School of Agriculture, Food and Ecosystem Sciences - Theses

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Cercosporoid fungi on Australian native plants

Beilharz, Vyrna Caldwell ( 1994-05)

Pseudocercospora is currently separated from Cercospora largely on the basis of its unthickened scars. The principal aim of this study was to test the validity of this criterion by studying the ultrastructural characteristics of scars of cercosporoid fungi growing on Australian native plants. Transmission electron microscope studies demonstrated considerable variation in scar morphology among species of Pseudocercospora. Scars varied from substantially thickened (as in P. loranthi) to unthickened (as in P. correae), with intermediate types. The external deposit can be too thin to be usually visible under the light microscope, as in Pseudocercospora clematidis, P. hardenbergiae and the Pseudocercospora on Eucalyptus macrorhyncha. The description of Pseudocercospora needs to be modified to permit the inclusion of species with external scar thickening. Wall involvement in conidiophore and conidium ontogeny were also studied at the ultrastructural level for species of Pseudocercospora and Verrucisporota. Conidiophores were generally holoblastic, but enteroblastic ontogeny was observed in several conidiophores of P. correae and P. platylobii. Conidia were always holoblastic, and secession was schizolytic. Proliferation of the conidiogenous cell was variously enteroblastic sympodial, pseudopercurrent or holoblastic sympodial.