Molecular Mapping and Character Tagging in Brassica juncea–I. Degree, Nature and Linkage Relationship of RFLPs and Their Association With Quantitative Traits

For molecular mapping and character tagging in Indian mustard (Brassica juncea), cultivar Varuna and exotic collection BEC 144 were chosen on the basis of morphological and molecular differences. High degree of RFLP was detected between them using genomic DMA clones of Psfi subgenomic library as probes. Of the 48 probe - enzyme combinations, 89.5% were polymorphic. Majority of the probes revealed duplicate loci and a high frequency of null alleles (71.4%). Segregation analysis in the F₂ population revealed significant deviation from expected 1:2:1 ratio for 32% of the markers. Using the computer package MAPMAKER, 15 markers could be placed in six linkage groups which covered a total length of 173.9 cM. Based on single factor analysis of variance, three significant marker-quantitative trait associations viz. BJG 59a -primary branches/plant, BJG 426b - secondary branches/plant and BJG 433-days to flowering could be identified. The BEC 144 alleles at the quantitative trait loci (QTL) in the marked genomic regions enhanced the trait expression. The putative gene action at these loci was found to be non-additive.