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SOYBEAN

Response of Old and New Soybean Cultivars to Heterodera glycines Ichinohe

Dep. of Agronomy, Iowa State Univ., 2104 Agronomy Hall, Ames, Iowa 50011-1010

^* Corresponding author (jsndbrn{at}iastate.edu).

Soybean [Glycine max (L.) Merr.] cyst nematode (Heterodera glycines Ichinohe; SCN) causes significant yield loss each year. New cultivars (released since 1997) have superior yield compared with older cultivars (released between 1938 and 1983), but responses to SCN have not been evaluated. Studies were established at three locations in Iowa for 2 yr to measure yield loss of 23 cultivars that differed in year of release and SCN resistance in locations with varying SCN population density and Heterodera glycines Type (HG Type). Initial SCN population densities (Pi) were <1000 eggs 100 cm^–3 (HG Type 2.7) at Whiting, between 1000 and 4000 eggs 100 cm^–3 (HG Type 1.2.5.7 and 2.5.7) at Nevada, and between 4000 and 12,500 eggs 100 cm^–3 (HG Type 0 and 7) at De Witt in 2005 and 2006. Analysis of simple effects from year x location interactions consistently showed that new SCN-resistant cultivars had lower final SCN population densities (Pf) and reproduction factors (Rf) compared with old and new SCN-susceptible cultivars. Among all locations, seed yield of new SCN-resistant cultivars was 14% greater than new SCN-susceptible cultivars and 32% greater than old SCN-susceptible cultivars. Yield increase was a result of increased seed production (seeds m^–2) and not from a change in seed mass. Yield of new SCN-susceptible cultivars was 18% greater than old SCN-susceptible cultivars but did not provide greater control of SCN. These data indicate that yield increases with new SCN-susceptible cultivars are not the result of improved SCN management. Data support the selection of SCN-resistant cultivars for fields in which SCN has been identified, regardless of Pi or HG Type to increase yield and reduce SCN population densities.

Abbreviations: SCN, soybean cyst nematode • HG, Heterodera glycines • Pi, initial SCN population density • Pf, final soybean cyst nematode population density • Rf, reproduction factor

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Received for publication July 9, 2008.