• Genetics, Inheritance Pattern and Genotype Selection in Isabgol (Plantago Ovata Forsk)

    Sougata Sarkar* and Raj Kishori Lal

     

    Department of Genetics and Plant Breeding, CSIR-Central Institute of Medicinal and Aromatic Plants (CIMAP), Lucknow, 226015, UP, India, Tel: +91-0522-271-8523, Fax: +91-0522-234-2666

    *Correspondence to: Sougata Sarkar

    Citation: Sarkar S, Lal RK (2018) Genetics, Inheritance Pattern and Genotype Selection in Isabgol (Plantago Ovata Forsk). SCIOL Genet Sci 2018;1:68-79

  • Abstract

     

    A set of six crosses consisting of six generations were raised to study the nature of gene action in Plantago ovata. Significance in the Scaling test was instrumental for tracing out interacting and non-interacting characters in crosses. Interacting crosses were analyzed for gene interactions. The interacting crosses were subjected to six parameter model (m, d, h, i, j, l) whereas, the non-interacting crosses were subjected to three parameter model (m, d, h). The interacting traits in the crosses were categorized to exhibit duplicate and complimentary epistasis. It is interesting to note that seed yield (cross P1 × P2) and husk yield/plant (cross P4 × P5) is in control of duplicate epistasis. Days to 50% flowering in crosses P1 × P2 and P1 × P7 and inflorescence husk yield/plant in crosses P1 × P2 and P2 × P7 exhibited the desirable significantly negative heterosis whereas, seed yield, husk yield/plant and swelling factor exhibited useful positive heterosis.

    Keywords


    Generation mean, Heterosis, Hybrid, Interacting cross, Non-interacting cross

    Introduction


    Psyllium (Plantago ovata, family - Plantaginaceae) is used as a safe and effective laxative for thousands of years in herbal medicine all around the world. The seeds have a mucilaginous coat that swell in water. The seeds and the husks contain high levels of fiber, which expand and become highly gelatinous when soaked in water [1]. By maintaining a high water content within the large bowel, they increase the bulk of the stool, easing its passage. They are used as a demulcent and as a bulk laxative in the treatment of constipation, dysentery and other intestinal complaints, having a soothing and regulatory effect upon the system. The jelly-like mucilage produced when psyllium is soaked in water has the ability to absorb toxins within the large bowel. Thus, it helps to remove toxins from the body and can be used to reduce auto-toxicity. The oil in the seed embryo contains 50% linoleic acid and has been used as a preventative of atherosclerosis and is also effective in reducing cholesterol [2,3] levels in the blood.

    India presently ranks first in the world in the production and export of isabgol. It is cultivated in more than 55,000 acres of land area in Gujarat and Rajasthan. In 2013-2014 India exported 632.31 tons seeds of isabgol, worth $314,405.30; and 32,465.58 tons of psyllium husk worth $314,405.30 [4]. As it grows exclusively in India, exports are growing up to 14% every year.

    Information on genetic components, heterosis and inbreeding are very meager in P. ovata crop as only few reports are available in the literature [5] therefore, a planned study was conducted for determination of genetic components like m, d, h, i, j and l, heterosis and inbreeding depression in isabgol crop for genetic improvement.

    Materials and Methods


    In order to delineate the gene-effects conditioning the expression of yield parameters of seed and husk of isabgol, best six crosses viz. P1 × P2, P1 × P5, P1 × P7, P2 × P7, P3 × P7 and P4 × P5 involving seven best parents (Table 1 and Figure 1) were selected among the crosses made in 7 × 7 diallel mating design [6] which were sampled on the basis of mean performances (Figure 2) and P1, P2, F1 (= P1 × P2), F2 (F1 self), BC1 (= F1 × P1) and BC2 (= F1 × P2) generations were developed in each cross. All the segregating and non-segregating generations in each cross were grown in compact family block design replicated thrice. Plot size in non-segregating families (P1, P2 and F1) comprised single row of 3m length each 50 cm apart and segregating families consisted of two rows of backcross (BC1 and BC2) and three rows for F2. Fourteen morphometric traits, namely days to flowering (50%), plant height (cm), branches/plant, leaf area (cm2), panicles/plant, peduncle length (cm), panicle length (cm), panicle weight (g), days to maturity, seed yield (g/plant), inflorescence husk yield (g/plant), husk yield/plant, 100 seed weight (g) and swelling factor (ml/g) were measured in each family of this experiment.

    Figure 1

     

    Figure 1: Variations in seven parents of Plantago ovata Forsk. View Figure 1

     

    Figure 2

     

    Figure 2: Mean performance of the seven selected parents for the fourteen traits in Plantago ovata Forsk. View Figure 2

     

    Table 1

     

    Table 1: Salient features of seven parental genotypes in Plantago ovata. View Table 1

     

    Statistical analysis

    The following analyses were carried out with data on generation means, analysis of heterosis and inbreeding depression:

    Scaling test

    To identify interacting (showing non-allelic interactions/epistasis) and non-interacting (no epistasis, additive/dominance action) crosses, A, B, C and D - the four scales were developed following Mather 1949 [7].

    Gene effects

    In case of non-interacting crosses, the three parameter model (m, d and h) by Jinks and Jones (1958) [8] and in interacting crosses, the six parameter model (m, d, h, i, j and l) by Hayman [9] were employed in development of corresponding estimates. The statistical symbols represent: m = mean, d = additive components, h = dominance components, j = additive × dominance, l = dominance × dominance interaction and i = additive × additive interactions.

    Estimation of heterosis

    It was estimated as percent increase or decrease in the mean values of F1 hybrids over superior or inferior parent (desirable heterosis) as follows.

    Heterosis % (over better parent) =  F ¯ 1  -  BP ¯ BP ¯  × 100

    Economic heterosos %(over economic parent)= F ¯ 1  -  EP ¯ EP ¯  × 100

    Where,

    F ¯ 1 = Mean of F1

    BP ¯ = Mean of better parent

    EP ¯ = Mean of economic parent

    Estimation of inbreeding depression

    The inbreeding in F2 over F1 was calculated in percentage by using the following formula.

    Inbreeding depression = F ¯ 1  -  F ¯ 2 F ¯ 1  × 100

    Where,

    F ¯ 1 = Mean of F1

    F ¯ 2 = Mean of F2

    The significance of the estimates of heterosis and inbreeding depression was tested with the help of 't' test, calculated on the basis of S.E. by the following formula:

    t = F ¯ 1  -  P ¯ S.E. (for heterosis)

    t = F ¯ 1  -  F 2 ¯ S.E. (for inbreeding depression)

    Heterosis (H) and inbreeding depression (ID) are the manifestation of one and the same phenomenon, i.e. heterozygosis, they occur as a consequence of hybridization between two inbred parents whereas, the heterosis is the superiority of F1 over either of two parents involved in a cross; the inbreeding depression is reduction in vigour in F2. In a simple symbolic terms:

    H = F1 > P and ID = F2 < F1

    Where, H = Heterosis; ID = Inbreeding Depression; P = Parent; F1 = Hybrid of parents; F2 = Self of F1.

    Results and Discussion


    In a set of six crosses - P1 × P2, P1 × P5, P1 × P7, P2 × P7, P3 × P7 and P4 × P5 six generations (P1, P2, F1, F2, BC1 and BC2) were generated to study the nature of gene action. However, before proceeding to derive inferences from the estimates obtained from these generations, it was deemed essential to test the additivity with the help of scaling test as under:

    Test of additivity (Scaling test)

    Adequacy of scale must satisfy two conditions namely, additivity of gene effects and independence of heritable components from non-heritable ones. The test of first condition provides information regarding absence or presence of gene interactions. The four scales - A, B, C and D were calculated where the significance of A and B represented the presence of additive × dominance (j), that of C indicated the presence of dominance × dominance interaction (1) and significance of D denoted the presence of additive × additive interactions (i). The values for all these scales in respect of all the six crosses for fourteen characters are given in Table 2.

    Table 2

     

    Table 2: Scaling tests in six cross-combinations for fourteen characters in Plantago ovata [7]. View Table 2

     

    The estimates of gene effects have a direct influence on efficacy of hybridization and selection. Information concerning dominance and epistatic gene effects is equally useful in the judicious exploitation of the total genetic variance. Generation mean analysis is the estimation of additive, dominance and epistatic gene effects from the mean of certain specific families/population usually P1, P2, F1, F2, BC1 and BC2. Hayman [9] and Jink and Jones [8] developed the six parameter model for the estimation of various components of genetic variance. Those characters which exhibited significance in any of the four scales A, B, C and D were subjected to six parameter analysis based on generation means for different traits in different cross (Table 3). In the absence of non-allelic interactions, Jink and Jones [8] used the three parameter model (Table 4). These techniques for estimating the components of variance provide information about the predominant type of gene action for important traits of a crop species. This helps in deciding on a suitable breeding procedure for the improvement of various quantitative traits of the species.

    Table 3

     

    Table 3: Genetic components of generation mean in six crosses for fourteen characters in Plantago ovata (Six parameter model) [9]. View Table 3

     

    Table 4

     

    Table 4: Three parameter model for non-interacting traits in different crosses in Plantago [8]. View Table 4

     

    In the present study, six selected crosses P1 × P2, P1 × P5, P1 × P7, P2 × P7, P3 × P7 and P4 × P5 were used for detecting the epistatic gene actions for the fourteen characters under study. Significance of any of the four scales (A, B, C and D) indicated the presence of interacting characters, while absence of significance indicated the presence of non-interacting (non-allelic) characters in all the crosses (Table 5).

    Table 5

     

    Table 5: List of traits showing allelic and non-allelic interactions in different crosses in isabgol. View Table 5

     

    Significant non-allelic interactions (Table 5) were evident for six characters namely, branches/plant, leaf area, days to maturity, inflorescence husk yield, 100 seed weight and swelling factor in the cross P1 × P2, for ten characters namely, days to 50% flowering, branches/plant, leaf area, panicle weight, days to maturity, seed yield, inflorescence husk yield, husk yield/plant, 100 seed weight and swelling factor in the cross P1 × P5, for ten characters leaf area, panicles/plant, peduncle length, panicle length, panicle weight, days to maturity, seed yield, husk yield/plant, 100 seed weight and Swelling factor in the cross P1 × P7, for eight characters namely, days to 50% flowering, branches/plant, leaf area, peduncle length, days to maturity, husk yield/plant, 100 seed weight and swelling factor in the cross P2 × P7, for twelve characters namely, plant height, leaf area, panicles/plant, peduncle length, panicle length, panicle weight, days to maturity, seed yield, inflorescence husk yield, husk yield/plant, 100 seed weight and swelling factor in the cross P3 × P7 and for ten characters namely, plant height, branches/plant, leaf area, peduncle length, panicle length, days to maturity, seed yield, inflorescence husk yield, 100 seed weight and swelling factor in the cross P4 × P5.

    Among the interacting characters (Table 5) additive × additive (i) interactions were exhibited by plant height and peduncle length in cross P1 × P2, plant height in cross P1 × P7, plant height, panicles/plant, panicle length, panicle weight and seed yield in cross P2 × P7, branches/plant in cross P3 × P7 and panicle weight in P4 × P5. Additive × dominance (j) interactions were exhibited by days to 50% flowering, plant height, panicles/plant, panicle length, panicle weight, seed yield and husk yield/plant in cross P1 × P2, plant height, panicles/plant and peduncle length in cross P1 × P5, days to 50% flowering, branches/plant, inflorescence husk yield in cross P1 × P7, panicle weight and inflorescence husk yield in cross P2 × P7 and panicles/plant, panicle weight and husk yield/plant in cross P4 × P5. Dominance × dominance (l) interactions were exhibited by panicle length and panicle weight in cross P1 × P2, peduncle length and panicle length in cross P1 × P5, plant height in cross P1 × P7, panicle length in cross P2 × P7 and days to 50% flowering in cross P3 × P7 and P4 × P5 (Table 6 and Table 7).

    Table 6

     

    Table 6: Character wise genetic interactions in six crosses of P. ovata. View Table 6

     

    Table 7

     

    Table 7: Crosses showing genetic interactions for different traits in P. ovata. View Table 7

     

    Among the fourteen morpho-metric traits, leaf area, days to maturity, 100 seed weight and swelling factor did not exhibit interacting characters in any of the crosses at all, instead they exhibited non-interacting characters for all the crosses - P1 × P2, P1 × P5, P1 × P7, P2 × P7, P3 × P7 and P4 × P5.

    Analysis of non-interacting characters in different crosses

    This was carried out by computing three parameters, namely m, d and h for different traits following additive-dominance model (Table 4).

    In the cross P1 × P2, m was significant for non-interacting traits namely branches/plant, days to maturity, inflorescence husk yield, 100 seed weight and swelling factor, whereas the other two components d and h were insignificant for all the five traits. In the cross P1 × P5, m was significant for non-interacting traits namely days to 50% flowering, panicle weight, days to maturity, 100 seed weight and swelling factor whereas the other two components d and h were insignificant in this cross. In the cross P1 × P7, m was significant for non-interacting traits namely peduncle length, days to maturity, husk yield/plant and 100 seed weight whereas the component d was significant for non-interacting trait seed yield and h component was insignificant for all the characters in this cross. In the cross P2 × P7, m was significant for non-interacting traits namely plant height, leaf area, days to maturity, 100 seed weight and swelling factor whereas the other two components d and h were insignificant in this cross. In the cross P3 × P7, m was significant for non-interacting traits namely peduncle length, days to maturity, husk yield/plant and 100 seed weight whereas the other two components d and h were insignificant in this cross. In the cross P4 × P5, m was significant for non-interacting traits namely plant height, branches/plant, leaf area, days to maturity, inflorescence husk yield, 100 seed weight and swelling factor whereas the component d was significant for non-interacting trait swelling factor and h component was insignificant for all the characters in this cross.

    Analysis of components of means for interacting characters

    In all the interacting crosses, the epistasis components pooled together (i + j + 1) were considerably larger than the main effects or non-epistatic components (d + h) which clearly indicates the significant role of epistasis for different traits in all the crosses (Table 3). Additive gene effects (d) were significant for days to 50% flowering and panicles/plant in the cross P1 × P2 and panicle weight in the cross P4 × P5. Dominance gene effects (h) were significant for days to 50% flowering and peduncle length, in cross P1 × P2, panicles/plant, panicle length, panicle weight and seed yield in cross P2 × P7, branches/plant in cross P3 × P7, panicle weight in cross P4 × P5 whereas both additive (d) and dominance (h) gene effects were significant for days to 50% flowering in cross P1 × P2, panicles weight in cross P4 × P5. All the types of epistatic interactions viz, i (additive × additive), j (additive × dominance) and 1 (dominance × dominance) were significant for panicle weight in cross P4 × P5. Both (i) and (1) interactions were significant panicle weight in cross P2 × P7, seed yield in cross P2 × P7, branches/plant in cross P3 × P7 and panicle weight in cross P4 × P5. Additive × dominance interaction (j) played a major role in days to 50% flowering in cross P1 × P2, panicle weight in cross P4 × P5. Both (j) and (1) interactions were involved in the inheritance of days to 50% flowering, panicle weight in cross P4 × P5 whereas both (i) and (j) were significant for only panicle weight in cross P4 × P5 (Table 3).

    It is evident from the study that epistatic component effects, the 1 component i.e. dominance × dominance interaction was disproportionately larger than the other two components for all the traits except husk yield/plant in the cross P1 × P2, panicles/plant in cross P1 × P5, plant height in cross P1 × P7, days to 50% flowering in crosses P3 × P2 and P4 × P5. For husk yield/plant in cross P1 × P2, panicles/plant in cross P1 × P5 j component was larger than l component, whereas i component was larger than j in days to 50% flowering, peduncle length, panicle length, panicle weight, seed yield and husk yield/plant in cross P1 × P2, in plant height, peduncle length, panicle length in cross P1 × P5, plant height, branches/plant, inflorescence husk yield in cross P1 × P7, in plant height, panicles/plant, panicle length, panicle weight, seed yield, inflorescence husk yield in cross P2 × P7, in days to 50% flowering, branches/plant in cross P3 × P7, in days to 50% flowering, panicles/plant, panicle weight and husk yield/plant in cross P4 × P5. Among the main effects the h component was larger than d for all the traits except panicles/plant, seed yield in the cross P1 × P2 and except panicles/plant, panicle length in the cross P1 × P5. In the cross P1 × P2, 1 component was larger than the other two components for all the traits except husk yield/plant, whereas, among the non-epistatic components h is greater than d for panicles/plant and seed yield. In the cross P1 × P5, among interacting components, l component was greater than j and i in all the characters except for panicles/plant in which j component is greater than I and l component. Among main effects h was larger than d in all the traits except panicle length where d is greater than h. In the cross P1 × P7, among epistatic components 1 component was larger than other two components for all the traits except plant height where i component was greater than other two components.

    Among non-epistatic component, h is greater than d for all characters. In the cross P2 × P7, among epistatic components 1 component was larger than other two components for all the traits. Among non-epistatic component, h is greater than d for all characters. In the cross P3 × P7, among epistatic components 1 component was larger than other two components in branches/plant but i component was greater than other two components in days to 50% flowering. Among non-epistatic component, h is greater than d for all characters. In the cross P4 × P5, among epistatic components 1 component was larger than other two components for all the traits except days to 50% flowering where i component was greater than other two components. Among non-epistatic component, h is greater than d for all characters (Table 3).

    Estimates of heterosis and inbreeding depression (from generation mean crosses)

    Heterosis is the manifestation of the beneficial effects of hybridization; the hybrids that are formed as a result of crossing generally exceed their parents in overall performance for many useful traits. This may be due to the individual parents having better combining ability, resulting in heterosis on hybridization. In order to know the degree of realized heterosis in different crosses the realized heterosis (%) was calculated over better parent involved in the cross (Table 8). A critical appraisal of the table revealed that the cross P1 × P7 manifested significant negative heterosis for days to 50% flowering followed by cross P1 × P2 and P2 × P7. The cross P1 × P2 manifested significant heterosis for plant height followed by cross P1 × P5. The cross P2 × P7 manifested positive heterosis for branches/plant followed by cross P1 × P5. The cross P2 × P7 manifested significant heterosis for panicles/plant. The cross P1 × P2 manifested significant heterosis for peduncle length. The cross P1 × P2 manifested significant heterosis for panicle length. The cross P1 × P7 manifested significant heterosis for panicle weight followed by cross P1 × P2. The cross P3 × P7 manifested positive heterosis for days to maturity. The cross P1 × P5 manifested positive heterosis for seed yield followed by crosses P3 × P7 and P2 × P7. The cross P1 × P5 manifested positive heterosis for husk yield/plant followed by the cross P1 × P2. The cross P3 × P7 manifested significant heterosis for 100 seed weight. The cross P2 × P7 manifested positive heterosis for swelling factor followed by crosses P1 × P7.

    Table 8

     

    Table 8: Realized heterosis over better parent (BP) and inbreeding depression (I) for fourteen traits in six cross-combinations in Plantago. View Table 8

     

    Inbreeding depression was significantly large and in positive direction for days to 50% maturity in P4 × P5 followed by P3 × P7, for plant height in P1 × P2 followed by P1 × P5, for branches/plant in P4 × P5, for panicles/plant in P2 × P7 followed by P1 × P7, for peduncle length in P1 × P2 followed by P1 × P5, for panicle length in P1 × P2 followed P2 × P7, for panicle weight in P1 × P7, for seed yield in P2 × P7, for 100 seed weight in P3 × P7 and for swelling factor in P1 × P7. Inbreeding depression was significant but in the negative direction for days to 50% maturity in P1 × P7, for plant height in P1 × P7, for branches/plant in P3 × P7, for panicle weight in P1 × P2, for inflorescence husk yield in P1 × P2, for swelling factor in P1 × P2 and P1 × P5 (Table 8).

    Among the interacting traits, the cross P1 × P2, days to 50% flowering, panicles/plant, peduncle length and seed yield exhibited duplicate epistasis whereas plant height, panicle length, panicle weight and husk yield/plant exhibited complementary epistasis (Table 9). In the cross P1 × P5, plant height, panicles/plant, peduncle length exhibited duplicate epistasis whereas panicle length exhibited complementary epistasis. In the cross P1 × P7, plant height, branches/plant, inflorescence husk yield exhibited duplicate epistasis whereas days to 50% flowering exhibited complementary epistasis. In the cross P2 × P7, plant height, panicles/plant, panicle length, panicle weight, seed yield and inflorescence husk yield exhibited duplicate epistasis whereas none of the characters exhibited complementary epistasis. In the cross P3 × P7, branches/plant exhibited duplicate epistasis whereas days to 50% flowering exhibited complementary epistasis. In the cross P4 × P5, days to 50% flowering, panicles/plant, panicle weight, husk yield/plant exhibited duplicate epistasis whereas none of the characters exhibited complementary epistasis (Table 9).

    Table 9

     

    Table 9: Interacting traits showing duplicate or complementary epistasis in different crosses. View Table 9

     

    Conclusion


    Through hybrid development in isabgol may be viable economic proposition for panicle weight followed by seed and seed husk yield, it is generally of limited consequence for panicle weight, seed and seed husk yields. This is reinforced by low amount of expected or theoretical heterosis based on its different components some specific cross combination showing no non-allelic interaction e.g. crosses P1 × P2, P2 × P7 and P4 × P5 for character panicle weight, crosses P1 × P2 and P2 × P7 for character seed yield and crosses P1 × P2 and P4 × P5 for character husk yield/plant. Complimentary epistasis (if non-allelic interactions are operative) e.g. crosses P1 × P5 and P2 × P7 for days to 50% flowering, crosses P3 × P7 and P4 × P5 for plant height, crosses P1 × P5, P1 × P7 and P3 × P7 for panicle weight and crosses P1 × P5, P1 × P7, P3 × P7 and P4 × P5 for seed yield were promising showing substantial heterosis. It is interesting to note from this study that the trait seed yield (cross P1 × P2) and husk yield/plant (cross P4 × P5) is in control of duplicate epistasis.

    Acknowledgements


    The first author acknowledges the Department of Science and Technology, Government of India for awarding the INSPIRE Fellowship for Ph.D. program at CSIR-Central Institute of Medicinal and Aromatic Plants, Lucknow, India. The authors are also thankful to the Director, CSIR-CIMAP for providing all the required facilities and encouragement.

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