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.
Field Response of Soybean in Maturity Groups III-V to Heterodera glycines in Kansas.
Soybean cultivars from maturity groups III-V were grown in Heterodera glycines-infested locations in northeastern and southeastern Kansas from 1991 through 1994. Yield performance and nematode reproduction were significantly (P <0.01) affected by host response to H. glycines and year, whereas effects of cultivars within host response categories and cultivar x year interactions were generally negligible. In northeastern Kansas, H. glycines-susceptible cultivars from maturity groups III-IV yielded 8% less than resistant cultivars across years, whereas in southeastern Kansas, susceptible cultivars from maturity groups IV-V yielded 38% less than resistant cultivars across years. Analyses of yield components suggested that number of pods per plant accounted for most of the differences in seed yields. Heterodera glycines reproduction rates (final population density/initial population density) averaged 0.7 and 1.3 for resistant cultivars and 8.7 and 15.9 for susceptible cultivars in northeastern and southeastern locations, respectively. Results indicated that the relative performance of resistant and susceptible cultivars can be reliably predicted based on preplant egg densities across most environments in eastern Kansas.
Interacting Effects of Soil Temperature and Type on Reproduction and Pathogenicity of Heterodera schachtii and Meloidogyne hapla on Sugarbeets.
In central Washington, Heterodera schachtii Schmidt (the sugarbeet cyst nematode) is associated with sugarbeets (Beta vulgaris L.) growing in fine-textured soils, and Meloidogyne hapla Chitwood (the nor thern root-knot nematode) is associated with sugarbeets growing in coarse-textured soils. T h e opt imum soil temperature for reproduct ion on sugarbeets is between 21 and 30 C for H. schachtii (2, 7, 8, 9, 11, 12) and between 24 and 30 C for M. hapla (unpublished). In 1975-77 temperatures 8-10 inches deep in several sugarbeet fields seldom exceeded 20 C during the growing season (March-October). Despite those relatively low soil temperatures, H. schachtii and M. hapla are important pathogens on sugarbeets in Washington. This study was undertaken to determine any relation between soil temperature and soil type on the reproduct ion and pathogenicity of H. schachtii and M. hapIa on sugarbeets. Preliminary results have been reported (10). H. schachtii was cultured on sugarbeets and M. hapla on tomato. Nematodes for inoculum were extracted by placing H. schachtii cysts and M. hapla-infected roots under mist for 24-48 hr. Inocnlations were made by pipett ing the desired number o[ nematodes into 50 ml of water and pouring the water around the plant roots. Sugarbeet seeds (U 8~ I Hybr id 8) were planted in methyl-bromide-fumigated silt loam (28.2% sand, 45.4~. coarse silt, 5.0% fine silt, 21% clay) or sandy loam (72.4% sand, 20.8% coarse silt, 1.8% fine silt, 5.0% clay) soil in l-liter plastic containers. T h e containers were placed in temperature-controlled water