Fungicides sensitivity in Alternaria solani populations in Limpopo province South Africa

Abstract

The main aim of this research was to assess A. solani populations in Limpopo province for their resistance to commonly used fungicide groups. Early blight caused by Alternaria solani is one of the major diseases of tomato worldwide. Application of fungicides is the most effective control measure used to manage the disease. However, continuous and indiscriminate use of different fungicides has resulted in the development of new resistant strains of A. solani. During growing season of 2015-2016, isolates of A. solani were collected from four locations in Limpopo and 34 were examined for their sensitivity to three commonly used fungicides in South Africa namely, chlorothalonil, (Bravo® 720 WP), copper oxychloride (Virikop® 50 WP) and mancozeb (Dithane® WG). Screening at different concentrations was done to determine sensitivity of collected isolates to the four fungicides. Each experiment was arranged in complete randomised design (CRD) with six treatments replicated four times. Results obtained in this study show that all tested fungicides significantly (P ≤ 0.05) reduced mycelial growth of the tested A. solani isolates across all the tested concentrations as compared to un-amended control. However, there was variation in the level of sensitivity as determined by pathogen isolate, area of collection and fungicide tested. Among the three fungicides, copper oxychloride was found to be the most effective fungicide in reducing the mycelial growth of A. solani isolates, followed by chlorothalonil and mancozeb, except in a situation where the isolate developed resistance.