Pathogenic Variability of Bipolaris oryzae Causing Leaf Spot Disease of Rice in West Africa

An assessment of rice crop resistance to Bipolaris oryzae, a causal agent of rice brown leaf spot or helminthosporium disease was carried out.  Ten (10) irrigated and upland rice varieties were used in this study. Seven (7) isolates of B. oryzae from Burkina Faso, seven (7) from Cote d’Ivoire and six (6) from Togo were used. The ten (10) varieties were inoculated with B. oryzae strains to assess their effect and determine the resistance level of these varieties to rice leaf spot ( Helminthosporium ). The varieties Bouake- AM, FKR60N, NIL130, V10, FKR62N and CY2 showed a good level of resistance against all the isolates. The incidence of the disease on leaves reached 62.22% of severity index. Results revealed also that the strain effects are not linked to their country of origin. The investigation on the pathogenicity of Bipolaris oryzae isolates displayed the existence of a pathogenic variability among the fungus populations. These findings suggest that the tested varieties possess resistance genes that can be used in varietal selection.