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

The population dynamics of Meloidogyne incognita juveniles (J2) in associat ion with the parasite Pasteuria penetrans was studied in a field in Martini que. Data obtained at three-week intervals for one year were analyzed to st udy the relationship between J2 density and endospore infestation levels. S ix crop sequences were evaluated in five replicates. They were: resistant t omato-okra-fallow-cabbage; susceptible tomato-okra-fallow-cabbage; bean-pep per-fallow-cabbage; eggplant-fallow; cucumber-velvetbean-fallow-cabbage; fa llow-pepper-cabbage-fallow-cabbage. The J2 densities showed fluctuating tre nds, 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 adherin g 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, wit h a similar synchronous decrease of the endospore infestation. This bend wa s also observed during the fallow periods in the other treatments. Suscepti ble crops allowed a sharp increase of the J2 densities. During these period s of population growth, the concomitant increase of the endospore infestati on levels was interrupted with fast growing J2 densities. In the last two c rop sequences, the J2 densities progressively decreased because of the non- host status of velvetbean and of a longer fallow, respectively. When all th e pooled data from the six treatments were considered, a significant linear correlation was observed between J2 densities and the corresponding endosp ore infestation values (P < 0.001). This relationship appeared related to t he density of females releasing J2 and/or endospores in the soil. All poole d mean densities also followed the Gutenberg-Richter power law distribution , indicating the occurrence of chaotic effects influencing their dynamics. Although chaos implies non-predictability of 52 numbers and endospore infes tation dynamics, it also suggests that large-scale fluctuations may induce local nematode suppression by P. penetrans.