Chloroplast substitution overcomes leaf chlorosis in a Moricandia arvensisbased cytoplasmic male sterile Brassica juncea

A male sterile Brassica juncea line based on Moricandia arvensis cytoplasm was developed previously by backcrossing the somatic hybrid M. arvensis + B . juncea, and the gene for restoring fertility was introgressed. The CMS li ne is very severely chlorotic because of the presence of alien chloroplasts and flowering is delayed by 30-40 days, making it unsuitable for the explo itation of heterosis. We have resorted to another cycle of protoplast fusio n between green fertile B. juncea and chlorotic male sterile B. juncea, and developed green male-sterile plants. Molecular analysis revealed that in g reen male-sterile plants chloroplasts of, M. arvensis origin were substitut ed by those from B. juncea, giving rise to intergeneric cytoplasmic hybrids with mitochondria of M. arvensis origin. With the development of dark-gree n male-sterile plants, the CMS fertility restoration system is suitable for the production of hybrid mustard.