Two Pathotypes of Xanthomonas oryzae pv. Oryzae Virulence Identified in West Africa

Pathotyping analysis of 50 Xanthomonas oryzae pv. oryzae (Xoo) isolates from seven West African countries against 18 rice cultivars was carried out to identify and characterize Xoo virulence. The study revealed two major pathotypes (Pta and Ptb) of Xoo virulence. Pta has 29 virulence (Vr) Xoo isolates while Ptb has 21 mildly virulence (MVr) Xoo isolates. Pta has three subgroup pathotypes (Pta1, Pta2 and Pta3) and Ptb has two subgroup pathotypes (Ptb1and Ptb2). At country level the study revealed the presence of Pta1, Ptb1 and Ptb2 in Niger, Pta3, Ptb1 and Ptb2 in Benin and Nigeria, Pta1, Pta3 and Ptb1 in Burkina Faso, Pta1, Pta3, Ptb1 and Ptb2 in Mali, Pta1, Pta2, Pta3, Ptb1 and Ptb2 in Guinea and Pta1, Pta2, Ptb1 and Ptb2 in the Gambia. The existence of five subgroups was likely due to mutations and interactions among isolates that originally constituted Pta and Ptb pathotypes. The study revealed information on Xoo virulent population structure in West Africa as well as possible Xoo pathogen migration between these countries and this provide useful information for selection and deployment of cultivars with durable resistance to BLB disease in West Africa.