Characterization of senegalese races of Xanthomonas oryzae PV. oryzae to identify resistance genes to use

Abstract

Bacterial blight (BB), is a disease caused by Xanthomonas oryzae PV. oryzae (Xoo), was first reported in Senegal by Trinh in 1980. BB represents a severe threat to rice cultivation in West Africa. Characterizing the pathotypic diversity of bacterial populations is a key to the management of pathogen-resistant varieties. Pathogenicity tests show that all strains are virulent on the susceptible rice variety Azucena, and interact differentially with twelve near-isogenic rice lines, each carrying a single resistance gene. On this rice panel, six races were identified, two of which were previously reported in Mali (A3) and Burkina Faso (A1). Four races (S2, S4, S5, and S6) are described for the first time in Africa. Races A1, isolated in Ndiaye and Ndioum areas is the most prevalent in Senegal. The Xa1 gene controls 100% of the isolates tested and xa5 controls all isolates except S4 strains. The geographical distribution of Xoo races is contrasted. Four races are detected in the North and two in the South East of the country. Race S4 can be a major risk to rice cultivation because strains from this race are the most virulent and can only be controlled by Xa1. To identify local sources of resistance, we screened Xoo strains representative of the various races on twenty-three rice varieties grown by farmers in Senegal. Four rice varieties namely Sahel210, Sangangbye, Dansna2, and Sahel305 effectively control all the isolates tested. Our characterization of the first collection of Senegalese Xoo strains provided insight into the races present in the country and identified sources of resistance in local rice varieties. This information will help design effective breeding programs for resistance to bacterial leaf blight in Senegal.