Introgression of Black Rot Resistance from Brassica carinata to Cauliflower (Brassica oleracea botrytis Group) through Embryo Rescue

Abstract

Black rot caused by <i>Xanthomonas campestris</i> pv. <i>campestris</i> (<i>Xcc</i>) is a very important disease of cauliflower (<i>Brassica oleracea botrytis</i> group) resulting into 10-50% yield losses every year. Since there is a dearth of availability of resistance to black rot disease in <i>B. oleracea</i> (C genome), therefore exploration of A and B genomes was inevitable as they have been reported to be potential reservoirs of gene(s) for resistance to black rot. To utilize these sources, interspecific hybrid and backcross progeny (B₁) were generated between cauliflower "Pusa Sharad" and Ethiopian mustard "NPC-9" employing <i>in vitro</i> embryo rescue technique. Direct ovule culture method was better than siliqua culture under different temperature regime periods. Hybridity testing of F₁ inter-specific plants was carried out using co-dominant SSR marker and <i>Brassica</i> B and C genome-specific (DB and DC) primers. Meiosis in the di-genomic (BCC) interspecific hybrid of <i>B. oleracea botrytis</i> group (2<i>n</i> = 18, CC) × <i>B. carinata</i> (2<i>n</i> = 4x = 34, BBCC) was higly disorganized and cytological analysis of pollen mother cells revealed chromosomes 2<i>n</i> = 26 at metaphase-I. Fertile giant pollen grain formation was observed frequently in interspecific F₁ hybrid and BC₁ plants. The F₁ inter-specific plants were found to be resistant to <i>Xcc</i> race 1. Segregation distortion was observed in BC₁ generation for black rot resistance and different morphological traits. The At1g70610 marker analysis confirmed successful introgression of black rot resistance in interspecific BC₁ population. This effort will go a long way in pyramiding gene(s) for resistance against black rot in Cole crops, especially cauliflower and cabbage for developing durable resistance, thus minimize dependency on bactericides.