Abstract: Based on the former study related to the reproduction and impact on hypha growth of three dominant nematode species isolated from edible mushroom growing substance, the effect of nematode density (5, 10, 20, 40, 80, 160 individuals per tube) on hypha growth of Auricularia auricular was investigated to find out the quantity threshold. The results showed that there was no obvious difference in hypha appearance of Auricularia auricular, compared with the control with the nematodes, Mesorhabditis sp. at the density of 5 and 10 individuals per tube after 2 weeks of inoculation. The amount of reproduction were 40 and 255 individuals per tube, respectively. The hypha appearance of A. auricular was slightly different after 3 weeks of inoculation. With the nematodes of Acrobeloides sp. and Aphelenchoides composticola Franklin at the density of 5 individuals per tube after 2 weeks of inoculation, the hypha appearance became yellow. The amount of reproduction were 55 and 93 individuals per tube, respectively. After 3 weeks, the hypha became brown, and half of it was bitten. The hypha was seriously affected at the tested densities of more than 20 individuals per tube of all the three species of nematodes. The hypha was bitten up almost after 3 weeks of inoculation. Therefore, for mushroom production, the amount of above 3 nematodes should be less than 5 individuals per tube (about 8 individuals per 100 g) in mushroom growing substance．

Key words: nematode, quantity threshold, edible mushroom substance, Auricularia auricular, hypha