Evaluation of Cowpea Germplasm by using Agro-Morphological Characters

Vigna Savi is a large pantropical genus with 104 species (Lewis et al., 2005). India is represented with 24 species of Vigna (Sanjappa, 1992) and probable secondary centre of species diversification. Cowpea (Vigna unguiculata L.) is the most important grain legume crop grown in tropical and subtropical regions of the world (Deshpande et al., 2018). Cowpea is important legume grown over 12 million hectares worldwide, (http://www.fao.org/faostat/en/#data/QC ). India is one of major grower of the cowpea as it grown in an area of about 3.9 million hectors. (Kalpana, 2000). The cowpea seeds are most often consume but young leaves, fresh or dry seeds and young pods served as valuable source of protein in human diets. The seeds contain 1.8% fat and 60.3% carbohydrates and a rich source of calcium and iron (Mafakheri, et al., 2017). Cowpea is also cultivated as a fodder and it has vigorous vegetative growth and covers the ground so well that it checks the soil erosion.

Assessment of local and regional plant genotypes is important for identifying diversity among germplasm and for crop improvement (Mafakheri, et al., 2017). Documentation, characterization and exploitation of traditional local populations could contribute to their conservation and utilization as sources of desirable characteristics (Lazaridi et al., 2017). Moreover, the characterization data on various morphological traits is fundamental to handling germplasm at seed banks. The objective of present study was to characterize cowpea accessions collected from various households of western Maharashtra, India by using morphological traits.

Thirty-one accessions of cowpea (Table 1) were collected from various villages in Palghar, Sindhudurg, Ahmednagar and Satara districts of Maharashtra during 2016-2017. The field experiments were conducted at BAIF Central Research Station Urulikanchan, during July to October (Kharif) 2018 and March to June (summer) 2019. The experiments were arranged in row design with minimum 10 individuals of each accessions spaced at 60 cm row to row and 30 cm plant to plant. Recommended package of practices were adopted throughout experimentation.



The visual observations were recorded on 15 qualitative traits (growth habit, growth pattern, stem pigmentation, leaf colour intensity, raceme position, pod twisting, pod curvature, pod color intensity, pod pigmentation pattern, pod texture, seed texture, seed shape, seed main color, seed secondary color, hilum colour. The quantitative traits viz. leaf length, leaf width, pods per inflorescence, pod length, pod width, seeds per pod, seed length, seed width, seed thickness and 100 seed weight were recorded in five replicates. Analyses of variance performed on each morphological data to test the significance of variation between accessions by using ANOVA. Principle component analysis (PCA) was performed by using PAST software to investigate and summarize the underlying trends of variation.

Qualitative characters
 
Among studied accessions semi-prostrate (41.9 per cent) was dominant habit followed by semi-erect (29.0 per cent), climber (12.9 per cent), erect (9.7 percent) prostrate (6.5 per cent). Ngompe-Deffo et al., 2017 also reported semi-prostrate habit was dominant trait represented by 27 per cent Cameroon accessions. Majority of accessions had determinate growth (77.4 per cent). Most of accessions (80.6 per cent) had slightly pigmented stem followed by dark pigmented (9.7 per cent) and moderately pigmented stem (9.7 per cent).

Most of accessions showed dark green coloured leaves and raceme covered under canopy (80.6 per cent) while 19.4 per cent accessions had medium green coloured leaves and exposed racemes. Only Lal wal accession collected from Kudal area showed pod twisting, remaining all thirty accessions were without twisting.  Straight pod (51.6 percent) was dominant trait followed by slightly curved 45.2 pods, coiled (3.2 percent) pods and curved (3.2 percent) pods. Coiled pod trait was morphological marker for Bangadi chavali collected from Jawhar area.

Dark green colour pods was dominant trait (45.2 percent) over medium green pods (35.5 percent) and light green pods (19.4 percent), however Rambabu et al., (2017) reported light green colour as dominant trait. Most of accessions pod were without any pigmentation (64.5 percent) pattern while 25.8 percent accessions showed pigmentation at only tips; irregular splashes of pigment were observed in 6.5 percent accession while only one accession (Mothi chavali) was observed with uniformly pigmented pods. The pod texture varies as smooth (45.2 percent), slightly rough (29.0 percent), moderately rough (19.4 percent) and rough (6.5 percent).

 Among studied accessions, smooth seed texture (71.0 percent) was dominant trait over wrinkled seed. Seed shape varies as elliptic, curved and kidney shaped; among which elliptic shape was dominant (67.7 percent) however Rambabu et al., (2017) reported kidney seed shape was dominant. Seed colour was most varied character among evaluated accessions; yellowish white (37.6 percent) was most dominant seed colour followed by brownish yellow (22.6 percent) and purplish brown (9.7 percent). Black and reddish brown seed colour observed in 6.5 percent accessions. Yellowish purple, yellowish brown, gray, brown and purplish yellow seed color were shown by each single accession.  Blotchy pattern on seed surface was observed in 16.1 percent accessions while 83.9 percent showed uniform seed main color. However, area around hilum showed brown colour in narrow area (48.4 percent), black colour in narrow area (19.4 percent) black colour in wider area (3.2 percent) brown colour in wider area (3.2 percent) and 25.8 percent accessions are without distinct colour at hilum.

Principal components analysis (PCA) performed for all multivariate data derived from qualitative characters with respect to each accession. The studied 31 accessions forms three groups based on PCA as shown in Fig 1.



The analysis revealed that accessions CP-14, CP-12, CP-21, CP-22, CP-23, CP-25 (Group I) while CP-9, CP-19, CP-27, CP-31, CP-33 (Group II) and CP-2, CP-5, CP-10, CP-26, (Group III) groups together and shown no association with specific vectors. Remaining accessions CP-1, CP-3, CP-4, CP-8 CP-7, CP-11, CP-13, CP-15, CP-18, CP-20, CP-24, CP-28, CP-29, CP-30 and CP-32 remains scattered with no specific association.
 
Quantitative characters
 
The mean values of quantitative characters of cowpea accessions are given in Table 2. The results of present study showed that pod length was most varied trait (37.21 percent), followed by petiole length (28.23 percent) and seeds per pod (26.90 percent). Among the studied traits, seed thickness showed the lowest variation (16. 09 percent). Analysis of variance showed that all the characters were highly significant among the accessions. The studied accessions showed leaf length ranged between 7.70 cm (CP-24) to 13.08 cm (CP-32) and leaf width ranged between 4.66 cm (CP-4) to 9.62 cm (CP-5). Petiole length ranged between 5.50 cm (CP-4) to 14.88 cm (CP-32).



Time for first flowering ranged from 28 days (CP-25) to 65 days (CP-28). Porbeni et al., (2016) found 40 to 60.28 days required for first flowering in Nigerian mutant lines. Pods per inflorescence ranged from 1 to 4; accessions CP-25, CP-23, CP-24 and CP-28 were found with maximum pods per inflorescence. The longest and widest pods observed in CP-18 i.e. 27.48 cm and 1.06 cm while CP-26 had shortest pod (9.60 cm) and CP-24 had narrowest pod (0.48 cm). Maximum seeds per pod observed in accession CP-31(16.40) while CP-6 had minimum (7.20) seeds per pod. Tripathi et al., (2019) reported longest pod (53 cm) while Patil et al., (2015) reported pod length between 11.16 to 17.47 cm and seeds per pod ranged between 10.36 to 14.05 in cowpea accessions collected from Sardarkhushinagar, Gujarat. The accession CP-18 exhibit longest (1.18 cm) and widest (0.74 cm) seeds while accession CP-14 had more (0.60 cm) seed thickness. The shortest (0.46 cm), narrowest (0.40 cm) and least seed thickness (0.36 cm) was observed in accession CP-24. The highest 100 seed weight was 36.00 g (CP-18) and lowest 12.00 g (CP-21). Tripathi et al., (2019) the 100-seed weight ranged between 4.3 to 24.42 g among studied 4,922 accessions. Depending on yield contributing characters like 100 seed weight, pod size, seeds/pod, pods per inflorescence accession CP- 25, CP-31, CP-33 found top three promising accessions. These traits are useful in varietal developmental programs and may be explored by plant breeders and researchers. Moreover, some additional studies on specific traits like stress tolerance and resistance to pest and disease may also be undertaken in future.

It could be concluded that studied cowpea accessions were morphologically distinct from each other and showed genetic diversity in many characters like growth habit, growth pattern, pod colour, pod curvature, pod length, seed colour, seeds per pod and 100 seed wt. Some accessions showed desirable characters like more pod/ inflorescence (CP-25, CP-23 CP-24 and CP- 28) profuse branching (CP-31, CP-33 and CP-30); longer pods (CP-20, CP-15 and CP-18); seeds per pod (CP-31, CP-33 and CP-25).  This diverse genepool could be further useful for plant breeder in developing cowpea variety with specific traits. Moreover, the findings of the study are useful for researchers in developing Distinctness, Uniformity and Stability (DUS) testing guideline for cowpea.

The authors are thankful to Rajiv Gandhi Science & Technology Commission, Government of Maharashtra for financial support; Maharashtra Gene Bank Project field team for their help in germplasm collection and experiment conduction; Member of research coordination committee, BAIF for their valuable suggestions and Mr. N. L. Phadke and Dr. R. A. Bahulikar for statistical analysis of data.