Unveiling Diversity: Morphological and Genetic Characterization of Cowpea Germplasm in the Southern District of Odisha

Cowpea [Vigna unguiculata (L) Walp.] is a self-pollinated legume with multiple common names. According to Vavilov et al., (1951), it is native to West Africa and is cultivated for its green vegetables, dry beans and forage. India is a major producer, but it faces low productivity due to various factors. According to Steele et al., (1976) these include the cultivation of diverse varieties, non-synchronous flowering and fruiting, susceptibility to stresses and poor harvest index. To address these issues, breeding programs need to focus on developing high-yielding and stress-resistant varieties. This study aims to investigate the morphological and genetic variations among cowpea genotypes in Odisha to provide a foundation for future breeding efforts.

The study investigated morphological and genetic variations in cowpea genotypes during the zaid season of 2024 at the Horticulture Research Farm of M S Swaminathan School of Agriculture, Centurion University of Technology and Management, Paralakhemundi, Gajapati, Odisha. The experiment involved 22 genotypes and 3 replications, with each genotype grown in individual plots. Observations were recorded on both qualitative and quantitative characteristics. Ten randomly chosen plants were evaluated for growth habit, pigmentation, leaf color, flower wing color, pod color, pod attachment to peduncle, pod curvature, seed color and pod height. The quantitative traits were plant height (cm), days to first flowering, days to 50% flowering, pod length (cm), pod diameter (cm), number of green pods per plant, green pod weight (g), 100 seed weight (g), number of seeds per pod, chlorophyll content (mg/g), green pod yield per plant (g) and total vitamin c (mg/100 g) (by titrimetric and colorimetric methods). Statistical analyses were performed using Windostat and the Shannon-Weaver diversity index was calculated for each character. To assess the extent of variation among the cowpea genotypes, the following statistical analyses were performed. Genotypic and phenotypic coefficients of variation were calculated based on the method proposed by Burton (1952) and heritability in Broad Sense (H) calculated using the method of Hanson et al., (1956) and expected genetic advance (GA) was estimated using the methods outlined by Lush (1949) and Johnson et al., (1955). The direct and indirect effects of various traits on green pod yield per plant were determined through path coefficient analysis, following the method established by Dewey and Lu (1959).

A study was conducted on 22 vegetable cowpea genotypes to analyze their morphological characteristics using NBPGR descriptors. Ten qualitative characters were recorded and analyzed, leading to the categorization of growth habits into five groups, with variations reported in plant pigmentation, leaf color and pod color. The genotypes also showed diversity in seed shape, plant hairiness, flower wing color, pod attachment to peduncle and pod curvature. Variations were observed in seed color as well, with different genotypes showing a range of colors such as brown, white, dark brown, red and dark red. Previous studies by Egbadzor et al., (2014) also reported significant variations in the morphological characteristics of cowpea genotypes, highlighting the genetic diversity within this crop. Biodiversity in crops is assessed through allelic evenness and allelic richness, with allelic evenness measured using the Shannon-Wiener Diversity Index and allelic richness determined by counting descriptor states. The richness signifies the number of genotypes in an area, while evenness represents the relative abundance of each genotype. A study on 22 cowpea genotypes revealed a mean diversity index (H’) of 1.284, indicating a high level of diversity (Table 1). Traits like plant pigmentation and pod colour showed the highest diversity index values. Traits with H’≥0.60 included pod colour, plant pigmentation and leaf colour. Intermediate diversity was observed in traits like plant hairiness and pod curvature. Studies by Yasin et al., (2021) in Ethiopia also showed high diversity in cowpea genotypes. The Shannon-Weaver index ranges from 0 to 4.6, with a value of 0 indicating uniformity and 4.6 showing even distribution among genotypes. A low H’ suggests a lack of diversity, while a higher value suggests variability. Overall, values below the mean indicate imbalanced frequency and lack of diversity in traits.



The study aimed to analyze variations in 12 quantitative characteristics of 22 cowpea genotypes. Panse (1957) suggested the analysis and revealed that mean squares due to genotypes were highly significant for all traits, indicating the justification of studying genetic variability using these genotypes (Table 2). The top four characters with the highest variance were green pod yield per plant, 10 pod weight, plant height and number of pods per plant, indicating a wide range of diversity. The mean performance pertaining to 12 quantitative characters of 22 cowpea genotypes was presented in Table 3. Plant height varied among genotypes, with the maximum being ‘Ankur Ketaki’ (94.86 cm) followed by ‘CP-645’ (94.00 cm). Early flowering leads to early production of pods, which can fetch higher market prices. Days to first flowering ranged from 35.00 to 41.66 days, with the minimum days taken in ‘Ankur Ketaki’ and ‘IC-259071’ (35.00 days) followed by ‘CP-732’ and ‘NS-24/8-2’ (35.33 days). The genotype ‘Arka Samrudhi’ took the maximum days for first flowering, similar to previous studies in Indian and African conditions.





Days to opening of first flower in 50% population ranged from 40.66 to 46.00 days, with the minimum days taken in ‘RHS-Kanakam’ (40.66 days) followed by ‘Arka Suman’ and ‘CP-601’ (41.66 days). The genotype ‘Arka Samrudhi’ took the maximum days for 50% flowering, similar to previous studies in Karnataka, Tamil Nadu, Rajasthan and Telangana conditions.

The study analyzed the pod diameter, pod weight, chlorophyll content, total vitamin C and total vitamin C content of cowpea genotypes. The pod diameter ranged from 0.51 cm to 0.76 cm, with the maximum and minimum pod diameters observed in genotypes IC-259071, C-1070 and Arka Samrudhi. The number of pods per plant also varied widely among genotypes, with the highest pod number produced by IC-202926 (33.73) and the lowest recorded by IC-202803. The mean seed weight was 11.89 g, with the maximum being CP-421 (12.87 g) followed by Ankur Ketaki (12.50 g) and the minimum in NS-24/8-2 (11.02 g). Chlorophyll content varied from 4.07 to 8.65 mg/g, with the maximum found in Ankur Ketaki (8.65 mg/g) and the minimum in C-1070 (4.07 mg/g). The maximum pod yield per plant was produced by genotype IC-202926 (394.47 g), followed by genotype IC-259071 (367.40 g). The maximum total vitamin C was found in genotype C-1133 (16.61 mg/100 g), while the minimum was in genotype C-1070 (9.50 mg/100 g). The genotypes IC-202926, IC-259071, C-1070, CP-732, Ankur Ketaki, Kashi Nidhi and RHS-Kanakam were found to be most promising in terms of green pod yield per plant. Ankur Ketaki had the highest chlorophyll content among all genotypes studied, suggesting that these genotypes could be utilized in future breeding programs in cowpea. In conclusion, the study provides valuable insights into the pod diameter, pod weight, chlorophyll content, total vitamin C and total vitamin C content of cowpea genotypes. These findings can be useful for future breeding programs and can help improve the quality and yield of cowpea.
 
Analysis of components of pod yield
 
Scientists have analyzed cowpea genotypes to determine their significance in fruit yield. This study examines genetic diversity and yield component analyses to identify important fruit yield components, aiming to define an ideal plant ideotype for cowpea crops.
 
Analysis of genetic variability and heritability
 
Genotypic and phenotypic coefficients of variation are commonly used to assess variability in a genetic population. The relative value of these types of coefficients gives an idea about the magnitude of variability present in a genetic population. Phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV) are categorized as low (0-10%), moderate (11-20%) and high (>20%). Phenotypic coefficient of variation (PCV) was marginally higher than the corresponding genotypic coefficient of variation (GCV), indicating that the apparent variation was not only due to genotypes but also due to the influence of environment in the expression of traits. In Table 4, PCV values varied between 3.45% and 27.41% for days to 50% flowering and pod yield per plant, while GCV values varied from 2.10% to 25.74% for days to 50% flowering and pod yield per plant. High PCV values were recorded for plant height (24.50%) and pod yield per plant (27.41%), while moderate PCV values were observed for pod length (12.77%), number of pods per plant (13.13%), pod diameter (12.99%), chlorophyll content (15.67%) and Total Vitamin C (13.88%). High to moderate magnitude of GCV and PCV generally indicated ample scope for improvement through selection. The present findings suggest the worth of all traits for the study of genetic variability in cowpea. The wide difference between phenotypic and genotypic coefficient of variation indicates their sensitivity to environmental fluctuation, while narrow differences show less environmental influence on the expression of these traits. Genotypic coefficients of variation do not estimate heritable variations, making heritability estimation necessary. Heritability is important for plant breeders as it measures the value of selection for character in various types of progenies and as an index of transmissibility. The heritability value becomes a measure of the genetic relationship between parent and progeny. Heritability, a concept proposed by Lush (1940), measures the proportion of genetic variation transmitted to offspring. It is classified as low (below 30%), medium (30-60%) and high (above 60%) by Johnson et al., (1955). High heritability estimates were recorded for plant height, pod length, pod diameter, number of pods per plant, chlorophyll content, total vitamin C and pod yield per plant. Medium heritability estimates were recorded for days to first flowering, days to 50% flowering, 10 pod weight, 100 seed weight and number of seeds per pod.



Singh et al., (1974) suggested that high heritability indicates less environmental influence in observed variation, suggesting that selection based on phenotypic expression could be relied upon. However, this broad sense heritability value may be overestimated as it cannot exclude variation due to different genetic components and their interrelations. Heritability alone cannot provide information on the amount of genetic progress that would result from selecting the best individuals. Genetic advance is the improvement in performance of selected lines over the original population. Johnson et al., (1955) suggested that heritability estimate combined with substantial amount of genetic advance would be more helpful than heritability alone in predicting the resultant effect from selecting the best individuals. GA was expressed as percentage of mean, with high heritability coupled with high genetic advance observed for plant height, pod diameter, chlorophyll content, total vitamin C and pod yield per plant. Moderate genetic advance was exhibited by traits pod length and number of pods per plant (Fig 1). Low values of genetic advance were found for traits days to first flowering, days to 50% flowering, 10 pod weight, 100 seed weight and number of seeds per pod, as they indicated dominance and epistatic effects, making selection for these traits unlikely and it was also observed by Dipankar et al., (2023) and Songsri et al., (2008).

The experiment found that genotypes IC-202926, IC-259071, C-1070, CP-732, Ankur Ketaki, Kashi Nidhi and RHS-Kanakam were most promising for green pod yield per plant. Ankur Ketaki had the highest Chlorophyll content, making it suitable for future breeding programs in cowpea. The yield component traits, pod diameter, number of pods per plant and 100 Seed weight, showed high positive direct effects on pod yield per plant. Other traits, like pod length and 10 pod weight, had low positive effects. D2 values showed significant genetic diversity among the genotypes. Cluster I contained sixteen genotypes, while cluster II contained four. The maximum inter-cluster value between cluster II and III indicated that these genotypes could be used as parents in hybridization programs to develop higher heterotic hybrids. Other genotypes, such as C-1133, Arka Samrudhi, Arka Suman, Kashi Kanchan, CP-601, V-585 and C-1126, could be considered good for breeding programs.

All authors declared that there is no conflict of interest.