REVIEW OF LITERATURE

2.1. Reproductive biology

2.1.1. Floral morphology

2.1.2. Floral phenology

2.1.3. Pollen viability and stigmatic receptivity

2.1.4. Reproductive success

2.1.5. Pollen pistil interaction

2.2. Genetic variation in plants

2.2.1. Phenotypic variations based on morphological characters

2.2.2. Variation in secondary metabolites

2.2.3. Association of morphological characters

2.2.4. Genetic divergence (D2 analysis)

2.2.5 Genotype-Environment Interaction

Chapter 2

REVIEW OF LITERATURE

It is known fact that plants represent an unlimited source of phytochemicals,

which exhibit remarkable bioactive compounds used for medicines to various

ailments like cancer, AIDS, diabetes, malaria and blood pressure disorders

(Subramanian and Sasidharan, 1997; Mali and Ved, 1999). According to World

Health Organization (WHO) “a medicinal plant is plant which, in one or more of its

organs, contains substance that can be used for therapeutic purpose, or which are

precursors for chemo-pharmaceutical semi-synthesis”. All humans are dependent on

medicinal plants in order to meet various requirements for survival (Philips and

Meilleur, 1998). Globally, about 85% of the traditional medicines used for primary

health care are derived from plants (Fransworth, 1988). Due to immense

pharmaceutical value combined with altering climatic conditions, forest fires, global

warming, over and illegal exploitation, several medicinal plants are facing the risk of

being endangered, vulnerable and extinction (Anonymous, 1994) and are no longer

found in the accessible habitats in large quantities (Vashistha et al., 2006). Hence,

there is need to study the biology of reproduction and genetic variation in medicinal

plants for the purpose of conservation and improvement program. Such basic studies

are crucial, especially in lesser understood tropical species (Zobel and Talbert, 1984;

Sher et al., 2010). The estimation of phenology, floral characteristics, pollen-pistil

interaction, hybridization technique and amount, cause and nature of variation

prevailing between and within population, association of chemo-agronomic

characteristics, diversity of population and their interaction with environments are

important for developing genetic improvement and conservation strategies.

Information on distribution and diversity of medicinal plants is not well

documented. Most of the earlier works by different botanists were related to

description of various species only. Information on population parameters, intra-

specific variation, phenology, breeding behaviour etc. is meagerly available which are

pre-requisite to effect genetic upgradation of any species. Similarly, availability of

germplasm is a building block of any breeding and improvement program.

Chomchalow (1980) has emphasized the importance of genotypic resources in

improvement of medicinal plants.

Rauwolfia serpentina (Sarpagandha) is a widely used medicinal plant,

producing useful alkaloids like reserpine (Sahu, 1983). Generally, it is collected from

wild and its uncontrolled collection from wild has resulted in its inclusion in the list of

threatened plant species (Ayensu, 1996). Wild plants of Rauwolfia serpentina grow in

shady moist or sometimes swampy areas. In cultivation trials, propagation is chiefly

done through seeds. In Rauwolfia serpentina the seed germination is very poor and

varies from 25-74 % in case of fully matured heavy seeds (Badhwar et al., 1955;

Dutta et al., 1963).

Gupta et al. (2005) reported that roots of Rauwolfia serpentina are

traditionally used for treatment of insomnia, insanity, epilepsy, asthma, high blood

pressure and snakebite in Ayurvedic system of medicine. More than 70 compounds

are known in Rauwolfia among which the reserpine, racenomin are used for control of

high blood pressure, whereas ajamalin and ajamalcin are used for cardiac disease

under modern system of medicine (allopathy).

The pharmacological activity of Rauwolfia is due to the presence of several

alkaloids of which reserpine is pharmacologically the most potent alkaloid, found in

all the Rauwolfia spp. The total alkaloid content in the root from different sources

varies considerably; it normally ranges from 1.7 to 3.0 per cent. There does not seem

to be any striking difference in the alkaloid content of the root with respect to the age

of the plant up to 3-4 years of its growth. The alkaloids are concentrated mostly in the

bark of the roots, the quantity being much less in the wood; the bark is reported to

yield about 90 per cent of the total alkaloidal content. The leaves and stems also

contain alkaloids but in smaller amounts than the root bark (Badhwar et al., 1955;

Mathur and Singh, 1965 and Bal, 1956).

The alkaloid content of the roots is reported to vary with the season. It was

indicated that the roots dug out in December, when the plants shed its leaves, are

richer in alkaloids than the roots harvested in August and lowest at the beginning of

the season when the growth is resumed. No significant difference has been observed

in the alkaloid content of the roots of plants growing in forest and irrigated

agricultural conditions (Badhwar et al., 1955; Biswas, 1956 and Wakhloo, 1963).

Considerable variation in the alkaloid content and potency of the roots obtained from

different localities in India, as well as the lots coming from the same areas has been

observed (Mukharji, 1955).

2.1. Reproductive biology

Knowledge of reproductive biology is a prerequisite for both evolutionary and

conservation studies (Anderson, 1995). Ideas that concern about species conservation

and recovery will remain ineffective without adequate knowledge on breeding system

and pollination mechanisms. Reproductive biology studies help in estimating the

genetic variation (Costich, 1995) and also they reveal about the quality and quantity

of seeds produced by a species (Nagrajan et al., 1996). Observation of features such

as floral morphology and phenology as well as pollination studies provide inferences

into plant breeding systems (Nagrajan et al., 1998; Gituru et al., 2002). Studies on

breeding system and floral morphology in turn give an idea about genetic variation

and genetic structure that exist both within and among populations (Loveless and

Hamrick, 1984).

2.1.1. Floral morphology

Several workers have studied about morphology of Rauwolfia serpentina

(Barrows, 1976; Schemske, 1976; Faegri and van der Pijl, 1979; Suzuki et al., 1987;

Sihag and Kaur, 1997; Sihag and Wadhwa, 2011). According to them inflorescence is

terminal and consists of small flowers in compact cymes forming a hemispherical

head at the end of a long peduncle. Flowers are small, pedicillate, complete and

hermaphroditic with five deep red and glabrous sepals. Five petals in gamopetalous

condition form a tubular corolla which is swollen in the middle and white to pink in

colour. Corolla tube measure 17.7 ± 0.22 mm (mean ± SD, n = 50) in length and 2.52

± 0.79 (mean ± SD, n = 50) mm in diameter (Sihag and Wadhwa, 2011). Five stamens

in epipetalous condition are enclosed within the dilated portion of the corolla tube.

Two connate carpals have a filiform style and large bifid stigma; a bilocular ovary has

two ovules in each locule. The flowers of Rauwolfia serpentina have highly narrow

and long tubular corolla (Sihag and Wadhwa, 2011).

2.1.2. Floral phenology

Phenological studies are essential to have knowledge of specific functions of

plant in natural populations, and they must be taken into account in conservation and

rational management schemes (Aronson et al., 1994). Short and rapid flowering

periods, delicate floral organs, difficulty in harvesting pollen, poor controlled crossing

techniques (Bawa and Webb, 1984), and genetic relatedness (Haber and Frankie,

1982) make hybridization and other related studies difficult among tropical species.

This can be overcome if the phenology is properly understood and exploited.

A number of workers (Ramani, 1995; Sihag and Kaur, 1995; Sihag and Priti,

1997; Sihag and Wadhwa, 2011) have reported that in Rauwolfia serpentina the

flowering occurred during peak summer starting last week of May, when maximum

and minimum temperatures ranged between 35.2-43 0C (maximum) and 20-29 0C

(minimum). The peak flowering continued for 43 days, when ambient temperature

fluctuated between 31-40.9 0C maximum and 20.9-30.7 0C minimum. Thereafter,

decline started till cessation in the first week of August when maximum and minimum

temperatures fluctuated between 32.6-36.3 0C and 25.0-26.5 0C.

Sihag and Wadhwa (2011) reported that in Rauwolfia serpentina, flowers

started opening in the early morning between 05.00-05.30 hr when ambient

temperature fluctuated between 24-29 0C. However, anthers did not dehisce on the

first day of flowering; it took place on the second day of flower opening between

07.00-07.30 hr at relatively higher temperature range of 28-31 0C. Under the semi-

arid sub-tropical conditions of Hisar, flower longevity was a little more than two

days, ranged between 54-58 hr (mean ± SD = 56.53 ± 2.20). Nectar secretion started on

the first day of flower opening between 08.00 to 08.30 hr in the morning and

continued up to 13.00 to 13.30 hr in the noon; it again started between 15.00 to 15.30

hr to continue till dusk at 17.30hr on both the days. Nectar production was for a

longer time and at wider range of temperature, 27 to 44 0C (Faegri and van der Pijl,

1979; Sihag and Kaur, 1997).

2.1.3. Pollen viability and stigmatic receptivity

Sihag and Wadhwa (2011) observed that pollen of Rauwolfia serpentina

remained almost fully viable and stigma fully receptive only for four hours.

Thereafter, viability of pollen and/or receptivity of stigma declined. These were low

after eight hours and very low after 10 hours. On the next day, flower completely lost

stigmatic receptivity, even fresh pollen did not produce seeds in the pollen-recipient

flowers. Therefore, pollination has to be completed on the first day itself, that too

within a short period (< 6hr).

Beside studies on reproductive biology in Rauwolfia serpentina, several

workers have studied reproductive biology in other species of the genera Rauwolfia

also. Lopes and Machado (1999) studied that the pollination and reproductive biology

of Rauwolfia grandiflora in natural populations in the forest of the Recife Botanical

Garden. R. grandiflora is a shrubby species (2 to 5 m), the flowers are hermaphrodite

and salverform. The corolla tube is white and the five free lobes of the corolla are

flushed with violet. The five stamens are attached to the corolla tube; the anthers are

introrse and form a cone situated immediately above the stigmatic head. There is a

space between the anthers and the stigmatic head, where the pollen is deposited. The

stigmatic head has three functional regions: a) an upper sterile region; b) a median

region that produces a sticky substance and c) a lower receptive region, which is

located beneath a basal collar. Sugar concentration in nectar was, on average, 31.7%.

The pollen viability was 97.4%. Rauwolfia grandiflora is melittophilous and in the

study area it was found to be pollinated by only one species of long-tongued bee,

Exaerete smaragdina. Rauwolfia grandiflora was found to be self-incompatible, and

the percentage of fruit set under natural conditions was low.

Herrera (1991) studied the reproductive characteristics of Nerium oleander,

and reported that plants produce massive showy flower. Hand-pollination

demonstrated full self compatibility. Automatic selfing is prevented by spatial

separation of stigma and anthers, and pollinators are thus necessary for reproduction.

Percentage fruit set of open-pollinated flowers was found to be extremely low (0.1-

4.9%), while hand-pollination increased fruiting levels to 34-50%. Direct and indirect

evidence point to consistently pollen-limited reproduction in the species. On average,

maximum number of ovaries developing into fruit within any inflorescence was 4. It

was suggested that, in this nectarless species, about 80% of the flower are `excess'

which contribute to increase pollinator attraction.

Wyatt et al. (2000) reported that unlike most highly outcrossing flowering

plants, milkweeds (Asclepiadaceae) have exceptionally low pollen-ovule ratios. They

counted the number of pollen grains contained within a pollinium sac and the number

of ovules contained within an ovary for 38 species of Asclepiadaceae. Across four

tribes of the Asclepiadaceae, the number of pollen grains per pollinium varied from

14 to 445, and the number of ovules per ovary varied from 4 to 229. Nevertheless, the

pollen-ovule ratio was constrained within a narrow range, generally 1 to 2. Similar

constraints on pollen-ovule ratios occur within mimosoid legumes (Acacia,

Calliandra, Inga) whose pollen also is dispersed in clusters (polyads).

Koch et al. (2002) reported reproductive biology of Rauwolfia sellowii Müll.

Arg. He reported occurrence of functional dioecy for the first time in Apocynaceae.

The occurrence of gynodioecy in Rauwolfia vomitoria Afzel was also demonstrated.

Behaviour of the visiting pollinators and small populations might have favoured the

development of dioecy in Rauwolfia sellowii to avoid endogamic depression. The

nonfunctional flower organs are particularly interesting; male flowers show all female

structures, including well-developed ovules. Only callose deposition in the ovules and

the absence of fruit development reveal their nature. Female flowers have empty

anthers. Such organs still play an important role for the reproductive mechanism and

he believes that this is responsible for their persistence.

Kaul et al. (2005) noted significantly higher differences in per cent fruit set,

seed set and germination between autogamy and xenogamy in Withania somnifera.

The number of pollen grains differentiating per anther was profuse, averaging 5800 ±

175.7. Pollen grains were spherical or sub-spherical in shape. Ovules per ovary range

between 29 and 53 (35.5 ± 5.85). Pollen to ovule ratio per flower averaged 817: 1.

Torres and Galetto (2008) reported in Mandevilla pentlandiana

(Apocynaceae) that the plant produces many inflorescences with a large number of

flowers but initiates few fruits (9%). The low natural fruit set was not related to pollen

limitation. Fruits were not distributed at random within inflorescences (earlier fruits

had the highest probability of maturation) but there were no significant differences in

fruit quality according to different fruit positions. Conversely, the time of fruit

initiation influenced most of the fruit-traits. Many developing fruits were aborted

(20%). An increase in the probability of abortion was detected when the whole

inflorescence was hand pollinated. In addition, a positive correlation was detected

between the abortions and the number of ripe fruits which developed before them.

Sihag and Wadhwa (2011) revealed in Rauwolfia serpentina, that the stigma,

at the age of two days old flower, was receptive only on the first day but anthers dehisced on the second day,

when stigma had become non-receptive. Therefore, flowers of Rauwolfia serpentina are cross-

pollinated, indicating protogyny as in umbelliferous plants (Sihag 1985a), in onion

(Sihag, 1985b) and all cultivars of litchi (Litchi chinensis Sonn.) (Ray and Sharma,

1995).

2.1.4. Reproductive success

Chandra (1956) reported observations on various aspects of floral biology and

Mital and Issar (1969) on mode of pollination, fruit setting and seed development in

Rauwolfia serpentina. There was remarkable variation in the number of flowers and

fruits per peduncle in the populations from Uttar Pradesh; the mean flower number

was 283.3 with maximum and minimum flower production of 632.3 and 33.7

respectively; the maximum fruit number was 56.7, the general mean being 21.0. Both

mean and range were significantly low in the selections from the Brazilian stock (EC

38708). Chandra (1956) concluded that large numbers of flowers need not necessarily

result in maximum fruit set.

Johnson et al. (1998) reported reproductive success as measured by fruit set

and found it is very low in most populations of Apocynum x-floribundum. Nagrajan et

al. (1998) found open pollinated fruit set was between 1 - 2% in tamrind. Controlled

pollination studies indicated that the species is predominantly an outcrossing species

with extremely low level of selfing. Variation in pollen size was observed and pollen

sterility was very low.

2.1.5. Pollen pistil interaction

Bernardello et al. (2003) reported that in Sophora fernandeziana, self-pollen

germinates and pollen tube grows down the style. However, pollen tubes were only

observed to enter the ovaries in open pollinated styles, suggesting the possibility of an

ovarian self-incompatibility mechanism.

Sogo and Tobe (2005) observed that in alders, where fertilization occurs ≈8

weeks after pollination, the pollen tube (male gametophyte) grows intermittently in

four steps in close association with the development of the ovary and its ovules.

Pollen tubes stop growing in the style at the ovarian locule and at the chalaza (ovule),

before reaching an embryo sac for fertilization. At this stage when the ovary develops

an ovule primordium in each of the two locules many pollen tubes germinate on the

stigma and a few of them reach the style.

2.2. Genetic variation in plants

The spontaneous origin of new variations in an organism is termed as

mutation. De Vries (1905) used this term for new phenotypes that arose abruptly in a

stock of plants. At the most basal level mutations found able to produce new

individuals (Buss, 1987; Smith, 1989). Further environmental interaction,

hybridization and polyploidy are some of the other reasons, which are found

responsible for development of diversity in morphology, phytochemical constituents

and genetically.

Various methodologies exist for the assessment of diversity / variability in

plant species. Variation or diversity among the populations / individuals / cultivars /

clones could be determined using morphological and biochemical markers. The

selection of a specific genotype based on marker system is commonly known as the

marker assisted selection or marker aided selection (MAS). It is a process, which is

commonly used for indirect selection of genetic determinants of a trait of interest and

identification and characterization of specific genotype (Segman et al., 2006).

Among the different marker systems, morphological traits represent the

preliminary and the earliest markers, which are used for the germplasm

characterization and management (Gitonga et al., 2008). Morphological

characteristics are the strongest determinants of the agronomic value and taxonomic

classification of plants. Compared with other means, morphological evaluation is

direct, inexpensive and easy (Li et al., 2009). Morphological assay generally require

neither sophisticated equipment nor preparatory procedures (Khan and Spoor, 2001).

These include the inspection of the visual or organoleptic markers such as shape,

colour, texture and odour of the herbs. However, these markers can be used as a

preliminary step for the identification of the plant variety.

Variation in medicinal plants is often noticed at chemical level, which is due

to the synthesis and accumulation of a wide variety of biochemicals that are often

plant specific. These compounds collectively grouped as secondary metabolites are

‘high-value low-volume’ compounds, biosynthetically derived from primary

metabolism which help plants to defend, tolerate, adopt and adjust themselves against

abiotic and biotic stresses including insect pests and fungal and other pathogenic

diseases. Some of these agents can also act within the human body against

microorganisms etc. and represent an important source of natural drugs. These

phytochemical constituents may also reflect the genetic diversity or epigenetic

responses or both.

Biochemical markers based on phytochemical constituents/secondary

metabolites are useful tool for the qualitative and analytical analysis of chemical

constituents but these showed rare polymorphism and difficult to distinguish closely

related species, because many of which, contains similar chemical components. In

case of chemical markers, the chemical contents of herbs may be affected by

physiological conditions, harvesting period, storage conditions and chemical

complexity (Joshi et al., 2004).

2.2.1. Phenotypic variations based on morphological characters

Morphological markers generally correspond to the qualitative traits that can

be scored visually. Much phenotypic variation depends on seasonal or developmental

changes that affect many individuals in a population regardless of genotype.

Vardarajan (1968) reported differences in root bark and wood ratio of different

ecotypes in Rauwolfia serpentina; the root samples from the North-Indian hills had a

lower ratio than those of Peninsular India. There was a greater physiological activity

of the species in the southern region due to the tropical climate than on the Himalayan

tract where the leaves are shed in winter. The author observed that there was no

difference in general mean of all the populations for plant height and leaf traits. There

was not much variation in populations from the three states for these traits.

Bhagat et al. (1980) studied Rauwolfia serpentina genetic resources from

several regions of India at New Delhi during 1970-76 to understand the variation

pattern for root yield and associated polygenic traits. The Uttar Pradesh populations

represented the widest range of diversity for most of the traits; the populations from

Assam possessed high root yield potential. In other states, too large variation was

evident. Root yield ranged from 25 to 200 and 20 to 174 g, respectively, in the 1972

and 1974 harvests, the maximum range being observed in the populations from Uttar

Pradesh followed by the collections from Assam. However, the mean root yield

calculated over both crop seasons was highest in material from Assam. It was

revealed that for root yield there was pronounced variation. The mean stem weight

was also highest in the collections from Assam. Higher ranges of variation for stem

weight were observed in the populations from Uttar Pradesh and Assam. It was

noteworthy that the coefficients of variation were high for all three characters in both

crop harvests of the Uttar Pradesh and Assam populations. Bhagat concluded that for

increased root yield and to increase in total area under Rauwolfia, genetic resources

need to be built up, particularly those from Assam.

Vashitha et al. (2006) surveyed and evaluated germplasm for domestication on

the basis of morphological variations in various natural populations of two species of

Angelica, viz. A. glauca and A. archangelica. A total of seven phenotypic traits i.e.

plant height, number of leaf, petiole length, leaf length, leaf width, rhizome length and

rhizome dry weight were observed among various population of A. glauca and A.

archangelica. The analysis of variance showed highly significant variation (P < 0.05)

among populations of the species for different morphological traits.

Brezinova et al. (2009) described the morphometric variability in 24 selected

genotypes of poppy (Papaver somniferum L.) using eight morphological characters.

The results revealed high coefficient of variation for different morphometric traits.

Bhargava et al. (2009) carried out Metroglyph analysis among 44 indigenous and

exotic germplasm lines of Chenopodium spp. for 10 quantitative characters. The

germplasm lines were categorized into 10 groups, which differed among themselves.

2.2.2. Variation in secondary metabolites

Phytochemical profiling establishes a characteristic chemical pattern for a

plant material. Thin layer chromatography (TLC) and high performance thin layer

chromatography (HPTLC) are routinely used as valuable tools for qualitative

determination of small amounts of impurities (Joshi et al., 2004). Studies on genetic

variation with respect to secondary metabolites in Rauwolfia serpentina are very

limited. It is well known now that the biochemical pathway as well as production and

accumulation of active substances in herbs and trees are different when they grow in

different types of soils and environmental conditions (Adjanohoun, 1996).

Wakhloo et. al. (1963) studied variation in total alkaloid content of Rauwolfia

serpentina with respect to ecological conditions. Large variation in total alkaloid

content in root in the range of 0.95 to 2.72% was observed in natural population of

Bihar (Dhar, 1965). Collections from Western Ghats of India were found to be

variable in chemo-botanical characters (Sethi et al., 1991). The author demonstrated

that populations collected from different ecological conditions harbours significant

genetic variation. Population from Coondapur region in Karnataka was superior in

morphological as well as total alkaloid and reserpine content, population from

Conacana, Goa was at par with these populations.

Ahmed et al. (2002) reported that the percentage of alkaloid for in field grown

plant material 0.71% in leaf and 1.43 % in root, respectively.

Gupta et al. (2005) reported high root and alkaloid yield in the variety CIM-

Sheel with defined reserpine content. It had shown about four times root yield

potential than the parent population. The dry root yield (per plant) potential of the

CIM-Sheel was found to be 43.23 g and 185.00 g as compared to the local check

(25.23 g and 54.63 g) for first and two year of growth, respectively. The reserpine

content (dry root basis) was 0.036 % and 0.029 % as compared to local check (0.020

% and 0.021 %) for first and two years age of plant respectively. The estimated yield

potential (dry root basis) was found 50-60 q per ha.

Kumar et al. (2010) studied the effect of different factors like climate, altitude,

rainfall and other conditions on growth of plants which resulted in variation in the

content active constituents in Rauwolfia serpentina. They recorded significant

variation in the content of reserpine in root samples which were collected from four

different parts of southern India. Sample collected from Coimbatore has shown

maximum amount of reserpine of 0.1442% whereas sample collected from

Shimoga has shown minimum amount of reserpine of 0.0382%. Variation in the

content of reserpine ranged from 0.0382 to 0.1442%.

There is little difference in the morphological features of Rauwolfia serpentina

roots obtained from various zones. However, the alkaloid content and potencies of

roots vary not only in samples from representative and geographically distinct areas

but also from lots coming from the same geographical area. (Sulochana, 1959).

2.2.3. Association of morphological characters

Biswas (1970) observed positive correlation between number of branches and

root yield per plant in clonal population of Rauwolfia serpentina.

Shivanna et al. (2007) studied genotypic and phenotypic correlations and path

coefficients for 12 economic traits in 17 genotypes of makoi (Solanum nigrum L.).

The genotypic correlation coefficients were higher than phenotypic correlation

coefficients for most of the traits. The total alkaloid yield had highly significant

positive genotypic and phenotypic association with dry herbage yield per plant. Days

to flower, bud initiation and days to 50 per cent flowering had significant positive

association at the genotypic level. Path coefficient analysis revealed maximum direct

effect of herbage yield on total alkaloid yield.

Kumar et al. (2008) studied genetic variability among 31 genotypes using nine

characters of Chlorophytum borivilianum of indigenous origin. Correlation analysis

for root yield (dependent variable) and the remaining seven plant traits (independent

variables) revealed that leaf number, leaf length and finger number had significant

associations with root yield.

Singh et al. (2008) studied variability and association of yield and its

contributing morphometrical traits over two micro-environmental conditions in Safed

musli (Chlorophytum borivilianum). They revealed the scope for genetic

improvement in major yield attributes with some limitations for root length and

diameter. An interrelationship among the yield and yield attributes indicated that

improvement in yield can be attained through improvement in root numbers, root

length, and diameter; however, more emphasis must be paid on root diameter for

organic conditions. The cause and effect study on the interrelationship exhibited the

importance of productive root yield as causation to improvement in yield.

Chitra and Rajamani (2010) studied character association and path analysis for

13 morpho-economic traits using 18 genotypes of Gloriosa superba L. Plant height,

number of leaves per plant, number of branches per plant, days to 50% flowering,

number of flowers per plant, number of pods per plant, number of seeds per plant,

fresh seed weight per plant, fresh seed yield per plant and fresh seed recovery were

found to have positive association with dry seed yield per plant. Fresh seed yield per

plant had highest positive effect on seed yield followed by number of pods per plant

and fresh seed weight per pod. These associated yield components suggested that they

may be good selection criteria to improve seed yield of glory lily (Gloriosa superb)

crop.

Karuppaiah and Kumar (2010) investigated 34 genotypes of African marigold

to assess association of yield components and their direct and indirect effects on flower

yield. Results of correlation analysis indicated flower yield per plant to be

significantly and positively correlated with number of branches per plant, flower size,

flower weight, number of flowers per plant and xanthophyll content. Days to first

flowering showed negative association with flower yield per plant. Path analysis

revealed high positive direct effects of number of flowers per plant and xanthophyll

content. Medium level of direct effect was recorded by flower diameter. Remaining

characters recorded low to very low direct effects.

Das et al. (2011) studied genetic variability, character association and path

coefficient analysis for yield (seed / leaf / root) and 11 yield related (including

chemical parameters) traits in 6 genotypes (parental cultivar and 5 macromutant lines)

each of high yielding recommended varieties Poshita and Jawahar 22 of Withania

somnifera (L.) Dun. (Ashwagandha; Family: Solanaceae; potential plant species of

commerce for therapeutic uses) for undermining attributes maximizing yield for

efficient breeding and further improvement of the elite genotypes for commerce. They

found that root length and total number of berries / plant are important selection

criteria for economic yield irrespective of the parental cultivars of W. somnifera.

2.2.4. Genetic divergence (D2) analysis

Kumar et al. (2007) studied six phenotypic characters and three withanolide

markers were assessed in 25 accessions of Withania somnifera collected from

different states of India for studying genetic variability. The variability ranges

observed at phenotypic and chemotypic levels were polymorphic. Based on D2 values

and PCA (Principal Component Analysis) of phenotypic traits like plant height,

number of branches per plant, number of seeds per berry, root length, root diameter

and root yield, these 25 accessions were grouped in five clusters. Five accessions–

AGB002 (Rajasthan), AGB003 (J&K), AGB004 (Madhya Pradesh), AGB006 (J&K)

and AGB009 (Punjab) representing clusters 2 and 4 exhibited maximum intra and

inter-cluster divergence. Cluster 5 representing accession AGB053 (Andhra Pradesh)

was having mixed traits. Chemically most of the accessions in cluster 3 showed

uniformity in presence of three marker withanolides Withaferin A, Withanone and

Withanolide A in the leaves.

Kumar et al. (2008) studied genetic divergence among 31 genotypes using

nine characters of Chlorophytum borivilianum of indigenous origin. The genotypes

were grouped into eight clusters. Intra-cluster distance was largest for cluster VIII

(nine genotypes), followed by cluster I (six genotypes). Inter-cluster D2 values

recorded high between cluster II and III and cluster III and VI indicated the possibility

of raising transgressed hybrids from cross hybridization programs using divergent

parents of these four clusters. The clustering pattern indicated that geographical

diversity was not necessarily related with genetic diversity. Leaf number contributed

most toward divergence (15.8%), followed by finger number, length and width (each

with at least 13% contribution) and leaf length (12.1%).

2.2.5. Genotype-Environment Interaction

Kaicker et al. (1978) reported stability of 10 cultivars of opium poppy for

morphine content and found existence of genetically conditional differences in the

stability of cultivars. Techniques employed to determine the adaptive potential (Finlay

and Wilkinson, 1963; Eberhart and Russel, 1966), relative stability and environmental

interaction showed the significant varietal differences when the cultivars' mean square

was tested over pooled deviations as the error term. Significant V x E (linear)

component suggests the existence of genetically conditional differences in the

stability of cultivars. Highest morphine content was observed in cultivar H and least

in R. Four cultivars exceeded the grand mean.

Dražić et al. (2007) studied stability of productive traits (fruit yield, essential

oil content) of varieties of cultivated medicinal plants belonging to the species of the

family Apiaceae (anise, coriander, dill, parsley and fennel) in five locations following

the method of Eberhart and Russell (1966). Least stable yield was recorded in

coriander and least stable essential oil content was found in fennel.

Review of literature as presented above point out paucity of studies on

reproductive biology and different aspects of genetic variability analysis in Rauwolfia

serpentina.