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To evolve high yielding,
drought resistant varieties better understanding of various
morpho-physiological characters like flag leaf area and weight,
epidermal cell size, stomatal size, tillers per plant, grains per
spike and grain yield per plant will need special attention. Equally
significant would be the proper choice of parents. They should not
only manifest the requisite traits but should also be capable of
producing hybrids with superior performance when crossed with other
parents. Combining ability analysis provides useful information in
this respect. Significant value of general and specific combining
ability effects (GCA and SCA) for flag leaf area (Prabhu and Sharma
1987), tillers per plant (Sarkar et al. 1987; Zubair et al. 1987;
Yadav and Singh 1988), grains per spike and grain yield per plant
(Sarkar et al. 1987; Malik et al. 1988; Yadav and Singh 1988) have
been reported. The diallel analysis approach (Griffing 1956) is not
practicable unless the number of parents involved is limited. A
diallel analysis using a limited number of parents gives poor
estimates of genetic parameters because of large sampling error with
an additional disadvantage that potentially superior parents may be
left untested. Line x tester analysis (Kempthrone 1957) is used in
this paper in order to evaluate nine parents for GCA and SCA.
Materials and methods
Three wheat varieties, Pak. 81 a commercial cultivar, LU26S a
drought tolerant variety and K1595 an elite line, which were used as
testers, were crossed with three high and three low abscisic acid
lines viz., High ABA 7, High ABA 9, High AB A 20, Low ABA 7, Low ABA
9, Low ABA 20, which were used as female parents (These high and low
abscisic acid lines, which will be referred to as HABA and LABA,
respectively, were acquired from Cambridge as such for drought
tolerance studies). The F1 seeds of the eighteen (3 x 6)
crosses along with their parents were planted in a triplicated
randomized complete block design during 1991-92. Each replication was
consisted of the nine parents and eighteen F1 crosses with
a five meter single row for each entry. Row to row and plant to plant
spacings were kept 30 and 15 cm, respectively. Fertilizer was applied
at the rate of 75 lbs nitrogen + 75 lbs phosphorous per acre. Data
for specific flag leaf area (Flag leaf area /flag leaf weight),
epidermal cell size (micro-meter2),
stomatal size (micro-meter2),
tillers per plant, grains per spike and grain yield per plant (g)
were recorded from ten randomly selected and guarded plants from each
entry. The data recorded were subjected to analysis of variance
according to Steel and Torrie (1980) to determine significant
differences among genotypes. Combining ability studies were made
using line x tester analysis as described by Kempthrone (1957).
Results and discussion
The perusal of the results presented in Table
1, show that the
female parents (called lines here) accounted significant differences
for specific flag leaf area, tillers per plant and grain yield per
plant. Male parents (called testers here) showed significant
differences for stomatal size and grains per spike. Interaction of
line x testers was significant in case of grains per spike only. Male
and female parents provided broad range of expression for various
traits (Table
2). Specific flag
leaf area was highest in HABA 9 and minimum in LU26S. Maxi mum
epidermal cell size was recorded in LU26S and minimum in HABA 20.
Stomatal size was largest in HABA 20 and smallest in LABA 7. Pak. 81
produced maximum number of tillers per plant, grains per spike and
grain yield per plant while minimum values for these traits were
recorded in HABA 71 LU26S and LABA 7, respectively.
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