PATHOLOGICAL RELATIONSHIP OF MELOIDOGYNE-HAPLA AND PHYTOPHTHORA-MEGASPERMA F SP MEDICAGINIS IN 12 MEDICAGO-SATIVA L CULTIVARS

Effect of prior inoculation with Meloidogyne hapla on the performance of 12 cultivars of alfalfa (Medicago sativa) with varying resistance to M. hapla was studied under greenhouse conditions. Inoculation with the fungus alone caused plant mortality in the fungus-susceptible cultivar Deseret but not in susceptible Vernal. None of the P. megasperma f. sp. medicaginis-resistant cultivars died from Phytophthora root rot (PRR). Inoculation with M. hapla alone resulted in mortality in nine of 12 cultivars. Combined inoculation of the two pathogens increased mortality in 10 of the 12 cultivars; only Nevada S Synthetic XX (Nev Syn XX) germplasm and Chief with dual resistance were unaffected by the addition of the nematode. Inoculation with the fungus alone suppressed the dry shoot weight in four cultivars, including Vernal and Deseret, both susceptible to P. megasperma E. sp. medicaginis. Meloidogyne hapla reduced dry shoot weights and reproduced on roots of all entries except Nev Syn XX. Meloidogyne hapla reduced root weights of four of six alfalfa cultivars resistant to the nematode and five of six cultivars susceptible to the nematode. The fungus suppressed root weights in four cultivars including Vernal and Deseret. Severity of PRR was lowest in the resistant cultivar Kingstar and highest in the susceptible cultivar Deseret. Overall, M. hapla increased the susceptibility of alfalfa to P. megasperma f. sp. medicaginis, but the fungus did not affect the resistance or susceptibility to M. hapla.