The nematode egg parasitic fungi, Niesslia gamsii and Polydomus karssenii, protect tomato against Meloidogyne hapla infection by priming and regulating the plant defence system

Interaction between plant parasitic nematodes and their host plants is a dynamic process. While plants employ different defensive strategies to limit or avoid nematode infection, plant parasitic nematodes utilise various strategies to suppress plant defence. However, in the meantime, beneficial microorganisms can support plants in enhancing their defence mechanisms against pathogens. Nematophagous fungi can reduce infection of plant parasitic nematodes via direct parasitism and triggering plant defence system, having positive impacts on plant growth. We investigated the effect of the two nematode egg parasitising fungi Niesslia gamsii and Polydomus karssenii on nematode suppression in soil using greenhouse experiments by evaluating the potential of these fungi on direct parasitism against nematodes and by analysing the expression of plant defence related genes using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). Niesslia gamsii and P. karssenii were originally isolated from naturally infested eggs of the cereal cyst nematode Heterodera filipjevi, and their nematode pathogenicity was proven through Koch’s postulates. Here we report on their parasitism towards the root-knot nematode Meloidogyne hapla on tomato, where both fungi could significantly reduce the number of nematode eggs or second stage juveniles (J2) in tomato roots as well as the nematode reproduction rate. Both fungi also impeded nematode root invasion by limiting nematode penetration into tomato roots 3 and 7 days after being inoculated with the M. hapla J2. The results obtained in this study showed a substantial effect of both fungi on inducing defence responses in tomato plants towards M. hapla. Pre-treatment with N. gamsii and P. karssenii led to the expression of different marker genes associated with pathogen response pathways, including salicylic and jasmonic acid/ethylene regulated defensive. These findings suggest that N. gamsii and P. karssenii could prime the plant host for enhanced defence upon nematode attack.