Microbial fermentation products elicit salicylic acid or jasmonic acid related defence pathways in Solanum lycopersicum

To explore the possibility of reducing plant diseases with integrated pest management strategies, microbial fermentation products (MFPs) are being explored as elicitors of plant defence. This work examined the impact of MFP application on tomato plants (Solanum lycopersicum) in a polytunnel environment. Two MFPs were assessed, at a concentration of 0.7% v/v, to determine their impact within 48-h of a foliar treatment application on the mRNA expression of common plant defence markers along with hydrogen peroxide and malondialdehyde levels, peroxidase and catalase activity, and leaf pigment concentrations. Treated plants were examined for indicators of different defence responses. AOS, LOX2 and malondialdehyde were targeted as indicators of a jasmonic acid related response, while PAL and PR1 were examined as indicators of a salicylic acid related response. A yield study was also conducted over two harvest seasons to determine the impact of the MFP applications on fruit productivity. MFP 1 upregulated gene expression of AOS, CAT, LOX2, PR2 and PA2. It also resulted in greater malondialdehyde concentrations in leaf tissue and resulted in higher levels of catalase activity. At 24 h plant chlorophyll a, chlorophyll b, carotenoids and total pigment concentrations were higher with use of MFP 1. MFP 2 increased the expression of CAT, LOX2, PAL, PR1, PR2, PR4, PR5 and PA2 genes, hydrogen peroxide levels and peroxidase activity also increased. Yield analysis revealed that neither of the MFP applications had a negative impact on productivity, fruit numbers and average fruit weight were significantly higher in year 1 with MFP1, while MFP 2 had greater fruit numbers in year 2. The data suggests, based on the behaviour of the plants in response to the MFP applications, that MFP 1 positively affected biomarkers associated with jasmonic acid defence responses (AOS, LOX2 and malondialdehyde) and MFP 2 affected markers associated with salicylic acid responses (PAL and PR1). The work indicates that MFPs could be used to elicit different defence responses in tomato plants, which could play a role in helping improve crop productivity. Eliciting plant defence against biotic stress is crucial in integrated pest management strategies, this work provides evidence that MFPs may play a crucial role in eliciting defences in tomato plants and other crops against a range of agronomically challenging diseases.