Host status and green manure effect of selected crops on Meloidogyne chitwoodi race 2 and Pratylenchus neglectus

The suitability of selected crops as hosts of Meloidogyne chitwoodi race 2 and Pratylenchus neglectus was evaluated in greenhouse and field microplots. Host status was based on reproductive factor (Rf = Pf/Pi). Sudangrass cv. Hidan 36 (Sorghum vulgare var. sudanense) and all oil radish (Raphanus sativus L.) cultivars were maintenance hosts (1 < Rf < 3). All buckwheat (Fagopyrum esculentum Moench) cultivars, rapeseed (Brassica napus L.) cv. Humus, sudangrass cv. Trudan 8 and cv. Sordan 79, horsebean (Canavalia ensiformis L.), velvetbean (Mucuna deeringiana Port.), castorbean (Ricinus communis L.), and corn (Zea mays L.) were either poor or nonhosts (Rf < 1) for M. chitwoodi. Most crops tested were either good hosts (Rf > 3) or maintenance hosts (1 < Rf < 3) for P. neglectus, but buckwheat cv. Tardo, horsebean, and velvetbean were poor hosts for P. neglectus. Stems and leaves of crops were incorporated as green manure into sterile soil in greenhouse pots. Pots were inoculated with M. chitwoodi race 2 (10 J2/cm(3) soil) and a 3-week-old tomato (Lycopersicon esculentum Mill.) seedling was planted and left to grow in each pot for 7 weeks. Incorporation of stem and leaf tissues of all crops reduced (P < 0.05) the total number of M. chitwoodi in pots compared to the control. Amending the soil with green manure residues of horsebean, velvetbean, castorbean, sudangrass cv. Hidan, rapeseed cv. Humus, corn, or oil radish cv. Trez more effectively reduced M. chitwoodi populations (79% to 94%) than either barley (77%) or tomato (68%). Buckwheat green manure was least effective in reducing nematode populations. The effect of oil radish cv. Trez and rapeseed cv. Humus as green manures in potato (Solanum tuberosum L.) crop rotations was investigated in field plots. Green manure crops were planted after harvest of wheat in mid August and incorporated as green manure in mid October. Potato was planted the following spring. Fall fallow treatments were included as a standard. After green manure incorporation and before planting potato, nematode population densities declined in all plots. However, plots planted to oil radish had significantly lower nematode population densities than fallow. During the subsequent growing season, M. chitwoodi soil populations increased on potato in all plots, but green manure plots had lower (P < 0.05) nematode populations than fallow plots. Soil population densities of P. neglectus did not change in any plot. Green manure treatments increased yield of marketable potatoes by 106-185%, and reduced M. chitwoodi tuber infection compared to fallow.