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Research Infection Biology of Crinipellis perniciosa on Vegetative Flushes of Cacao. G. A. Frias, Former Graduate Student, Plant Pathology Department, University of Florida, Gainesville 32611. L. H. Purdy, and R. A. Schmidt. Professor, Plant Pathology Department, University of Florida, Gainesville 32611, and Professor, Forestry Department, University of Florida, Gainesville. Plant Dis. 75:552-556. Accepted for publication 14 December 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0552.

Infection biology of Crinipellis perniciosa on vegetative flushes of cacao (Theobroma cacao) was studied by fluorescent microscopy. Basidiospores germinated only if they landed on wet tissue or were suspended in water and sprayed onto the plant parts; those that landed on dry surfaces were no longer viable. Interruption of the period of wetness during the prepenetration phase resulted in irreversible termination of the infection process. Growth of germ tubes on the surface of young flushes was strongly oriented toward natural infection sites (stomata) and wounds. On hardened flushes, growth of germ tubes was random. Germ tubes penetrated through stomata on any of the organs of young developing flushes. Penetration into the basal cells of fallen or collapsed multicellular trichomes on fully expanded but unhardened flushes also occurred. Substomatal vesicles were commonly observed in unhardened tissues 12 hr after inoculation. Infection sites were not equally susceptible; in some instances, intercellular hyphae grew freely throughout the infected tissue, whereas in others, mycelial growth stopped shortly after penetration. The failure to colonize host tissue after penetration was associated with a change in the fluorescence of host cells at and around the infection site. Penetration through stomata was also observed on hardened flushes, but substomatal vesicles or intercellular hyphae did not develop.

Keyword(s): cocoa, disease resistance, epidemiology, germ tube tropism, witches’-broom.