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Mutation breeding is one of the efficient ways to create new genotypes. The starting material of this study was the 'Amasya', a Turkish apple cultivar. This study aimed to identify optimal mutagen dosage that is the most important prerequisite to create a proper mutant population, and evaluate the genetic variability for morpho-agronomic traits (e.g. tree height and fruit number) in the putative apple mutants of 'Amasya' irradiated at the optimal mutagen dosage. In the first year of the study, to determine the optimal mutagen dosage, dormant 'Amasya' scion woods were irradiated at 0, 10, 20, 30, 40, 50 and 60 gray dosages using 60Co source. The optimal mutagen dosage was determined as 29.01 gray for 'Amasya' concerning the 50% shoot length reduction in comparison to the nonirradiated control plants. In the following year, more or less 2000 dormant 'Amasya' scion woods were irradiated at the optimal mutagen dosage to generate a mutant population of 'Amasya' apple cultivar. Mutation frequency based on the visual observations of plant abnormalities was observed. Then three years, genetic uniformity was analyzed through the growth of the mutant population, and mutation frequency (%) determined. These results indicated that there was considerable genetic variability in response to irradiation for evaluated traits. Most of the plants in the putative mutant population, nearly 80%, had a significantly shorter tree height and trunk cross-sectional area than standard 'Amasya'. The mutants/genotypes identified in this study could be used improvement of new promising apple cultivars with good agronomical traits. [ABSTRACT FROM AUTHOR]

Consumers appreciate ‘Amasya’, the most important local apple cultivar of Turkey, but not producers because of several production constraints that complicate management of the cultivar (e.g., low yield, biennial bearing, early blooming and poor fruit skin colouring). Based on this background, ‘Amasya’ scions were irradiated to obtain mutants. Irradiated buds were grafted by bench grafting on M.9 rootstocks, and 857 trees were obtained in the nursery. Phenotyping of the mutant population for architectural traits, precocity, floral phenology and fruit characteristics was conducted under orchard conditions to identify variation among individuals. Induced mutation highly affected all variables studied. Cluster and principal component analyses confirmed considerable variation in the population. Some of the mutants were determined as superiors for the studied variables. Based on the recorded data as well as visual observations, we conclude that genotypes M181, M229, M274, M285, and M472 indicated superiority in the architectural characteristics. The five mutants (namely M112, M129, M293, M383, and M489) showed quite a late flowering in comparison to the others. [ABSTRACT FROM AUTHOR]

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