Studies on the expression of resistance to stem rust of wheat caused by Puccinia graminis f.sp. tritici.
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Date
1991
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Abstract
The endogenous cytokinin levels of healthy primary leaves and seeds of a stem-rust
susceptible wheat cultivar Little Club were compared with those of Little Club containing
the stem rust resistance gene Sr25. Use was made of paper, column and high
performance liquid chromatography techniques to separate the endogenous cytokinins
in the plant material, and the soybean callus bioassay was used to test for cytokinin-like
activity of the chromatography fractions. Leaf material of the resistant Little Club Sr25
had a higher level of total cytokinin activity than Little Club, whereas seed material of
Little Club Sr25 did not always have higher levels of cytokinins than Little Club. A
number of cultivars would have to be tested before the usefulness of cytokinin levels
as an indicator of resistance could be determined.
The development of urediospore-derived infection structures of Puccinia graminis
f.sp. tritici in wheat, barley, sorghum and maize was examined by scanning electron
microscopy (SEM). Infection on and in the four species followed a similar pattern up
to, and including, primary infection hyphae formation. In wheat, barley and maize,
when a primary infection hypha abutted onto a host epidermal cell, a septum was laid
down delimiting a primary haustorial mother cell (HMC); primary HMCs did not form
in sorghum. Secondary infection hyphae arose on the substomatal vesicle side of the
primary HMC septum; infection did not progress further in maize, but in wheat and
barley secondary infection hyphae branched, and proliferated intercellularly forming the
fungal thallus. Secondary HMCs were delimited when an intercellular hypha abutted
onto host cells. In all four species atypical infection structures were also observed.
In an attempt to determine the timing and expression of stem rust resistance gene Sr5,
infection structure development of Puccinia graminis f.sp. tritici race 2SA2 in a
resistant line (ISr5Ra) and a susceptible line (ISr8Ra) was compared quantitatively
using a fluorescence microscopy technique. The results indicated that there were no
significant differences in numbers of specific infection structures observed in the two
near-isogenic lines up to, and including, 48 hpi, by which time race 2SA2 had
successfully formed secondary HMCs in both lines.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.
Keywords
Wheat--Diseases and pests., Wheat--Disease and pest resistance--Genetic aspects., Wheat--Varieties., Puccinia graminis., Wheat rusts., Theses--Plant pathology.