RELATIONSHIP BETWEEN MELOIDOGYNE-INCOGNITA AND ROTYLENCHULUS-RENIFORMIS AS INFLUENCED BY SOYBEAN GENOTYPE

The effect of soybean genotype on competition between Meloidogyne inco gnita race 2 (Mi) and Rolylenchulus reniformis (Rr) was evaluated in g reenhouse and microplot replacement series experiments. Soil in pots c ontaining seedlings of 'Davis' (susceptible to Mi) or 'Buckshot 66' (r esistant to Mi) was infested with 1,000 vermiform individuals in the f ollowing Mi:Rr ratios: 0:0, 100:0, 75:25, 50:50, 25:75, or 0:100. Afte r 91 days, the relative nematode yields (number of nematodes in mixed culture divided by the number in nonmixed culture) of each species wer e calculated based on soil and root nematode populations expressed as nematodes per gram of dry root tissue. To define the relationship betw een the two species, calculated relative nematode yields were compared with a theoretical noncompetition model using lack-of-fit regression. In the greenhouse, Mi populations on 'Davis' were stimulated in the p resence of Rr. In microplots, low Mi and Rr population densities likel y resulted from severe galling and destruction of feeder roots that pr obably occurred early in the season. Enhanced susceptibility to Mi was not observed on 'Buckshot 66', which remained resistant to hii even w hen colonized by Rr. Host resistance is a key factor in determining th e nature of the relationship between Mi and Rr.