Evaluation of Soybeans in Maturity Groups I-IV for Resistance to Heterodera glycines.
Forty-seven private and public soybean (Glycine max) cultivars in maturity groups I, II, III, and IV were evaluated in the field for resistance to Heterodera glycines race 3 and race 4 at two sites, Kilbourne and Urbana, Illinois. The soil at Kilbonrne was an irrigated sand infested with race 3. The soil at Urbana was a nonirrigated silty clay loam infested with race 4. Yield of nematode-susceptible controls was reduced at both locations, and yield differences were observed among the other cultivars. Soybeans grown in sand yielded less than the soybean grown in silty clay loam. Although populations of H. glycines recovered at planting were lower at Kilbourne than at Urbana, a greater percentage of loss in yield was associated with the sand at Kilbourne. Several soybean cultivars had a high level of resistance to both populations of H. glycines.
Distribution of Heterodera glycines Races in Illinois.
Because the race scheme for Heterodera glycines was expanded recently from 5 to 16 races, the occurrence and distribution of races in Illinois need clarification. Forty-four populations of H. glycines were collected from sites in 23 of the 88 infested counties. Populations were tested using the differential soybean lines Pickett 71, Peking, PI 88788, and PI 90763. Lee 68 and Williams 82 were used as standards. Seedlings were grown in 7.5-cm-d clay pots and inoculated with 1,000 eggs and second-stage juveniles obtained from H. glycines-infested field soil. Plants were maintained in a greenhouse at 22-28 C. After 1 month, the number of first-generation white females that developed on each differential was determined and the race of the population was designated. Twenty-eight populations were race 3, twelve were race 1, two were race 5, one was race 2, and one was race 4. Populations of races 3 and 1 were widely distributed in the state. In 26 of the 28 race determinations, race designations using Williams 82 and Lee 68 were the same, indicating that if Lee 68 is not available, Williams 82 may be a suitable alternative for race tests done in the north central United States.
Interactions between Meloidogyne incognita, M. hapla, and Pratylenchus brachyurus in Tobacco.
In a greenhouse pot experiment on the pathogenicity and interactions of Meloidogyne incognita, M. hapla and Pratylenchus brachyurus on four cultivars o f tobacco the cultivars 'Hicks' and 'NC 2326' were susceptible to each nematode and "NC 95' and 'NC 2512' resistant only to M. incognita.Mean heights of susceptible plants were depressed but fresh weight of tops did not differ significantly. Meloidogyne spp. increased fresh weight of susceptible (but not the resistant) roots.Reproduction of M. incognita was decreased in the presence of P. brachyurus in one case. M. hapla reproduction was less with either of the other nematodes in five out of eight cases. In 12 combinations involving P. brachyurus, reproduction of this species was depressed in seven, not affected in four and increased in one.Mechanisms involved in associative interactions were not identified but appeared to be indirect and to involve individual host-nematode responses.