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The study entitled “Identification of core set in fodder cowpea (Vigna
unguiculata (L.) Walp) germplasm accessions” was carried out at Department of Plant
Breeding and Genetics, College of Agriculture, Vellayani during December 2020-May
2021 with the objective of assessing variability in the fodder cowpea germplasm
accessions, constitute a representative core set and to evaluate the representativeness of the
core set vis a vis base collection.
143 fodder cowpea (Vigna unguiculata (L.) Walp) genotypes collected from
NBPGR, New Delhi and bush type cowpea varieties of KAU along with 3 check varieties
formed the base collection. There were 2 experiments, in which experiment 1 was
evaluation of seedlings and experiment 2 was field evaluation of fodder cowpea variability
and identification of core set. Experiment 1 i.e., seedling evaluation of 146 accessions was
carried out in Completely Randomized Design with 2 replications. Various seedling
characters such as germination %, shoot length, root length, seedling length, fresh weight
per plant, dry weight per plant, vigor index and relative growth index were observed. Oneway ANOVA and Principal Component Analysis were also carried out using GRAPES
software of KAU. All the genotypes significantly differ each other in all the character. The
biplot was constructed using the first two PC’s, in which genotypes like EC723987,
IC39908, IC402125, IC398992, NR/18-105 showed maximum scattering and
demonstrated maximum genetic divergence among the accessions.
Evaluation of variability was carried out in the field using Augmented Block
Design. The seeds were sown at a spacing of 15 cm x 30 cm during January 2021. Every
accessions were sown in two rows of ten plants each and the check varieties were replicated
in all the 13 blocks. The cultural operations were done according to the recommendation
of KAU Package of Practices.
The genotypes were evaluated for 20 biometric characters and seven qualitative
characters. The genotypes showed significant differences for all the characters except
secondary branches per plant and stem girth. Biochemical character such as crude protein
and crude fibre content for top genotypes which showed high green fodder yield per plant
was estimated and all the treatments significantly differ from each other. Genetic parameter
analysis was performed for twenty biometric characters and for all the characters PCV
values were higher than GCV values indicating the influence of environment. The
phenotypic and genotypic coefficient of variation were maximum for Leaf Area Index
(LAI), green fodder yield per plant, stem dry weight per plant, leaf dry weight per plant,
seed yield per plant etc. and minimum for days to maturity. Heritability and genetic
advance was high for number of leaves per plant, LAI, green fodder yield per plant, stem
dry weight per plant, leaf dry weight per plant, plant height, seed yield per plant etc.
The correlation studies revealed positive correlation of leaf dry weight, stem dry
weight, dry matter yield, LAI with green fodder yield per plant. A negative significant
correlation was seen in between stem girth and days of 50% flowering.
The path analysis provides information on contribution of traits by partitioning
the total correlation into direct and indirect effects. Path analysis of fourteen characters
revealed high and positive direct effect of stem dry weight, leaf dry weight, primary
branches per plant, days of 50% flowering on green fodder yield. High indirect effect on
green fodder yield was observed for many characters. Residual effect obtained was 17.6%
which indicates that 82.4% variation in yield was contributed by characters under study.
Cluster analysis was done using UPGMA (Unweighted Pair Group Method with
Arithmetic Mean) method. The 146 accessions were grouped into 30 clusters. Cluster X
with 21 genotypes was the largest followed by cluster XI (20 genotypes), cluster XIV (13
genotypes), cluster I (12 genotypes), cluster VII (10 genotypes), cluster II (8 genotypes),
cluster IV (7 genotypes), cluster XII and cluster XXVI1 (6 genotypes each), cluster XVII
(5 genotypes), cluster VI, cluster VIII, cluster XIX and cluster XXIX (4 genotypes each),
cluster XIII (3 genotypes), cluster IX, cluster XV, cluster XVIII and cluster XXIV (2
genotypes each) and the remaining were solitary clusters.
Core analysis was carried out using power core (v.1.0) software. The core set
formed comprised of 24 accessions (16 per cent) of the entire collection. A comparison of
geographical distribution of accessions in core set and base collection were done. The base
collection comprised of accessions from India- 34%, Philippines- 14%, Nigeria, USA,
African countries, Europe, Australia etc. The core collection contained accession mostly
from India with representation from Philippines, Nigeria, USA, Chad, Hungary. A
comparison of frequency distribution of qualitative traits in core and base collection were
estimated using chi square test and all the characters showed non significance among each
other indicated the true representation of core with respect to qualitative characters.
Comparison of statistical parameters viz., mean, range and variance with respect to 20
quantitative traits in both core set and base collection were also done using two tailed t-test
for comparing mean and homogeneity test (F test) for comparison of variance. In this case
also all the character showed no significant difference between the two population revealed
that the core set included as much genetic diversity as possible. Phenotypic diversity among
core and base was assessed using Shannon-Weaver diversity index (H‟). All character has
obtained higher H‟ value with comparable overall mean of 2.008±0.11 and 2.138±0.12
respectively. Percentage of diversity in core set over base collection was 101.5%.
The core set seems to be a good subset of fodder cowpea germplasm accessions
which covers most of all existing diversity in base collection and eliminated the duplicates.
This can form a great population which can further utilize for various breeding aspects.