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Ultrastructural Formation of Sclerotia of Macrophomina phaseoli. T. D. Wyllie, Associate, Department of Plant Pathology, University of Missouri, Columbia 65201; M. F. Brown, Assistant Professor, Department of Plant Pathology, University of Missouri, Columbia 65201. Phytopathology 60:524-528. Accepted for publication 22 October 1969. DOI: 10.1094/Phyto-60-524.

The ontogeny, form, and structure of sclerotia of Macrophomina phaseoli were determined using transmission and stereoscan electron microscopy. Sclerotia are formed primarily by intertwining of primary branches originating from major hyphal filaments. Associated cells enlarge, become globose in form, and become tightly compacted into a single unitized structure possessing heavy cell walls and cemented together by a heavily pigmented gelatinous matrix. Incorporated cells apparently maintain their capacity to germinate, since they contain 1 to 3 nuclei, mitochondria, lipid droplets, and other organelles typical of intact cells. Cytoplasmic continuity is retained via septal pores.