COMPARATIVE-ANALYSIS OF MICROSATELLITE DNA POLYMORPHISM IN LANDRACES AND CULTIVARS OF RICE

Genetic polymorphisms of ten microsatellite DNA loci were examined amo ng 238 accessions of landraces and cultivars that represent a signific ant portion of the distribution range for both indica and japonica gro ups of cultivated rice. In all, 93 alleles were identified with these ten markers. The number of alleles varied from a low of 3 or 4 at each of four loci, to an intermediate value of 9-14 at five loci, and to a n extraordinarily high 25 at one locus. The numbers of alleles per loc us are much larger than those detected using other types of markers. T he number of alleles detected at a locus is significantly correlated w ith the number of simple sequence repeats in the targeted microsatelli te DNA. Indica rice has about 14% more alleles than japonica rice, and such allele number differences are more pronounced in landraces than in cultivars. The indica-japonica differentiation component accounted for about 10% of the diversity in the total sample, and twice as much differentiation was detected in cultivars as in landraces. About two-t hirds as many alleles were observed in cultivars as in landraces; anot her two-thirds of the alleles in the cultivar group were found in mode rn elite cultivars or parents of hybrid rice. The majority of the simp le sequence repeat (SSR) alleles that were present in high or intermed iate frequencies in landraces ultimately survived into modern elite cu ltivars and hybrids. The greater resolving power and the efficient pro duction of massive amounts of SSR data may be particularly useful for germplasm assessment and evolutionary studies of crop plants.