Studies on Puccinia recondita f. sp. tritici with special emphasis on adult plant resistance in wheat.
Loading...
Date
1986
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Leaf rust (Puccinia recondita f.sp. tritici) of wheat
(Triticum aestivum) was widespread in South Africa
during 1983, 1984 and 1985 and often reached epidemic
levels, especially on autumn-sown spring wheat in the
Cape Province. Nine physiologic races were identified
during the study period. The most common race was
avirulent to the leaf rust differential genes Lr3a,
3bg, 3ka, 11, 16, 20 and 30 and virulent to Lr1, 2a,
2b, 10, 14a, 15, 17, 24. Resistance genes Lr9, Lr19,
Lr21 and Lr26 were effective to all isolates tested.
Evaluation of wheat genotypes for components of resistance,
viz. infection type, latent period, number
of uredinia and uredinium size, revealed three phenotypic
reaction classes. The first group exhibited
negligible resistance, the second was susceptible or
moderately susceptible as seedlings but resistant as
adult plants while the third group was resistant at all
growth stages tested. Adult plant resistance was expressed
by hypersensitive or non-hypersensitive reactions
and the combination of components conditioning
resistance varied. Adult plant resistance conferred by
gene Lr22a was characterized by a long latent period,
small uredinia, reduced sporulation and an absence of a
differential interaction between components of resistance
and different races of Puccinia recondita f.sp.
tritici. Numbers of uredinia on flag leaves of RL6044
(Lr22a) were equal to those of a susceptible check,
Line E. Lr22a was inherited as a partially recessive
gene in crosses with Zaragoza and SST33. Assessment of
latent period, number of uredinia and infection type in
F4 and FS families homozygous for Lr22a and derived
from crosses between RL6044 and Zaragoza or SST33,
revealed significantly different levels of resistance
between families. Differences were attributed to other
genes modifying the expression of Lr22a. Adult plant
resistance of Era, Glenlea, RL6044 and sinton was expressed
prior to the fifth-leaf stage. Latent period
increased and number of uredinia decreased as each
wheat matured. While the latent period of the flag,
flag-l and flag-2 leaf was similar within Era, Glenlea
and RL6044, differences between these genotypes occurred.
The latent period of flag leaves of Sinton was
shorter than that of the two lower leaves. Significantly
fewer uredinia developed on the flag-2 leaf of
Glenlea. A reduction in temperature from 21 C to 15 C
significantly increased latent period in Era, Glenlea
and RL6044, and also restricted uredinium size on flag
leaves of RL6044. The adult plant resistance of Glenlea
crossed with Line E was conferred by two partially
recessive genes. Additionally, F2 to FS progenies of
this cross eXhibited high levels of hypersensitive
seedling resistance at 29 - 31 C to certain isolates.
The latter resistance was not conferred by Lr1 or by
the LrT2 gene for mature plant resistance in Glenlea.
The high-temperature expression of resistance could be
due to a second gene for adult plant resistance or to a
previously undetected seedling gene.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.
Keywords
Wheat--Diseases and pests., Wheat--Disease and pest resistance--Genetic aspects., Leaf rust of wheat., Puccinia recondita., Wheat rusts., Theses--Plant pathology.