POTENTIAL USE OF RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) TECHNIQUE TOSTUDY THE GENETIC DIVERSITY IN INDIAN MUSTARD (BRASSICA-JUNCEA) AND ITS RELATIONSHIP TO HETEROSIS

RAPD assays were performed, using 34 arbitrary decamer oligonucleotide primers and six combinations of two primers, to detect inherent varia tions and genetic relationships among 12 Indian and 11 exotic B. junce a genotypes. Of 595 amplification products identified, 500 of them wer e polymorphic across all genotypes. A low level of genetic variability was detected among the Indian genotypes, while considerable polymorph ism was present among the exotic ones. Based on the pair-wise comparis ons of amplification products the genetic similarity was calculated us ing Jaccard's similarity coefficients and a dendrogram was constructed using an unweighted pair group method was arithmetical averages (UPGM A). On the basis of this analysis the genotypes were clustered into tw o groups, A and B. Group A comprised only exotic genotypes, whereas al l the Indian genotypes and four of the exotic genotypes were clustered in group B. Almost similar genotypic rankings could also be establish ed by computing as few as 200 amplification products. In general, a hi gh per cent of heterosis was recorded in crosses involving Indian x ex otic genotypes. On the other hand, when crosses were made amongst Indi an or exotic genotypes, about 80% of them exhibited negative heterosis . Results from this study indicate that, despite the lack of direct co rrelation between the genetic distance and the degree of heterosis, ge netic diversity forms a very useful guide not only for investigating t he relationships among Brassica genotypes but also in the selection of parents for heterotic hybrid combinations.