Gigaspora gigantea: parasitism of spores by fungi and actinomycetes

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Fungi and actinomycetes were isolated monthly for one year from spores of the arbuscular mycorrhizal fungus Gigaspora gigantea recovered from a maritime sand dune. Spores in four different stages of vigour (newly formed, greenish-yellow healthy; yellow, moribund, mottled with brown spots; brown; and dead, blackened and collapsed) were used for isolation. From 272 isolates cultured from crushed, surface-disinfected G. gigantea spores, 44 species of fungi and six actinomycete species were recovered. The five most frequently isolated organisms were Acremonium sp., Chrysosporium parvum, Exophiala werneckii, Trichoderma sp. and Verticillium sp. The species lists derived from the four spore types differed significantly. Thirty-one of the isolated species were tested for their ability to parasitise healthy G. gigantea spores and to invade spores killed by a hot water treatment. Twenty-two species could function as pathogens, forming internal projections (IP), fine radial canals (FRC) or both in the spore wall. IP were induced by Acremonium sp., Chrysosporium parvum, Cladosporium sp., Geomyces pannorum, Oidiodendron sp., Sporothrix sp., Verticillium sp. and by the actinomycetes Nocardia sp. and Streptomyces sp. The IP length was positively correlated with duration of exposure to the parasites. In the bioassay, both IP and FRC were formed by live spores, while heat-killed spores possessed only FRC after penetration by the test microorganisms. Pathogenicity differed among the parasites and was greatest for Verticillium and Acremonium. © 1994, British Mycological Society. All rights reserved.

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Mycological Research