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Materials and methods
Seed of five improved wheat cultivars i.e., HD 2135, HD 2160, HD
2189, HD 2285 and Vaishali (test cultivars), was obtained from
Division of Genetics, IARI, New Delhi. Cultivar, Agra Local (AL), was
used as a susceptible parent in making crosses.
The above test cultivars were crossed with AL to get F1
seed. Reciprocal crosses were also attempted to study the role of
cytoplasm in inheritance of resistance. HD 2189 and HD 2285 were also
crossed with isogenic wheat lines Sr11 and Sr30 for
test of allelism. After emergence of ear heads crossing was attempted
following emasculation procedure. A few F1 seeds were kept
in reserve while others were multiplied to raise F2 seed.
A part of F2 seed was further advanced to get
F3 seed for testing. To identify whether resistance is
similar or different in test cultivars, they were crossed among
themselves except in reciprocal manner, to make diallele crosses.
For testing, parents, F1, F2 and F3
seedlings were raised in aluminium trays (11" x 4" x 3") filled with
soil and farmyard manure. The see&as in trays were ready for
inoculation after 10 days of sowing. A set of differentials (Bahadur
et al. 1985) was also sown along with each set for ascertaining the
purity of the pathotype. The urediospore inoculum of various
pathotypes was obtained from Directorate of Wheat Research, Regional
Station, Flowerdale, Shimla. The urediospore-inoculum of each
pathotype was multiplied on AL, following standard procedures (Josh)
et al. 1988). The urediospore suspension of the pathotype was
prepared in a clean petri plate by mixing spore dust with a few drops
of water and a pinch of tween 20 to break the surface tension.
Adequate water was added to make the spore suspension and filled in
an atomizer and sprayed uniformly on the seedlings. Pots/trays were
sprayed with tap water and kept in moist chambers for 48h for
incubation at a temperature 20-25C. The above cultivars were also
grown along with isogenic lines and inoculated with 12 pathotypes
11(79G31), 21(9G5), 21A-2(75G5), 34-1(l0G13), 40-A(62G29),
40-1(62G29-1), 42(19G35), 117- 1(166G2), 117-A(36G2), 117A-1(38G18),
122(7G11), 295(7G43) for matching Sr genes following Bahadur
et al. (1993).
The differential sets were recorded after 15 days of inoculation when
disease developed. The infection types were noted according to the
classification of Stakman et al. (1962). Further minor variations in
infection types were recorded by putting + and - signs after the
number, where - sign indicated infection type lower and + sign higher
than normal categories. Symbols represent 0= immune, 0;=nearly
immune, 1 = very resistant, 2 = resistant, 3 = moderately
susceptible, 4 = susceptible, and N = Necrosis.
F2 seedlings, showing different infection types were
grouped separately and counted to determine F2 ratios.
F3 seedlings of each family, were also recorded for their
segregation into resistant, segregating and susceptible families. The
chi square test (chi2) for goodness of fit,
described by Panse and Sukhatme (1967) was used for testing validity
of observations in relation to expected one in segregating population
on the basis of Mendelian segregation.
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