Population dynamics of Meloidogyne incognita and infestation levels by Pasteuria penetrans in a naturally infested field in Martinique.

TLDR: Although chaos implies non-predictability of J2 numbers and endospore infestation dynamics, it also suggests that large-scale fluctuations may induce local nematode suppression by P. penetrans.

Abstract: The population dynamics of Meloidogyne incognita juveniles (J2) in association with the parasite Pasteuria penetrans was studied in a field in Martinique. Data obtained at three-week intervals for one year were analyzed to study the relationship between J2 density and endospore infestation levels. Six crop sequences were evaluated in five replicates. They were: resistant tomato, okra, fallow, cabbage; susceptible tomato, okra, fallow, cabbage; bean, pepper, fallow, cabbage; eggplant, fallow; cucumber, velvetbean, fallow, cabbage; fallow, pepper, cabbage, fallow, cabbage. The J2 densities showed fluctuating trends, frequently synchronous with fluctuations of endospore infestation. The highest J2 numbers observed ranged between 1 000 and 1 500 nematodes/100 g of soil in the first four crop sequences, and between 150 and 250 J2/100 g of soil in the last two. The highest percentages of nematodes with adhering endospores ranged between 50 and 70%. The resistant tomato crop showed a sharp decrease in the nematode density at the end of the crop sequence, with a similar synchronous decrease of the endospore infestation. This trend was also observed during the fallow periods in the other treatments. Susceptible crops allowed a sharp increase of the J2 densities. During these periods of population growth, the concomitant increase of the endospore infestation levels was interrupted with fast growing J2 densities. In the last two crop sequences, the J2 densities progressively decreased because of the on-host status of velvetbean and of a longer fallow, respectively. When all the pooled data from the six treatments were considered, a significant linear correlation was observed between J2 densities and the corresponding endospore infestation values (P 0.001). This relationship appeared related to the density of females releasing J2 and/or endospores in the soil. All pooled mean densities also followed the Gutenberg-Richter power law distribution, indicating the oc-currence of chaotic effects influencing their dynamics. Although chaos implies non-predictability of J2 numbers and endospore infestation dynamics, it also suggests that large-scale fluctuations may induce local nematode suppression by P. penetrans.