Endophyte effects on reproduction of a root-knot nematode (Meloidogyne marylandi) and osmotic adjustment in tall fescue

In a 2 x 2 x 2 factorial experiment, plants of one genotype of tall fescue (Festuca arundinacea) were grown in soil in pots in a glasshouse on two occ asions. The treatments were either with (E+) or without (E-) infection by t he fungal endophyte Neotyphodium coenophialum; with (N+) or without (N-) in oculation by the root-knot nematode Meloidogyne marylandi; and with or with out water deficit stress. In the first experiment, nematode numbers after 5 weeks had increased 10 times in the E-/N- watered pots and 22 times in the E-/N+ stressed plants. Root dry weight was decreased in all E-/N+ pots, co mpared with E-/N-. In contrast, nematode numbers in all E+/N+ pots decrease d to nearly zero and root dry weight was unaffected. Osmotic adjustment in the growing zone of stressed plants was -0.35 MPa in E-/N- pots, but only - 0.10 MPa in E-/N+ pots. Osmotic adjustment was greatest (-0.64 MPa) in E+ p ots of both nematode treatments and almost no nematodes survived in the Npots. In the second experiment, there was complete nematode mortality in th e E+ pots. Plant water relations were unaffected by treatments, however. It is concluded that endophyte-enhanced persistence of tall fescue in M. mary landi-infested soils that are prone to drought may be explained at least pa rtly by endophyte protection of roots from nematode damage. Nematode inhibi tion by the endophyte may operate in addition to direct influences of the e ndophyte on enhancing drought tolerance of the host.