抄録
The incidence of recessive male and female sterility mutants concealedin cultivated buckwheat populations in Japan was estimated by examining the segregation of such mutants in about 2000 full-sib families. The incidence per gamete varied among the populations, in contrast with a rather uniform incidence of chlorophyll-deficient mutants. The average incidence of female sterility mutants was 11.7%, with a range of 1.6-21.9%, while that of male sterility mutants was 8.3%, with a range of 2.0-14.5%. In addition to these, male semisterility mutants were also segregating in the populations; their incidence ranged from 0.0 to 19.3%, with an average of 9.4%. The Geihoku and several other populations showed an extremely high incidence of sterilizing mutants; this raised the possibility that there were several segregating loci, each with a mutant allele frequency greater than 0.01. This was investigated by comparing the incidence of sterilizing mutants per gamete with the frequency of recessive homozygotes in randomly mating populations. Although some mutants affected both male and female sterilities simultaneously, most mutants affected either the male or the female organs alone. By combining previous studies with the present one, the total genetic load carried by buckwheat populations was estimated to be 1.96 lethal equivalents per gamete, which falls within the range previously reported for outcrossing angiosperm species. This load comes mostly from the detrimental effects of mutants at the reproductive stage, that is, male and female sterilizing mutants and polygenes reducing the number of seeds per plant. The genetic loads expressed at the germination and seedling stages were also large, 0.23 and 0.25 lethal equivalents per gamete, respectively, but they consisted of only one fourth of the total load.
