Variation in somatic chromosome number found in radiation-induced mutants of Chrysanthemum morifolium hemsl. CV. yellow delaware and delaware

Abstract

Young plants of Chrysanthemum morifolium CV. Yellow Delaware and Delaware were irradiated chronically with 60Co gamma rays in the gamma field. The total exposures were 5, 10 and 20 kR. Many whole-type sports were produced after irradiation, thus the method of internal disbudding by radiation treatments demonstrated earlier, (18) was confirmed to be efficient in enlarging mutation sectors. Cytological examination of 19 mutant and 12 apparently normal shoots produced after irradiation revealed that the somatic chromosome numbers ranged from 49 to 55 with an exceptional doubled number of 110. Some of the shoots were chimeric cytologically. None of the shoots examined had higher chromosome numbers than the control plants (2 n = 55) except for the 110-chromosome shoot. More reduction of chromosome number was caused with higher exposures. Reduction of chromosome number was also correlated with the type of mutation and with the size of inflorescence.