Genetic Divergence in Rice

Seventy five strains comprising Indica (Assam Rice Collection, or ARC, and non-ARC), japonica, ponlai and javanica rice were grouped into 13 clusters using D² statistic. The association of ARC strains with javanica in the same group has great significance. Sixty seven ARC strains revealed high order of genetic diversity, indicating the importance of the northeastern region of India as a rich source of diverse rice germplasm and in tracing the centre of origin of cultivated rice. The possibility of existence of intergrades between various subspecies in this region cannot be ignored. Genetic drift and selection pressure were inferred to have played a great role in bringing about genetic divergence among the strains. The ARC strains also generated noteworthy variability among themselves with regard to intra-and intercluster distances. Two characters, viz., 100-grain weight and number of grains per panicle, were the highest contributors to D² values. Six clusters consisting of 14 strains (10 in ARC, 2 in javanica, and 2 in ponlai) have been judged as important for use as base material (from this study) for varietal improvement programme on the basis of their greater intercmster distances and higher cluster mean values tor the aforementioned two characters.