The Mycorrhizal FungusGlomus macrocarpumas a Cause of Tobacco Stunt Disease

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Abstract
Tobacco plants inoculated with sievings contained endogonaceous spores from soils suspected of containing the tobacco stunt pathogen developed stunt symptoms identical to those of naturally stunted plants. Glomus macrocarpum sporulated first on stunted plants, followed by G. microcarpum. Stunting was correlated with sporulation by G. macrocarpum and less strongly with sporulation by G. microcarpum. Stunting was correlated with colonization of roots by arbuscules and external hyphae. Isolates of G. macrocarpum from soils containing the stunt pathogen caused stunting in tobacco seedlings, but an isolate of G. fasciculatum shown to benefit growth of several woody plants did not. Shoots and roots of tobacco seedlings inoculated with single spores of G. macrocarpum were stunted, the degree being related to the number of colonization structures (arbuscules, vesicles, external hyphae, or spores) present. These data suggest that G. macrocarpum and perhaps G. microcarpum cause tobacco stunt disease.