Morphological Characterization and Genetic Variability Study on Early Maturing Pigeonpea [Cajanus cajan (L.) Millsp.] Lines

Cajanus cajan (L.) Millsp., also known as pigeonpea, Arhar, redgram or Tur is an often cross pollinated crop belonging to the family fabaceae. The crop is significantly propagated through seeds and is cultivated majorly in the tropical semi-arid regions of the world. In India the crop stands second to chickpea in terms of importance. It is mostly cultivated in the states of Karnataka, Maharashtra andhra Pradesh, Madhya Pradesh, Punjab, Rajasthan and Haryana. Being rich in seed protein (21-24%) it is consumed as a dhal or split peas (Chaudhary et al., 2021). As of 2020-21 pigeonpea is cultivated in 35.21 mha area with a production of 1005 kg/ha and productivity of 35.87 mt (INDIASTAT, 2022). Despite being drought tolerant and having high seed protein content the cultivation of pigeonpea is fraught with various biotic and abiotic stresses (Khalekar et al., 2014). India being the primary centre of origin of pigeonpea there is a potential scope of variation existing among the Indian germplasm lines. Such prospective variability of the population is lucrative to the plant breeders for targeted crop improvement, improving quality traits and achieving productive sustainability. To achieve such utility of the germplasms proper cataloguing and characterization of the accessions is necessary. To this aspect clear guidelines for distinctness (D), uniformity (U) and stability (S) laid down by plant variety protection under general agreement on trade and tariff (GATT) have been very useful (Sahu et al., 2018). Hence considering the current production statistics of pigeonpea and with the ultimate objective of sustainable crop production by the farmers, such categorization and characterization of germplasm accessions would enable accurate identification of a particular line based on the clearly defined stable phenotypic characters needed for successful variety development programmes. The inherent genetic diversity of the population is further clarified from such evaluations. Genetic diversity is fundamental to crop improvement. Study of genetic parameters and their relative correlation illuminates superior traits and henceforth effective selections as well. Hence with the objective of characterizing new pigeonpea accession lines and understanding their genetic variability the present investigation classifies 200 hundred pigeonpea germplasm lines as per the DUS descriptors and also estimates the genetic parameters along with correlation among the yield and yield attributing characters.

The trial was conducted during Kharif 2020-21 and 2021-22 at the dryland crop research field of Pulses Section, Department of Genetics and Plant Breeding, CCS Haryana Agricultural University, Hisar. The experimental materials consisted of 193 germplasm lines along with seven check varieties sown in augmented block design (ABD) (Suppl. Table 1). The genotypes were sown in a single row of 3 m length with a spacing of 45 ×15 cm (Fig 1). The observations recorded were days to flowering, days to maturity, number of branches per plant, number of pods per plant, number of seeds per pod, 100 seed weight, plant height and seed yield per plant. Eventually the accessions were then subsequently characterized as per the DUS descriptors for pigeonpea. For each character observations were recorded from five randomly selected plants for each genotype. The mean data obtained for the yield and yield attributing traits was then subjected to analysis of variance as laid down by Mahalanobis (1936). Estimation of genetic parameters, genotypic coefficient of variation, phenotypic coefficient of variation, heritability and genetic advance at 5% selection intensity and correlation coefficients were done as per Singh and Chaudhary (1979). Data analysis were carried out in R studio software v. 4.2.2.
 

 

DUS characterization
 
The two hundred pigeonpea germplasm lines were characterized as per twenty-one different morphological DUS descriptors (Table 1). The twenty-one different DUS characters were catalogued at different crop growth stages. Across the accessions twelve out of twenty-one descriptors exhibited variations viz., the characters for time to 50% flowering, plant height, branching pattern, plant growth habit, colour of base of petal, pattern of streaks on petal, pod colour, pod number of seeds, pod size, seed colour, seed colour pattern, seed shape and seed size. The trait time of 50% flowering exhibited two states early flowering (61-90 days) and medium flowering (91-130 days) having 194 and 6 genotypes respectively. Similarly, the trait plant branching pattern showed 197 genotypes having semi-spreading (30°-60°) branching and three genotypes having erect (<30°) branching pattern (Fig 2). Two different states for plant height were observed 199 genotypes were tall (>150 cm) and one genotype was medium (100-150 cm) in plant height (Fig 3). The trait plant growth habit exhibited two different states, 194 genotypes displayed indeterminate growth habit whereas 6 genotypes showed determinate growth habit (Fig 4). Flower: Colour of base of petal (Standard) displayed three types of variations, 96 genotypes showed light yellow flowering, 102 showed yellow and only two genotypes showed orange yellow flower petal colour (Fig 5). Maximum variation was observed for the trait flower: pattern of streaks on petal (standard) wherein 7 genotypes showed absence of streaks, 171 genotypes displayed sparse streaks, 21 genotypes displayed medium streak patterns and only one genotype showed dense streak patterns (Fig 6). Among the pod characters, the trait for pod colour had two states one genotype with green pods and rest 199 genotypes displaying green with purple streaks (Fig 7). Pod size exhibited two kinds of variations, 176 genotypes had pod length of 4-5 cm and 24 genotypes showed more than 5cm pod length (Fig  8). Pod; number of seeds showed two states of variation out of three, 194 genotypes had 4 seeds and 6 genotypes had 3 seeds (Fig 9). Among the seed characters two genotypes displayed cream seed colour, 191 displayed brown and seven genotypes showed dark brown coloration (Fig 10). 195 genotypes exhibited uniform colour pattern whereas five genotypes showed mottled seed colour pattern (Fig 11). Similarly, 188 genotypes showed oval seed shape whereas five and seven genotypes were showing globular and elongate seed shape (Fig 12). With respect to seed size: 100 seed weight: 31 genotypes were small (<7 g), 159 were medium (7-9 g) and 10 genotypes were large (>9-11 g). Chaudhary et al., (2021) reported DUS descriptor studies on 200 germplasm lines wherein variations in pattern of streaks on standard petal, time of flowering, pod size and seed size were reported. Ranjani and Jayamani (2021) conducted DUS characterization studies on 60 genotypes and variations were reported in plant height, pattern of streaks on standard petal, seed shape, seed colour and seed size. Padma Priya et al., (2022) also reported DUS evaluation of 55 early maturing pigeonpea genotypes and variations were observed in flower colour, pattern of streaks on petals, pod colour, seed colour, seed shape and seed size.
 

 

 

 

 

 

 

 

 

 

 

 

 
ANOVA, genotypic coefficient of variation, phenotypic coefficient of variation, heritability and genetic advance
 
The analysis of variance was executed for the eight different biometrical characters. Significant variability was apparent across the accessions under study for all the eight biometrical phenological and morphological traits except among the checks for the character seeds per pod (SPP) as justified from the p values (<0.01) (Table 2). From the ANOVA table, it is clear that the environmental variance for all the characters is comparatively less. Such results justify that the characters are completely under genetic control with least environmental influence. Hence the uniformity and stability of the traits based on the DUS descriptor defined characterization is justified. Reports of low environmental variances were also found in the investigations of Saroj et al., (2013), Bishnoi et al., (2019). For the estimation of role and extent of genetic variation existing in the test material the study of genotypic (GCV) and phenotypic coefficient of variations (PCV) are important (Sharma et al., 2022). As per the findings of Deshmukh et al., (1986), PCV and GCV values less than 10% are considered as low, values between 10 and 20% to be medium and the values greater than 20% are regarded as high. Hence from the Table 3 it could be inferred that the highest GCV and PCV value was obtained for seed yield per plant (19.91 and 21.31 respectively) and the characters days to flowering (10.86 and 11.11), branches per plant (BPP) (16.67 and 18.39), Pods per plant (PPP) (16.09 and 18.08) and 100 seed weight (HSW) (10.49 and 11.07) had medium GCV and PCV values which connotative of fruitful genetic improvement through selection for these traits. On the contrary the characters days to maturity (DM) (4.33 and 4.93), plant height (PH) (4.68 and 7.35) and seeds per pod (SPP) (3.31 and 4.38) exhibited low GCV and PCV values. Shukla et al., (2022) also mentioned low GCV and PCV values for DM (3.71 and 3.82% respectively). All the yield attributing characters showed high to medium heritability indicating that selection for the characters for crop improvement would be highly effective. The character DF exhibited highest broad sense heritability (h²_BS) (95.74%). Similarly, the characters HSW (89.76), SYPP (86.63), PPP (79.17) and DM (77.02) also showed high heritability. High heritability coupled with high genetic advance is a requisite for effective crop improvement. Highest genetic advance (GA) was observed for the trait PPP (42.34) followed by DF (19.7) and PH (14.05). This justifies the early flowering character of the population which could be selected for breeding for earliness in pigeonpea. Similarly, high heritability values for HSW, SYPP and PPP are suggestive that effective selections could be exercised for bold seeded character along with high yield. Highest genetic advance as percent of mean (GAM) was seen for SYPP (38.24). The characters DF, BPP, PPP and HSW also displayed high GAM (Table 3). This is implicative of underlying additive gene action and hence direct selection for these traits would be highly beneficial for pigeonpea improvement. Congruently, high h²_BS coupled with high GA for DF, DM, PPP and SYPP were found in the reports of Mourya et al., (2022). Synonymous outcomes were mentioned in the published reports of Sharma et al., (2023); Bhagat et al., (2022). It was noted that the characters PH and SPP have low GAM (6.14 and 5.16 respectively) which implies that despite having high heritability the mean improvement of traits through selection would be less and hence careful trait selection has to be done for breeding objectives.
 

 

 
Correlation analysis
 
Correlation between characters is a consequence of underlying gene actions which manifest itself in form of phenotypic alterations in the plants. The direction and the extent of character association with yield are explained in the correlation studies. Useful correlation between economic characters could be exploited and such correlation of different characters henceforth enables plant breeders in selection of superior genotypes (Sharma et al., 2022). The present investigation reveals high positive correlation between SYPP with PPP (0.580) which implies that higher seed yield could be obtained through direct selection for plants having high pod numbers (Table 4). Congruent results were reported by Singh et al., (2019); Sharma et al., (2023); Chaudhary et al., (2022). Similarly, fair positive association was found for BPP (0.149). In concurrence to the reports of Chauhan et al., (2021) in the current study the character for PH also showed high correlation with seed yield (0.185) which is indicative that tall plant character contributes significantly towards yield enhancement. The character DF was also found to be positively correlated with DM (0.600) justifying the early maturing character of the population. Significantly negative correlations were found between HSW with DF and PPP which are however contrary to the findings of Vanniarajan et al., (2021) wherein positive associations between HSW with PH and DF were reported. Probable reason for such could be that small seeded trait contributes towards early flowering and higher photosynthate partioning towards pods so as to compensate for plant biomass output. Hence for future crop improvement investigations this point should be kept in mind.

Identification and selection of suitable germplasms is an important activity in plant breeding for crop improvement. The current investigation characterizes 200 pigeonpea accessions as per DUS descriptors and further evaluates the genetic variability of the population through genetic parameters along with correlation among yield and yield attributing traits. Twelve out of twenty-one DUS descriptors exhibited variation. In terms of genetic variability, significant but stable variation exists in the population as evident from the analysis of variance and other genetic parameters. High to medium heritability for all the traits was observed indicating the stability of traits and henceforth effective trait selection benefits. The highest GCV and PCV value was obtained for pods per plant whereas the characters days to flowering, branches per plant, pods per plant and 100 seed weight displayed medium GCV and PCV values. Highest genetic advance was observed for the trait pods per plant and highest genetic advance as percent of mean was obtained for seed yield per plant. Thus an underlying additive gene action is evident and fruitful crop improvement through trait selections could be sustained. Correlation analysis among the characters for yield revealed significant positive correlation between seed yield per plant with pods per plant and plant height. Hence it could be concluded that the present germplasm comprising of extra early and high yielding accessions is stable, uniform and has sufficient genetic variability which could be utilized in future breeding programmes for pigeonpea improvement.

None.