MSc

The study entitled “Heterosis, combining ability and gene action for yield in shade
tolerant lines of grain cowpea (Vigna unguiculata (L.) Walp.) was carried out at the College
of Agriculture, Vellayani and Farming Systems Research Station, Sadanandapuram during
2021 – 2023 with the objective of estimation of heterosis and combining ability using Line x
Tester mating design in shade tolerant grain cowpea genotypes.
The research comprised two experiments, involving the hybridization of selected
genotypes in a Line x Tester mating design and the evaluation of parents and their hybrids
under field conditions. Eight parents were chosen based on the findings of the previous study
titled 'Genetic Variability Studies in Grain Cowpea (Vigna unguiculata (L.) Walp.)' (Darshana,
2020). The selected genotypes were crossed using Line x Tester (5 x 3) mating design. The
chosen female parents (Lines) CHESCP 03(L1), CHESCP 32(L2), CHESCP 17(L3), Sreya
(L4), and CHESCP 19 (L5) were characterized by high yield and shade tolerance, while the
selected male parents (Testers) Subhra(T1), KYLMVU 10 (T2), and Hridya (T3) exhibited
short duration and high protein content. In the second phase of the experiment, fifteen hybrids
were produced and cultivated alongside the parents, undergoing evaluation under field
conditions. The field experiment was conducted in a randomized block design (RBD) with
three replications.
Observations were made on twenty-seven characters and subjected to Line x Tester
analysis to estimate heterosis, combining ability, and gene action in the inheritance of yield
and yield-attributing traits. Analysis of variance revealed the significant differences among
both parents and hybrids across twenty-three treatments for all the traits. Non-additive gene
action, predominantly manifested through a higher magnitude of specific combining ability
(SCA) variances compared to general combining ability (GCA) variances is evident for all
characters except dry matter content, number of seeds per pod, crop duration, and leaf area
duration, where general combining ability plays a more substantial role. A preponderance of
additive gene action is present in the case of dry matter content, number of seeds per pod, crop
duration, and leaf area duration.
In parents, positive and significant GCA effects were evident for yield-related traits,
such as the number of pods per plant (in L1 and L4), number of seeds per pod (in L2), 100
seed weight (in L3, L4, L5), seed yield per plant (in L3, L4), and harvest index (in L1, L3, L4).
Among crosses, L4xT1, L2xT1, L3xT1, L3xT3, L2xT3, L1xT1, and L5xT1 showed positive
and highly significant SCA effects for traits including the number of pods per plant, 100-seed
weight, seed yield per plant, soluble protein content, seed protein content, leaf area, and plant
height, respectively. Significant negative GCA effects were observed in L1 and T3 for days to
50% flowering, while L2, T2, and T3 exhibited negative GCA effects for plant height.
Additionally, L2 and T2 showed negative GCA effects for crop duration.
Significant heterosis was observed for all the characters under study. The hybrids
L2xT2 and L3xT2 exhibited the highest relative heterosis and heterobeltiosis for the number
of primary branches per plant and seed yield per plant, respectively. In contrast, L2xT3 showed
maximum heterosis across all types, including standard heterosis, for the length of the leaf
parameter. Measurement of heterosis was carried out considering the parent Sreya (L4) as
standard check and results revealed that the crosses, L1xT1, L1xT2, L4xT1, L3xT2, L3xT3,
and L4xT2, were exhibited positive and significant standard heterosis for yield and yield
related traits. The hybrids viz., L3xT2, L2xT2, L2xT3, and L5xT3 exhibited negative and
significant standard heterosis for days to 50% flowering, crop duration, and plant height.
Considering the mean performance, SCA effects, and standard heterosis, the cross
combinations namely, L1xT1, L1xT2, L2xT3, L3xT1, L3xT3, L4xT2, L5xT2, and L5xT3 were
identified as the superior performing hybrids for protein content.
Cowpea varietal improvement requires identifying superior genotypes from
hybridization-induced variability and understanding the gene action controlling grain yield and
related traits, with combining ability studies providing insights for selecting effective breeding
parents. Additionally, assessing heterosis magnitude aids in identifying potential cross
combinations, fostering variability in segregating generations for conventional breeding
programs.
The results of this investigation highlight potential implications, particularly between
lines L3 and L4, which are identified as effective general combiners for seed yield and most
yield components. Similarly, among testers T1 and T2, they are recognized as proficient
general combiners for seed yield and most of the yield components. Line L1, along with tester
T3, exhibited negative general combining ability effects for days to 50% flowering. In contrast,
Line L2, along with testers T2 and T3, displayed unfavourable GCA effects for plant height.
These findings suggest that these lines and testers could be strategically employed in breeding
programs focused on developing short-duration varieties. The crosses L3xT2, L4xT2, and
L4xT1, were found to have superior mean, SCA effects, and standard heterosis for the number
of seeds per pod, 100 seed weight, number of pods per plant, and seed yield per plant,
respectively. Hence, these crosses could be advanced through recurrent selection procedures to
exploit both additive and non-additive gene actions and obtain high-yielding segregating
generations.