Tree Genetics and Molecular Breeding 2015, Vol.5, No.1, 1
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5
Growth during the initial years is crucial for
Hevea
brasiliensis
especially with respect to the attainment
of tappable girth (Sethuraj and George, 1980). The
elite mother tree OR1 attained highest girth (84.4 cm)
followed by OR2 (82.2 cm) and OR9 (81.5 cm) at
the opening of tapping (Table 3). Following the
trend highest annual girth increment before opening
of tapping was recorded in OR1 (10.16 cm)
followed by OR2 (9.91 cm) and OR9 (9.86 cm).
However, after commencement of tapping annual
girth increment over eight years was recorded
highest in OR7 (4.68 cm) followed by OR6 (4.43 cm)
and OR5 (4.13 cm) (Table 3). Similar performance
of seedlings also has been reported from Konkan
region of Maharastra (Birari et al., 1998;
Chandrasekhar et al., 2002) and from the
northeastern region (Sasi kumar et al., 2001; Mondal
et al., 2006). Clear bole volume is an indicator of
timber yield. Among the elite mother trees the bole
volume ranged between 0.13 m³/tree (OR9) to as
high as 0.50 m³/tree (OR 10) (Table 3). The high
timber volume attainment of polyclonal seedlings
over multiclonal population further meets the need
of the preferred high yielding “latex-timber”
planting material. Bark thickness was recorded
highest in OR10 (13.00 mm) followed by OR3
(12.00 mm) and OR2 (11.00 mm) (Table 3).
The polyclonal seedlings exhibited early attainment
of tappability, high girth, girth increment, and high
timber volume and bark thickness compared to
multiclonal population. Polyclonal population was
found more wind resistant and with almost
negligible reports of tapping panel dryness. Further
most, the significant good yield and in particular two
to three folds higher yield of selected elite mother
seedling trees offers the possible scope of selection
of promising clones/genotypes for the dry sub humid
region.
Polyclonal seedlings are expected to adapt well to
new areas due to their genetic heterogeneity
(Simmonds, 1989). The climate change and further
requirement of expansion of cultivation to less
congenial marginal regions has necessitated the
selection of advanced polycross progenies. The
selection of poly cross progenies can be further
useful to the normal hand pollination programme
(Tan et al., 1996). The polyclonal seedlings exhibit
excellent variability and suggest the scope of further
selection of desired superior genotypes. Over the
years, ten elite selections from polyclonal population
yields significantly higher than the multiclonal
population and clearly suggests the need to be
cloned and evaluated further for ascertaining the
genetic potential to evolve the most suitable planting
material for the region. Accordingly, the selected ten
elite mother trees were further multiplied. Bud
grafted trees derived from theses mother genotypes
were field planted and under further evaluation to
ascertain their genetic potential to include them as
clonal composites/ recommended planting material
in the region.
The present study reveals the existing variability and
superiority of polyclonal trees, particularly in
growth, yield, timber and adaptability and selection
of ten elite polyclonal trees. The present study
suggests the importance of maintenance of genetic
variability through planting of polyclonal seedlings
and possible development of clones for stressful
environment.
2 Materials and Methods
The study was conducted at the Regional Research
Station of Rubber Research Institute of India at
Kadalipal, Dhenkanal (20˚ 49’40’’ N, 85˚ 30’ 45” E,
altitude 100 m above msl)) in Dhenkanal district of
Odisha. The soil is an Alfisols order with pH 5.5 and
is of lateritic in nature. The fertility status shows that
the soils are low in organic carbon, available
phosphorus and potassium. The available
magnesium was in the high range. The region
represents dry sub-humid climate with stressful
conditions. In the present study compared the
budded multiclonal population comprising of RRII
105, RRIM 600 and GT 1 with a nearby similar aged
polyclonal seedling population and identified elite
polyclonal trees. The clones under study are most
popular and widely planted planting material in
India. RRII 105 occupies the dominant position with
85.0 percent share in the total rubber planted area.
Clones RRIM 600, GT 1 and polyclonal trees have a
dominant position in the nontraditional region,
besides satisfactory planted area in the traditional
region of the country (Veerputharan, 1998).
Generally rubber plantations are raised from clonal
bud grafts; though polyclonal tree plantations have
high genetic variation in growth and yield. These
