Pectic Zymograms and Water Stress Tolerance of Endophytic Fungi Isolated from Western Australian Heaths (Epacridaceae)

Abstract

Forty-nine isolates of root-inhabiting fungi were obtained from thirteen species of eleven genera of native Epacridaceae and compared in relation to host taxonomy and habitat of origin. Pectic zymograms of extracts of the cultured endophytes showed a marked degree of homogeneity of banding patterns amongst isolates from a mesic wetland site, whereas those from dryland habitat displayed more heterogenous banding. It is speculated that host species can operate with only a limited number of fungal associates under mesic conditions but require a higher degree of endophyte variation when combating dry and impoverished environments. Considerable distinction between the geographically diverse endophytes isolated from the common host Lysinema ciliatumsuggested that selection of endophytes was not driven primarily by host taxonomy. Ascribing functional significance to the observed differences between endophytes was studied by examining responses of cultured isolates to polyethylene glycol induced-water stress covering a range of potentials from -0.16 to -2.96MPa. Three response types were observed: ( a) the isolate produced minimal radial growth at all water potentials tested, ( b) maximum growth of the isolate occurred under least water stress, with progressive suppression of radial extension with decreasing water potential and ( c) maximum growth of the isolate occurred under a degree of water stress. The broad range of responses to water stress observed was suggested to reflect the diverse habitat tolerance displayed by epacrids and their endophytic partners in south west Australia.