Morphogenetic diversity of Colletotrichum species infecting Sorghum bicolor in the lake basin regions of Kenya

Abstract C. sublineolum is among the most destructive sorghum pathogens causing anthracnose in Kenya. Both preventive and breeding for resistance approaches have been developed. However, its continuous evolution into new strains is still a threat to sorghum production especially in tropics and sub-tropics. The pathogen is confirmed to be genetically and morphologically diverse but such information is lacking in Kenya and there is no known number of strains identified to cause the disease in Kenya. Systematic random and biased sampling was conducted in two districts within Lake Basin region where most sorghum is grown to collect anthracnose infected stem, leaf and panicle tissues only. Ten farms separated by four kilometers each were surveyed per district. Ten isolates were obtained per tissue per site, giving a total of sixty isolates for the whole study. Identification of the isolates was done using previous descriptions of the fungus and genetic diversity assessment was performed using simple sequence repeat (SSR) marker. A total of 15 morphologically diverse isolates were isolated from leaf, stem and panicle tissues. Leaf isolates were more diverse followed those infecting the panicle tissues. The stem was frequently infected by isolates resembling C. gloeosporioides. Genetic diversity assessment indicated the presence of two major sub-species with one sub-species showing low stability through evolution into two sub-groups. Only one universal primer amplified the bands thus there is need to involve several other primers to confirm these findings. This study also recommends Koch's postulate on C. gloeosporioides to ascertain its host range.