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Results and
Discussion
Analysis of variance due to crosses showed the significant
differences among the hybrids attributable to the differences
existing among the lines and testers (Table
1). The variances
due to lines and testers were also significant for three
physiological characters. The significant differences of lines x
testers was also observed for all the traits studied.
The ratio of general combining ability (gca) variance to sca variance
effects indicated that the nature of gene action was predominately
additive type for relative water content while non-additive gene
action was noticed for proline content and total chlorophyll content
(Table
1). These
findings indicated that both allelic and non-allelic interactions are
operating for the expression of these characters.
The general combining ability effects of the parents for proline
content indicated that varieties, JNK 6-1-184, A 9-30-1, NP-200
among testers and only MACS-9 among lines, possess favourable
genes (Table
2). And for
relative water content three testers (JNK 6-1-184, A 9-30-1 and NP
406) and two lines (HD 4502 and Meghadoot) showed desirable gca
effects. Similarly, for total chlorophyll content, two lines (NP 406
and N-59) and two testers (HD 4513 and MACS-9) indicated significant
additive effects. The parents involved in this study have been bred
particularly, for drought prone and rainfed areas of India. Hence
many parents have indicated fixable type gene action for all the
physiological characters. Since the gca effects are of practical use
to the breeder, these nine parents could be utilized for
inter
mating population
involving all possible crosses among them and adopting breeding
methods like biparental matings as well as mating among the selected
plants in early segregating generations. Such population would serve
the maximum scope for selection of stress tolerance/resistance
types.
Seventeen cross combinations indicated significant sca effects for
one or two physiological characters (Table
3). These crosses
were also in the combination of high
x high (H x H), high
x low (H x L), low x high (L x H) and low x
low (L
x L)
combining lines. The cross of H x H combination involves genetic
interactions of additive x
additive types which
were fixable in nature and also less prone to adverse environmental
conditions. Therefore, desirable segregants with fixable types were
expected from such cross combinations. As observed in our study,
several crosses would throw some desirable segregants; MACS-9 x A
9-30-1 and MACS-9 x NP200 for proline content and Meghadoot x JNK
6-1-184 and Meghadoot x A 9-30-1 for relative water
content.
The crosses involving in high x low and low x low combinations were
considered to be in dominant x additive and dominant x dominant types
in nature, respectively. Since the latter combination was
unpredictable because of non-allelic interactions, the possibility of
selecting the desirable characters in the subsequent generations will
be very rare. However, the former combinations (high x low or low
x high)
might throw some desirable transgressive segregants, if the additive
genetic system present in one of the parents complements the
epistatic effect present in the cross. As noticed in our study, nine
crosses for proline content, five crosses for relative water content
and five crosses for total chlorophyll content could be exploited
extensively for increasing the gene frequencies of desirable
alleles.
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