Association of Root-Knot Nematode (Meloidogyne incognita) Infestation and Tomato Brown Rugose Fruit Virus Incidence in Greenhouse Tomatoes Following Dimethyl Disulfide Soil Treatment

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 weaken 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), a sulfur-based soil fumigant with antimicrobial activity, 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. 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%, as determined by RT-PCR, with no phytotoxic effects observed at any application rate. Correlation and regression analyses incorporating all treatments revealed a strong positive relationship between root rot severity and ToBRFV incidence (Pearson's r = 0.785, p = 0.0367). Linear modelling showed that variation in root damage explained 61.6% of the variation in ToBRFV incidence (R² = 0.616), indicating that reduced root damage was strongly associated with lower viral incidence. These findings provide the first experimental evidence that ToBRFV incidence co-varies with M. incognita severity in tomato under greenhouse conditions, demonstrate the utility of nematode suppression gradients for disentangling virus–nematode associations, and identify DMDS as an effective and sustainable soil fumigation strategy for RKN suppression, within which ToBRFV This is a provisional file, not the final typeset article incidence consistently declined along the nematode suppression gradient in intensive production systems.