A novel bacterial blight resistance gene fromOryza nivaramapped to 38 kb region on chromosome 4L and transferred toOryza sativaL.

Abstract

Summary: Bacterial blight (BB) of rice caused byXanthomonas oryzaepvoryzae(Xoo) is one of the major constraints to productivity in South-East Asia. The strategy of using major genes, singly or in combination, continues to be the most effective approach for BB management. Currently, more than two dozen genes have been designated but not all the known genes are effective against all the prevalent pathotypes. The challenge, therefore, is to continue to expand the gene pool of effective and potentially durable resistance genes. Wild species constitute an important reservoir of the resistance genes including BB. An accession ofOryza nivara(IRGC 81825) was found to be resistant to all the sevenXoopathotypes prevalent in northern states of India. Inheritance and mapping of resistance inO. nivarawas studied by using F₂, BC₂F₂, BC₃F₁and BC₃F₂progenies of the cross involvingOryza sativacv PR114 and theO. nivaraacc. 81825 using the most virulentXoopathotype. Genetic analysis of the segregating progenies revealed that the BB resistance inO. nivarawas conditioned by a single dominant gene. Bulked segregant analysis (BSA) of F₂population using 191 polymorphic SSR markers identified a ∼35 centiMorgans (cM) chromosomal region on 4L, bracketed by RM317 and RM562, to be associated with BB resistance. Screening of BC₃F₁and BC₂F₂progenies and their genotyping with more than 30 polymorphic SSR markers in the region, covering Bacterial artificial chromosome (BAC) clone OSJNBb0085C12, led to mapping of the resistance gene between the STS markers based on annotated genes LOC_Os04g53060 and LOC_Os04g53120, which is ∼38·4 kb. Since none of the knownXagenes, which are mapped on chromosome 4L, are effective against theXoopathotypes tested, the BB resistance gene identified and transferred fromO. nivarais novel and is tentatively designated asXa30(t). Homozygous resistant BC₃F₃progenies with smallest introgression region have been identified.