SummaryCommercially available sorghum cultivars were tested for resistance to Meloidogyne incognita in order to select cultivars that combine fodder production with M. incognita population management. Initially in a pot test with 12 sorghum cultivars, ‘Kyushuko 3 go’, a sorghum hybrid, supported very low M. incognita reproduction approximately 40 days after inoculation (dai) with 500 second-stage juveniles (J2) pot−1, similar to the resistant green manure ‘Tsuchitaro’. Further tests for development of M. incognita in roots (20 dai with 150 J2 (root system)−1) indicated that the resistance of ‘Kyushuko 3 go’ acts after nematode root penetration. In field tests in 2015 and 2016, ‘Kyushuko 3 go’ suppressed M. incognita population densities, although some variations in field conditions may influence reproduction of M. incognita on ‘Kyushuko 3 go’. These findings demonstrated M. incognita-resistant fodder sorghum cultivars could be a useful alternative to susceptible cultivars for root-knot nematode management.

Solanum torvum, a wild Solanum species, is widely used as a rootstock and is known for its resistance to several pathogens and pests including root‐knot nematode (RKN, Meloidogyne spp.). Virulence to S. torvum was observed in several Meloidogyne species such as M. hapla, but M. hapla populations isolated from Japan have not been tested for parasitism. We performed inoculation assays on S. torvum cultivars and control plants (S. melongena, eggplant; S. lycopersicum, tomato) inoculated with Japanese M. hapla populations, and we then evaluated the host suitability based on the eggmass number. The assays were carried out using nursery plants in small plastic pots. The first assay revealed that S. torvum cultivars that are commercially available in Japan were susceptible to M. hapla. In the second assay, three M. hapla populations obtained from geographically distant areas produced a number of eggmasses on S. torvum roots. The S. torvum cultivars were all resistant to M. incognita, as a control species of Meloidogyne, in both assays. Our examination of the number of eggs per eggmass of M. hapla demonstrated that the values of S. torvum under inoculation of two M. hapla populations were significantly lower than those of S. lycopersicum, implying some difference in the fecundity of M. hapla depending on the host plants. The series of experiments revealed the virulence and reproductivity of Japanese M. hapla populations to S. torvum, posing a potential risk that S. torvum cannot suppress RKN damage in agricultural fields under infestation of such Meloidogyne species.

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Summary The suppressive effect of a black oat, Avena strigosa, breeding line KH1a on Meloidogyne spp. was examined in pot tests and on Meloidogyne incognita in pot and field tests. In pot tests, roots of black oats were examined 42-46 days after inoculation of 500 second-stage juveniles. There were significantly fewer egg masses on the roots of KH1a than on 12 black oat cultivars examined. KH1a was a poor host for four isolates of M. incognita, two isolates of M. arenaria and one isolate of M. javanica, and a non-host for one isolate of M. hapla. The effect of autumn and spring cropping of KH1a on soil nematode density was examined in M. incognita-infested fields. Nematode density after autumn cropping of KH1a was significantly lower than that after susceptible black oat, resulting in significantly lower Pf/Pi in KH1a (0.10 and 0.13) than in susceptible black oat (0.42 and 0.74). Damage indices of the succeeding crop, sweet potato, were significantly lower in KH1a plots than in susceptible black oat plots. In spring cropping, there were significantly fewer soil nematodes in KH1a plots than in susceptible black oat plots 3 weeks after cultivation. In both autumn and spring cropping, there was no significant difference in soil nematode density between KH1a and bare fallow. These results suggested that KH1a is a good alternative to current susceptible cultivars for the management of M. incognita.

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