Breeding soybean for resistance to iron-deficiency chlorosis and soybean cyst nematode

Iron-deficiency chlorosis (IDC) and soybean cyst nematode (SCN) result in yield and income losses for soybean growers in the U.S. Breeding programs are identifying soybean genotypes with resistance to IDC using calcareous soils infested with SCN, where SCN might interfere with evaluation. Our first objective was to examine whether associations could be established for chlorosis symptoms with SCN infestation of soybean grown on SCN-infested calcareous soils. Two breeding populations, their parents, and five SCN-susceptible, IDC-control genotypes (IDC controls) were evaluated for IDC symptoms on SCN-infested calcareous soils in 2000 and 2001. In general, no significant correlations were detected between chlorosis expression and SCN infestation in either year, although a negative correlation (r = - 0.93, p less than or equal to 0.05) was observed for the IDC controls in 2001. For our second objective, we examined the relationship between genotype resistance to SCN and IDC. Although IDC controls were all equally susceptible to SCN and chlorosis observed in the field and nutrient solution was similar, SCN-resistant genotypes expressed resistance to IDC in the field, but severe susceptibility to IDC in nutrient solution. Our third objective was to investigate the value of calcareous soil properties to predict IDC in soybean grown on SCN-infested calcareous soils. For one breeding population in 2001, positive correlations (p less than or equal to 0.05) were detected for chlorosis with calcium carbonate (r = 0.62) and electrical conductivity (r = 0.59), and a negative correlation (r = -0.41) with soil Fe-DTPA-TEA. No significant correlations were observed for the remaining genotypes. Our study indicated that associations between IDC, SCN, and calcareous soil properties are dependent on genotype and environment. In addition, our study demonstrated a potential association between plant health and SCN reproduction in SCN-susceptible genotypes, the possibility that SCN-resistant genotypes may be sensitive to iron availability, and the importance of genotype on the detection of associations between IDC expression and SCN infestation.