Suppression Mechanisms of Meloidogyne arenaria Race 1 by Pasteuria penetrans

The biological control of Meloidogyne arenaria on peanut (Arachis hypogaea) by Pasteuria penetrans was evaluated using a six x six factorial experiment in field microplots over 2 years. The main factors were six inoculum levels of second-stage juveniles (J2) of M. arenaria race 1 (0, 40, 200, 1,000, 5,000, and 25,000 J2/microplot, except that the highest level was 20,000 J2/microplot in 1995) and six infestation levels of P. penetrans as percentages of J2 with endospores attached (0, 20, 40, 60, 80, and 100%). The results were similar in 1994 and 1995. Numbers of eggs per root system, J2 per 100 cm³ soil at harvest, root galls, and pod galls increased with increasing nematode inoculum levels and decreased with increasing P. penetrans infestation levels (P ≤ 0.05), except that there was no effect of P. penetrans infestation levels on J2 per 100 cm³ soil in 1994 (P> 0.05). There were no statistical interaction effects between the inoculum levels of J2 and the infestation levels of P. penetrans (P > 0.05). When the infestation level was increased by 10%, the number of eggs per root system, root galls, and pod galls decreased 7.8% to 9.4%, 7.0% to 8.5%, and 8.0% to 8.7% in 1994 and 1995, respectively, whereas J2 per 100 cm³ soil decreased 8.8% in 1995 (P ≤ 0.05). The initial infestation level of P. penetrans contributed 81% to 95% of the total suppression of pod galls, whereas the infection of J2 of the subsequent generations contributed only 5% to 19% suppression of pod galls. The major suppressive mechanism of M. arenaria race 1 by P. penetrans on peanut is the initial endospore infestation of J2 at planting.