Abstract
Behm, J.E., G.L. Tylka, and S.R. Cianzio. 1996. Evaluations of soybean genotypes for tolerance to soybean cyst nematode. Phytopathology 86 (supplement):98.
Studies were conducted in noninfested and soybean cyst nemtode-infested fields to evaluate 19 susceptible soybean genotypes for tolerance to the nematode. Linear regression analyses of relative plot yield [RY = (individual plot yield/experiment mean yield)×100] versus log-transformed initial nematode egg densities revealed inverse relationships for all genotypes and significant differences among genotypes. Slope for susceptible 'CX366' (-6.16) did not differ from slope for resistant 'Jack' (-3.88); slopes for all other susceptible genotypes ranged from -7.40 to -12.09 and were less than that of 'Jack'. Tolerance indices derived from ratios of relative yield in infested versus noninfested fields ranged from 86.6 for 'Jack' to 67.6 for susceptible 'Sturdy' and were correlated (r2=0.85) with the regression slopes described above. For greenhouse evaluation of tolerance, each genotype was grown in 1.75-L pots infested with 0, 100, 500, 1,000, 2,000, or 4,000 soybean cyst nematode eggs per 100 cm3 potting mix, and plant growth parameters were assessed weekly for eight weeks. Significant inverse linear relationships between shoot dry weight and initial egg densities were detected for 13 genotypes, however, slopes were poorly correlated with regression slopes of field data.