The pycnidial stage of the walnut branch wilt fungus, exosporina fawcetti
1949
Wilson, E.E., University of California, California (USA). Division of Plant Pathology
In December, 1947, at Davis, California, pycnidial stromata developed beneath the bark of young Persian walnut trees inoculated some months earlier with Exosporina fawcetti, the pathogen of walnut branch wilt. Isolates from pycnospores produced a toruloid conidial (arthrospore) stage which proved similar to E. fawcetti in morphology, temperature requirements, and pathogenicity to walnut, peach, and apricot trees. Nattrass, in 1933, described and named a fungus, Hendersonula toruloidea, which produced both a toruloid and a pycnidial stage on apples, peaches, and apricots in Egypt. Judging from Nattrass descriptions and illustrations, the California fungus resembles this organism closely. Studies of type specimens of H. toruloidea confirmed this view. It is concluded, therefore, that Exosporina fawcetti is the conidial stage of H. toruloidea. Under the rules of nomenclature the fungus should be designated Hendersonula toruloidea providing Nattrass was first to described it. Both Fawcett and the writer, however, have mentioned the similarity between the toruloid stage of the California fungus and that of Torula dimidiate Penz. Described from Italy in 1887. Since Penzig"s description is meager, substitution of the species dimidiate for toruloidea does not seem justified at this time.
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