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.
Effect of the rhg 1 Gene on Population Development of Heterodera glycines 1
The effect of the rhg1 gene on equilibrium population densities (E) and reproduction factors (Rf) of Heterodera glycines was studied by comparing the nematode population development on two near-isogenic soybean lines (NIL), differing at the rhg1 locus. The NIL were inoculated with a series of initial egg densities (Pi) in the greenhouse. The relationships between final population densities (Pf = females per plant or eggs per plant) or Rf (final egg density/Pi) on both NIL and Pi were adequately described by quadratic models. The rhg1 gene suppressed Pf and Rf at all Pi of a population of H. glycines race 3 (HG Type 0−); E and maximum Rf were higher on the NIL-S line than on the NIL-R line. After two generations of culture of the race 3 population on the NIL-R line, the population selected by the rhg1 gene (R-eggs) had higher Pf and Rf on the NIL-R line than the population cultured on the NIL-S line (S-eggs) at all Pi. Both R-eggs and S-eggs produced similar egg numbers on the NIL-S line, which was higher than the egg number of either population on the NIL-R line at all Pi. The ratio of E in female numbers on the NIL-R line to E on the NIL-S line increased from 29% for the original race 3 population (S-eggs) to 46% for the rhg1-selected population (R-eggs). Regardless of different egg sources, a trend of increase in the number of eggs per female with the rise of Pi was observed on the NIL-S line. In contrast, female fecundity of both populations declined with the increase of Pi on the NIL-R line. At most inoculum densities, the highest number of eggs per female was observed on the NIL-S line inoculated with the R-eggs, whereas the lowest number of eggs per female was detected on the NIL-R line inoculated with the S-eggs. This study demonstrated that the E and maximum Rf determined by the quadratic models are useful measurements of plant resistance to nematodes.
The Lunar Rocks
Book on lunar rocks covering pre-Apollo lunar scientific knowledge, Apollo and future lunar mission planning, lunar mineralogy, petrology and geochemistry, etc