Tree Genetics and Molecular Breeding 2015, Vol.5, No.1, 1
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adopted for evolving new clones (Fernando, 1974;
Marattukalam et al., 1990). Some of these are still
used as planting materials in different rubber growing
countries (Tan et al., 1996). The Polycross seedling
population has also facilitated the evolvement of high
timber yielding clones in India (Mydin et al., 2005).
Polyclonal seeds are collected from polyclonal seed
gardens where different clones are planted in an area
with specific layout. Plantations raised from seeds are
considered to have high inherent genetic variability.
Therefore elite polycross mother seedling trees offer
possibilities in the development of clones with high
yield and tolerance to biotic and a biotic stress
(Varghese et al., 2006). The potential of poly cross
population for outstanding genotypes in any new
environment has been widely accepted (RRII, 2002).
High temperature, low rainfall and strong winds are
the major constraints curtailing the growth and
productivity of the natural rubber crop in the Odisha
state (17˚ N and 87˚ E) located in the eastern region of
India. Rubber is comparatively a new crop introduced
in this nontraditional dry sub humid region of Odisha
state; though preliminary study reported wide
variability in growth and yield among polycross
population (Gupta et al., 2001). Another study
reported selection of ten ortet from the polyclonal
seedlings and ample scope of evolving of clone for the
dry sub humid climate (Krishan, 2013). The present
study reports the performance of another set of ten
elite mother polyclonal seedlings identified among
polycross population and attempts to compare the
performance of the polycross seedling population and
a multiclonal population under the sub optimal
environmental conditions of Odisha.
1 Results and Discussion
The region where rubber tree plantation were studied
represents dry sub humid climate with stressful
climatic conditions and sub optimal rubber growing
conditions. The region received an annual rainfall of
1296 mm during the study period and mainly confined
to mid-June to October. The distribution of rainfall is
far from satisfactory which results in long dry spells
extending from November to May, during which the
drought conditions become very severe. The summer
months exhibited severe soil moisture stress
conditions. The daily minimum temperature was low
in November, December, and January and in the
remaining months they were considerably higher.
Daily maximum temperature exceeds 35˚C during
March, April, and May. During the month of May, the
mean maximum temperature nearly 40˚C was
recorded. The sunshine hours during July and August
were low, moderate in June and September and more
than seven hours daily in the remaining months (Figure 1).
Figure 1 Weather parameters of experimental site (1991-2006)
