Studies onDiplodiaandDiplodia-like fungi: III. Variation inDiplodia natalensisfrom grape in California

Abstract

Single-spore colonies of Diplodia natolensis P. Evans originating from individual pycnidia were compared with each other and with those from different pycnidia from the same grape cane, different canes from the same vineyard, and different vineyards, to evaluate the natural range in variation and stability of taxonomic characters currently used to delimit this species. Distinct colony types were recognized-in some cases as many as four originating from an individual pycnidium. Colony type per se is not considered to be useful for taxonomic purposes. Results suggest that several genera now recognized in this group are congeneric, and indicate a great need for determination of the inherent variation that these fungi are capable of exhibiting.

Studies onDiplodiaandDiplodia-like fungi: V. Effects of carbon:nitrogen ratio on growth, pycnidia, and pycnidiospore formation

“…We have concluded that the isolates included in the present study represant the same species. It is possible that differences observed in laboratory cultures would be more stable on natural substrates, although this was not the case in a previous study of D. natalensis isolates from grape (Webster, Hewitt, and Polach, 1969) and in a study by Taubenhaus (1915) in which isolates were compared on sweet potato.…”

“…Media for studies in liquid culture differed only in omission of the agar. Potato dextrose agar was prepared fresh as described previously (Webster, Hewitt, and Polach, 1969).…”

“…Mycelial dry weights were determined by standard methods. Methods used for making observations and measurements have been described previously (Satour, Webster, and Hew itt, 1969a, b;Webster, Hewitt, and Polach, 1969). Cultures on agar media were incubated at 24°C for 30 days in continuous light (Gro-Lux type) of ap proximately 250 ft-c.…”

“…Sizes of the pycnidiospores, as ob served in different treatments, are given in table 4. Methods for measur ing have been described previously (Webster, Hewitt, and Polach, 1969). Spore size was determined from 30 spores from each of three replicate cul tures.…”

“…The major differences commonly used to distinguish between the genera Bi- plodia and Botryodiplodia (Fries, 1846(Fries, -1849Zambettakis, 1953Zambettakis, , 1954 are con cerned with distribution of pycnidia (scattered vs. caespitose) and presence or absence of a stroma. However, the validity of this separation has been challenged (Taubenhaus, 1915;Stevens, 1941;Webster, Hewitt, and Polach, 1969). At present we are evaluating the taxonomic criteria currently used under a wide range of culture condi tions to determine which characters will serve for a more meaningful taxonomy of the group.…”