The Eleventh Regional Wheat Workshop For Eastern ... - Cimmyt

Sources ofvariability ofgenes for yellow rust resistance - Singh a,!d Huerta-Espino
least of 4 additive genes (Table 4). Resistance of Chapio and Tukuru was based on the
additive interaction of at least 5 minor genes.
All resistant parents included in the genetic analysis are likely to carry the durable slow
rusting gene Yr18 (Singh, 1992; McIntosh, 1992) as they show the linked leaf tip necrosis of
adult plants. At least the lines derived from the crosses involving Pavon 76 are also likely to
carry minor genes Yr29 and YrJO. These genes are known to be present in Pavon 76 and are
very closely linked! pleiotropic to the genes Lr46 and Sr2 that confer durable slow rusting
resistance to leaf and stem rusts, respectively. Based on the results from genetic analysis it
appears that resistance to yellow rust, approaching near-immunity, can be developed by
combining slow rusting genes that have minor/ intermediate but additive effects. The wheat
lines listed in Table 4 or 5 should be used in the future crossing program if aim is to achieve
high level of minor genes based resistance. Resistance of cultivars carrying such genes should
prove to be durable.
REFERENCES
Ma, H. and R.P. Singh. 1996. Expression ofadult resistance to stripe rust at different growth stages of wheat.
Plant Dis. 80: 375-379.
McIntosh, RA. 1992. Close genetic linkage ofgenes conferring adult-plant resistance to leaf rust and stripe rust
in wheat. Plant Pathol. 41: 523-52i
McIntosh, R.A., Hart, G.E., Devos, K.M., Gale, M.D. and W.J. Rogers. 1998. Catalogue of gene symbols for
wheat. Slinkard, A.E. (ed.) Proc. 9 th Int. Wheat Genetics Symp., 2-7 Aug. 1998, Saskatoon, Canada.
Vol 5: 1-235.
Peterson, R.F., Campbell, A.B. and A.E. Hannah. 1948. A diagrammatic scale for estimating rust intensity of
leaves and stem of cereals. Can. J. Res. Sect.' C. 26: 496-500.
Roelfs, A.P., Singh, RP. and E.E. Saari. 1992. Rust tiiseases of wheat: Concepts and methods of disease
management. CIMMYT, Mexico, D.F. 8lpp.
Singh, RP. 1992. Genetic association ofleaf rust resistance gene Lr34 with adult plant resistance to stripe rust
in bread wheat. Phytopathology, 82 : 835-838.
Singh, RP., Nelson, J.C. and M.E. Sorrells. 2000. Mapping Yr28 and other genes (or resistance to stripe rust in
wheat. Crop Sci. 40: 1148-1155.
Singh, RP, and S. Rajaram. 1992. Genetics of adult-plant resistance to leaf rust in ' Frontana' and three
CIMMYT wheats. Genome, 35: 24-31.
Singh, R.P., Rajaram, S. and J. Huerta-Espino. 1999. Combining additive genes for slow rusting type of
resistance to leaf and stripe rusts in wheat. pp, 394-403. In: Proc. The 10 th Regional Wheat Workshop
for Eastern, Central and Southern Africa. Addis Ababa, Ethiopia: CIMMYT.
Questions and Answers:
Colin R. WeIlings: The F3 distribution ofR x S crosses were presented as a distribution.
Were these means for LAI within lines, as one would expect segregation to susceptible in a
proportion ofthe material?
Answer: For the estimation of gene number, we use the four categories (HPTR, HPTS, SegI
and SegS). Severity mean of the lines is a useful tool to show the pattern ofthe distribution of
the lines.
HarjU Singh: Since there are a number ofexamples where slow rusting resistance has been
found to be race specific, will it be appropriate to label "slow-rusting" as "race non-specific"
as you have done in your presentation?
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