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Introduction
1. INTRODUCTION
Casuarina (derived from the Latin word Casuarius meaning Cassowary) belongs to the
family Casuarinaceae and is a native of Australia (Subbarao and Rodriguez, 1993).
Casuarinaceae belongs to the Gondvanic family and consists of four genera
(Allocasuarina, Casuarina, Ceuthostoma and Gymnostoma) and 97 species including
monoecious or dioecious trees (Johnson and Wilson, 1989). Casuarinas are very
distinctive and superficially resemble coniferous species with their wire like foliage and
woody fruiting structures (Johnson and Wilson, 1989). Among the four genera, the
species of Casuarina L. Johnson and Allocasuarina L. Johnson are commercially
cultivated in many tropical and subtropical regions of the world, while, other two genera
Gymnostoma L. Johnson and Ceuthostoma L. Johnson occur as wild species only
(Yasodha et al., 2004). About 15 species of Casuarina and Allocasuarina have been
recognized for their multiple utilizations. Casuarina species are cultivated in China,
India, South East Asia, Malaysia, Pacific islands and subtropical regions, where
introduced populations are grown, and the species are more common outside its area of
origin (Diouf et al., 2008).
India has more than 8.0 lakhs hectares of Casuarina plantations mostly along the
coastal tracts. Casuarinas are grown in places where most other trees fail to grow and
used for reclaiming mines, salinity affected and wind-prone areas (Doran and Hall,
1983). However, currently there is increasing tendency to grow multipurpose species of
Casuarina either as agro-forestry tree on farm land or fuel wood blocks on waste land.
Casuarinas are widely accepted for landscaping, timber, medicine, dye, tannin, poles, raw
material for pulp and paper, soil stabilization, nitrogen fixation and amenity planting.
Species are tolerant to adverse soil and climatic conditions and more remunerative than
most of arable crops in the long run (Pan et al., 1996).
In Karnataka there are ten agro-climatic zones, out of which five are classified as
dry zones. Northern dry zone is the largest among them and second largest zone in the
country which occupies an area of 4.19 million hectares, out of which 6.6 per cent is
under forests and the rest is under arable crops or fallow. The average annual
consumption of firewood is estimated to be 8.0 m3 per household and fuel wood
productivity, 5 tonnes ha-1 year-1 (Read et al., 1995). Casuarinas were introduced first in
the coastal district of Karwar in Karnataka in 1668 (Ataia, 1983). There is a rising
demand for Casuarina products by local populations mainly for firewood due to its
calorific value (4950 Kcal kg-1) which is the highest among the fire wood trees (Kondas,
1983). Hence larger area of Casuarina plantation is needed to produce the required
volume of fuel wood in Northern dry zone of Karnataka.
It has been estimated that about one-third of area in Northern dry zone of Karnataka
has been rendered unproductive by drought, salinity and vast stretches of land have been
abandoned and neglected. The cultivation of field crops in these degraded soils has
become uneconomical due to adverse environmental conditions and poor fertility of soil.
In most of the areas under black cotton soil, fertility has been depleted and altered due to
salinity caused by flood irrigation, fertilizers and pesticides application. An extensive
plantation of Casuarina species is the suitable alternative to reutilize black cotton saline
soil area (Halos, 1983).
Casuarina species are generally propagated by seeds for raising high density
plantations for short rotation, hence huge quantity of quality seed is required every year
to meet planting stock demand (Lal et al., 1996). The seed source of Casuarina is
originated from a narrow genetic base, which was developed into a land race
domesticated by farmers. Seed germination is poor and inconsistent, apparently because
of nonviable seeds or underdeveloped shrunken embryos (Shivakumar et al., 2007).
Further, the seeds have short storage life and loose viability rapidly which is a major
problem for tree planting programmes. Genetic constitution of the seed determines the
potential of planting material as to whether it is going to produce good or poor tree
growth. Even a small increase in growth rate using the quality seed source to grow the
planting stock can lead to a much enhanced return on investment. Imperceptible genetic
gains through traditional breeding for improvement of seed sources are slow and difficult
to capture. Hence, there are several methods that can be used to genetically improve
seeds for immediate planting. Grading the seed in sieve is one of widely used techniques
to separate large seeds from ungerminable seeds through their sizes with perforation of
sieve (Jerlin and Srimathi, 1997). Pre-treatment is second commonly employed for
breaking dormancy of seeds to ensure uniform germination and substrata also have a
significant role in seed viability.
In India, genotype testing in forest trees has been focused on five major species viz.,
Tectona grandis, Azadirachta indica, Acacia nilotica, Dalbergia sissoo and Pinus
roxburghi. Casuarinas have not been taken into consideration for species testing in
Northern dry zone of Karnataka. Genetic diversity plays an important role in Casuarina
improvement programme, since growth and morphometric traits of species of diverse
origin display greater diversity than those between closely related individuals of half sib.
However, a clear understanding of phenological behavior, synchronization of male and
female flowers and mode of pollination are necessary for hybridization programmes
between species (Warrier et al., 2001). Significant variation in tree biomass were
observed between species but information on quantum of seed produced and diversity of
species from seedling seed orchard of Casuarina is meagre (Pinyopusarerk and Williams,
2000). Hence, it is essential to develop a seedling seed orchard after selection of superior
species from half sib population. This orchard is an endeavour to establish a Casuarina
germplasm bank for supply of quality planting seeds material in South India. In the
present investigation, in order to identify suitable species of Casuarina for Northern dry
zone of Karnataka by evaluating growth performance and other morphometric traits, the
research was under taken with the following objectives.
OBJECTIVES
1.
To assess the performance of different Casuarina species in black cotton soil of
Northeren Dry Zone of Karnataka.
2.
To study the phenology of different Casuarina species grown.
3.
Evaluation of variability in fruit / cone and seed quality parameters.
4.
To find out the suitable substrata and pretreatment methods to improve seed
germination.
5.
To assess the variability of the half sib population.