Characterization of groundnut resistance to bacterial-wilt caused by Ralstonia solanacearum by forward and reverse genetics methods

Bacterial wilt caused by casual agent Ralstonia solanacearum (Rs) is a serious disease in groundnut and great many other plant species. Forward and reverse genetics strategies were adopted in our study. From the view point of forward genetics, the peanut RILs including 300 F9 progenies derived from Yueyou 92 × Xinhuixiaoli were tested of disease resistance through inoculation with R.solanacearum in the field. Resistance to R.solanacearum is a quantitative trait. Three QTLs were mapped on an interval 15 cM using a linkage map with SSR and related SNP markers. An Tir-NBS-LRR resistance gene AhqBW3 was found closely linked with a BW resistance molecular marker SNP79 which was mapped in a gene locus next to the R gene. AhqBW3 was showed downregulation under the challenge of Rs inoculation. From the view point of reverse genetics, a novel NBS-LRR resistance gene AhRRS5, an LRR-RLK gene AhRLK1 and an unkown gene AhRRS22 were upregulated by Rs inoculation which were screened from microarray hybridization. They showed resistance phenotypes in transgenic tobacco overexpressing of these three genes. Among of them, Overexpression of AhRRS5 significantly enhanced the resistance of heterogeneous tobacco to R. solanacearum, with diverse resistance levels in different transgenic lines. Several defense-responsive marker genes in hypersensitive response, including HR, SA, JA, and ET signals, were considerably upregulated in the transgenic lines as compared with the wild type in response to R. solanacearum. NPR1 and NDR1 were also upregulated in response to the pathogen. These results indicate that AhRRS5 participates in the defense response to R. solanacearum through the crosstalk of multiple signaling pathways and the involvement of NPR1 and R gene signals for its resistance. These studies may guide the resistance enhancement of peanut and other economic crops to bacterial wilt disease.