A Study of the Association of Agronomic Characters in Vanilla planifolia Andrews
Natural vanillin is a flavouring agent of high esteem. This is obtained from the processed beans of three species of the orchid genus Vanilla among which Vanilla planifolia Andrews is the most popular and it yields vanillin of superior quality. In spite of its overwhelming importance, studies on the diversity and improvement of the crop are very limited. Most of the agronomic characters of vanilla are polygenic in nature and they show different levels of interrelationship due to sharing of common genes. This phenomenon leads to different levels of interrelationship and association of these characters. The most important agronomic characters of this plant have been analyzed presently for their association by factor analysis so as to group them in to groups with maximum gene sharing and also to identify the lead characters. Eleven accessions/genotypes of Vanilla planifolia collected from the major vanilla growing areas of Kerala State and adjacent states of India were utilized for the present study. The plants were grown in randomized block design with three replications and 12 plants per plot and maintained as per the recommendations of Spices Board, India. Vanilla vine cuttings of 33 cm length were used for planting and live Gliricidia plants pruned and maintained permitting 50% light to penetrate were used as standards to train the vanilla vines. The plants started to flower in the third year. Artificial hand pollination was carried out to ensure pod setting. Yield got stabilized by the fifth year after planting and the data collected during the fifth year have been used for the present analysis. Internodal length, vine length, number of inflorescences per plant and leaf area have been identified as lead characters in the present study. Due weightage can be given to these characters in further studies on the diversity and improvement of this species.
May 13, 2010; Accepted: July 17, 2010;
Published: September 02, 2010
The genus Vanilla Mill (Plum. Ex.L) belongs to the orchid family, Orchidaceae,
which is the largest family of flowering plants, with about 700 genera and 20,000
species. Orchidaceae comprises of a very natural, distinctive and highly advanced
group of monocotyledons. They are perennial herbs which are widely distributed
throughout the world with the greatest number in the tropics. They exhibit a
wide range of life forms and have terrestrial, climbing, epiphytic and saprophytic
species (Purseglove et al., 1981). The genus Vanilla
Mill. was first described by Miller in 1754 taking the name from the Spanish
vainilla (small pod) in reference to the long, slender, pod like fruit. The
members of the genus are stout, terrestrial, climbing, branched herbs; branches
giving rise to adventitious roots; leafy or leafless. Leaves when present are
coriaceous or fleshy. Racemes usually axillary, sub sessile or peduncled. Flowers
are large, sepals and petals sub equal, spreading. Lip is adnate by a claw to
the base of the column and embracing it in its concave limb, entire or 3-lobed.
Column is elongate. Anthers are incumbent, cells separate and pollen granular.
Capsules are long, fleshy and one celled (Fisher, 1928).
Withner et al. (1974) pointed out that evolutionary
development of the vining habit of Vanilla perhaps depended up on the
greater efficiency for water conduction by vessel elements as compared to the
basic tracheids. Recent studies have indicated that interspecific hybridization
and polyploidization might have played an important role in the evolution of
the genus. Mating system diversity exists in Vanilla and this genus could
be a good model to study the role of fragrance in orchid evolution (Bory
et al., 2008).
The genus Vanilla consists of about 110 species. Three species of Vanilla
namely Vanilla planifolia Andrews, Vanilla tahitensis J.W.
Moore and Vanilla pompona Schiede are commercially exploited and cultivated.
Of these, Vanilla planifolia is the most preferred commercially and hence,
widely cultivated and the two other species are occasionally cultivated and
yield an inferior product (Purseglove et al., 1981).
Vanilla planifolia is native to the humid tropical rain forests of South
Eastern Mexico, Central America, the West Indies and the northern part of South
America. Vanilla tahitensis is indigenous to Tahiti, the French Oceania
group of islands in the Pacific Ocean and Vanilla pompona is indigenous
to South Eastern Mexico, Central America, Trinidad and North and South America
(Correll, 1953; Purseglove et al.,
1981). Vanilla planifolia Andrews is a herbaceous perennial vine,
climbing up trees or other supports to a height of 10-15 m by means of adventitious
roots. In cultivation it is trained to a height which will facilitate hand pollination
and harvesting. Long, whitish, aerial adventitious roots of about 2 mm in diameter
are produced singly opposite the leaves and adhere firmly to the support plant.
The roots at the base ramify in the humus or mulch layer. The stem is long,
cylindrical, succulent and branched. It is 1-2 cm in diameter and is dark green
and photosynthetic with stomata. The internodes are 5-15 cm in length. Leaves
are large, flat, fleshy, sub sessile, alternate, oblong-elliptic to lanceolate.
They are 8-25 cm long and 2-8 cm broad. The tip is acute to acuminate and the
base somewhat rounded. Venation is parallel and the veins are distinct. The
petiole is thick, short and canalized above. Flowers are large, waxy, fragrant,
pale greenish yellow, bisexual and zygomorphic. Perianth lobes are six in number
(3+3) and they look alike. The lower petal of the inner whorl is short, broad
and it is modified into a labellum. The lower part of the labellum envelops
a central structure called the column (gynostemium) (Purseglove
et al., 1981). Gynostemium is formed by the union of stamen, style
and stigma (Lawrence, 1951). A tuft of hairs is seen in
the middle of the disc. The tip of the column bears a single stamen with two
pollen masses (pollinia) covered by a cap or hood like structure called rostellum
which prevents natural pollination. The slender stalk like portion is the ovary,
which is 4-7 cm in length and 3-5 mm in diameter. The fruit is a capsule, which
is dehiscent in Vanilla planifolia and in trade it is known as a bean.
The bean is pendulous, narrowly cylindrical, obscurely three angled, 10-25 cm
long and 5-15 mm in diameter. Each bean when ripe contains thousands of minute
globose seeds, which are liberated by longitudinal splitting of the capsule
(Purseglove et al., 1981). The product from Vanilla
planifolia is known as Mexican vanilla, Bourbon vanilla or Indonesian vanilla
based on the method of processing (George, 1989).
Vanilla is one of the most valuable spices and is often referred to as the
prince of spices. Natural vanillin could find wide application in confectioneries,
cakes, beverages, puddings, chocolates, ice creams, perfumery and pharmaceuticals.
Most of the agronomic characters of crop plants are polygenic
in nature and the same is the condition in vanilla also.
|| Accessions of Vanilla planifolia studied for character
|| Factor analysis in the case of Vanilla planifolia-
Such characters show different levels of association based on the quantum
of genes shared by them. The present experiment was carried out to find out
the association of characters in Vanilla planifolia and also to identify
the lead characters among them so that future experiments can be based on such
lead characters. Eleven agronomical characters were analyzed for the present
study based on the observations collected form eleven accessions of Vanilla
planifolia collected from different vanilla growing regions of South India
(Table 1, 2).
MATERIALS AND METHODS
The experiment was carried out in the Genetics and Plant Breeding Division
of the Department of Botany of University of Calicut, Kerala, India during 2003-2007.
The experimental field is located at 11°25-11°45 N
latitude and 75°45-75°50 E longitude and it enjoys an annual
rainfall of about 300 cm. Eleven accessions/genotypes of Vanilla planifolia
collected from the major vanilla growing areas of Kerala State and adjacent
states of India have been utilized for the present study (Table
1). The plants were grown in randomized block design with three replications
and 12 plants per plot and maintained as per the recommendations of Spices Board,
India (Anonymous, 2002). Vanilla vine cuttings of 33 cm
length were used for planting and live Gliricidia plants pruned and maintained
permitting 50% light to penetrate were used as standards to train the vanilla
vines. The plants started to flower in the third year. Artificial hand pollination
was carried out to ensure pod setting. Yield got stabilized by the fifth year
after planting and the data collected during the fifth year have been used for
the present analysis. Association of agronomical characters of the species has
been studied presently by factor analysis as suggested by Sneath
and Sokal (1973) based on 8 growth characters and 3 yield characters (Table
2). The statistical software STATISTICA was used for the analysis.
RESULTS AND DISCUSSION
The agronomic characters of many crop plants show polygenic type of genetic
control and as a result they show different levels of interrelationships and
association. The level of association will depend on the extent of gene sharing.
Study of these aspects in any crop is highly important since this information
will provide the foundation for further breeding and improvement programmes
in it. Eleven such characters of Vanilla planifolia have been studied
presently for character association by factor analysis. The characters could
be grouped into three factors based on factor loading (Table 2-4).
The first factor group consisted of the characters internodal length and vine
length. The second factor group consisted of three characters namely, number
of inflorescences per plant, yield per plant and number of nodes per metre.
Six characters namely, leaf area, number of flowers per inflorescence, length
of velamen roots, vine girth, thickness of velamen roots and leaf thickness
were grouped under the third factor. Internodal length showed the maximum factor
loading in the first group, number of inflorescences per plant in the second
group and leaf area in the third group. These characters can be considered the
lead characters in the respective groups and it shows that internodal length,
number of inflorescences per plant and leaf area can be considered the most
important characters in Vanilla planifolia while practicing selection
and other crop improvement programmes. Vine length is also an important character
in Vanilla planifolia since it also shows comparatively high factor loading.
The percentage of variance contributed by the characters coming under the first
factor is 34.68, that contributed by the characters coming under the second
factor is 20.55 and that contributed by the characters coming under the third
factor is 15.21. These three factors cumulatively contribute 70.45% of the total
variance in the case of the characters studied presently.
Factor analysis can be used as an efficient tool to study character association
and also to group variables so as to effect data reduction by identifying the
lead variables of each group. This method has been used for data reduction,
grouping of variables and also to find out the lead variables in different crops
like cardamom (Radhakrishnan et al., 2004; Hrideek
et al., 2008) and coffee (Nikhila et al.,
||Factor analysis in the case of Vanilla planifolia-
eigen values, percentages of total variance, cumulative eigen values and
cumulative percentages of variance
||Factor analysis in the case of Vanilla planifolia-
characters associated as per factor analysis
Their studies have contributed significantly towards finding out lead variables
in the crops and also towards reduction of multiplicity of variables and concentrating
on the lead variables for crop improvement programmes.
The present study in Vanilla planifolia has been useful to group the
major agronomic characters of the crop in to three groups based on factor loading,
to assess the extent of variability contributed by them and also to identify
the lead variables from each group. Internodal length, vine length, number of
inflorescences per plant and leaf area have been identified as lead characters
in the present study. These lead variables are important since they are interlinked
the maximum with other agronomic characters. Study of the genetics, genetic
variability and extent of diversity of the gene pools in the crop has been attempted
very limitedly. The works of Verma et al. (2008)
and Divakaran et al. (2008) are some such efforts
carried out recently and they have emphasized the importance of developing conservation
strategies for the crop. The present study emphasizes the need of reorienting
crop improvement programmes in the crop based on analysis of lead variables
among the agronomically important characters. It looks in to the interrelationship
of the agronomic characters of the crop so as to have a better idea on sharing
of genes by them.
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