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Material and methods
Experiments were conducted under natural environment in a small
piece of land (clay loam soil) with negligible soil-heterogeneity.
Ten seeds each of 90 diverse wheat (Triticum aestivum L.)
accessions were planted in separate rows with 10cm and 23cm distance
between seeds and rows respectively. Two sets of seeds were planted
in time and one set was planted late (60 days after first sowing).
Genotypes with poor germination or less than 10 plants were rejected
and ultimately 69 entries were used for further analysis. Three
plants with uniform morphology and flowering time, from each row in
the first set were subjected to manual defoliation 90 days after
sowing and remaining plants were maintained as a control.
Simultaneously, all the genotypes in the second set were sprayed with
0.25% of KI solution. This concentration was chosen on the basis of
earlier reports (Mahalakshmi et al 1994; Royo and Blanco 1998) and
also by our preliminary observations. Spraying was carried out until
whole plant including tillers was fully drenched. Days to anthesis
and physiological maturity was noted in all the four treatments viz.,
manual defoliation, KI spray, late sowing and control. Matured main
shoot-spike of three plants of each accession from all the four
treatments was sampled for studying grain development. Spikes were
threshed manually and each grain was separated with maximum care.
Grain weight and grain number in each spike was recorded. Standard
deviation expressed as a percent of mean (coefficient of variation)
was used to explain the variability in response of accessions to
different treatment.
Results and discussion
There was remarkable reduction in grain growth period (from 41
days to 23 days) when genotypes were planted late mainly due to
continuous rise in temperature. Potassium iodide (KI) brought about
gradual decrease in chlorophyll content in leaves as reported in
earlier studies (Mahalakshmi et al. 1994; Royo and Blanco 1998).
However, in defoliated plants spike remained teen or longer time.
Significant difference in flowering time of accessions was recorded
with days,to anthesis and maturity ranging from 77 to 97 days and 129
to 137 days after sowing, respectively. As a result, defoliation or
KI spray carried out on the same day exposed genotypes to these
treatments 0 to 20 days after ear emergence (Table
1). Breeders dealing with segregating material often come across
such constraints, wherein comparison between response of accessions
becomes difficult. However, to have a realistic interpretation 'of
data, accessions were categorized into four groups on the basis of
stage of crop at the time of treatment. The accessions. in the first
two groups were exposed to defoliation or KI treatment before or at
the time. of anthesis. Accessions in the other two groups were
exposed to these treatments one week or two weeks after anthesis.
Early stages of grain development were more prone to damage caused by
defoliation, KI treatment or high temperatures.
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