Root-Knot Nematode Resistant Cowpea Cover Crops in Tomato Production Systems

Received for publication November 29, 2004. Root-knot nematodes, Meloidogyne spp., are serious pests of many crops worldwide. Recent limitations on the use of nematicides have enhanced the need to develop alternative management strategies, including host plant resistance. This study was conducted to determine the effectiveness of nematode-resistant cowpea [Vigna unguiculata (L.) Walp.] genotypes used as cover crops for suppressing populations of M. incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood and protecting susceptible tomato (Lycopersicon esculentum Mill.) grown in rotation. In six field experiments, susceptible and resistant cowpea was grown to flowering stage and the dried tops incorporated or not incorporated into the soil. These treatments were compared to wet and dry fallowing and were conducted on nematode-infested and noninfested plots. The experiments were conducted in the Coachella and San Joaquin Valleys, California. Resistance conferred by genes Rk and Rk2 reduced loss of cowpea biomass and M. incognita soil populations and partially suppressed M. javanica compared with susceptible cowpea, but not as effectively as fallow treatments. Incorporation of cowpea tops into the soil promoted tomato growth irrespective of nematode presence. On infested plots, tomato fruit yield was higher following growth and incorporation of resistant cowpea compared with growth and incorporation of susceptible cowpea or nonincorporation of cowpea and fallow treatments. We conclude that root-knot nematode-resistant cowpea is an effective cover crop for protecting susceptible vegetable crops grown under irrigation, and its beneficial effects are enhanced by incorporation of its green biomass.