Soil moisture content
Soil moisture content (%) of field varied from 3.1 to 7.8 in 2015 and 3.8 to 9.5 in 2016 during the cropping season. Further, it was 7.8 and 8.0 at the time of sowing and 3.1 and 3.8 at time of harvest in the year 2015 and 2016, respectively (Fig 1).
Range of variation
The descriptive statistics including the extreme mean values of genotype and the means together with their standard errors obtained on the basis of average data for both the year are summarized in Table 1. In general, clusterbean genotypes showed wide range of variability for most of the characters and the traits exhibited broad spectrum of ranges between maximum and minimum mean values during both years. For instance, the days to 50% flowering ranged from 26.4 to 33.0 during 2015-16 and 24.3 to 34.0 during 2016-17 with mean value of 26.4 and 28.6 respectively. The wide range of variability was also observed for different yield attributing characters. The number of clusters plant
-1 varied from 5.8 to 14.9 (2015-16) and 8.0 to 30.7 (2016-17) with the mean value of 10.8 and 16.1 respectively. Similarly, the number of pods cluster
-1 and number of seeds pod
-1 also ranged from 2.3 to 4.7 and 5.3 to 7.4 during 2015-16 and 3.7 to 7.0 and 7.0 to 8.7 during 2016-17 with mean value of 3.1 (2015-16) and 4.8 (2016-17) for number pods cluster
-1 and 6.7 (2015-16) and 8.0 (2016-17) for number of seeds pod
-1. The seed yield (g plant
-1) ranged from 4.0 to 9.7 with a mean of 6.1 during 2015-16 and 7.2 to 18.9 g/plant with a mean value of 13.5 during 2016-17. Thus, it is possible to succeed in improving grain yield by direct selection. The results obtained under study for the traits such as the number of pods plant
-1 at harvest and seed yield plant
-1 were corresponds well with the works of
Kumhar et al., (2012) as they obtained (31.1) and (10.12 g), respectively for the traits under one among different INM treatment (application of 100% RDN through Urea + Rhizobium + PSB). The works of
Om Vir and Singh (2015),
Singh et al., (2017), Pathak et al., (2009), Saini et al., (2010) and
Shabarish et al., (2012) also confirm the above findings. The total biomass yield (g plant
-1) ranged from 15.7 to 28.7 with a mean value of 21.6 during 2015-16 and 5.0 to 16.1 with mean value of 10.4 during 2016-17. As far as physiological and biochemical characters are concerned, specific leaf area, relative water content, total sugar and phenol content also showed vide variability among the different genotypes as shown in Table 1. Thus, significant variation was present between the accessions for all the recorded traits. This variation is very important for the plant breeders and selection is effective when magnitude of variability in the breeding population is too enough.
Estimation of genotypic and phenotypic coefficient of variation
The analysis of variance showed highly significant differences among the genotypes for all the 13 characters studied and the phenotypic variance was higher than genotypic variance for all the characters. The physiological and biochemical characters also showed wide genetic variability among the genotypes. High genotypic (Vg) and phenotypic (V
p) variances observed for the characters such as specific leaf area and total sugar content, whereas, the characters like number of seeds pod
-1, number of pods cluster
-1, number of branches plant
-1 and seed yield plant
-1 showed low.
The coefficient of phenotypic and genotypic variance was also calculated for all the traits under study. The phenotypic coefficient of variance (PCV) was higher than the genotypic coefficient of variance (GCV). The GCV values ranged up to 26.6 during 2015 and 31.79 during 2016 while the PCV value ranged up to 31.8 during 2015 and 40.2 during 2016. This higher PCV than GCV indicating that the little influence of environment on the expression of the characters and these findings are in accordance with the results of
Shabarish et al., (2012), Malaghan et al., (2013), Kumar et al., (2015), Santhosha et al., (2017) and Preeti and Prasad, (2018) who also observed greater value of phenotypic coefficient of variation than genotypic coefficient of variation. High GCV and PCV were observed for total sugar content, specific leaf area at 30 and 45 DAS, number of branches plant
-1, number of clusters plant
-1, number of pods cluster
-1 and seed yield plant-1. It indicates existence of broad genetic base, which would be amenable for further selection. Similar results were also observed by
Hanchinamani (2004),
Malaghan (2012),
Rai et al., (2012) and
Santhosha et al., (2017) for number of branches plant
-1 and number of clusters plant
-1;
Prakash et al., (2008), Dwivedi (2009) and
Santhosha et al., (2017) for number of pods cluster
-1.
The difference between PCV and GCV values was high for number of branches plant
-1, number of pods cluster
-1 and number of seeds pod
-1 indicating the influence of environment on these characters. However, this difference was low for days required for flowering, specific leaf area, plant height, number of clusters plant
-1, phenol and sugar content and seed yield plant
-1 suggesting minimal influence of environment on the expression of the characters, thereby having the highest estimates of heritability. Similar result was found by
Yucel et al., (2006) for days to flowering, plant height and harvest index. Low GCV and PCV were observed for relative water content, number of seeds pod
-1 and days to 50% flowering. These results are in conformity with results of
Saini et al., (2010), Singh et al., (2010) and
Manivannan and Anandakumar (2013) for the number of seeds pod
-1. This low GCV and PCV obtained under study for the above traits indicating the narrow genetic base and hence, variability has to be generated in these characters either through introduction or hybridizing divergent genotypes to recover transgressive segregates or by mutation breeding. Since the variation depends upon the magnitude of the measuring units of the traits, coefficient of variation is independent of the measuring units so it is more useful in comparing the population. The highest genotypic and phenotypic coefficient of variation indicates that selection can be applied on the traits to isolate more promising line.
Estimation of heritability in broad sense and genetic advance
Estimates of heritability in broad sense ranged from 25.61% for number of seeds pod
-1 to 98.6 % for relative water content during 2015-16 and 20.0% for number of seeds pod
-1 to 93.3% for sugar content during 2016-17 (Fig 3). According to Singh (2001), if heritability of a character is very high, say 80% or more, selection for such characters could be fairly easy. This is because there would be a close correspondence between the genotype and the phenotype due to the relative small contribution of the environment to the phenotype. On the other hand, for characters with low heritability, say 40% or less, selection may be considerably difficult or virtually impractical due to the masking effect of environment. Considering this bench-mark, heritability estimate was high (>80%) for total sugar and phenol content, relative water content, number of branches plant
-1, number of clusters plant
-1 and seed yield plant
-1. Similar results were also obtained by Hanchinamani (2004), Anandhi and Oommen (2007), Malaghan (2012),
Rai et al., (2012) and
Santhosha et al., (2017) for the number of clusters plant
-1.
Genetic advance under selection (GA) refers to the improvement of characters in genotypic value for the new population compared with the base population under one cycle of selection at a given selection intensity
(Singh et al., 2001). The characters those exhibit maximum heritability and high genetic advance as percentage of mean could be used as powerful tool in selection process such characters are controlled by the additive genes and less influenced by the environment (
Panse and Sukhatme, 1995). For efficient selection, we cannot solely believe on heritability and the combination of high heritability with high genetic advance will provide a clear base on the reliability of that particular trait in the selection of variable entries. The genetic advance as percentage of mean ranged from 6.49 to 69.5% during 2015-16 and 4.28 to 61.6 % during 2016-17. The high estimates of heritability coupled with high values of genetic advance over mean (GAM) were observed for the characters, total sugar content, specific leaf area at 45 DAS, number of clusters plant
-1 and seed yield plant
-1. This indicates predominance of additive component for these traits and hence direct selection would be more effective in improving these traits. These traits are highly reliable during selection process of the accessions.
Correlation studies
Correlation study revealed that number of clusters plant
-1 (0.81**, 0.84**), number of pods cluster
-1 (0.69**, 0.86**), pod dry weight (0.99**, 0.67**) showed positive significant correlation with seed yield plant
-1 during both the years which indicates strong association of these characters with seed yield plant
-1 (Table 2a and 2b). Therefore, by increasing the value of these component traits, yield may easily push up suggesting that selection for these characters will be useful in improving seed yield plant
-1. These results are in agreement with the earlier findings in clusterbean by
Preeti and Prasad (2018),
Rai and Dharmatti (2014),
Girish et al., (2012), for number of clusters plant
-1, number of pods cluster
-1 and hundred seed weight. The positive significant correlation was also measured between number of clusters plant
-1 and number of pods cluster
-1 (0.50*, 0.82**). Similar findings were also observed by
Saini et al., (2010).