Inoculum Density on Heterodera glycines Development in Resistant and Susceptible Soybean Cultivars

A series of factors can affect populations of H. glycines and even its life cycle, including inoculum density and genetic resistance of soybean cultivars. This study evaluated whether resistance reaction to H. glycines is effective in reducing nematode development under high inoculum concentration, as well as if such resistance reaction and inoculum density affect juvenil penetration and survival rate of H. glycines. Two trials were done using three soybean cultivars- one susceptible (BRS Valiosa RR) and two resistant (BRSGO Chapadões and BRSGO 8860RR) to H. glycines. The cultivars were subjected to four inoculum density (1,000, 2,500, 5,000 and 10,000 eggs and J2 per pot). The experimental design was completely randomized, in a 3 × 4 factorial scheme, with twelve replications. Two evaluations were done at 10 and 30 days after inoculation (DAI). Juvenile penetration in the roots was evaluated at 10 DAI and the number of females in the roots was estimated at 30 DAI. The survival rate was determined using both evaluations. Increasing initial density of H. glycines inoculum resulted in the increase of nematode final population in the susceptible cultivar, and the resistance reaction of soybean cultivars was not affected by the inoculum concentration. Penetration of J2 in the roots increased as inoculum density increased regardless of cultivar resistance or susceptibility. Nematode survival rate was greater in the susceptible cultivar.