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Penetration, post-infectional development, reproduction, and fecundity of Meloidogyne arenaria races 1 and 2 were studied on susceptible (CNS), partially resistant (Jackson), and highly resistant (PI 200538 and PI 230977) soybean genotypes in the greenhouse. The ability to locate and invade roots was similar between races, but more juveniles penetrated roots of susceptible CNS than the resistant genotypes. At 10 days after inoculation, 56% and 99% to 100% of race 1 second-stage juveniles were vermiform or sexually undifferentiated in CNS and the resistant genotypes, respectively. In contrast, only 2%, 42%, 44%, and 62% of race 2 juveniles had not initiated development in CNS, Jackson, PI 200538, and PI 230977, respectively. By 20 days after inoculation, 88% to 100% of race 2 nematodes in roots of all genotypes were females, whereas only 25% and 1% of race 1 were females in CNS and the resistant genotypes, respectively. For all four genotypes, race 1 produce 85% to 96% fewer eggs per root system 45 days after inoculation than race 2. At 45 days after inoculation race 2 produced more eggs on CNS than the other genotypes.

The cellular responses induced by Meloidogyne arenaria races 1 and 2 in three soybean genotypes, susceptible CNS, resistant Jackson, and resistant PI 200538, were examined by light microscopy 20 days after inoculation. Differences in giant-cell development were greater between races than among the soybean genotypes. M. arenaria race 1 stimulated small, poorly formed giant-cells in contrast with M. arenaria race 2, which induced well-developed, thick-walled, multinucleate giant-cells. The number of nuclei per giant-celt was variable, but fewer nuclei were usually present in giant-cells induced by race 1 (mean 16 nuclei) than in giant-cells induced by race 2 (mean 41 nuclei). Differences observed in giant-cell development were related to differences in growth and maturation of M. arenaria races 1 and 2 and host suitability of the soybean genotypes.

Resistant plant introductions, PI 230977 and PI 200538, and partially resistant Jackson and susceptible CNS were evaluated for seed yield in response to races 1 and 2 of Meloidogyne arenaria. Initial soil population densities (Pi) of the nematode were 0, 31, 125, and 500 eggs/100 cm(3) soil. At the highest Pi, yield suppressions of CNS, Jackson, PI 230977, and PI 200538 were 55, 28, 31, and 29%, and 99, 86, 66, and 58% for races 1 and 2 compared with uninfested controls. Numbers of second-stage juveniles (J2) present in roots 14 days after planting increased as Pi increased, but did not differ between the two races. At the highest Pi, fewer race 1 (40-57%) and race 2 (53-68%) J2 were present in roots of the plant introductions than in roots of Jackson. Soil population densities of race 1 J2 at 135 days after planting were 83-89% lower on the resistant genotypes than on CNS. These numbers did not differ for race 2. Reproductive factors were considerably higher for race 2 compared to race 1 for all genotype by Pi combinations, except for CNS at the highest Pi.