SUPPRESSION MECHANISMS OF MELOIDOGYNE-ARENARIA RACE-1 BY PASTEURIA-PENETRANS

The biological control of Meloidogyne arenaria on peanut (Arachis hyoo gaea) by Pasteuria penetrans was evaluated using a six x six factorial experiment in field microplots over 2 years. The main factors were si x 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 h ighest level was 20,000 J2/microplot in 1995) and six infestation leve ls of P. penetrans as percentages of J2 with endospores attached (0, 2 0, 40, 60, SO, and 100%), The results were similar in 1994 and 1995. N umbers of eggs per root system, J2 per 100 cm(3) soil at harvest, root galls, and pod galls increased with increasing nematode inoculum leve ls and decreased with increasing P. penetrans infestation levels (P le ss than or equal to 0.05), except that there was no effect of P. penet rans infestation levels on J2 per 100 cm(3) soil in 1994 (P > 0.05). T here were no statistical interaction effects between the inoculum leve ls of J2 and the infestation levels of P. penetrans (P > 0.05). When t he 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 cm(3) soil decreased 8.8% in 1995 (P less than or equal to 0.05). The initial infestation level of P. penetrans contributed 81% to 95% of t he total suppression of pod galls, whereas the infection of J2 of the subsequent generations contributed only 5% to 19% suppression of pod g alls. The major suppressive mechanism of M. arenaria race 1 by P. pene trans on peanut is the initial endospore infestation of J2 at planting .