DISPERSAL OF THE CONIDIA OF COLLETOTRICHUM-GLOEOSPORIOIDES BY RAIN AND THE DEVELOPMENT OF ANTHRACNOSE ON ONION

Abstract

The conidia of Colletotrichum gloeosporioides were found to be dispersed during rainfall by wash-off and splash mechanisms. The initiation and development of onion anthracnose was found to depend on the frequency of rainfall and the movement of conidial inoculum during rainfall. Experiments conducted under controlled conditions in the laboratory employing splash and wash-off assemblies showed that impacting incident water drops (splash) and flowing water (wash-off) liberated the conidia from the anthracnose lesions of the onion leaf/peduncle. Peak liberation of conidia occurred with 3 to 5 water drops and most of the conidia were removed from the source within 90 seconds. A possibility of the dispersal of conidia of C. gloeosporioides from soil to lower leaf by splash mechanisms and then from the leaves to the neck of the onion bulb and to the bulb by wash-off mechanisms is indicated.