Application of thifluzamide to stem rot in peppers: Infection and control mechanisms of sclerotium rolfsii

In recent years, the fungal disease 'pepper stem rot', contracted from the soil-borne pathogen sclerotium rolfsii, has been increasing year by year, causing significant losses to the pepper (Capsicum annuum L.) industry. To investigate the infection mechanism of stem rot, the fungus S. rolfsii was used to infect the roots of pepper plants, and was found to affect root morphology and reduce root activity, which subsequently inhibited root growth and development. With fungal infestation, its secretions (oxalic acid, PG and PMG enzyme) were able to break normal tissues in the stem base and induced the burst of the active oxygen, which leads to injury aggravation. Morphological observations of the site of damage at the base of the stem using SEM revealed that the vascular bundles and stomata were completely blocked by hyphae, resulting in a blockade of material exchange in the plant. It was subsequently found that most of the stomata in the leaves were closed, which caused the leaves to lose their ability to photosynthesize, then turned yellow, wilt, shed, and the plant died. Commercialized fungicide thifluzamide with excellent in vitro (EC50 = 0.1 μg/mL) and in vivo curative (EC50 = 29.2 μg/mL) antifungal activity was selected to control the stem rot disease in peppers. The results demonstrated that it was able to suppress the secretion of associated pathogenic factors and reduce the outbursts of reactive oxygen species, thus reducing the damage caused by S. rolfsii at the base of the plant's stem and also enhancing the root activity of the infected plant, thereby promoting root growth. It could also inhibit fungal growth, unblock the vascular bundles and stomata, maintain a balance of material and energy exchange within the plant, and thus restore the damaged plant to its normal growth capacity. All the results will provide an adequate reference for the prevention and control of stem rot disease on peppers with thifluzamide.