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 t o M. hapla was studied under greenhouse conditions. Inoculation with t he fungus alone caused plant mortality in the fungus-susceptible culti var 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 o f 12 cultivars. Combined inoculation of the two pathogens increased mo rtality in 10 of the 12 cultivars; only Nevada S Synthetic XX (Nev Syn XX) germplasm and Chief with dual resistance were unaffected by the a ddition 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 hapl a reduced dry shoot weights and reproduced on roots of all entries exc ept 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 fou r cultivars including Vernal and Deseret. Severity of PRR was lowest i n the resistant cultivar Kingstar and highest in the susceptible culti var Deseret. Overall, M. hapla increased the susceptibility of alfalfa to P. megasperma f. sp. medicaginis, but the fungus did not affect th e resistance or susceptibility to M. hapla.