A study on the ultrastructure and control of the gladiolus rust pathogen, Uromyces transversalis.
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Date
1988
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Abstract
The substomatal vesicle of Uromyces transversalis develops in five distinct stages after the
formation of a single infection peg in the host plant Gladiolus spp. The primary hyphae of
the substomatal vesicle orientate at right angles (rather than at acute angles or parallel) to
the stomatal slit and the parallel veins of a gladiolus leaf or to those of the non-host, Zea
mays. The transverse orientation of Uromyces transversalis uredia is apparently a
genetically controlled phenomenon. The two primary hyphae normally develop
asynchronously on opposite sides of the substomatal vesicle, and, after the formation of a
haustorium mother cell, secondary hyphae branch off. These subsequently form basal cells
each of which give rise to one or more holoblastic protruberances on its distal surface. A
septum delimits the protruberance from the basal cell to form a urediospore initial, which
in tum elongates and, by septum formation, forms a pedicel and a urediospore. The
urediospore is seceded mechanically through the process of schizolysis. The pedicel of a
spore thus formed remains on the basal cell and becomes a collar around the next
protruberance. The basal layer of the two-layered septum, that delimited the pedicel from
the basal cell, grows out to form the wall of the subsequent protruberance, in the process
rupturing and laterally displacing the terminal septal layer. A new basipetal septum forms
to delimit the subsequent urediospore initial. Therefore, successive urediospores are
formed enteroblastically and give rise to a series of basipetal collars.
Cultivars, naturally occurring species and breeding lines of gladiolus were evaluated for
rust resistance. The cultivars showed no sign of resistance, whereas the populations of
wild species and breeding lines had similar resistance profiles. The species G. daleni and
G. tristis var. tristis showed promise for breeding. Infection of these species caused an
almost immune, fleck reaction. The resistance of the species G. daleni was manifested by
the abortion of primary hyphae prior to the formation of the haustorial mother cell. The
intercellular hyphae of gladiolus rust only partially adhered to the mesophyll cell of the
resistant host. The haustorial apparatus that did form in the mesophyll cells in the
resistance reaction was inhibited at various stages of its development. The rust disease
could be controlled chemically by either bitertanol or triadimefon. Triadimefon, however,
caused a shortening of the internodes of the flower spike. The early development of U.
transversalis infection structures in bitertanol-treated leaves was inhibited at, or shortly
after, substomatal vesicle development. A number of mature substomatal vesicles with
intercellular hyphae, however, did develop in the bitertanol-treated leaf tissue, probably
because this fungicide undergoes limited translocation in the gladiolus lamina.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1988.
Keywords
Gladiolus--Diseases and pests., Gladiolus--Diseases and pests--Control., Rust fungi., Theses--Plant pathology.