Abstract
Meloidogyne javanica has showed less reproductive success than M. incognita in watermelon genotypes. This study was conducted to elucidate the low reproduction of M. javanica in watermelon. The post-infection development of M. javanica in watermelon ‘Sugar Baby’ was determined at progressively higher initial population (Pi) levels at two time points during the life cycle. Plants were inoculated with 0, 25, 50, 100, 200, and 300 second-stage juveniles (J2)/plant. The increase in Pi was correlated with the penetration rates (R2= 0.603, p<0.001) and total numbers of nematodes in the root (R2 =0.963, p< 0.001) but there was no correlation between the Pi and the reproduction factor (eggs/plant/Pi). The population in the roots at 26 days post-inoculation (dpi) consisted primarily of third-stage juveniles (J3) with a small presence of J2 and fourth stages, and egg-laying females. The dominance of the J3, when egg-laying females are expected, point to the malfunction of the feeding sites that failed to support nematode development beyond the J3 stage. The similarities in egg-laying females at 26 and 60 dpi imply the disruption of the life cycle. Watermelon compensated for M. javanica parasitism by increasing vine length (19% to 33%) and dry top weight (40%) in comparison with the non-inoculated plants. The area under the vine length progress curve was significantly larger as the Pi progressively increased (R²=0.417, p<0.001). Physiological variation was detected between the M. incognita populations. M. arenaria had less ability to invade watermelon roots than did M. incognita and M. javanica.
Highlights
Root-knot nematodes (RKN) of the genus Meloidogyne are polyphagous obligate sedentary endoparasites that depend on the induction of feeding sites in the roots to complete their life cycle
The increase in Pi was correlated with the penetration rates (R2 = 0.603, p
The nematode completed its life cycle and produced offspring in watermelon, and the Rf was highest at the lowest Pi (25 J2/plant) (Fig. 2b)
Summary
Root-knot nematodes (RKN) of the genus Meloidogyne are polyphagous obligate sedentary endoparasites that depend on the induction of feeding sites in the roots to complete their life cycle. Secondstage juveniles (J2) penetrate the root; migrate through the intercellular space to enter the vascular cylinder in order to induce the formation of a feeding site. Physiological variability among RKN species, in terms of penetration rates, root galling severity, and final population densities (Pf) were found among isolates of these RKN species in watermelon (Winstead & Riggs, 1959; Edelstein et al, 2010; Cohen et al, 2014; López-Gómez & Verdejo-Lucas, 2014). Meloidogyne javanica showed less ability than M. incognita to form galls, produce egg masses (EM), and lay eggs
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