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

Plants employ different defensive strategies to limit or avoid nematode attacks, including the recruitment of beneficial microorganisms that can support plants by enhancing their defence mechanisms. We investigated the effect of the two nematode egg parasitising fungi, Niesslia gamsii and Polydomus karssenii , on nematode suppression on tomato using greenhouse experiments. Their potential against Meloidogyne hapla was evaluated by analysing direct parasitism and the expression of plant defence-related genes, through quantitative reverse transcriptase 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. Fungal treatments with N. gamsii and P. karssenii reduced by 32–31% M. hapla egg numbers per root system, respectively. Both treatments also significantly lowered the nematode reproduction rate (Rf value) when compared to the control. Both fungi affected the nematode root invasion by limiting penetration of M. hapla second-stage juveniles (J2) into tomato roots, 3 and 7 days after inoculation. The results 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.