Identification and survival of the causal organism of leaf smut disease ofcowpea in Nigeria

Protomycopsis phaseoli (Ramak and Subram) is the causal agent of the cowpea leaf smut disease in Nigeria and not Entyloma vignae as claimed by some au thors. This pathogen formed dark ash-grey to sooty-black lesions of 3-10 mm in diameter, while young lesions had yellow haloes. P. phaseoli produced d ark reddish-brown chlamydospores that are globose to oval measured 23.8 mum , thick-walled and rugose. The chlamydospores germinated and produced globo se vesicles. The pathogen grew on potato dextrose agar only when the leaf t issue was dipped in acidified water (1% H2SO4). The organism was slowly gro wing at 24-28 degreesC with snow white colour. Chlamydospores of P. phaseol i in infected cowpea leaves survived longer when buried in the soil for fiv e months than when they were left on the soil surface for the same period a t temperatures (26-27 degreesC) and humidity (70-82%) prevailing in Ibadan. Destruction of leaf debris before crop emergence, long period of rotation and no tillage cropping are suggested to prevent the onset and spread of le af smut disease of cowpea.