Variation in lipid reserves of second-stage juveniles of Meloidogyne exigua in a coffee field and its relationship with infectivity

Abstract

In this study we assessed the variations in lipid content of second-stage juveniles (J2) of Meloidogyne exigua, recovered from a coffee field, by staining and quantifying the neutral lipids using image analysis. Our results showed that annual variations in J2 stained lipid area correlate with temperature, rainfall and total number of J2 per 100 cm3 of soil. Laboratory and glasshouse experiments showed that decreases in the lipid stained area of J2 of M. exigua led to decreased infectivity and reproduction on tomato. The susceptibility of tomato cvs Kada and Nemadoro to M. exigua varied according to the stained lipid area of the J2 inoculated on roots. Only J2 containing an average of 80% stained lipid area were able to infect cv. Nemadoro, which contains the Mi resistance gene, whereas J2 containing 20% stained lipid area were still able to infect cv. Kada, considered to be highly susceptible. In this study we show for the first time the dynamics of lipid variation in J2 of M. exigua in a coffee field and the dependence of infectivity and parasitism on the resistance level of tomato cultivars and the lipid stained area in J2.