VIEW ARTICLE

Cytology and Histology

Histological and Physiological Aspects of Infection of Sclerotia of Two Sclerotinia Species by Two Mycoparasites. P. B. Adams, Plant pathologist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, Science and Education, U.S. Department of Agriculture, Beltsville, MD 20705; W. A. Ayers, microbiologist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, Science and Education, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 73:1072-1076. Accepted for publication 23 February 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/Phyto-73-1072.

Macroconidia of the mycoparasites Sporidesmium sclerotivorum or Teratosperma oligocladum when applied to sclerotia of Sclerotinia minor or S. sclerotiorum germinated within 3- 5 days on the surface of the sclerotia. The germ tubes penetrated the rind and proliferated beneath the surface of the sclerotia. In sectioned sclerotia the germ tubes of the mycoparasites penetrated between the cells of the rind and cortex without the aid of specialized penetration structures. Frequently hyphal strands on the sclerotial surface branched, and each branch appeared to infect the sclerotium, resulting in multiple infections. Once within the medullary region of the sclerotium, the infection hyphae branched and grew out intercellularly. The hyphae were convoluted and assumed the shape of the intercellular spaces. After proliferating within the medulla, the mycoparasites grew to the surface of the sclerotium, where they sporulated abundantly. Sclerotial cells were not invaded by either mycoparasite. Live sclerotia were much more extensively invaded than autoclaved sclerotia. Glucanase activity that hydrolyzed α- and β-glucans was detected in noninfected sclerotia of S. minor and S. sclerotiorum, and glucans were extracted from host sclerotia. Specific β-glucanase activity was increased by infection of sclerotia by S. sclerotivorum. S. sclerotivorum did not grow in a medium with glucan of Sclerotinia as sole carbon source, but did so when the glucan was previously incubated with glucanase extracted from host sclerotia. It is suggested that the mycoparasites utilize glucose and possibly other monosaccharides released from the extracellular matrix of the medulla by physiological interaction of the enzymatic systems of their hosts.