Transfer of Ogu cytoplasmic male sterility to Brassica juncea and improvement of the male sterile line through somatic cell fusion

Abstract

Male sterility conferred by ogu cytoplasm of Raphanus sativus has been transferred to Brassica juncea cv lsquoRLM 198rsquo from male-sterile B. napus through repeated backcrossing and selection. The male-sterile B. juncea is, however, highly chlorotic and late. It has low female (seed) fertility and small contorted pods. To rectify these defects, protoplasts of the male sterile were fused with normal lsquoRLM 198rsquo (green, self fertile). Four dark green, completely male-sterile plants were obtained and identified as putative cybrids. All the plants were backcrossed three times with lsquoRLM 198rsquo. Mitochondrial and chloroplast DNA analysis of backcross progeny confirmed hybridity of the cytoplasm. The restriction pattern of the chloroplast DNA of progeny plants of three cybrids (O_g 1, O_g 2, O_g 3) was similar to that of the green self-fertile lsquoRLM 198rsquo and indicated that the correction of chlorosis resulted from chloroplast substitution. The chloroplast DNA of the lone progeny plant of the fourth cybrid (O_g 10) could not be analyzed because the plant was stunted and had only a few leaves. When total cellular DNA was probed with mitochondrial probes coxI and atpA it was found that the cybrids had recombinant mitochondria. The chlorosis-corrected plants were early flowering and had vastly improved seed fertility.