Soybean cyst nematode population development and associated soybean yieldsof resistant and susceptible cultivars in Minnesota

The soybean cyst nematode (SCN), Heterodera glycines, is a major soybean yi eld-limiting factor, and the use of resistant cultivars is one of the most effective means to manage the nematode. During the past decade, a number of resistant cultivars in maturity groups I and II have been developed and ma de available to growers. A total of 47 resistant cultivars and nine suscept ible cultivars were evaluated at 15 SON-infested field sites and two noninf ested sites during 1996 to 1998 in Minnesota. As expected, more nematodes d eveloped on susceptible cultivars than on resistant cultivars. Egg density on susceptible cultivars increased by 1.9- to 10.6-fold during the growing season at 12 sites and did not change at the other three sites. Average egg density decreased over time for resistant cultivars at all sites, except w here the initial egg density was low (less than or equal to 455 eggs per 10 0 cm(3) soil). Nematode reproduction factors (Rf = egg density at harvest/e gg density at planting) for individual resistant and susceptible cultivars were highly consistent across the eight sites where initial SCN density was more than 1,000 eggs per 100 cm(3) soil. Resistance, however. varied among the cultivars, with the average Rf of individual resistant cultivars acros s the sites ranging from 0.3 to 1.7. Resistant cultivars produced an averag e yield of 3,082 kg/ha compared with 2,497 kg/ha by susceptible cultivars a t eight of 10 sites where egg density at planting was greater than 700 eggs per 100 cm(3) soil. In contrast, no difference in yield was observed betwe en resistant and susceptible cultivars at sites where egg density at planti ng was lower than 500 eggs per 100 cm3 soil. Yield differences between resi stant and susceptible cultivars increased with increasing initial SCN egg d ensity. In six fields infested with initial densities of more than 5,000 eg gs per 100 cm(3) soil, resistant cultivars produced 28.4% (676 kg/ha) more yield on average than susceptible cultivars. Soybean yield increased when c ultivars with increasing resistance to the SCN (lower Rf or females formed on roots) were grown in fields infested with SCN. Average relative yield (y ield of a cultivar/average yield of all resistant cultivars at a site) of i ndividual resistant cultivars across all SON-infested sites ranged from 0.7 6 to 1.10. Yield consistency of soybean cultivars was low among the differe nt sites, indicating that many other factors affected yield. Our results su ggest growing resistant cultivars is an effective method to manage SCN in M innesota while minimizing yield loss due to SCN.