# Association of root-knot nematode (Meloidogyne incognita) infestation and tomato brown rugose fruit virus incidence in greenhouse tomatoes following dimethyl disulfide soil treatment

## TL;DR

This study shows that reducing root-knot nematode infestation with dimethyl disulfide also lowers the incidence of a damaging tomato virus in greenhouses.

## Contribution

The first experimental evidence linking nematode severity to Tomato brown rugose fruit virus incidence using a nematode suppression gradient.

## Key findings

- DMDS reduced nematode populations by up to 94.14% at 60 g/m².
- ToBRFV incidence decreased by up to 86.04% with no phytotoxic effects observed.
- Root damage severity explained 61.6% of the variation in ToBRFV incidence.

## Abstract

Tomato (Solanum lycopersicum L.) production is increasingly constrained by root-knot nematodes (RKNs, Meloidogyne spp.) and Tomato brown rugose fruit virus (ToBRFV), two destructive pathogens that frequently co-occur in protected cultivation systems. Meloidogyne incognita induces severe root galling that weakens plant vigor, while ToBRFV is a highly stable, mechanically transmitted virus responsible for substantial yield losses. This study examined the association between nematode-induced root damage and ToBRFV incidence in tomato using a nematode suppression gradient generated by dimethyl disulfide (DMDS) under field conditions.

Greenhouse experiments were conducted across two consecutive cropping cycles using replicated greenhouse plots, with all disease and treatment responses evaluated at the plot level. The first crop experienced near-complete failure due to severe RKN infestation accompanied by ToBRFV symptoms. Before establishing the second crop, DMDS was applied at six rates (10–60 g/m2) to selectively reduce nematode pressure. Nematode suppression, ToBRFV incidence (determined by RT-PCR), and phytotoxic effects were assessed. Correlation and regression analyses were performed to evaluate the relationship between root damage severity and viral incidence.

DMDS markedly suppressed nematode populations, achieving 94.14% control at 60 g/m². Across the same gradient, plot-level ToBRFV incidence decreased by up to 86.04%, with no phytotoxic effects observed at any application rate. Statistical analyses revealed a strong positive correlation between root rot severity and ToBRFV incidence (Pearson’s r = 0.785, p = 0.0367). Linear modelling showed that root damage explained 61.6% of the variation in ToBRFV incidence (R2 = 0.616).

These findings provide the first experimental evidence that ToBRFV incidence co-varies with M. incognita severity in tomato under greenhouse conditions. The study demonstrates the utility of nematode suppression gradients for disentangling virus–nematode associations and identifies DMDS as an effective soil fumigation strategy for RKN suppression, within which ToBRFV incidence consistently declined along the nematode suppression gradient.