Impacts of Sunnhemp and Piegon Pea on Plant-Parasitic Nematodes, Radopholus similis and Meloidogyne spp., and Beneficial Bacterivorous Nematodes

Abstract

Plant-parasitic nematodes such as burrowing nematode (Radopholus similis) and root-knot nematode (Meloidogyne spp.) are dominant in the banana, Musa spp., ecosystem.  Beneficial nematodes such as bacterivores are also found in banana fields. A tropical cover crop, sunn hemp (Crotalaria juncea) (SH), can be used to suppress plant-parasitic nematodes and enhance beneficial bacterivorous nematodes. However, SH cultivation in Hawaii is under the threat of the flour beetle.  Thus, two experiments: Trial-I and Trial-II were conducted to compare the effects of another tropical cover crop, pigeon pea (Cajanus cajan) (PP) with SH and no-cover crop control (CC) on R. similis and Meloidogyne spp. suppression and beneficial bacterivorous nematodes enhancement. In both experiments soils infested with R. similis and Meloidogyne were sampled and amended with cover crop treatments (SH or PP) or CC and kept for two weeks. At the end of each experiment, nematodes were extracted through the Baermann funnel technique. The results of Trial-I and Trial- II showed that SH and PP did not reduce R. similis number (P > 0.05). However, Meloidogyne numbers were reduced by SH and PP in Trial-I (P < 0.05).  In Trial II, Meloidogyne was not found in SH and PP. In both experiments, SH consistently increased beneficial bacterivorous nematodes number (P < 0.05). Cover crop PP increased beneficial bacterivorous nematode numbers in Trial -I (P < 0.05), but not in Trial –II (P > 0.05).  However, the trends associated with the numbers of beneficial nematodes were consistently higher in PP compared to CC. Farmers could choose PP as an alternate to SH, as a cover crop for Meloidogyne suppression and beneficial nematode enhancement.