Infectivity of pine and eucalypt isolates of Pisolithus tinctorius (Pers.) Coker & Couch on roots of Eucalyptus urophylla S. T. Blake in vitro

SUMMARY An ultrastructural comparison of early stages of mycorrhiza formation on Eucalyptus urophylla was carried out using two isolates of P. tinctorius, one cultured from a sporocarp collected under pine and the other cultured from a sporocarp collected under eucalypt. Major differences at the fungus–root interface were observed 2 and 4 d following inoculation. Eucalypt root cells in contact with the isolate from pine developed a thickened cell wall, whereas the isolate from eucalypt was associated with an accumulation of extracellular fibrils. The fibrils stained positively for carbohydrates and protein. They were absent with the isolate from pine. Four days after inoculation with the isolate from eucalypt, acid phosphatase activity was detected along the fungal plasmalemma at the interface with host cells. This enzyme activity was not detected with the isolate from pine. Vacuolar acid phosphatase activity was detected in both fungal isolates when in contact with Eucalyptus roots. It is suggested that host recognition of ectomycorrhizal symbionts can be manifested within hours of inoculation with the fungal partner.