Greenhouse and growth chamber studies were conducted to determine the pathological relationship of ectoparasitic nematodes on crested wheatgrass (Agropyrom cristatum and A. desertorum) cultivars. Crested wheatgrass cultivars, 'Hycrest, 'Fairway, and 'Nordan, were parasitized by Merlinius brevidens, Tylenchorhynchus acutus, and Xiphinema americanum under greenhouse conditions. Merlinius brevidens and T. acutus were more pathogenic than X. americanum on all grasses. Dry shoot weights of Fairway and Nordan were reduced (P 0.05) at Pi of 1.0 and 2.0 nematodes/cm soil, whereas shoot growth of Hycrest was reduced only at 2.0 nematodes/cm soil. Root growth of all cultivars was reduced by the 3 nematode species at both levels of inoculum with the greatest reductions at 2.0 nematodes/cm soil. The nematode reproductive factors (Rf = final nematode population/initial nematode population) were similar for M. brevidens and T acutus, whereas the X. americanum population did not reproduce on any c
