Suppressive effects of root-knot nematode-suppressive black oat ‘KH1a’ on root-lesion nematodes, Pratylenchus penetrans and P. coffeae, were examined in inoculation and field tests. Results of inoculation tests indicated that ‘KH1a’ was as poor a host for P. penetrans as black oat ‘Hay oats’, which is a common P. penetrans-suppressive green manure crop in Japan. In field tests, ‘KH1a’ reduced soil P. penetrans density significantly lower than bare fallow and the effect was not different from those of ‘Hay oats’ or ‘Saia’. These results indicated that ‘KH1a’ can be used as a P. penetrans-suppressive crop like ‘Hay oats’ and ‘Saia’. Although ‘KH1a’ and ‘Hay oats’ were poor hosts also for P. coffeae in inoculation tests, field nematode densities after cultivation of these black oats were not significantly different from that after bare fallow, indicating that the suppressive effects of these black oats on P. coffeae were not comparable to those on P. penetrans.
