Introduction

Terminalia chebula Retz. commonly known as Harar having a trade name of chebulic myrobalans, belongs to family Combretaceae and is indigenous to India and South East Asia. In India, it is distributed throughout the greater part except arid zone (Troup 1921). It is an important herbal drug in Ayurvedic pharmacopeia and called the “king of medicines” (Khan and Jain 2009) because of its multi-therapeutic value. Traditionally, T. chebula has been used to treat kidney and urinary disorders, nervous disorders, colic pain, chronic cough, sore throat, asthma, etc. It is also used as laxative, antitussive, diuretic, digestive, antidiabetic, and as a cardiotonic remedy (Khare 2007; Chander and Chauhan 2014). The fruit is rich in tannin and its content varies with geographical distribution (Jayaramkumar 2006). It contains 14 component of hydrolysable tannin. Other important constituents include phenolics such as chebulinic acid, ellagic acid and anthraquinones. Some of the other minor constituents are polyphenols such as corilagin, galloyl glucose, punicalagin, terflavin A, maslinic acid, etc. In clinical trials, the fruit of T. chebula is reported to be hepatoprotective (Tasduq et al. 2006), anti-hyperlipidimic (Israni et al. 2010), anti-arthritic (Nair et al. 2010), antihelmintic (Dwivedi 2008), immune modulator (Aher and Kumar 2010), antibacterial (Bag et al. 2009), cytoprotective (Na et al. 2004), cardioprotective (Reddy et al. 1990), antimutagenic (Gandhi and Nair 2005), anticarcinogenic (Reddy et al. 2009; Saleem et al. 2002, 2010), anti-HIV (Ahn et al. 2002) and antidiabatic (Kannan et al. 2012). Myrobalans are also used in the preparation of ink and in dye as a mordant for the basic aniline dyes.

Fruit pulp of T. chebula is also used in many of the standard preparations such as ‘triphala’ and ‘chayvanprash’ which is use as food supplement. In some states of India and gulf countries fruit jam is used as food supplement. Large sized fruits fetch a minimum three times more price than the wild variety. They are used in making ‘murabba’ and are, therefore called as ‘murabbi’ variety and are three to five times large to wild variety called ‘kachri’ (Singh et al. 2003). Due to its commercial importance several farmers have shown interest in bringing the species under cultivation.

“Domestication is human-induced change in the genetics of a plant, to adapt it to human agro-ecosystems; this process ultimately culminates in the plant’s inability to survive in natural ecosystems” (Harlan 1975). The ideotype concept has been developed and modified for a number of different crops, including forest trees, over the last 35 years. Ideotype concept based on the systematic characterisation of the tree-to-tree variation is more useful for agroforetry trees (Leakey et al. 2000) and in recent years it has been used in the domestication of agroforestry trees producing agroforestry tree products (AFTPs), as an aid to the multiple-trait selection of superior trees for cultivar development (Leakey and Page 2006).

Knowledge of the genetic variation within the species is essential to design a strategy to promote the use and conservation of indigenous trees meant for on-farm cultivation (Haq et al. 2008). This study aims at assessment of variability of fruit characteristics in five different geographically distinct populations in Himachal Pradesh. Study of variability within and between populations in fruit characters will help in domestication of this medicinal important tree species. Superior trees will serve as initial breeding population and scion material for vegetative multiplication of improved genotype.

Materials and methods

Location and climate

The present study was confined to five natural populations of T. chebula Retz. distributed in three districts of Himachal Pradesh (Fig. 1). The physical description of natural populations is given as Table 1. According to Champion and Seth (1968) classification of forests, the natural populations of T. chebula Retz. predominantly occurs in Lower Shivalik Chir pine forests, forest type/sub type 9/C1a in Himachal Pradesh where top storey of forest is occupied by Pinus roxburghii and harar and other associate tree species. The major forest communities in the study area are P. roxburghii, T. chebula, Mallotus philippinensis, Emblica officinalis, Terminalia bellerica, Cassia fistula, Acacia catechu, etc. distributed along altitudinal gradient 500–1100 m above mean sea level. The climate of study sites is sub-tropical with cold winters. The temperature goes up to a maximum of 42 °C in summer and minimum of 3 °C in winters and most of rainfall is received in monsoon. The rainfall pattern is typical monsoon type concentrated from July to September. Drought like conditions occurs during April, May, and June just before the start of monsoons and in October and November, which sometime results in serious fire hazard in the area Mean annual meteorological data of natural populations is given as Table 1. The soil parent material consists of sandstone, conglomerate, slate and clay in the study areas and the texture varies from clay to loam and sandy loam.

Fig. 1
figure 1

Location map of different natural populations of Terminalia Chebula

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Table 1 Description of sites of natural population
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Fruit collection and measurement

Fruits of T. chebula were collected from five natural populations in Himachal Pradesh. Twenty mature trees were selected in each population for collection of fruits. To ensure maximum genetic variation within the population, the selected trees were kept at least 100 m apart from each other. The fruits were collected in month of January, 2013 when the seed inside the fruit was fully mature. About 30 fruits were randomly collected from each tree and then divided into three lots of 10 fruits forming three replications of each selected tree. Immediately after collection fruit breadth and fruit length (mm) and fresh fruit mass (g) were measured. From the fresh fruits, pulp and stone (seeds along with hard coat) were separated and fresh pulp recorded. Separated pulp and stone from individual fruit were initially allowed to dry in open and then oven dried at 105 °C till constant mass achieved and dry pulp and stone mass measured. By adding dry mass of pulp and stone dry fruit mass derived for individual samples.

Statistical analysis

The statistical model used was:

$${\text{Y}}_{\text{ijklm}} = \mu {\text{ + p}}_{\text{i}} {\text{ + m}}\left( {\text{p}} \right){\text{j}}_{{ ( {\text{i)}}}} {\text{ + e}}_{\text{ijk}}$$

where µ is the grand mean, pj is the effect of ith natural population (j = 1,2…..p), m(p)k(j) is the jth mother tree effect within each ith natural population, eijk is the interaction of the kth observation and jth mother tree in the ith natural population.

Natural population effects were considered fixed and all other effects were considered random. The analyses of variance (ANOVA) for all traits were conducted with the statistical analysis system (SAS) generalized linear model (GLM) procedure type III sums of square. LSD test was used to determine if differences among Natural population and families were significant. Approximate F tests were made using the procedure proposed by Satterthwaite (1946). Variance components were estimated by the VARCOMP procedure (SAS Institute 1990), (SAS Institute 1990).

For the natural populations, we cannot estimate the heritability coefficient at the population and individual tree level since in these cases genetic factors cannot be separated from environmental influence. In this case, repeatability coefficient can be used which can be seen as the upper limit of relation of genetic and phenotypic variance (Falconer and Mackay 1996). These coefficients also indicate the percentage of among population variation related to total variation and the percentage of between tree variations related total population variation (Sanou et al. 2006).

Natural population repeatability co-efficient

$$R_{p} = \frac{{\sigma_{p}^{2} }}{{\sigma_{p}^{2} + \sigma_{mt}^{2} }}$$

Mother tree repeatability co-efficient

$$R_{mt} = \frac{{\sigma_{mt}^{2} }}{{\sigma_{mt}^{2} + \sigma_{w}^{2} }}$$

where, \(\sigma_{p}^{2}\) is natural population variance \(\sigma_{mt(pop)}^{2}\) is mother tree within natural population variance, \(\sigma_{w}^{2}\) is within tree variance and r represents number of observation.

Results

Phenotypic variation between natural populations

There were significant differences (p ≤ 0.0001) in all the fruit characteristics among five natural population of T. chebula (Table 2). The fresh fruit mass was heaviest in the PRR (15.44 ± 2.02 g), whereas, the lightest fresh fruits were observed in JKS (12.78 ± 3.93 g) population. Population PRR had heaviest dry fruit mass (6.57 ± 0.93 g), which was at par with BCW (6.42 ± 0.90), whereas, the lightest dry mass of fruits were observed in RKR and populations (5.47 ± 1.03 g). Fruits were lengthiest in BCW (46.33 ± 3.75 mm) followed by PRR (46.19 ± 4.25 mm) and smallest in JKS (36.43 ± 5.52). The fruits were broadest in the PRR (24.39 ± 1.22 mm) and narrowest in RKR (23.31 ± 2.37 mm) (Table 3). Overall, for the fruit character PRR was the best population. There were significant differences (p ≤ 0.0001) in pulp biomass among five natural population (Table 2). Fresh pulp mass was highest in BCW (13.46 ± 2.02 g) followed by PRR (13.27 ± 1.87 g) and lowest in JKS (11.02 ± 3.65 g). Dry pulp was heaviest in PRR (5.24 ± 0.86 g), which was not significantly different to BCW (5.12 ± 0.89 g) and lightest in RKR (4.38 ± 0.92 g) (Table 3).

Table 2 Analysis of variance results for fruit trait
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Table 3 Natural population variation for Fruit and pulp characteristics in Terminalia chebula
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Phenotypic variation between mother trees within natural population

There were significant differences (p ≤ 0.0001) in tree within natural seed sources for fruit characters (Table 2). Within population, maximum variation observed in JKS. Across all the population, an individual tree with heaviest fresh fruit was JKS-09 (20.38 ± 0.61 g), and lightest fresh fruit mass observed in JKS-07 (6.94 ± 0.45 g). Heaviest dry fruit observed in BCW-13 (8.37 ± 0.21 g) and lightest dry fruit mass observed in RKR-15 (3.70 ± 0.57 g) (Fig. 2). Longest fruit observed in RKR-07 (53.53 ± 0.93 mm) whereas shortest in JKS-12 (29.72 ± 2.17 mm). The thickest fruit was recorded by JKS-09 (29.18 ± 0.43 mm) and thinnest seeds in RKR-15 (18.49 ± 1.32 mm) (Fig. 3). An individual mother tree with heaviest fresh pulp mass was JKS-09 (18.03 ± 0.41 g) and lightest fresh pulp mass was in JKS-07 (5.66 ± 0.41 g). However, heaviest dry pulp mass was recorded by mother tree BCW-13 (7.22 ± 0.17 g) and lightest pulp mass in JKS-07 (2.89 ± 0.14 g) (Fig. 4).

Fig. 2
figure 2

Variation for fresh fruit and dry fruit mass (g) between individual mother trees of T. chebula

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Fig. 3
figure 3

Variation for fruit length and breadth (mm) between individual mother trees of T. chebula

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Fig. 4
figure 4

Variation for fresh pulp and dry pulp mass (g) between individual mother trees of T. chebula

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Genotypic variation

The variation in phenotype of fruit and pulp character were highly attributed due to mother tree. Mother tree variance was higher as compared to the population and error variance for all the fruit and pulp characters. Relative contribution of mother tree variance to the total variance was higher for fruit breadth (84.30 %), fresh pulp mass (80.70 %), fresh fruit mass (78.50 %), dry pulp mass (74.60 %) and dry fruit mass (70 %), however contribution by mother tree shown for fruit length (50.30 %). Within mother tree variation contributed very low to low in total phenotypic variation. Mother tree repeatability co-efficient was higher for all the fruit and pulp parameters ranging from 0.81 for dry fruit and dry pulp mass value to 0.91 for fruit length. Population repeatability co-efficient was low for all the parameters except fruit length where it was moderate (0.47) (Table 4).

Table 4 Variance component, and repeatability coefficient fot fruit and pulp characters in T. chebula
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Discussion

To meet substantial need of domestication of T. chebula owing to its higher demand and farmers preference, knowledge of intra-specific diversity is fundamental. The diversity found between and within populations is important for domestication purposes and tree improvement through selection and breeding. Information regarding fruit and pulp character variation in T. chebula is required in order to identify the elite trees with the desirable combinations of different traits that would be appreciated by different markets (e.g., fruits and endocarp for medicinal products and pulp for tannin industry). Present investigation showed that there is significant variation, both between natural populations and family within natural populations, for fruit, endocarp and pulp characteristics. Overall, PRR was superior in all the fruit, pulp and endocarp characters except fruit length and kernel length where it was next to BCW. In most of traits, different tree were superior for different traits. Further, very high tree to tree variation within population indicates existence of different races within population. This suggests all populations could be used for seed source but distribution should be consciously done recognizing existence of races (Munthali et al. 2012). The results are supported by Zobel and Talbert (1984) who have indicated that more than 90 % of the variation in forest trees resides within population. Similar higher tree to tree variation for fruits and seed characters has been reported in other tree species (Sehgal et al. 1994, 1995; Chauhan and Sehgal 2001; Anegbeh et al. 2003, 2005; Atangana et al. 2001, 2002; Leakey et al. 2002; Loha et al. 2009; Munthali et al. 2012; Zheng and Sun 2008). This is further supported by higher variance for tree within population observed for all fruit, pulp and endocarp characters. The patterns of variation (based on coefficient of variation) exhibited for various characters were substantially different. The presence of such difference among populations has probably been produced by different intensities of natural selection acting upon these traits in their natural habitat (Ginwal et al. 2004, 2005). Mother tree variance accounted more variation in all the fruit and pulp characters. All the traits were having low co-efficient of variation, higher mother tree within population variance and higher mother tree repeatability co-efficient. Although repeatability is an upper limit of heritability, the supposed limited environmental effect within the population suggests that this value is a good indicator of selection efficiency (Sanou et al. 2006). Hence, for further improvement individual tree within provenance selection is better option for improvement maintaining genetic diversity and avoidance of inbreeding within breeding population established from selection. This has important implications for domestication of the species. Domestication starting from candidate plus trees could potentially improve quantity and/or quality of harvested plant parts compared to domestication based on the overall provenance. Furthermore, such a domestication strategy could help maintain a broad genetic base within the species being domesticated, as within each provenance a different collection of cultivars can be developed (Leakey et al. 2003).

Conclusions

Significant variation found between provenance and family within provenance suggests that the best primary approach for domestication and improvement of T. chebula would be selection of individual within provenance and establishing clonal orchard/vegetative garden. Higher heritability and large phenotypic variation between and within populations can be exploited by for higher genetic gain from selection and systematic breeding programme accommodating diverse best performing individuals within natural population and development of ideotypes having desired combinations of fruit trait.