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Wheat Information
Service
Number 82: 29-30 (1996)
Research Information
II.
Research Information
Transfer
of stripe rust resistance to Unnath Sonalika and Unnath
Kalyansona
R. N. Brahma and M Sivasamy
Indian Agricultural Research Institute, Regional Station,
Wellington-643231, Tamil Nadu, India
Unnath Sonalika and Unnath Kalyansona, improved varieties of Sonalika
and Kalyansona respectively (Kochumadhaven et al. 1988), carrying
linked resistance genes Sr24 + Lr24,
were initially susceptible only to stripe rust. However, recently
these varieties also became susceptible to stem rust. An attempt was
made to transfer unidentified stripe rust resistance from the two
hexaploid wheat lines in the background of Unnath Sonalika and Unnath
Kalyansona.
Crosses of Unnath Sonalika and Unnath Kalyansona with the two wheat
lines,. i.e., CPAN 3057 and CPAN 3063, were made at Indian
Agricultural Research Institute, Regional Station, Wellington, The
Nilgiris, South India. The location is a 'hot spot' for all wheat
diseases, where all the three wheat rusts occur in epiphytotic form
throughout the year. Resistant hybrids were backcrossed to recurrent
parents and lines showing resistance to stem, leaf and stripe rusts
were constituted after fifth successive backcrosses. Screening for
rust resistance was made under natural epiphytotic conditions.
Crosses of Unnath Sonalika and Unnath Kalyansona with the two wheat
lines were successful. The lines constituted from the respective
crosses between Unnath Sonalika and the two wheat lines were
completely free to stripe rust, while the lines from the crosses
between Unnath Kalyansona and the two wheat lines showed low
incidence of stripe rust (TMR) (Table
1). These two
wheat lines thus appeared to he good contributor for stripe rust
resistance, though these failed to provide immunity to stripe rust in
the latter case indicating that these lines are not virtually immune
to stripe rust. It appears that a heavy inoculum load on the lines
also leads to the breakdown of genetic resistance.
Interestingly, the new lines also exhibited good resistance to stem
rust (TR), while Unnath Sonalika and Unnath Kalyansona were
susceptible to stem rust (Table
1). Unnath
Sonalika and Unnath Kalyansona and their derivatives were immune to
leaf rust indicating the effectiveness of leaf rust resistance gene
Lr24. The
reason for breakdown of effective resistance gene
Sr24 in Unnath
Sonalika and Unnath Kalyansona is not exactly known. Crossing-over
between the two resistance genes can be ruled out, since these two
genes are tightly linked to each other (McIntosh 1988). Occurrence of
stem rust on a new resistance line could be due to previously unknown
or new race with matching pathogenecity. However, under the same
experimental conditions at Wellington, the original Australian line
TR-380 14* 7/3 Ag 14 from which the linked resistance genes
Sr24 + Lr24 were
transferred to Unnath Sonalika and Unnath Kalyansona, was free to
stem rust. The stem rust race involved in the attack of Unnath
Sonalika and Unnath Kalyansona was also not race 40-1 which is known
to knock down the resistance gene Sr24,
but it was only 40A, a common virulence of the Nilgiri hills.
However, the Australian line was quite effective against the race
40A.
Thus, good resistance observed against stem rust in the new wheat
lines possibly was due to combined effect of resistance gene
Sr24 and the
additional unidentified gene(s) transferred from the two wheat lines
which were resistant to stem rust (Table
1). It has been
reported that rust resistance provided by single gene is not
effective and durable resistance is provided only by a few gene
combination (McIntosh 1988; Roelfs 1988; Roelfs et al. 1992). Since
the new lines were simultaneously resistant to stem and stripe rust,
it is possible that the resistance genes for stem and stripe rust
derived from the donor parents are linked to each other.
Reference
Kochumadhavan K, Tomar SMS and Nambisan PNN (1988) Transfer of
rust resistance genes into commercial cultivars of wheat. Ann Wheat
News Letter 34: 54-55.
McIntosh RA (1988) The role of specific genes in breeding for durable
stem rust resistance in wheat and triticale. In: Breeding strategies
for resistance to the rusts of wheat. Ed:NW Simonds and S. Rajaram.
CIMMYT Report: 1-9.
Roelfs AP (1988) Resistance to leaf and stem rusts in wheat. In:
Breeding strategies for resistance to the rusts of wheat. Ed:NW
Simonds and S. Rajaram. CIMMYT Report: 10-22.
Roelfs AP, Singh RP and Saari EE (1992) Rust disease of wheat:
Concepts and methods of disease management. CIMMYT Report
81.
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