The effect of rhg1 on reproduction of Heterodera glycines in the field and greenhouse and associated effects on agronomic traits

The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) continues to be the most damaging soybean pest [Glycine max (L.) Merr.] in the USA. A major gene that provides partial resistance to SCN is rhg1, which is located on linkage group (LG) G. The objectives of this study were to test the effect of rhg1 on SCN reproduction in both the field and greenhouse and on agronomic traits in the field. Two populations of near isogenic lines (NILs) that segregated for rhg1 were developed to test the effect of the gene. These NIL populations were tested for their ability to support SCN cyst development in a thermo-regulated water bath in a greenhouse and egg production estimated from soil samples taken from each plot in field tests. The NIL populations were evaluated for agronomic traits in field plots to determine the associated effects of rhg1 on these traits. In the greenhouse, NILs predicted to be carrying the resistance allele for rhg1 on the basis of a linked marker supported significantly (P < 0.01) fewer cysts than NILs carrying the susceptibility allele. In field tests, the final egg population density (Pf) was significantly lower and there was a smaller reproductive rate (Rf) in NILs carrying the resistance allele at rhg1 than susceptible NILs for both populations across and within environments in 2003. In only one population did the resistant NILs out-yield the susceptible NILs, and this occurred only when the initial SCN pressure was high [> 500 SCN eggs (100 cm(3)soil)(-1)]. These results show that resistance at rhg1 can have a large effect on SCN reproduction and may result in a significant yield increase.