Sensitivity of Colletotrichum gloeosporioides Isolates from Diseased Avocado Fruits to Selected Fungicides in Kenya

Abstract

Colletotrichum gloeosporioides is a serious postharvest pathogen of avocado fruits worldwide. Kenya lacks any registered fungicides for the management of the disease. Nevertheless, farmers commonly use commercially available fungicides such as Bayleton 25WP (Triadimefon 250 g/Kg), Milraz 76WP (Propineb 70% and Cymoxanil 6%), and Copper oxychloride 500WP for disease management. Te efcacy of these fungicides against C. gloeosporioides is not known. Te purpose of this study was therefore to test the inhibitory efect of these fungicides against 46 C. gloeosporioides isolates from avocado fruits collected from varieties grown at diferent agroecological zones in Murang’a County, a popular avocado-growing region in Kenya. Mycelial growth rate and sporulation for each isolate were measured in vitro on PDA plates amended with diferent concentrations of the fungicides. Plates were arranged in a completely randomized design with three replications per treatment. All fungicides were efective in vitro but there were signifcant diferences in sensitivity among isolates. Bayleton had the highest mycelial inhibition followed by Milraz, while copper oxychloride had the lowest mycelial inhibition rates, ranging from 81% to 88%. However, copper oxychloride was more efective in inhibiting sporulation. Te inhibitory efect of each fungicide was concentration-dependent, where twice the recommended concentration had the highest inhibitory efect, followed by the recommended concentration. Our results show that the fungicides used by farmers against C. gloeosporioides, the causal agent for anthracnose, are efective. We, however, recommend further feld tests in diferent avocado-growing areas so as to validate their efcacy against various isolates and under diferent environments.