Morphology, development, and cytochemistry of the hyphae and sclerotia of species in the Rhizoctonia complex

Abstract

A detailed comparison of the gross morphology of hyphae, monilioid cells, and sclerotial formation and structure of 17 isolates of species in seven genera of the Rhizoctonia complex were studied. Cytochemistry of both hyphal and sclerotial cells was also studied. Gross morphology of hyphae was similar in many of the isolates and was considered of limited taxonomic value. Sclerotial formation in species of Thanatephorus, Waitea, Aquathanatephorus, and possibly Ceratobasidium was of the monilioid cell type. That of Athelia was of the hyphal strand type. Although initially similar, mature sclerotia in each of the genera showed great diversity. Most sclerotia of Thanatephorus were constructed of loosely arranged monilioid cells. Those in Ceratobasidium developed a marginal rind; Aquathanatephorus, a pitted surface and hyphal mat; Waitea, a bilaminate condition with elongate marginal and globose medullary cells; and Athelia, a complex tetralaminate structure. Distribution and concentration of carbohydrates, proteins, and lipids differed in the various genera. The strong dextrinoid reaction of the cytoplasm of Thanatephorus and Aquathanatephorus, accompanied by higher total lipids in cell walls and septa, was of significance. Stronger reactions for cellulose were found in species of Ceratobasidium, while cellulose appeared more concentrated in sclerotial cells than in hyphal cells of Thanatephorus. Lipids were deposited more abundantly in sclerotial cells than in hyphal cells.