Biocontrol agents in combination with moringa oleifera leaf extract for integrated control of botrytis cinerea of tomato.

Abstract

Tomatoes and tomato-based foods provide essential nutrients beneficial to human health. Despite these benefits from tomatoes, postharvest losses result in unprofitable tomato production in some parts of the world. During ripening and harvesting, tomato becomes susceptible to diseases resulting in shorter shelf life. Susceptibility of tomato plants to Botrytis cinerea which causes grey mould infection can occur at any growth stage and the most susceptible growth stage is during ripening and senescing. Factors such as mechanical injuries, inadequate storage conditions, inappropriate handling, and transport affect tomato quality. The use of chemicals not only negatively affects farmers' yield by further enhancing pesticide resistance to crop pathogens but also influences other sectors of communities through contamination of drinking water sources which is an environmental hazard. There is a need to emphasise and encourage sustainable agricultural strategies such as biological control and plant extracts as alternative strategies which are eco-friendly and economically sustainable. Therefore, the main aim of this research was to examine the effect of biocontrol agents and Moringa oleifera leaf extract, individually and in combination, to control B. cinerea on tomatoes in vitro and in vivo. A total of 48 biocontrol agents were isolated from different parts of tomato leaves, citrus leaves, mushrooms and erect prickly pear. The isolates were screened against B. cinerea for the inhibitory effect and as potential control of the pathogen on potato dextrose agar (PDA) and tomato fruits. Serratia marcescens, Bacillus pumilus and Bacillus safensis inhibited B. cinerea by more than 50% in vitro. During in vivo screening, Serratia and Bacillus isolates inhibited grey mould incidence on ‘Jam’ tomatoes by more than 70%. The scanning electron microscopy images of the pathogen samples treated with biocontrol agents showed swollen and lysed mycelia. Moringa leaf extracts (MLE) were prepared into four concentrations MLE 1%, MLE 2%, MLE 3% and MLE 4%. The MLE concentrations were tested for their antifungal activity on the pathogen growth during in vitro studies. High concentrations were found to have some inhibitory effect on the mycelial growth of B. cinerea. There was no significant difference observed in the control, MLE 1% and MLE 2% since no mycelial inhibition was observed after 7 days at 25°C. For in vivo studies, all the concentrations had some inhibitory effect against grey mould on ‘Jam’ tomatoes. This was evidenced

by lower disease incidence observed on the fruits treated with the moringa leaf extract compared to the control treatment. Scanning electron micrographs showed morphological changes in the hyphae on the samples treated with concentrations of MLE and there was also a breakage on the pathogen hyphae. Furthermore, this study evaluated the integrated control of B. cinerea using S. marcescens, B. safensis and B. pumilus integrated with MLE 2% and MLE 3% in vitro and in vivo. S. marcescens, B. safensis and B. pumilus integrated with MLE 2% and MLE 3% successfully suppressed mycelial growth of B. cinerea in vitro. Treating tomato fruits with S. marcescens, B. safensis and B. pumilus integrated with MLE 2% and MLE 3% reduced the disease incidence of grey mould compared to the control. The SEM images of the mycelial growth of B. cinerea showed shrinkage, and breakage of pathogen mycelia and the spores were damaged showing breakage and immature spores both in vitro and in vivo. Integrating moringa leaf extract, Serratia spp. and Bacillus spp. have the potential to be an alternative to synthetic fungicides to control postharvest pathogens.