IRRIGATION OF SOYBEAN CULTIVARS SUSCEPTIBLE AND RESISTANT TO SOYBEAN CYST NEMATODE

Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) infests soils throughout the mid and lower Mississippi River Valley and the southeastern Coastal Plain in the USA, a region where irrigation is widely practiced. This study was conducted to determine the effect of irrigation on number of SCN cysts and seed yield of three soybean [Glycine max (L.) Merr.] cultivars that have varying levels of SCN resistance when grown in monoculture on SCN-infested Dundee silt loam (fine-silty, mixed, thermic, Aeric Ochraqualf) that has a perched water table. Cultivars (all MaturitY Group V) were Forrest (resistant to SCN Race 3), A5474 (resistant to SCN Races 3 and 4), and Bay (susceptible to SCN). Bay was grown with and without nematicide applied after planting. Irrigation treatment was either with or without supplemental water during reproductive development of soybean. Neither seed yield nor number of SCN cysts at planting or harvest were significantly (P = 0.05) affected by irrigation on this soil. Application of nematicide to Bay plots reduced the number of SCN cysts at harvest, but did not significantly affect seed yield. Number of SCN cysts was lowest in A5474 plots, and seed yield of A5474 was highest in the second and third year of the study. Irrigation did not significantly interact with cultivar or nematicide to affect cyst number or seed yield. We conclude that irrigation during reproductive development of soybean did not affect (i) cultivar response to infection with SCN, (ii) the capability of SCN to maintain cysts on any cultivar, or (iii) the yield-limiting effect of SCN on susceptible cultivars. This suggests that SCN effects on soybean are more complex than simply restricting water uptake by roots.