A mechanistic approach to assessing the potential for cover crops to serve as trap crops for the soybean cyst nematode
The effects of cover crops on the biology of the soybean cyst nematode (SCN), Heterodera glycines, are not well established. It is possible that cover crops may reduce SCN population densities by acting as trap crops. Cover crops with potential to serve as trap crops may stimulate hatching and/or attract hatched SCN juveniles and also may be penetrated by large numbers of nematodes that cannot feed. Experiments were conducted to determine if root exudates and soil leachates (RE+SL) from various cover crop plants affected SCN hatching and chemotaxis and if there were significant differences in SCN juvenile root penetration among different cover crop plant types. In fourteen-day-long hatching experiments, there was greater SCN hatching in crimson clover (Trifolium incarnatum) RE+SL than in RE+SL from all other cover crop treatments in the experiments. No other cover crop RE+SL significantly affected hatching. In chemotaxis experiments, SCN juveniles were attracted to RE+SL from annual ryegrass (Lolium multiflorum) and cereal rye (Secale cereal) after 24 hours. In greenhouse experiments, significantly more SCN juveniles penetrated the roots of single cultivars of crimson clover, mustard (Brassica juncea), and rapeseed (Brassica napus) than 11 other cover crop species/cultivars evaluated in the experiment over the course of 20 days. Few SCN juveniles penetrated the roots of annual ryegrass and cereal rye. The results suggest crimson clover, grown as a cover crop, has the most potential to act as a trap crop for SCN. Cover crop plants may affect SCN biology in ways other than the mechanisms investigated in these experiments.