Histology, amino acid leakage, and chemical composition of normal and abnormal sclerotia of Sclerotinia sclerotiorum

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Abstract
This comparative study investigated the structure, amino acid leakage, and chemical composition of normal, slightly abnormal, and grossly abnormal sclerotia of Sclerotinia sclerotiorum collected from diseased sunflower heads. Histological studies showed that the normal sclerotia contained a relatively intact rind layer two or three cells wide, a cortex two to four cells wide, and a large white medullary region with numerous darkly stained, loosely arranged interwoven hyphae embedded in an amorphous matrix. In contrast, the abnormal sclerotia had a severely fractured rind and a brown medullary region with sparse, lightly stained filamentous hyphae embedded in the amorphous matrix which was often highly vacuolated. Cultural studies showed that the viable cells in abnormal sclerotia are mainly confined to the white medullary region and there is little evidence of hyphal growth from the brown-colored medullary tissue. Paper chromatographic analyses indicated that leakage of amino acids is greater in abnormal sclerotia than in normal ones. Chemical analyses revealed that protein, alcohol-soluble substances, and oil content are similar in normal and abnormal sclerotia, but the amount of ash is significantly higher in the abnormal ones. The effect of structural malformation on viability and survival of sclerotia is discussed.

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