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Molecular Plant Breeding 2011, Vol.2, No.12, 83
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cost, long-term of field evaluation, environment
factors and limited number of available phenotypic
markers (Sugimura et al., 1997; Manimekalai et al.,
2006). However, since molecular markers are
detectable at all stages of development and can cover
the entire genome, they, which detect variation at
DNA level, overcome most limitations of
morphological and biochemical markers, (Ashburner
et al., 1997; Lebrun et al., 1998; Rohde et al., 1995;
Perera et al., 1998, 1999, 2000, 2001, 2003; Rivera et
al., 1999; Teulat et al., 2000; Dasanayake et al., 2003;
Upadhyay et al., 2004; Zizumbo-Villarreal et al., 2006;
Manimekalai et al., 2006, 2007). Among various
available molecular marker techniques, simple
sequence repeat (SSR) markers provide good signal in
evaluating genetic diversity and genetic relationships
in plants. The increased number of SSR markers
greatly improves the previously established genetic
relationships among coconut varieties/populations.
The first coconut type introduced to China from
Southeast Asia is traditional Tall during Han Dynasty
approximately 2000 years ago (Tang et al., 2006). In
Hainan province, the palms are traditionally planted
around villages, along roadsides and within cities,
while the large plantations can be found in some
locations. This cross-pollinating Tall coconut belongs
to the Pacific group A3 (Lebrun et al., 2005). The
self-pollinating Dwarf coconut was introduced from
Malaysia during the 20th century (Martinez et al.,
2009), belonging to the Pacific group A1 (Lebrun et
al., 2005). Hybrids between the Malayan Yellow
Dwarf (MYD) and the local Tall are planted in a few
large plantations. However, little information is
available on the genetic diversity among China
coconut varieties/populations. The coconut is
extensively planted in Hainan province (especially in
Wenchang, Qionghai and Lingshui), where it is an
integral part of spiritual and social life of indigene.
For sustainable breeding, adoption and conservation in
situ, it is necessary to develop a strategy to use
diversity of coconut landraces for socio-economic
benefits (Batugal and Oliver, 2003). In this study, we
analyzed 45 coconut individuals from 10 accessions
by using 30 SSR markers. Moreover, we had several
objectives as follows: (i) to evaluate the genetic
diversity of coconut varieties/populations in Hainan,
China; (ii) to understand the genetic basis of chinese
coconut varieties; (iii) to provide the groundwork for
their genetic improvement and breeding; and (iv) to
make good suggestions on protecting coconut
varieties/populations in China.
1 Results and Analysis
1.1 Overall diversity parameters
In this study, we analyzed 45 individuals using 30
SSR primers. A total of 26 SSR primers showed
greater allelic variability, which were clear, specific
and reproducible. These 26 SSR primers revealed 188
alleles in the 45 individuals, whereas 163 alleles were
polymorphic. The percentage of polymorphic alleles
(
PPA
) was 84.65%. Table 1 shows that the
polymorphic information content (
PIC
), observed
heterozygosity (
Ho
), expected heterozygosity (
He
) of
CAC03, CAC06, CAC08, CAC10, CAC21, CAC39
and CN11A10 exhibited higher levels than those of
other loci, indicating that these seven primers are
suitable for detecting the genetic diversity of coconut
accessions in China. Furthermore, SSR analysis also
showed that the gene flow of coconut in Hainan was
0.279 5, suggesting that the gene exchange between
individuals was limited. The estimated out crossing
rate (
t
) was 1.594 7, suggesting that this species is a
typical plant with a cross-pollinate system.
Table 1 and Table 2 show that the observed and
expected heterozygosities were slightly higher than
the average values of the Pacific group A3 (0.248 and
0.263, respectively), but they were lower than the
average values of the Pacific group A4 (0.487 and
0.512, respectively). The overall genetic structure in
coconuts from Hainan province was explored by
Wright's
F
statistics (Table 3). The
F
IT
expresses the
deviation of the whole Tall population from
Hardy-Weinberg equilibrium. It was significantly
different from zero, showing a slight deficit of
heterozygotes. The
F
ST
represents the contribution of
the divergence between populations to this deficit,
which was also positive and significantly different
from zero, indicating that allelic frequencies are
different among accessions. If the whole population is