Damage Threshold and Population Dynamic of Meloidogyne javanica on Tomato Plant

Abstract

The root-knot nematode Meloidogyne javanica is a significant pathogen that causes substantial yield losses in tomato plants. Moroccan farmers generally lack knowledge regarding the density of this pathogen, which can trigger visible and localised symptoms. Additionally, regional studies that establish damage thresholds for this issue are scarce. This study investigated the damage threshold of M. javanica on tomato plants using nine initial population densities (Pi) of second-stage juveniles (J2s): 0, 0.5, 1, 2, 4, 8, 16, 32 and 64 J2s (g dry soil)⁻¹. Aboveground growth (plant height and fresh and dry shoot weight) and belowground growth (root length and diameter) were assessed after 90 days. The plant growth parameters were significantly reduced at higher inoculum densities. The Seinhorst model fitting revealed the highest minimum relative yield (m) for shoot fresh weight (m = 0.761 ± 0.012) and the lowest for root diameter (m = 0.509 ± 0.026). The tolerance limit (T) varied, with the highest shoot dry weight (T = 1.657 ± 0.329 J2s (g soil)⁻¹) and lowest root diameter (T = 0.095 ± 0.019 J2s (g soil)⁻¹). The production of eggs by M. javanica increased significantly with increasing initial population density, rising from 211 ± 64 eggs (g roots)⁻¹ at 0.5 J2s (g soil)⁻¹ to 3735 ± 380 eggs (g roots)⁻¹ at 64 J2s (g soil)⁻¹, representing a 17.7-fold increase. Tomato plants exhibited the maximum galling index at lower nematode densities. Symptoms began at densities as low as 0.095 J2 (g soil)⁻¹, with severity increasing with nematode density. Given the severe damage caused at low densities, Moroccan farmers must adopt early detection and effective management strategies.