INTER AND INTRA-SPECIFIC GENETIC DIVERSITYAMONG BRASSICA SPECIES EVALUATED BY MORPHOLOGICAL AND MOLECULAR MARKERS

Abstract

Brassica species are characterized by extensive morphological diversity and the ability to adapt to a wide range of habitats and growing environments. The objective of this study was to assess the genetic divergence available in different species of Brassica for the identification of genetically diverse and agronomically superior genotypes of Brassica seed, which may generate putative transgressive segregates on hybridization. Genetic diversity in Brassica germplasm was evaluated by agro-morphological traits, total seed protein and SSR analysis. For this purpose 153 genotypes of Brassica belonging to different species, obtained from Plant Genetic Resources Program (PGRP), National Agricultural Research Center (NARC), Islamabad, Pakistan were evaluated. Brassica germplasm was evaluated over two years in the field. Altogether, 22 agro- morphological characters were determined in the collected population and multivariate analyses were performed. There was generally considerable divergence in all characters. Both principal component and cluster analyses disclosed complex relationships among the accessions and characters. Accessions with potential genes of interest to improve earliness, yield components, oil and protein contents have been identified. Length of growing period and yield components contributed most for divergence and clustering pattern. Oil, glucosinolate and protein contents also varied among the species but not so much within species. Intra and inter species diversity was also analyzed with the help of seed storage proteins by using SDS-PAGE. On the basis of banding pattern zymogram (diagrammatical representation of different protein bands) were sketched, by which molecular weight of species specific bands were calculated on the basis of Rf values of the bands on the gel. Five polymorphic markers were identified from seed proteins. These polymorphic markers clearly distinguished these Brassica species. A total of 31 protein bands were recorded ranging from the molecular weight (MW) of 10 KDa. to 114 KDa. The similarity estimates among these groups ranged from 33 to 97%.Through statistical analyses dendrogram was formed and genotypes were clustered into different groups by applying UPGMA (unweighted pair group mean analyses). xiiiThe microsatellite technique (SSR) is well described as a highly polymorphic, co- dominant marker system for animals and plants. Seventy five morphologically diverse Brassica genotypes were analyzed by PCR with 25 data base derived SSR markers to detect the genetic divergence among Brassica species at molecular level. All the primers produced polymorphism among genotypes tested except Ra2-A11 and Na12-F03. The number of alleles per microsatellite locus varied from 2 to 4. The size of the alleles ranged from 150 bp to 318 bp. The present investigation revealed high level of inter- species and medium level of intra-species variation in the accessions evaluated. These results are in accordance with the previous findings and this information will help us in early identification of the purity of genetic resources.