Brassicaceous seed meals as soil amendments to suppress the plant-parasitic nematodes Pratylenchus penetrans and Meloidogyne incognita.

Brassicaceous seed meals are the residual materials remaining after the extraction of oil from seeds; these seed meals contain glucosinolates that potentially degrade to nematotoxic compounds upon incorporation into soil. This study compared the nematode-suppressive ability of four seed meals obtained from Brassica juncea 'Pacific Gold', B. napus 'Dwarf Essex' and 'Sunrise', and Sinapis alba 'IdaGold', against mixed stages of Pratylenchus penetrans and Meloidogyne incognita second-stage juveniles (J2). The brassicaceous seed meals were applied to soil in laboratory assays at rates ranging from 0.5 to 10.0% dry w/w with a nonamended control included. Nematode mortality was assessed after 3 days of exposure and calculated as percentage reduction compared to a nonamended control. Across seed meals, M. incognita J2 were more sensitive to the brassicaceous seed meals compared to mixed stages of P. penetrans. Brassica juncea was the most nematode-suppressive seed meal with rates as low as 0.06% resulting in > 90% suppression of both plant-parasitic nematodes. In general B. napus 'Sunrise' was the least nematode-suppressive seed meal. Intermediate were the seed meals of S. alba and B. napus 'Dwarf Essex'; 90% suppression was achieved at 1.0% and 5.0% S. alba and 0.25% and 2.5% B. napus 'Dwarf Essex', for M. incognita and P. penetrans, respectively. For B. juncea, seed meal glucosinolate-degradation products appeared to be responsible for nematode suppression; deactivated seed meal (wetted and heated at 70 °C for 48 hr) did not result in similar P. penetrans suppression compared to active seed meal. Sinapis alba seed meal particle size also played a role in nematode suppression with ground meal resulting in 93% suppression of P. penetrans compared with 37 to 46% suppression by pelletized S. alba seed meal. This study demonstrates that all seed meals are not equally suppressive to nematodes and that care should be taken when selecting a source of brassicaceous seed meal for plant-parasitic nematode management.