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Casuarinas are one of the popular and fast growing hardwood trees planted widely
for multiple purposes in the tropical regions. They are actinorhizal plants which can
form endosymbiotic associations with species of
Frankia, an actinomycete able to fix atmospheric nitrogen
(Diem et al., 2000). In coastal areas,
casuarinas are planted for protection against wind, tsunami
(Zucchi et al., 2003) and stabilization of sand dunes.
In India, the species C. equisetifolia has been identified as one of the suitable species
for farm forestry and it is used as the source of paper pulp, fuel wood, poles and timber.
Utility value and growth performance of C.
equisetifolia led to the initiation of genetic improvement programs in the form of provenance trials and clonal
selection (Pinyopusarerk et al., 2004). Genetic improvement and domestication of
casuarinas has been supplemented with molecular markers like allozymes, which are used to
estimate genetic relationships existing among the populations of
casuarinas (Moore and Moran, 1989; and
Moran et al., 1989). Genome size of the members of Casuarinaceae has
been determined (Van der Nest et al., 2000), followed by the use of dominant DNA
markers like RAPD, ISSR and FISSR markers to study the genetic diversity within and
between species and to differentiate the species and clones (Leroy
et al., 2001; Kantety et al., 2002; and Yasodha
et al., 2004). However, advanced molecular genetic
improvement programs require codominant and multi-allelic markers such as Simple Sequence
Repeats (SSRs) or microsatellites for the development of high resolution linkage maps and
in marker assisted selection/breeding (Brondani
et al., 1998; and Gupta and Varshney,
2000). The presence of abundant repeat regions in tropical tree genomes was described
by Condit and Hubbell (1991); since then several reports have been published on
isolation and characterization of microsatellites. |
