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Ultrastructural Morphology of Uromyces transversalis Infection of Resistant and Susceptible Gladiolus Hosts and a Nonhost, Zea mays. J. F. Ferreira, Plant pathologist, Fynbos Research, Vegetable and Ornamental Plant Research Institute, Private Bag, Elsenburg 7607; F. H. J. Rijkenberg, Professor, Department of Microbiology/Plant Pathology, University of Natal, P.O. Box 375, Pietermaritzburg 3200, Republic of South Africa. Phytopathology 81:596-602. Accepted for publication 10 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-596.

The infection structures of gladiolus rust, Uromyces transversalis, on and in host leaves of the susceptible gladiolus cultivar (Goldfield) and resistant species (Gladiolus daleni) and in leaves of the nonhost (Zea mays) were examined by scanning and transmission electron microscopy. The number of germinated urediospores that formed appressoria on the resistant host was significantly fewer than the number formed on the susceptible host. The major determinant of resistance in the host was manifested in the significant proportion of substomatal vesicles with primary hyphae that aborted before the formation of haustorial mother cells and/or secondary hyphae. This was correlated with a similar reaction in the nonhost. The abortion was attributed to the putatively incomplete adhesion of haustorial mother cells to mesophyll cells. In the nonhost, although no secondary hyphae were formed, some haustorial mother cells were formed, and a significant proportion of primary hyphae did not form haustorial mother cells and/or secondary hyphae.