Recovery of Phytophthora Cinnamomi From Naturally Infected Jarrah Roots.

Are jarrah (Eucalyptus marginata)trees killed byPhytophthora cinnamomior waterlogging?

“…I Jarrah deaths are caused by P cinnamomi. This hypothesis is supported by the association of deaths with infested sites (Podger et al 1965, Podger 1968, Podger 1972, by the isolation of P cinnamomi from extensive lesions on large roots and at the root collar, and on vertical roots of dying trees (Dell and Wallace 1981, Shearer et al 1981, Shea et al 1982. Although early investigations failed to find such lesions (Harding 1949, Stahl andGreaves 1959), this might have been because tree excavations were not sufficiently thorough.…”

“…There were also investigations of isolated dying jarrah trees. Dell and Wallace ( 1981) and Shearer et at. ( 1981) showed that P. cinnamomi could be isolated from cankers and from adjacent xylem, on large roots and at the stem base.…”

“…Although early investigations failed to find such lesions (Harding 1949, Stahl andGreaves 1959), this might have been because tree excavations were not sufficiently thorough. Jarrah deaths result from severe water deficits, and in dying trees with extensive lesions, P. cinnamomi can be isolated from the root and stem xylem (Dell and Wallace 1981, Shearer et al 1981, Shea et al 1982, so extensive xylem infection could be the cause of severe water deficiency (Shea et al 1982). But when jarrah stems and roots are wound inoculated with P. cinnamomi, the main tissue invaded is the inner bark not the xylem (Tippett et al 1983) and, at least initially, there is no inhibition of sap flow adjacent to an infection (Davison et al 1994).…”

Predictions of where minimal damage to jarrah roots could result in tree death

“…extensi\e lesions on vertical roots (Shea et al, 1982) or lesions at the root collar and stem base (Dell & Wallace, 1981 ;Shearer el al., 1981).…”

“…known locally as dieback sites, can be recognized by Podger (1972) proposed that jarrah deaths resulted tbe death of many mid-and understorey plant from fine root necrosis caused by P. cinnamomi, species (Podger, 1972). On these sites jarrah too whilst others have suggested that deaths result from might be affected, and symptoms in this species extensive infections on vertical roots (Shea et al, include gradual dying back ofthe crown, or sudden 1982) or at the root collar and stem base (Dell & wilting and death of groups of trees (Podger, 1972;Wallace, 1981;Shearer, Shea & Fairman, 1981). In Shearer & Tippett, 1989).…”