Assessment of genetic diversity in cowpea (Vigna unguiculata L.)

Cowpea (Vigna unguiculata L. Walp) is an important legume crop valued for its adaptability, high protein content, and soil enriching properties. The present study was conducted to assess the genetic variability, trait associations, and genetic divergence among thirty diverse cowpea genotypes for ten yield and yield contributing and quality - related traits, with high heritability and high genetic advance recorded for plant height, yield per plant, number of branches, number of pods per plant, indicating the influence of additive gene action and potential for effective selection. correlation and path coefficient analyses revealed that number of pods per plant,100- seed weight, plant height and number of branches were the most influential traits contributing to seed yield, both directly and indirectly. Genotype Phule Sonali showed highest seed yield (23.89 g/plant)and number of pods (18.18), while TPTC-1 exhibited the tallest plants (85.50 cm) and CPD-32 had the highest number of seeds per plant (13.06) GCP-6 and CPD-119 recorded the highest protein (30.66%) and methionine content (36.48%) respectively, highlighting their superiority. Genetic divergence using Mahalnobis D2 statistics grouped the genotypes into seven clusters, with maximum inter-cluster distance observed between cluster II and VII, indicating wide genetic diversity. Genotypes from these clusters, particularly high -yielding and nutritionally superior types are recommended for hybridization to develop improved cowpea varities.

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100 Seed weight (g) and Days to maturity: Phule Sonali vs TPTC -1 vs M-10 vs IC-20108Close ×

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Yield per plant (g) and Protein content (%): KBC-WS-1 vs CPD-119 vs Phule Sonali vs Cavu-702Close ×

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Introduction

Cowpea (Vigna unguiculata L. Walp) is an important annual herbaceous crop from the genus Vigna legume crop cultivated widely in tropical and subtropical regions of world. It is a major source of dietary protein especially in vegetarian diets and play a crucial role in food security, soil enrichment through nitrogen fixation and climate resilience due to its drought tolerance and adaptability to marginal environments. In India, cowpea grown for both grain and fodder purposes and contributes significantly to the livelihood of smallholder farmers. A high level of morphological diversity is found within the species with large variation in size, shape and structure of the plant. Cowpea were domesticated in Africa and secondly found in Asia. Vigna unguiculata is a member of Vigna (Pea and beans) genus. Unguiculata is latin for "with a small claw", common names black eye pea, southern pea etc. belong to the Fabaceae family. Despite its importance, cowpea yield remains low and unstable due to limited genetic improvement, narrow genetic base and lack of systematic selection. Understanding the extent of genetic diversity is essential for crop improvement programs as it helps identify suitable parents for hybridization and selection strategies. Several studies have reported variability in cowpea using both morphological and molecular markers, however, comprehensive evaluations combining agronomic and nutritional traits such as protein and methionine content remains limited. Hence, assessing diversity using multiple traits can provide more reliable and useful information for breeding purposes. The present study was undertaken to evaluate thirty cowpea genotypes for genetic variability using key agronomic and nutritional traits. The study aims to estimate genetic parameters, Divergence among the genotypes play a vital role in cultivar improvement because, crosses involving genetically diverse parents likely to produce high heterotic effects and also more variability in segregating generations D 2 statistics is powerful tool for quantifying the divergence between two populations analyze clustering patterns and identify promising genotypes for future hybridization programs. This research contributes to developing a broader genetic base for cowpea improvement in Indian circumstances.

Materials and Methods

The experimental material consisted of 30 cowpea genotypes used in the study were collected from various agricultural research institutions, including RARI Durgapur, POCRTC Pandharpur, SDAU, SK, Nagar, UAS Dharwad, Dr. BSKKV Dapoli, RARS, ANGRAU, Tirupati evaluated at the Post Graduate Institute Rahuri, during the kharif season 2024. The trail was laid out in a randomized block design (RBD) with 3 replications. Standard cultural practices were followed throughout the growing season. The genotypes sown in two rows of each genotype of spacing 45 × 10 cm. The observations were recorded on five randomly selected plants from each treatment in each replication for 10 morphological, yield contributing along with quality parameters viz., Data was were recorded on days to 50% flowering, days to maturity, plant height (cm), number of branches per plant, number of pods per plant, number of seeds per pod, 100 seed weight, yield per plant, protein content and methionine content. The collected data were subjected to analysis of variance (ANOVA) and genetic parameters including genotypic and phenotypic coefficients of variation (GCV and PCV), heritability and genetic advance were computed. Genetic diversity was assessed using Mahalanobis D 2 statistics, cluster analysis, and principal component analysis (PCA). The correlation analysis was performed at both genotypic (above diagonal) and phenotypic (below diagonal) levels to understand the relationships among yield and its contributing traits in cowpea.

Result and discussion

Result and discussion

At the genotypic level, seed yield per plant exhibited a highly significant and positive correlation with: Number of pods per plant (r = 0.744**), Plant height (r = 0.487**),100Path coefficient analysis was carried out at the genotypic level to partition the correlation coefficients into direct and indirect effects, thereby providing insight into the true relationships between yield and its component traits in cowpea.

Direct Effects on Seed Yield

The highest positive direct effect on seed yield was observed for: Number of pods per plant (0.8915**),100 seed weight (0.5990**), Plant height (0.0278) These results indicate that these characters are the most important direct contributors to yield per plant. Improvement in these traits is likely to result in a significant increase in yield. Other traits such as days to maturity (0.1800) and number of branches per plant (0.1834) also showed positive but lower direct effects, suggesting their moderate contribution to yield.

Indirect Effects on

Indirect Effects on

Residual Effect

The residual effect was 0.219, indicating that the majority (around 78%) of the variability in seed yield was explained by the characters included in the analysis. This confirms the adequacy of the model. The path coefficient analysis clearly suggests that number of pods per plant, 100 seed weight, plant height, and number of branches per plant are the most promising characters for direct selection to improve seed yield in cowpea. These findings are in agreement with earlier correlation results and reinforce the importance of yield component traits in cowpea breeding strategies.

Conclusion

The present study revealed substantial genetic variability among thirty cowpea genotypes for key yield and yield contributing characters along with quality traits. High heritability combined with high genetic advance was observed for plant height, number of pods per plant and seed yield, indicating of predominance of additive gene action and potential for effective selection. Correlation and path coefficient analyses identified number of pods per plant, 100 seed weight and number of branches per plant as the most important contributors to seed yield both directly and indirectly. Among the genotypes, Phule sonali exhibited the highest seed yield (23.89 g/plant) and number of pods (18.18) while TPTC-1 recorded maximum plant height (85.50 cm) and CPD-32 showed maximum seeds per plant (13.06). The above genotypes show positively significant for yield and yield contributing characters viz., number of branches per plant, plant height and 100 seed weight. For quality traits, CPD-119 had the highest methionine content (36.48%) and GCP-6 highest protein content (30.65%). Genetic divergence analysis grouped genotypes into seven clusters, with the maximum inter-cluster distance between cluster II and VII, indicating wide genetic diversity.

Genotypes from this divergent clusters, especially high yielding and nutritionally rich types like Phule sonali, CPD-32, TPTC-1 and GCP-6, are ideal for use in hybridization programs to develop superior cowpea cultivars.

Figures and tables from the paper

Sr. No.	Name of genotype	Days to 50% flowering	Days to maturity	Plant Height (cm)	Number of pods per plant	Number of seeds per plant	Number of branches	100 Seed weight (g)	Yield per plant (g)	Protein content (%)	Methionine content (%)
1	CPD -1	48.00	74.00	44.70	14.03	8.8	8.8	13.51	17.48	28.52	36.36
2	CPD-10	52.33	81.66	34.56	11.16	10.76	10.00	14.41	18.76	26.06	27.58
3	CPD-32	66.66	86.00	34.80	10.00	10.90	7.23	13.46	12.98	25.88	28.67
4	CPD-119	45.33	73.66	34.86	9.50	11.20	7.86	10.33	12.12	27.68	36.48
5	CP-23-2	54.66	84.66	40.46	11.23	11.53	9.06	12.06	14.57	26.03	27.16
6	Cavu-702	46.33	67.66	40.15	11.36	8.4	9.06	12.27	18.14	30.24	31.23
7	GC-1	61.66	86.33	67.28	12.43	11.7	11.50	14.17	19.35	25.94	25.99
8	GC-3	66.00	86.33	52.48	14.56	9.3	8.1	13.35	19.33	25.44	27.12
9	GC-0502	52.00	76.00	34.08	17.90	10.35	7.8	11.90	19.67	27.11	31.52
10	GC-9202	65.33	93.33	59.20	15.55	10.08	8.2	10.35	16.84	26.39	29.10
11	DC-18-1	55.00	80.66	36.20	15.00	10.20	7.1	10.96	16.95	25.56	27.11
12	DC-19-6	48.00	70.33	34.73	15.13	9.4	7.3	13.16	17.07	27.79	31.16
13	DCP-5	56.33	74.33	34.56	15.16	10.20	10.03	9.4	15.44	28.39	28.15
14	DCS-6	60.33	84.66	41.90	10.96	11.71	8.4	12.11	13.75	29.76	30.09
15	DLCP-6	43.33	60.00	44.60	8.16	10.33	7.6	11.70	10.11	27.88	29.56
16	V-240	54.00	80.33	31.63	9.76	8.7	10.33	7.3	6.6	27.06	27.87
17	V-8981	45.66	66.33	40.15	11.03	8.3	9.1	12.56	12.10	25.82	27.95
18	Kokan safed	55.66	70.66	34.83	11.73	10.23	9.8	9.6	14.96	26.23	27.13
19	Kokan sadabahar	52.66	76.33	47.23	12.43	11.26	10.93	13.15	20.06	25.73	27.59
20	Kudalwal	48.66	80.00	39.70	9.70	11.13	9.53	13.66	14.98	27.38	33.29
21.	JLCP-5	55.66	83.33	38.10	13.16	10.93	11.16	7.2	11.02	25.77	28.10
22.	IC-20108	49.66	80.33	42.38	16.06	8.33	11.06	11.26	19.05	26.55	27.90
23.	M-10	47.83	72.83	80.20	17.33	11.76	11.20	9.28	20.18	26.45	28.16
24.	TPTC -1	65.83	88.33	85.50	16.03	10.18	16.20	13.12	21.36	24.79	28.28
25.	KBC-WS-1	44.66	76.33	40.04	17.03	9.3	12.03	11.39	19.08	30.45	30.47
26.	Phule Cowpea -1	54.33	78.50	40.76	13.23	11.16	11.10	11.70	18.31	25.44	30.26
27.	Phule Pandhari	59.33	86.33	42.11	16.41	10.50	10.30	9.5	17.39	25.13	29.21
28.	Phule Vithai	60.33	80.33	44.83	15.13	10.46	9.5	10.55	16.21	25.45	28.27
29.	Phule Rakhmai	48.00	80.33	42.86	13.13	10.26	6.1	10.68	13.42	26.45	27.80
30.	Phule Sonali	48.00	75.00	56.00	18.18	11.78	7.4	10.33	23.89	27.15	30.46
	Mean	53.72	78.50	44.69	13.41	10.31	9.47	11.48	16.37	26.82	29.33
	Range	43.33-66.66	60.00- 93.33	31.63- 85.50	8.16-18.18	8.30-11.78	6.16-16.20	7.20- 14.41	6.60- 23.89	24.79- 30.45	25.99-36.48
	S.E.	0.854	1.1331	1.3598	0.5081	0.4394	0.4357	0.3793	0.7160	0.5377	0.4716
	C.D. 5%	2.4176	3.2075	3.8494	1.4385	1.2440	1.2333	1.0738	2.0270	1.5222	1.3349
	C.V.	2.7535	2.500	5.2692	6.5586	7.3777	7.9618	5.7199	7.5727	3.4725	2.7841

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Table 1Close ×

Mean performance of 30 genotypes for 10 characters in cowpea

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Sr. No.	Character	Mean	Range	GCV (%)	PCV (%)	ECV (%)	Heritability (bs) (%)	Genetic Advance	Genetic Advance % of Mean
1	Days to 50% flowering	53.72	43.33-66.66	12.80	13.09	2.75	95.6	13.85	25.78
2	Days to maturity	78.50	60.00-93.33	9.18	9.51	2.50	93.1	14.32	18.24
3	Plant Height (cm)	44.69	31.63-85.50	29.16	29.63	5.26	96.8	26.42	59.11
4	Number of pods per plant	13.41	8.16-18.18	20.37	21.40	6.55	90.6	5.36	39.94
5	Number of seeds per pod	10.31	8.30-11.78	9.34	11.90	7.37	61.6	1.55	15.10
6	Number of branches	9.47	6.16-16.20	20.53	22.02	7.96	86.9	3.73	39.77
7	100 Seeds weight	11.48	7.20-14.41	15.92	16.91	5.72	88.6	3.54	30.86
8	Yield per plant	16.37	6.65-23.89	22.31	23.56	7.57	89.7	7.13	43.53
9	Protein content (%)	26.82	24.79-30.45	5.14	6.20	3.47	68.7	2.35	8.77
11	Methionine content (%)	29.33	25.99-36.48	8.43	8.88	2.78	90.2	4.84	16.50

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Genetic variability parameters for yield and yield contributing characters of cowpea

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Sr. No	Name of character	Days to 50% flow.	Days to maturity	Plant Height (cm)	Number of pods per plant	Number of seeds per pod	Number of branches per plant	100 Seed weight (g)	Protein content (%)	Methionine content (%)	Yield per plant (g)
1.	Days to 50% flowering	1.000	0.803**	0.288**	0.106	0.240*	0.209*	0.066	-0.537**	-0.451**	0.098
2.	Days to maturity	0.786**	1.000	0.272**	0.206	0.304**	0.226*	0.032	-0.477**	-0.302**	0.152
3.	Plant Height (cm)	0.279**	0.256*	1.000	0.391**	0.287**	0.517**	0.121	-0.305**	-0.211*	0.531**
4.	Number of pods per plant	0.116	0.194	0.371**	1.000	-0.086	0.205	-0.183	-0.108	-0.076	0.744**
5.	Number of seeds per pod	0.185	0.2348	0.220*	0.016	1.000	-0.007	0.0004	-0.274**	-0.060	0.177
6.	Number of branches	0.202	0.215*	0.482**	0.188	0.018	1.000	-0.029	-0.214*	-0.227*	0.295**
7.	100 Seed weight (g)	0.067	0.038	0.131	-0.165	-0.0009	-0.021	1.000	0.016	0.130	0.404**
8.	Protein content (%)	-0.439**	-0.369**	-0.236	-0.076	-0.174	-0.156	0.033	1.000	0.561**	-0.114
9.	Methionine content (%)	-0.433**	-0.299**	-0.196	-0.082	-0.082	-0.228	0.119	0.460**	1.000	-0.021
10.	Yield per plant(gm)	0.094	0.163	0.487**	0.662**	0.132	0.249*	0.350**	-0.048	-0.030	1.000

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Estimates of genotypic (above diagonal) and phenotypic correlation (below diagonal) among seed yield and yield contributing

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Sr. No	Name of character	Days to 50% flowering	Days to maturity	Plant Height (cm)	Number of pods per plant	Number of seeds per pod	Number of branches plant	100 Seed weight (g)	Protein content (%)	Methionine content (%)	Genotypic correlation with Yield per plant (g)
1.	Days to 50% flowering	-0.0036	-0.1446	-0.0080	0.0951	0.0783	0.0384	0.0389	-0.0174	0.0218	0.0989
2.	Days to maturity	-0.0029	-0.1800	-0.0076	0.1840	0.0992	0.0415	0.0189	-0.0155	0.0146	0.1523
3.	Plant Height (cm)	-0.0010	-0.0491	-0.0278	0.3488	0.0936	0.0950	0.0716	-0.0099	0.0102	0.5314**
4.	Number of pods per plant	-0.0004	-0.0371	-0.0109	0.8915**	-0.0282	0.0377	-0.1082	-0.0035	0.0037	0.7446**
5.	Number of seeds per pod	-0.0009	-0.0549	-0.0080	-0.0733	0.3255**	-0.0014	0.0003	-0.0089	0.0029	0.1773
6.	Number of branches per plant	-0.0007	-0.0407	-0.0144	0.1835	-0.0025	0.1834	-0.0173	-0.0069	0.0110	0.2953**
7.	100 seed weight (g)	-0.0002	-0.0058	-0.0034	0.1638	0.0001	-0.0054	0.5890**	0.0005	-0.0063	0.4048**
8.	Protein content (g)	0.0019	0.0859	0.0085	-0.0969	-0.0894	-0.0393	0.0096	0.0324	-0.0272	-0.1145
9.	Methionine content (%)	0.0016	0.0544	0.0059	-0.0683	-0.0197	-0.0417	0.0768	0.0182	-0.0484	-0.0211

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Estimates of genotypic direct (diagonal) and indirect effects (above and below diagonal) of component characters on seed yield in

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Cluster	I	II	III	IV	V	VI	VII
I	7.52 (56.55)	9.68 (93.70)	9.94 (98.80)	10.02 (100.40)	9.96 (99.20)	13.09 (171.34)	14.90 (222.01)
II		0.00	9.23 (85.19)	13.06 (170.56)	11.17 (127.01)	16.64 (276.88)	18.30 (334.89)
III			0.00	10.50 (110.25)	9.98 (99.60)	18.02 (324.72)	17.00 (289)
IV				0.00	6.77 (45.83)	9.64 (92.92)	7.87 (61.93)
V					0.00	10.99 (120.78)	10.17 (103.42)
VI						0.00	8.97 (80.46)
VII							0.00

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Average intra (bold) and inter-cluster D and D2 values (in

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