Pathogenic and molecular characterization of Pythium species inducing root rot symptoms of common bean in Rwanda

A series of 231 samples of bean plants affected by bean root rot were collected from different areas of Rwanda in order to characterize the causal agents. The collected samples were used to isolate 96 typical Pythium colonies which were classified into 16 Pythium species according to their respective molecular sequences of the ribosomal ITS fragments. Inoculation assays carried out on a set of 10 bean varieties revealed that all identified species were pathogenic on common bean. However, the bean varieties used in this investigation showed differences in their reaction to inoculation with the 16 Pythium species. In fact, the varieties CAL 96, RWR 617-97A, URUGEZI and RWR 1668 were susceptible to all the Pythium species while the varieties G 2331, AND 1062, MLB 40-89A, VUNINKINGI, AND 1064 and RWR 719 showed a high level of resistance to the all Pythium species used in our study. This high level of resistance to Pythium root rot disease found in diverse varieties of common bean grown in Rwanda constitutes a real advantage to be exploited as source of resistance in breeding programs aiming to increase resistance to the disease in the most popular bean varieties grown in Rwanda.