CORRECTION OF CHLOROPHYLL DEFICIENCY IN ALLOPLASMIC MALE-STERILE BRASSICA-JUNCEA THROUGH RECOMBINATION BETWEEN CHLOROPLAST GENOMES

Brassica juncea cv. Pusa Bold carrying B. oxyrrhina cytoplasm (oxy cytoplasm) was male sterile and chlorotic under field conditions at low temperature (Prakash & Chopra, 1990). Leaf protoplasts of the chlorotic male sterile alloplasmic line (2n = 36) were fused with hypocotyl protoplasts of green male fertile, B. juncea cv. RLM-198 (2n = 36) using polyethylene glycol. Of the 1043 plants regenerated from 10 fusion experiments, 123 had 'gigas' features and were identified as presumptive fusion products. Among field-grown population, one plant was dark green even at low temperatures and male sterile. It possessed 72 chromosomes which formed 36 bivalents at late diakinesis of meiosis-1. This plant was back-crossed to B. juncea cv. Pusa Bold (the maintainer line) for three successive generations. One male sterile, normal green BC3 progeny plant with 2n = 36 was analyzed for organelle constitution. Probing its total DNA with the mitochondrial gene for cytochrome oxidase subunit I revealed that it possessed mitochondria of B. oxyrrhina. Southern hybridization pattern with the gene for ribulose bisphosphate carboxylase oxygenase-large subunit (rbcL) revealed that the chloroplast genome of the chlorophyll deficiency-corrected plant had characteristics of both B. juncea and B. oxyrrhina. The deficiency correction has been attributed to recombination between chloroplast genomes of the two species.