The influence of root diffusate and host age on hatching of the root-knot nematodes, Meloidogyne chitwoodi and M. fallax

Abstract

The root-knot nematodes, Meloidogyne chitwoodi and M. fallax, cause severe damage to economically important crops and, in 1998, both species were listed as quarantine pests in Europe. Comparative studies were made on the effects of root diffusates and host age on the in vitro hatching of M. chitwoodi and M. fallax. There is a marked contrast in the hatching response of the two species. Hatching of second-stage juveniles (J2) of M. chitwoodi produced on young plants did not require host root diffusate stimulus, whereas at the end of the plant growing season, egg masses contained a percentage of unhatched J2 that require host root diffusate to cause hatch. This form of obligate quiescence at the end of the host growing season was not found in M. fallax. This species hatched well in water and did not require hatch stimulation from root diffusate, irrespective of the age of the plant on which the egg masses were produced. The number of eggs per egg mass for M. fallax collected on senescing plants was significantly greater than the number of eggs per egg mass for M. chitwoodi. The number of eggs per egg mass of M. chitwoodi decreased with plant age. The results are discussed in the context of the differing survival strategies of the two species.

Quantitative Analysis of the Effects of Diffusates from Plant Roots on the Hatching ofMeloidogyne chitwoodifrom Young and Senescing Host Plants

“…These results indicate that the root diffusates from tomato and carrot had delaying effects on the hatching of M. chitwoodi eggs from young host plants rather than other root diffusates, and that some of these diffusates had stronger effects on the egg masses from the young host plants than those from the senescing host plants. Taken together with our previous study, 8) these results clearly indicate that host age affects the hatching of root-knot nematodes. Inserra et al reported that the actions of root diffusates fluctuated in the hatching of M. chitwoodi eggs as compared with distilled water.…”

“…Moreover, our comparative studies have shown that the effects of tomato root diffusates on the hatching of M. chitwoodi egg masses were different from those on the hatching of M. fallax egg masses. 8) Meloidogyne chitwoodi has a very wide host range, and it can cause damage at various levels. Moreover, it can survive in the soil without the host plant through the resting stage into egg masses, or into alternate host plants.…”

The effect of temperature on hatch and activity of second-stage juveniles of the root-knot nematode, Meloidogyne minor, an emerging pest in north-west Europe

“…The M. minor eggs remaining once hatch had ceased appeared to be degenerating, but we cannot be certain that there were no viable eggs amongst them. It is possible that addition of root diffusate may have increased hatch rates; while most species of Meloidogyne hatch in water, hatch rate of some species may be enhanced by host root extract, especially at certain times of the year (Wesemael et al, 2006). This study shows that the minimum temperature for M. minor hatch is between 10 and 15…”

“…In our study, the low hatch (49%) in October might be interpreted as eggs being in diapause but not having experienced a long enough cold period. However, similar low hatch (47%) was also seen in May, so other factors must be involved, such as age of females, or condition of soil and/or plant (Huang & Pereira, 1994;Gaur et al, 2000;Wesemael et al, 2006). The M. minor eggs remaining once hatch had ceased appeared to be degenerating, but we cannot be certain that there were no viable eggs amongst them.…”

Vertical distribution of the plant-parasitic nematode, Meloidogyne chitwoodi, under field crops

“…The later generations can be formed on crops that are starting to senesce. Wesemael et al (2006) found that egg masses of M. chitwoodi collected from senescing tomato plants contained a % of unhatched J2 that required root diffusate to cause hatch and 6-10% remained unhatched. This pattern could be a reason for the decline of the population in fodder beet before the harvest date and the slow decline after carrot.…”