In the presence of potato plants cv. Golden Wonder, Globodera pallida exhibited delayed in-soil hatch compared to that of G. rostochiensis, with significantly fewer G. pallida second-stage juvenile nematodes hatching in the first two weeks, though the difference disappeared after four weeks. Inoculation of potato plaits with arbuscular mycorrhizal fungi eliminated this delay in G. pallida hatch, so that the two potato cyst nematode (PCN) species exhibited similar in-soil hatch rates. When the corresponding in vitro hatching activities of root leachate from uninoculated and mycorrhiza-inoculated plants were compared, similar effects were revealed. G. pallida hatch in root leachates from uninoculated plants increased significantly from one-week-old to two-week-old plants, but this increase was not significant in the mycorrhizal-inoculated plants. When the in-soil experiment was repeated using the potato cyst nematode non-host plant strawberry, mycorrhizal inoculation induced no significant increase in G. pallida hatch. The results indicate that mycorrhizal inoculation of potato plants stimulates production of G. pallida-selective hatching chemicals, either hatching factors or hatching factor stimulants. (C) 2000 Elsevier Science B.V. All rights reserved.