Study of heritability, genetic advance and variability in scoparia dulcis L

Individual organisms can alter their development, physiology and life history depending on environmental conditions. These environmental responses are both trait and resource specific, and represent evolved characteristics that vary among genotypes, populations and species.1 The capacity of genotype to express different phenotypes in different environments, phenotypic plasticity and for any crop improvement it depends on magnitude of genetic variability present in base population.2 Environmental effects influence the total observable variations of quantitative traits. Therefore, partitioning of overall variance due to genetic and non–genetic causes becomes necessary for effective breeding programme. The genotypic coefficient of variation estimates the heritable variability, whereas phenotypic component measures the role of environment on the genotype. High phenotypic coefficient of variation and low genotypic coefficient of variation for a character indicated high influence of environment in its expression. The phenomenon of transmission of characters from parents to offspring is usually measured in terms of heritability. Therefore the estimates of heritability and genetic advance would help to formulate a sound breeding programme. The heritability, genetic advance and variability of the medicinally important plant Scoparia dulcis L. of the family Plantaginaceae was studied presently.


Introduction
Individual organisms can alter their development, physiology and life history depending on environmental conditions. These environmental responses are both trait and resource specific, and represent evolved characteristics that vary among genotypes, populations and species. 1 The capacity of genotype to express different phenotypes in different environments, phenotypic plasticity and for any crop improvement it depends on magnitude of genetic variability present in base population. 2 Environmental effects influence the total observable variations of quantitative traits. Therefore, partitioning of overall variance due to genetic and non-genetic causes becomes necessary for effective breeding programme. The genotypic coefficient of variation estimates the heritable variability, whereas phenotypic component measures the role of environment on the genotype. High phenotypic coefficient of variation and low genotypic coefficient of variation for a character indicated high influence of environment in its expression. The phenomenon of transmission of characters from parents to offspring is usually measured in terms of heritability. Therefore the estimates of heritability and genetic advance would help to formulate a sound breeding programme. The heritability, genetic advance and variability of the medicinally important plant Scoparia dulcis L. of the family Plantaginaceae was studied presently.
The plant selected for the present study is S. dulcis. It is native to South America and it was introduced in to India in 1843. It is a perennial herb found in almost all localities, mainly distributed in the tropical and sub tropical region. The plant grows abundantly in rainy season. The plant has been reported to have weed status also. The plant has short life cycle, it takes nearly three months. The plant has high power to overcome environmental stress. It is distributed on road side, pathways, salty areas, marshy and wet lands. The plant reproduces vegetatively and sexually. In wet areas the root system of the plant always active so new leafy branch arises from the base of the stem. As a result of sexual reproduction numerous seeds may form. These plants have high medicinal importance. The plant of S. dulcis is known to possess anti-diabetic activity, antiulcer activities antioxidant activity, anti-kidney stone activity, antimalarial activity, sedative, hypnotyic, antioxidant, antitumor, which supports the therapeutic effects claimed by traditional practitioners. The active principles present in S. dulcis have been shown to exhibit cytotoxic and antitumor activity. Traditionally the plant widely used for the treatment of kidney stone in the indigenous peoples of Kerala like Kurichyas. Study of folk medicine was largely conducted in Bangladesh, toothache and stomach trouble, bronchitis, gastric disorder, haemorrhoids, insect bite, skin wound and hypertension etc. High medicinal importance of the plant is due to the presence of various chemical compounds like terpenoids, phenols, steroids, coumarins, phenols, saponins, tannins, amino acids, catecholamine, noradrenaline, adrenaline (having sympathomimetic effects), acacetin, amyrin, apigenin, benzoxazin. 3 In Sanskrit literature it is mentioned for the treatments of kidney stone, and so it is commonly known in Malayalam as kallurukki.
When compared to other medicinal plant, this plant may show wide distribution. This phenotypic plasticity is influenced by both genetic and phenotypic traits. The main aim of the present study is to analyse the variation present within the species of S.dulcis understanding the source of phenotypic variation and response of organism with the environment. Variation in the phenotypic traits may be a product of current environmental differences between sites (phenotypic plasticity), a product of heritable differences (genotype differences=ecotypes) between the subpopulations at different sites, or a combination of both. 4

Materials and methods
The area of the present study is extended mainly in three North Malabar districts of Kerala, India: Kasargod, Kannur and Kozhikode ( For the present study the fields were frequently visited and the observations were made on required aspects. Plants from thirty accessions (Table 1), ten accessions each from Kasargod, Kannur and Kozhikode districts were collected and analysed. Nine plants were collected from each accession randomly. Data were collected for three consecutive growing seasons of 2016-17. Nine genetically stabled morphometric characters viz length of tap root, number of secondary roots, length of main shoot, number of primary branches, length of primary branch, number of secondary branches, number of nodes on primary branches, inter nodal length and leaf area were studied.
Collected data were statistically analysed for variability of traits by using Analysis of variance (ANOVA). Analysis of variance (ANOVA) was carried out to test the significance of variations in terms of the different characters studied presently. F value was calculated for the purpose and Test of significance was done with reference to standard F-Table. 5 CD was calculated with the formula: Heritability (broad sense) is estimated as the percentage of genotypic variance over phenotypic variance. 8 Genetic advance is the genetic improvement of the progeny possible through selection over the original population. Genetic advance was calculated using the following formula: 7 Where H 2 =heritability (broad sense); p σ =phenotypic standard deviation; K=selection differential which is 2.06 at 5% intensity of selection in large samples. 9

Results and discussion
The existence and progression of a genetic stock is governed by the magnitude of genetic variability accessible in terms of heritable traits. Genetic improvement is generally accomplished by selecting the genotypes with desirable qualities from the available populations.
Analysis of variance is a statistical procedure to compare the extent of variations between populations with the extent of variations within populations so as to determine the significance of variability between populations or accessions. 10 All the traits studied in the case of S. dulsis excluding leaf area showed significant variation at 1% level of significance showing the significance of variation between them in the case of the characters. However, leaf area showed no significant variation showing that their variation is narrow between the accessions. The reason of this variability may be both genetic as well as environmental. Genotypic variation between cultivars or populations is the expression of their genetic differences and phenotypic variation is the result of interaction between genetic differences and environment. Genotypic and phenotypic variations have been studied presently in the case of 30 accessions of S. dulsis on genotypic variance, phenotypic variance, genotypic coefficient of variation and phenotypic coefficient of variation Table 2. Table 2 Genotypic variance, phenotypic variance, genotypic coefficient of variation, phenotypic coefficient of variation, heritability (broad sense) and genetic advance in the case of 9 characters of Scopariadulcis L. In S. dulsis, in all the cases of significant variation, phenotypic variance was higher than genotypic variance indicating the polygenic nature of the traits under study and also the involvement of additive genes in the control of the characters. Genotypic coefficients of variation were also lower in all the cases of significant variation when compared to phenotypic coefficients of variation showing the different levels of influence of environmental factors on the expression of the traits under study. Among the growth traits the highest GCV and PCV were shown by inter nodal length (71.9 % and 90.6 % respectively) followed by leaf area (52.1% and 76.2% respectively) and number of secondary branches (28.0% and 67.7% respectively) showing the wide variability of these traits among the accessions studied. Heritability (broad sense) is the ability of a trait to get inherited to the progeny. Oligogenic traits show high heritability whereas the heritability of polygenic trait is controlled by the number of polygenes involved and the involvement of the environment on their expression. Most of the agronomic traits of S. dulsis are polygenic in nature and they show different levels of significance. In the case of S. dulsis, among the growth traits, the highest heritability were shown by leaf area (48.6) followed by length of tap root (48.6) and intermodal length (42.3%). Heritability of number of primary branch and number of secondary branches was comparatively low thus showing the influence of environment on the expression of these traits.

Characters
Percentage of genetic advance possible under selection is a measure of the quantum of improvement possible and a parameter that can be used to find out the utility of characters in crop improvement programmes. In S. dulsis, among the growth characters studied, genetic advance was found to be the highest in inter nodal length (96.2%) followed by leaf area (76.3%). This shows that these characters can be effectively used for selecting superior genotypes.