SAPROPHYTIC AND PREDACIOUS ABILITIES IN ARTHROBOTRYS-OLIGOSPORA IN RELATION TO DEAD AND LIVING ROOT-KNOT NEMATODES

An adhesive hyphae forming isolate of Arthrobotrys oligospora clearly responded to the condition of its food source, i.e. living, inactivate d or dead second-stage juveniles (J2) of the root-knot nematode Meloid ogyne hapla. Second-stage juveniles (J2) immobilized by heating and on ly able to move the anterior region or the stylet, were surrounded by ring structures similar to fully mobile juveniles. However, ring struc tures were principally developed around the moving head. The fungus pe netrated dead, but intact J2 (obtained after treatment with gamma-irra diation or sodium azide), through its buccal cavity with a corkscrew-l ike structure. Dead J2 with a broken cuticle were totally overgrown by the fungus with thin vegetative hyphae. Evidently, the isolate of A. oligospora switched between nutritional modes while exploiting differe nt food sources. The saprophytic and predacious ability appeared not t o be mutually exclusive. Addition of dead juveniles to a fungal colony prior to live juveniles did not affect attachment or the development of trophic hyphae through the latter. But one day after addition of th e living juveniles, the proportion of live juveniles with ring structu res raised in comparison with all juveniles added at the same time. Th e development of trophic hyphae in killed J2 was delayed in the presen ce of live J2. The results refute the commonly held assumption that po or conditions for saprophytic growth are a prerequisite for a predacio us mode of feeding.