THE SUBEPIDERMAL FUNGI OF CEREAL GRAINS II. THE NATURE, IDENTITY AND ORIGIN OF THE MYCELIUM IN WHEAT

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Abstract
An internal fungal mycelium between the epidermis and cross‐layer cells in normal wheat grains is shown to consist of extracellular septate hyphae forming a network on the inner surface of the epidermis, whose cells are occasionally penetrated. The mycelium, which is first observed at a comparatively late stage of maturation of the grain, usually remains as a loose network, although sclerotia and plate‐like structures suggestive of drought forms are occasionally present. These appearances support the view, derived from comparison of the drying rates of grain under various climatic conditions, that the spread of the subepidermal mycelium is finally restricted by desiccation beneath the epidermis during the drying out of the ripening grain.Cultures from surface‐sterilized grains of Bersée wheat have shown that the most common subepidermal fungus is Alternaria tenuis (in 64.4% of the grains). Bacteria (28.8%), Mycogone sp. (?) (7.7%), Cladosporium herbarum (5.8%), Pullularia pullulans (4.8%), Fusarium sp. (1.9%), Botrytis cinerea (1.9%) and Stemphylium botryosum (0.9%) were also isolated.The subepidermal mycelium apparently arises either from systemic infection of the wheat plant or from fungal spores and hyphae present on the outside of the developing grains and among the dead floral parts.

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