Characterization of physiologic races of sugarcane smut (Ustilago scitaminea) in Kenya.

Sugarcane smut disease caused by the fungus Ustilago scitaminea significantly reduces the yield and quality of sugarcane. The disease was first reported in Kenya in 1958, in Nyanza and Coastal provinces and currently occurs in all major sugarcane growing areas of Kenya. Planting resistant varieties is the main smut control measure in Kenya. Planting smut resistant varieties was made compulsory in Kenya in 1963. However, varieties previously confirmed resistant are now susceptible. Reports indicate that some varieties are resistant to smut in one zone and susceptible in another. An attempt was thus made to identify physiologic races of sugarcane smut in Kenya. Sugarcane smut teliospores were collected from the major sugarcane growing zones of Western Kenya in South Nyanza, Nyando, Mumias, Busia, Nzoia and west Kenya. A set of 11 sugarcane cultivars which had previously shown differential response to smut in Kenya and elsewhere were each artificially inoculated with a mixture of smut spores from each zone by dipping in a suspension of smut spores that contained 5 x 10 6 teliospores per ml. Susceptibility of the cultivars to smut was measured by recording the number of smut whips that appeared within 6 to 7 months after planting. The reaction of the cultivars to smut from the various zones varied from resistance to susceptible. Three cultivars were seen in smut reaction in two tests. The results suggested existence of smut races in Kenya.