In vitro and in vivo effects of fungicides on angular leaf spot pathogen ( Pseudocercospora griseola f. griseola ) and common bean

Angular leaf spot, caused by Pseudocercospora griseola , is a destructive fungal disease inducing yield losses up to 80% in common bean-growing areas of tropics and subtropics. Although various fungicides are used against the disease, their potential side effects on host plants are not well-documented. This study aimed to assess efficacy of six commercial fungicides (azoxystrobin, carbendazim, chlorothalonil, difenoconazole, mancozeb, and thiram) with different action mechanism and chemical groups against P. griseola in vitro , and to evaluate their effects on seed germination and seedling growth of common bean (cv. Gina) in vivo . Solid nutrient medium containing the fungicides were used for in vitro experiments, while seed germination tests described by International Seed Testing Association (ISTA) were used for in vivo experiments. As a result, all the fungicides significantly ( P ≤ 0.01) inhibited conidium germination in vitro and their effectiveness were ranked from the highest to the lowest one as follows: difenoconazole, azoxystrobin, mancozeb, carbendazim, thiram, and chlorothalonil, respectively. However, in vivo results showed that the tested fungicides significantly reduced seed germination of common bean compared to controls, but carbendazim and chlorothalonil caused the highest reductions, 23.7% and 23.5%, respectively. Fungicide treatments also significantly increased abnormal germination rate. Furthermore, all the fungicides led to notable reductions, 24.4% and 68.4%, in emergence rates and plant height, respectively. These findings indicate that although all the tested fungicides can inhibit conidium germination of P. griseola in vitro , they also exhibit significant phytotoxic effects on common bean in vivo by negatively affecting seed germination, seedling emergence, and growth.