Phytotoxicity of filtrate extracts of fungal pathogens on selected tomato (Solanum lycopersicum L.) cultivars

Abstract

The phytotoxic effect of culture filtrates of selected fungal pathogens on the morphology and anatomy of different tomato cultivars was evaluated in this study. Four tomato cultivars namely; Roma Savanna, Riogrande, Roma VF and Tropimech were treated with 21 days old culture filtrates of fungal pathogens namely; Alternaria triglochinicola, Aureobasidium pullulans, Pythium ultimum and Sclerotium rolfsii grown on Potato Sucrose Broth (PSB). These fungal filtrates were extracted using water, dichloromethane (DCM) and ethylacetate (EA). Healthy leaves excised from two months old tomato plants were inoculated by dipping their petioles in 20ml of each fungal filtrate for 3 days and observed for the appearance of disease symptoms. A. pullulans accounted for the highest necrotic and chlorotic leaf tissue area on all the studied tomato cultivars. The aqueous extracts were more biologically active, inducing the highest occurrence of mean total leaf necrosis (14.69%) and chlorosis (57.21%), compared to ethyl acetate (6.04% necrosis and 7.03% chlorosis) and dichloromethane (6.57% necrosis and 4.02% chlorosis). Filtrate extracts of A. pullulans showed significantly higher negative effect (P≤0.05) on anatomical features such as the thickness of epidermis, cortex and diameter of the vascular bundle of all the tomato cultivars. Further isolation and identification of phytotoxic compounds synthesized by the studied fungi are required for a better understanding of their mechanisms of disease initiation and yield reduction.