Ultrastructure of stromatal anamorphs in the Sclerotiniaceae

Abstract

As part of comparative anatomical, histochemical, and ultrastructural studies of stromata in the Sclerotiniaceae, mature stromata produced in vitro by 11 species representing six genera and one form-genus were examined using transmission electron microscopy. Sclerotial-stromatal taxa were Sclerotinia sclerotiorum, S. trifoliorum, S. minor, Sclerotium cepivorum, Botrytis cinerea, B. porri, Monilinia fructicola, and Myriosclerotinia borealis. Substratal-stromatal taxa were Sclerotinia homoeo-carpa, Rutstroemia sydowiana, and Lambertella subrenispora. Three types of rind were observed: a living cellular rind, a dead cellular rind, and a stromatal rind. Sclerotial species were distinguished from stromatal species not only by the rind type, but also by the confluent extracellular matrix around cortical and medullary cell walls. Presence of lacunae in this matrix distinguished Sclerotinia spp. and M. borealis from Botrytis spp. and Monilinia fructicola. Rind, cortical, and medullary cells contained abundant storage vacuoles in most taxa. The distribution and proportion of organelles to storage vacuoles differed among taxa. Plugged septal pores with associated Woronin bodies were similar among the taxa where they were observed. Sclerotia of Sclerotium cepivorum, which has no known teleomorph, are ultrastructurally most like sclerotia of Sclerotinia or Botrytis anamorphs of Botryotinia species. Substratal stromata of S. homoeocarpa showed unusually complex cellular organization. Sclerotial stromata of M. fructicola contained unusual storage vacuoles with heterogeneous contents.