Resistance of Popular Grown Kenyan Cassava Cultivars to Cassava Bacterial Blight

Abstract

Cassava bacterial blight threatens cassava cultivation as majority of the cultivars currently in fields are susceptible to the disease. The disease is associated with two casual agents Xanthomonas phaseoli pv. manihotis and Xanthomonas axonopodis pv. cassavae. Resistance has been poised as the best management option against the disease in an integrated disease management system. Therefore, this study was done to identify cassava bacterial blight resistant cultivars among the popularly grown cassava varieties in Kenya.  A greenhouse experiment was conducted twice to evaluate seven cassava varieties for cassava bacterial blight resistance in a factorial treatment structure within a randomized complete block design. Each variety was inoculated on the stem and leaf with 1 x 10⁶ CFU/ml of the two causal agents either individually or in combination. A control inoculated with sterile distilled water was also included. Disease development was recorded at an interval of six days’ post inoculation using a severity scale of 1-5 for six weeks. We observed that Xanthomonas phaseoli pv. manihotis was more severe on the varieties as it had the highest severity scores and area under disease progress curve values of more than 70% compared to those infected with Xanthomonas axonopodis pv. cassavae and a combination of both pathogens. The most affected varieties were mm 96/2480, Naro 56, and mm 96/1871. However, none of the varieties evaluated were resistant to the disease making it necessary to test more varieties for resistance.