Guar genotypes revealed significant variations in their morphological attributes
A total of six morphological quantitative traits were assessed for 40 guar genotypes and the data showed considerable variation among varieties and IC lines for most of the traits
viz. plant height (5.6±0.31 cm to 53.0± 0.27 cm), chlorophyll content (26.2±0.2 to 5.4±0.2), pods/ cluster (1-2 to 7-9), Clusters/ plant (1-2 to 6-7), days after flowering (56 to 86). The results revealed huge variation among indigenous under-utilized guar genotypes. RGC-936 was found to be early maturing genotype (56 DAF) with maximum pod/cluster (7-9), while HG-832 was observed to have maximum clusters/plant was observed, although pods/ cluster were same as for RGC-936. IC lines were found to be shorter (IC-421826) and late maturing genotypes (IC-324032 and IC-421837). Chlorophyll content was found to be highest in (M-83 85.4±0.2) and lowest in BG-2 (26.2+0.2) genotypes. 100 seeds weight ranged between 1.39 and 3.19 g among different genotypes as shown in (Table 1). Most of the genotypes (28) showed pink colour flower trait, whereas only 11 genotypes exhibited white flower colour. These results were consistent with what is expected in a natural setting. Further, our morphological data grouped HG-16, HG-870, RG-1002, BG-2, HG-2-20, HG-884, HG-832, HG-258, RGC-1066, HG-75, HG-563, HG-11, HG-119 into same clusters as observed previously
(Sultan et al., 2012b; Kumar et al., 2013; Boghara et al., 2016). Besides, it also observed that guar varieties from arid regions like Rajasthan and Haryana were clustered into same group, while the IC-lines were grouped separately as shown in the previous study
(Kumar and Ram, 2015).
Principal component analysis of morphological characters
Principal component analysis (PCA) for morphological parameters such as plant height, chlorophyll content, pods/ cluster, clusters/ plant, days after flowering and 100 seeds weight grouped the 40 guar genotypes into six co-ordinates based on scoring (Table 2.) However, the clustering of PCA between coordinate 1 and coordinate 2 divided the genotypes based on the highest percent of Eigen values (Euclidean similarity index) (as 59.67% to 30.13%) (Fig 3).
PCA has grouped the 40 genotypes into 4 clusters from 0 to 3 (Fig 4). Cluster 0 has 14 genotypes followed by Cluster 1 containing 13 genotypes, Cluster 2 containing 7 genotypes and Cluster 3 containing 5 genotypes, respectively. Coordinate 1 (Plant height) consisted of highest Eigen value in RGR-7 (31.7). Apart from that, coordinate 2 (chlorophyll content) consisted of highest values in RGR-13-1 (31.5). In addition, coordinate 3 (pod/cluster) had highest value in RGC-1031 (18.1), followed by Co-ordinate 4 (cluster/plant) having a highest value in RGC-936, Co-ordinate 5 (days after flowering) had highest value in HG-832 (2.2) and co-ordinate 6 (100 seed weight) had highest value in IC-415102 (0.79), respecively.
Biochemical characterization of guar genotypes
The biochemical results of 40 cluster bean genotypes revealed significant genotype variability for the traits studied in this study. Total protein content and galactomannan content are presented in Table 3. The total protein content varied from 11.8±0.10% (RCG-1055) to 20±0.38% (IC-329639) with mean of 22±0.4%. Genotypes with total protein content higher than 25% were categorized as high protein group, between 25 and 15% as medium protein group and those with less than 15% as low protein group (Table 3).
Pathak et al., (2011) also reported RGC-1038 variety to be the highest in terms of protein content among tested genotypes.
Naik et al., (2013) reported highest protein values of 27.73% and 34.27% in RGC-1028 and RGC-986, respectively.
Muftuoglu et al., (2019), also reported the yield and protein content range in edible guar genotypes with 4.38-17.22% crude protein and 65.40-75.25% digestible protein. Also, they confirmed green pod yields had significant positive correlations with the digestible protein content. Similarly, H.W.
Ashwini et al., (2019) highlighted comparable to RGC-1033 (35.07%), RGC-1038 (33.40%) and HG-870 (33.10%), the genotype RGC-1002 had a noticeably greater proportion of crude protein (35.80%). Nonetheless, the genotypes RGC-986 (25.43%) had the lowest crude protein content.
In contrast, galactomannan content ranged from 7.67% to 30.93% in our study. The highest content of galactomannans were seen in RGC-1055 (30.93 ± 0.06%), whereas lowest galactomannan content was found in HG-100 (7.67±0.36%) (Table 3). Similar results were reported by
Naik et al., (2013). However, H. W.
Ashwini et al., (2019) reported that the genotype HG-870 recorded the highest percentage of gum (35.23%) in comparison to RGC 986 (34.73.%) and RGC-1002 (33.47%). This variation might be due to the fact that seeds were taken at different developmental stages for analysis as well as from different geographical regions.
One important aspect of this study was the micro-nutrient analysis including Fe and Zn content in guar genotypes which has not been reported so far. Fe and Zn are two of the most important essential micronutrients whose deficiency has been referred to as “Hidden hunger” by World Health Organization (WHO). The Fe content in guar genotypes ranged from 189 to 869 ppm in our study with an average Fe content of 373.3±0.4 ppm. Maximum Fe content was recorded in IC-415102 (869±10.44 ppm) whereas minimum Fe content was noted in genotypes HG-258 (189±9.29 ppm) (Table 3). However, the Zn content ranged from 34 to 68 ppm with an average value of 44.4± 6.0 ppm. Maximum Zn content was found in genotype IC-421826 (68.33±3.21 ppm), whereas minimum Zn content was observed in IC-415102 (34.33±2.31 ppm) (Table 3). A summary of the average values of all the morpho-biochemical traits in the present study of different guar genotypes have been given in Table 4.
Our results revealed that IC-415102 and IC-421826 genotypes have highest Fe and Zn content which means that these genotypes are of nutritional significance. Genotypes with moderate to high protein, iron and zinc content (as IC-421826, HG-11-1 and Pusa Navbahar) can be used as food crops, while genotypes with high gum content mentioned above can be further improved to be used for industrial purposes. Interestingly, some varieties (Pusa Navbahar, HG-832 and RGC-936) were found to be rich in all the traits in the present study. These genotypes might be of considerable interest for plant breeders and biotechnologists to develop novel guar varieties with desirable nutritional and gum profiles.
Correlation, PCA analysis between morphological and other biochemical factors
Pearson correlation analysis (p value < 0.05) between various morphological and biochemical parameters demonstrated significant variation (Fig 5a). Between morpho-biochemical parameters, seed weight was found to have significant positive correlation with plant height (0.47 cm) followed by chlorophyll content which correlated positively with protein content (0.2%) and gum content (0.16%). Among morphological parameters clusters/plant was found to have positive correlation with pods/cluster (0.41). However, negative correlation was observed between plant height and DAF (-0.61). After analyzing biochemical parameters, it was observed that all traits are positively correlated with each other except gum and Zn (-0.09). Correlation between galactomannan and protein content (0.08%) was also positive but not significant. However, no correlation was observed between seed weight and chlorophyll content as shown in Fig 5b.
Principal component analysis based on variance-covariance matrix demonstrated that maximum variance was observed in PC1
i.
e., protein (97.06%) followed by PC2 iron (1.46%) and minimum in PC09
i.
e. clusters/plant (0.0042%) followed by PC10
i.
e. seed weight (0.00044%) as shown in Fig 5c. Scoring of genotypes based on all morpho-biochemical traits have been shown in Table 4.
Genetic diversity was analyzed using neighbour-joining (NJ) clustering method for various morpho-biochemical parameters and classified 40 guar genotypes based on euclidean similarity index (ESI) into two subgroups A and B as shown in Fig 6. Further, Subgroup A was divided into five clusters (I to V) while subgroup B into three clusters (VI- VIII). The four nutritionally important guar genotypes rich in Fe and Zn content was found in the same cluster IV which was significantly correlated with our biochemical data showing highest Fe content in IC-415102 (869±10.44 ppm) followed by Pusa Navbahar (678.33±10.79 ppm), HG-11-1 (613.33±8.96 ppm) and HG-16 (570.33±8.14 ppm) whereas IC-421826 with highest Fe content (68.33 ± 3.21 ppm) was found to be located in cluster III. Here, Cluster I was found to be galactomannan rich genotypes (IC-421825 and IC-324032) whereas cluster VI with single genotype IC-32969 was found to be rich in all three nutritional traits
viz protein, Fe and Zn.