WINDBORNE SPREAD OF ERGOT DISEASE (CLAVICEPS-AFRICANA) IN SORGHUM A-LINES IN ZIMBABWE

Ergot disease spread rapidly in Zimbabwe amongst replicated plots of m ale-sterile sorghum A-lines, from a group of centrally situated and pr ecociously inoculated plants. Prominent secondary conidiation by the p athogen, Claviceps africana, on the surface of exuded honeydew provide d airborne spores which were trapped in a Burkard continuous spore tra p and showed diurnal peaks of concentration in air close to the primar y source of inoculum. The rate of disease spread (r = 0.2; range 0.14- 0.58) closely matched that recorded for other plant pathogens such as Phytophthora infestans and Puccinia graminis tritici, and it is conclu ded that the characteristic secondary conidia of C. africana were the principal epidemiological agents within the experimental area. Ergot s pread by windborne secondary conidia has significant epidemiological a nd economic implications for sorghum hybrid breeding in southern Afric a.