Morphological Characterization and Genetic Diversity among Indigenous Collections of Pigeonpea [Cajanus cajan (L.) Millsp]

Pigeonpea [Cajanus cajan (L.) Millsp.] is the second most important pulse crop of India, which contributes significantly to the nourishment of Indian population. It plays an important role in food security, balanced diet and alleviation of poverty because of its diverse usages as food, fodder and fuel (Rao et al., 2002). India is the largest producer and consumer of pigeonpea covering 85% of world pigeonpea share. Globally pigeonpea covers an area of 6.99 mha with an annual production of 5.96 mt coupled with a productivity of 852 kg per ha. In India pigeopea covers an area of 4.23 mha with an annual production of 3.89 mt and productivity of 919 kg per ha. Pigeonpea is mainly grown in the states of Karnataka, Maharashtra, Madhya Pradesh, Uttar Pradesh and Gujarat. In Karnataka currently it is grown in an area of about 13 lakh ha with production of 9.1 lakh tons. (AICRP, Pigeonpea Annual report, 2020-21).
       
Variability studies are important to know the genetically divergent genotypes useful in crop improvement. Considering the choice of diverse parental material in the study, lot of diversity is expected to be generated for various characters. Genetic diversity analysis was therefore used to identify the divergent genotypes to utilize these genotypes to exploit heterosis. The genetically diverse parents are likely to produce not only heterotic effect but also desirable segregates to be selected.
               
Morphological characters are stable across environments owing to oligogeneic nature. Hence, they serve as morphological marker in breeding which can be used in varietal or genotypic identification, varietal purification and even in seed production. Keeping above points in view, the genotypes were categorized based on morphological characters. From characterization, a number of conclusions can be drawn. The variability that is identified by characterization needs to be conserved and should be made available to both germplasm collectors and breeders.

Present experiment was carried out during Kharif  2020 at Zonal Agriculture Research Station (ZARS), Kalaburagi, which is situated in agro-climatic zone-2 (North Eastern dry zone) of Karnataka state with 17^o 20' Latitude (N), 76^o 49' Longitude (E) and at an altitude of 443.88 meters above mean sea level.
       
A total of 266 indigenous collections of pigeonpea obtained from ICAR-National Bureau of Plant Genetic Resource (NBPGR), New Delhi and three checks BSMR-736, Asha and PT-012 were sown in augmented block design (ABD) consisting of 9 blocks with 33 genotypes in each block, checks were repeated randomly. Each genotype was sown in two rows of three meter length with spacing of 90 cm between rows and 20 cm between plants. Standard agronomic practices were followed and plant protection measures were taken as and when required by following the recommended package of practices (Anonymous., 2017). Observations were recorded on nine quantitative traits in five randomly selected plants from each genotype, viz., days to 50% flowering, days to maturity, plant height, number of primary branches, number of secondary branches, pod bearing length, number of pods per plant, seed yield per plant and 100 seed weight. Data recorded on five plants were averaged and average values were subjected to statistical analysis. The analysis of variance (ANOVA) was carried out for all characters individually. The data was analyzed using WINDOSTAT ver. 8.5 software developed by Indostat services, Hyderabad as per the principles of Mahalanobis (1936) and clustering by Tocher’s method (Rao, 1952) respectively.
               
Morphological characterization of 14 qualitative traits was recorded as per the key guidelines provided by PPV and FR (protection of plant varieties and farmer rights) authority, New Delhi and seed characteristics were recorded as per ICRISAT/ IBPGR (1993) (international bureau of plant genetic resources) guidelines.

Analysis of variance (ANOVA) exhibited highly significant difference among genotypes for all the traits (Table 1). Based on D² values the genotypes were grouped into 12 clusters using Tocher’s method given by Rao (1952). Of the 12 clusters, cluster I and II are the largest comprising 105 genotypes each followed by cluster IV (28 genotypes), cluster III (20 genotypes), eight clusters (V, VI, VII, VIII, IX, X, XI, XII) were solitary with  single genotypes each. These results are similar to observations of Muniswamy et al., (2014), Patel et al., (2018) and Satish et al., (2023). Katiyar et al., (2004), observed 14 clusters while grouping of 221 genotypes, Nethravathi and Patil (2014) obtained  nine clusters using 196 genotypes.
 

       
Generation of more clusters in general and sole clusters in specific is a representative of existence of huge amounts of diversity between the set of genotypes. The genotypes viz., IC339062, IC343954, IC339074, IC418976, IC343931, IC437078, IC355599 and IC384490 belongs to solitary cluster, which more usually have some distinctive characters which make them divergent. Furthermore, the genotypes which have congregated into a cluster which exhibit narrow range of genetic diversity among them while, broad range of variability was recorded between clusters. The generation of such clusters may be due to total isolation arresting the gene flow or rigorous natural or human selection for diverse adaptive complexes. These results are similar to the findings  of  Muniswamy et al., (2014), Patel et al., (2018) and Satish et al., (2023). The grouping of 266 germplasm lines into twelve clusters is presented in Table 2.
 

       
The highest intra cluster distance was noticed in cluster IV (6881.6) followed by III (5306.7), I (4932.53) and II (4694.3). The inter cluster D2 values were maximum (167349.3) between clusters VIII and XI indicating these two clusters distantly placed, followed by cluster V and XI (149790.6), IX and XI (144435.1). It is sensible to select genotypes from clusters showing high inter cluster distance for further crossing programme (Table 3). These results are in agreement with the earlier findings of Sreelakshmi et al., (2010) Muniswamy et al., (2014), Patel et al., (2018) and Satish et al., (2023).
 

       
Cluster mean analysis (Table 4) indicated that cluster VIII (80.00) and VII (95) are comprised of early flowering genotypes. Cluster VIII (133.00) comprised early maturing genotypes followed by cluster VII (148.00). The highest cluster mean for number of pods per plant was recorded in cluster XI (418.00) followed by cluster IV (291.43). The highest cluster mean for seed yield per plant was recorded in cluster IV (43.32) followed by cluster XI (42.40). The maximum cluster mean for 100 seed weight was recorded in cluster X (13.00) followed by cluster IX (12.50). Thus, the genotypes IC 343931 and IC437078 of the cluster IX and X have more seed weight. The cluster XI was solitary cluster which contains IC 355599 genotype and it is unique among all genotypes as indicated by more inter cluster distances and highest cluster means for number of pods per plant. Similar results were also obtained by Muniswamy et al., (2014) Patel et al., (2018) and Satish et al., (2023).
 

       
Contribution of individual characters towards divergence have been calculated (Table 5) which revealed that relative contribution of number of pods per plant was maximum (63.75%) followed by plant height (17.89%), days to 50 per cent flowering (6.84%), number of days to maturity (6.80%), seed yield per plant (3.61%)  and rest of the characters have shown very negligible or no contribution towards diversity. Therefore, selection of genotypes for character like number of pods per plant should receive maximum importance as they contributed more towards genetic divergence. These findings conformity with pervious results of Muniswamy et al., (2014), Singh et al., (2010), Bhadru (2011), Hariprasad et al., (2018) and Satish et al., (2023).
 

 
Morphological characterization
 
Out of 266 genoytpes, morphological variation was not observed for plant growth habit, leaf pubescence and pod pubescence. Unique genotypes were observed for seed colour pattern like mottled (IC 343859) and mottled and specked seeds (IC 343818). The traits like early plant vigour, branching pattern, base flower colour, stem colour, streak pattern of base petal, pod colour, seed characteristics exhibited lot of variation and the results of characterization of genotypes for morphological traits are presented in Table 6. Similar findings for plant vigor and plant growth habit were observed by Muniswamy et al., (2014) and Kumar et al., (2016). Hariprasad (2018) found similar results for branching pattern and stem colour. Kallihal et al., (2016) observed similar morphology in case of, streaks pattern on base petal, pod shape and pod colour. Similar findings for seed colour pattern and base seed colour was recorded by Muniswamy et al., (2014) and Satish et al., (2023).
 

               
Germplasm lines IC339062, IC343954, IC339074, IC418976, IC343931, IC437078, IC355599 and IC384490 fall into solitary cluster and are more often likely to have some unique characters which make them divergent like IC339062 had least plant height, IC418976 was early to flower and mature, IC437078 was having more 100 seed weight, IC355599 had more number of pods etc.  Based on mean performances for yield and yield related traits, the genotypes IC329120, IC405218, IC468129, IC468130, IC468145 and IC468146 were found promising. The genotypes IC355599 and IC343931 are trait specific for seed weight and pods per plant. Hence, afore said genotypes can be used for the further studies for improving the yield as a parent in the future breeding programme.

Authors are thankful to Director, National Bureau of Plant Genetic Resource (NBPGR), New Delhi for providing seed materials and for funding the CRP-AB pigeonpea project through Indian Institute of Pulses Research Institute (IIPR), Kanpur.

Conceptualization of research: S. Muniswamy, Neeta Singh, Sushil Pandey, and I.P. Singh.  Designing of the experiment: S. Muniswamy, Neeta Singh and Sushil Pandey. Execution of field/lab experiments and data collection: S. Muniswamy and Geeta. Writing-original draft preparation: S. Muniswamy and Geeta. Writing-review and editing: Neeta Singh, Sushil Pandey, and I.P. Singh.
       
All authors have read and agreed to the published version of the manuscript.

The authors declare no conflict of interest.