BIOLOGICAL RELATIONSHIP OF MELOIDOGYNE-HAPLA POPULATIONS TO ALFALFA CULTIVARS

Greenhouse and growth chamber studies were established to determine if there are pathological and physiological differences among Meloidogyn e hapla populations from California (CA), Nevada (NV), Utah (UT), and Wyoming (WY) on alfalfa cultivars classified as resistant or susceptib le to root-knot nematodes. In the greenhouse, plant survival was nor c onsistent with resistance classifications. While all highly resistant Nevada Synthetic germplasm (Nev Syn XX) plants survived inoculation wi th all nematode populations, two cultivars classified as moderately re sistant ('Chief and 'Kingstar') survived (P less than or equal to 0.05 ) inoculation with M. hapla populations better than did 'Lobo' cultiva r, which is classified as resistant. Plant growth of Nev Syn XX was su ppressed by only the CA population, whereas growth of the other alfalf a cultivars classified as M. hapla resistant or moderately resistant w as suppressed by all nematode populations. Excluding Nev Syn XX, ail a lfalfa cultivars were severely galled and susceptible to all nematode populations. Except for Nev Syn XX, reproduction did not differ among the nematode populations on alfalfa cultivars. Nev Syn XX was not as f avorable a host to CA as were the other cultivars; but, it was a good host (reproductive factor [Rf] = 37). Temperature affected plant resis tance; the UT and WY populations were more pathogenic at 15-25 C, and CA was more pathogenic at 30 C. Nev Syn XX was susceptible to all nema tode populations, except for CA, at only 30 C, and all other alfalfa c ultivars were susceptible to all nematode populations at all temperatu res.