribution of mutated tissue in the MV1 shoots derived from the irradiated buds could be formed. The majority of the mutated sectors (62%) covered more than one node; 36% of the sectors comprised a complete shoot, and these proportions were increased when only stunted MV1 shoots from irradiated buds were considered. The fact that the mutated sectors were so frequently large and normally included the entire circumference of the shoot, is taken as a strong indication that in this cultivar very few cells are concerned in the production of any one histogenic layer after irradiation. Thus, cell death caused by the irradiation, and the possible resulting mixing of one histogenic layer of cells with those from another could lead to solid" (i.e. non-chimeral) mutant plants being produced at an acceptable frequency by a mutation breeding program using normal propagation techniques. © 1979."