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Wheat Information Service
Number 93: 32-34 (2001)
Research information
'Thatcher'-avirulent Ieaf rust pathotypes from
India
A. N. Mishra1, Kamini Kaushal1, S. K
Jain2 and H. N. Pandey1
1Indian Agricultural Research Institute, Regional
Wheat Research Station, Indore 452 001, India
2Directorate of Wheat Research (DWR), Regional Station,
Flowerdale, Shimla 171,002, India
Bread wheat cultivar Thatcher is documented to carry a single gene (
Lr22b ) for adult plant resistance to leaf rust (McIntosh et
al. 1995), while its seedling is susceptible to wheat leaf rust.
Therefore, it has been used as the genetic background to develop the
near-isogenic lines for resistance to leaf rust. However, leaf rust
pathotypes avirulent to Thatcher seedlings have been known to occur
in Ethiopia and Morocco until now (Huerta-Espino and Roelfs 1992).
The present communication reports three Indian leaf rust pathotypes
carrying avirulence to Thatcher seedlings. These three pathotypes of
leaf rust, OR8, 0R8-1, and OR9, belonging to standard leaf rust races
11, 63, and 106 are maintained at the DWR-Shimla. These pathotypes
were also avirulent to seedlings of the 14 near-isogenic lines with
Thatcher background carrying a resistance gene to leaf rust, Lr1,
2a, 2c, 3a, 10, 13, 14a, 15, 17, 18, 19, 23, 24 or 26.
They showed virulence to a bread wheat Agra Local, to which the
Ethiopian and Moroccan isolates were avirulent (Mishra 1996). These
three pathotypes produced the low infection types on Thatcher
seedlings with minor, but consistent differences (Table
1). These pathotypes were tested with 20 lines each of bread and
durum wheats (Table 1), since the Thatcher-
avirulent leaf rust isolates from Ethiopia and Morocco tended to be
avirulent to bread wheats but virulent to durum wheats (Huerta-Espino
and Roelfs 1992). Leaf rust pathotype 121R63-1 (77-5), carrying
virulence to Thatcher and many of the known Lr genes, was also
included for comparison. Seedlings of the test lines including
suitable cheeks were evaluated at 18-27C (temperatures mostly ranging
between 20-25C) using standard glasshouse procedures (Stakman et al.
1962). While the three Thatcher- avirulent pathotypes were generally
avirulent to bread wheats, they displayed differential interaction
with durum wheats (Table 1). In contrast,
pathotype 121R63-1 (77-5) was virulent to all the bread wheat lines,
but avirulent to most of the durum wheats (Table
1). Similar differences in the seedling response of durum wheat a
and bread wheat to the leaf rust races 77 and 106 have earlier been
reported from India (Pandey and Rao 1984). These findings emphasize
the need for separate protocols with regard to the choice of leaf
rust pathotypes for evaluating leaf rust resistance in bread and
durum wheats.
One wheat cultivar Kanred, a parental line of Thatcher, was
speculated as the source of seedling resistance to the
Thatcher-avirulent Ethiopian leaf rust isolates based on their
comparison of the infection types (Mishra and Roelfs 1995). The
source of seedling resistance in Thatcher to the three
Thatcher-avirulent Indian leaf rust pathotypes is not known, and
further studies are being conducted to explain it.
E-mail: iariindore@sancharnet.in
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