(go to
KOMUGI Home) (go
to WIS List) (go to NO.92
Contents)
Materials and methods
The plant materials used in this investigation are listed in
Table 1. To transfer leaf rust and stripe
rust resistance from diploid Aegilops species with C or U
genomes to hexaploid wheat, amphiploids were developed between these
species and susceptible T. durum cultivars. To synthesize
amphiploids, the coleoptiles of 4-5 day-old F1seedlings,
of these crosses, were treated with 0.25% colchicine in 2% DMSO
solution for four hours (Gill et al. 1988).These amphiploids were
used as the bridge for the transfer of leaf and stripe rust
resistance genes into cultivated hexaploid wheat. To induce
homoeologous chromosome pairing these amphiploids were first crossed
with T. aestivum cv. Chinese Spring carrying the
PhI gene from Ae. speltoides (Chen et al.
1994; Aghaee-Sarbarzeh et al. 2000) and further backcrossed to
Chinese Spring.
The parents, F1's, amphiploids, and the derivatives of
their crosses with Chinese Spring (CS) were scored for field reaction
to leaf rust and stripe rust by recording terminal disease severity
and response to individual rust pathotypes. The disease severity
under field conditions was recorded as percentage of leaf area
covered by rust following modified Cobb's scale as developed by
Peterson et al. (1948). According to this scale, at 100 % disease
severity, the actual leaf area covered by rust pustules is 33 %. The
response of individual plant/entry was recorded as follows; 0:
resistant, no infection, R: resistant, necrotic areas with or without
minute uredia, MR: moderately resistant, small uredia surrounded by
necrotic areas, MS: moderately susceptible, medium sized uredia with
no chlorosis, S: susceptible, large uredia without necrosis or
chlorosis, X: intermediate, variable size uredia, some with necrosis
or chlorosis. In addition, these materials were also evaluated for
seedling resistance to individual pathotypes of leaf rust and stripe
rust. First leaves of five to seven day-old seedlings were inCulated
with urediospores mixed with talc using lancet needle (Nayar et al.
1997). The inCulated seedlings were incubated for 24 hours at 20 plus
or minus 1C for leaf rust and 8-9C for stripe rust at 100 % relative
humidity. Subsequently, plants were placed on benches in the glass
house at temperature around 20-25C for leaf rust and 15-20C for
stripe rust. About 11 to 15 days after inCulation, infection types
were recorded according to a modification of 0-4 scale (Knott 1989)
given by Stakman et al. (1962) as follows; 0: immune, no visible
infection, 0;: no uredia, hypersensitive flecks present, 1:
resistant, minute nonsporulating uredia surrounded by distinct
necrotic areas, 2: resistant to moderately resistant, small uredia
with slight sporulation surrounded by chlorotic or necrotic areas, 3:
moderately resistant to moderately susceptible, medium sized
sporulating uredia, chlorotic areas may be present, 4: susceptible,
large sporulating uredia with no chlorosis or necrosis, X: resistant,
heterogeneous, variable size uredia distributed over leaves.
Variations were indicated by the use of - (less than the average for
the class) and + (more than the average for the class) as
superscripts.
Results and discussion
The accession 13749 of Ae. umbellulata was resistant under
field conditions as well as at seedling stage to pathotype N of
stripe rust and pathotypes 77-4, 77-5, 104B, and 104-2 of leaf rust
(Table 2). However, the durum wheat
cultivars, Bijaga Yellow (BY) and Malvi LCal (ML) were susceptible to
both the rusts under the field conditions. The cultivar BY was
resistant to races 77-4 and 77-5 of led rust and race N of stripe
rust, but susceptible to races 104B and 104-2 of leaf rust, whereas,
the durum wheat cv. ML, showed susceptibility to all the pathotypes
of rusts , except 104B of leaf rust, at seedling stage (Table
2).
<--Back | -->Next
(go to
KOMUGI Home) (go
to WIS List) (go to NO.92
Contents)