First Time Morphological and Molecular Isolation of Epicoccum sorghinum Pathogenicity in the Cassava Brown Leaf Spot Disease in Kenya

Abstract

Cassava brown leaf spot (BLS) is among the most damaging diseases that significantly reduce cassava root yields. There has been need to find varieties resistant or tolerant to BLS. Hence, in this study drought-resistant cassava varieties were being agronomically screened in an experimental farm in Kitui County-Kenya. One variety in the plots, commonly referred to as Kasukari, was found to exhibit abnormal morphological aberrations whose cause necessitated systematic studies. Morphological, microscopic and DNA molecular identification techniques were applied on the isolates to identify the causal agent(s). 162 samples of the Kasukari variety were used to determine the prevalence and severity of the disease, while 15 samples were used to determine effects of the disease in the plots. The prevalence within the plots had no significant difference (ꭓ2 = 6, p-value = 0.1991). However, there was significant difference in the severity (ꭓ2 = 53.013, p-value = 1.166e-09). Pathogenicity tests of ten isolates were conducted in vitro whereby the spore suspension was made from each isolate and inoculated in detached fresh Kasukari variety leaves. Polymerase chain reaction performed by the universal primer, internal transcribed spacer (ITS) marker identified Alternaria sp, Epiccocum sp, Preussia sp, and Cladosporium sp. However, it was the Epiccocum sp that was reisolated from the reinfected Kasukari Cassava variety and hence confirmed as the main causal agent. Mycological keys found this fungus to be Epicoccum sorghinum. This is the first time for E. sorghinum to be associated with BLS in Kenya. Morphologically, the disease distorted leaves and reduced root quality. This infection necessitates further enriching and screening of the cassava genome for more resistant and tolerant varieties especially in light of the climate change phenomenon.