Interrelationship of Meloidogyne hapla and Ditylenchus dipsaci on Resistant and Susceptible Alfalfa.

Simultaneous inoculations of alfalfa with Meloidogyne hapla larvae and Ditylenchus dipsaci at 16, 20, 24, and 28 C did not depress penetration of either nematode in 'Nev Syn XX' -a selection resistant to M. hapla and D. dipsaci, 'Vernal 298' -a selection resistant to M. hapla and susceptible to D. dipsaci, 'Lahontan' -a cultivar resistant to D. dipsaci and susceptible to M. hapla, and 'Ranger' -a cultivar susceptible to both M. hapla and D, dipsaci. Infection with D. dipsaci depressed growth of susceptible 'Vernal 298' and 'Ranger' at all soil temperatures, except for 'Vernal 298' at 16 C. Infection with M. hapla alone did not depress growth of any of the alfalfas. A combination of M. hapla and D. dipsaci resulted in a synergistic weight depression on 'Ranger' at all soil temperatures. Inoculation of the four alfalfas with D. dipsaci 2, 4, 6, and 8 wk before inoculation with M. hapla at 16, 20, 24, and 28 C did not influence the resistance or susceptibility of 'Nev Syn XX,' 'Lahontan,' or 'Ranger.' However, galling of 'Vernal 298' by M. hapla was affected by soil temperature, plant age, and inoculation with D. dipsaci.