Population genetics of cultivated common buckwheat, Fagopyrum esculentum Moench. VII. Allozyme variability in Japan, Korea, and China

Allozyme variability at 19 loci affecting 12 enzymes were analyzed electrophoretically in 24 Japanese, 3 Korean, and 16 Chinese populations of common buckwheat. Most of the populations were polymorphic at 8 loci, Adh, Dia-2, Got-2, Mdh-1, Mdh-3, 6-Pgdh-1, Pgm-2, and Sdh-1. The percentage of polymorphic loci was 31.6-42.1% and the average heterozygosity was in the range of 0.110-0.138. The level of variability was almost the same as that found in Nepal and India, and was slightly higher than the average of other outbreeding plant species. The allelic frequencies did not vary much among the populations studied, although the Chinese populations had slightly more genetic variability than the Japanese and Korean populations. The present results together with those for the Indian and Nepali populations (Ohnishi and Nishimoto, 1988) led to the following conclusions. The allelic frequencies at the polymorphic loci did not vary much among Asian populations extending from Nepal to Japan; geographical differentiation of allozyme frequencies, due mostly to the loss of alleles, has occurred only at the margins of the distribution, such as in the Kumaun and Garwhal hills and in Kashmir in India. This rather unexpected uniformity of allelic frequencies seems to be due to large population size, panmixis within populations, and gene flow between populations, conforming to the theoretical models of Maruyama (1971) and Kimura and Maruyama (1971). Buckwheat does not have a strict center of genetic diversity, but the highest within-population variability was found in the region from southern China to Nepal. Based on the observed minor differences in allozyme frequencies between populations, possible processes of the spreading of buckwheat cultivation in Asia are discussed.