Mutation breeding in root and tuber crops, a review

Some breeders argue that mutation breeding is hard to practice because the low frequency of positive mutation which displays useful characters. The effective application of mutation breeding onto root and tuber crops requires clonal progenies developing on a large scale. In most of the successful cases to obtain the desired mutation in such crops, more than thousands of vM2 materials were dealt with. Even in the conventional cross breeding of potatoes or sweet potatoes, more than ten thousands of F1 seedlings per year are subjected to the selection at each practical breeding unit. Thus only a single segregant selected over several years may be released as a registered cultivar. Howard (1970) reckoned that in potatoes, the chance of any seedling becoming a useful variety is about one in ten thousand, and in the breeding program using wild species, as low as one in a hundred thousand. In the conventional cross breeding of sweet potatoes carried out for 35 years, the probability of true seeds becoming a useful cultivar is estimated to be 1.37 x 10-5. The practical works of mutation breeding in root and tuber crops are still in premature stage, and yet any successful mutant cultivar cannot be found throughout the world. (Kako, I.)