reported in sunflower, a flowering plant of the same
family, the transferability of these markers to marigold
was also evaluated. Among the three methods, the ISSR
technique was found to generate the highest percentage
of polymorphic SSRs (Fig. 1), indicating that it is an effective
method for developing SSRs in marigolds. However,
a SSR-enriched genomic DNA library is more practical for
generating large numbers of SSRs. The low level of transferability
of SSRs between sunflower and marigold
suggests that the SSR-flanking regions are not well conserved
between these species. Even though low numbers
of alleles per locus were observed, according to
Kalinowski (2002), this has no effect on the estimation
of genetic distances and equivalent results can be accomplished
using alleles within or across the loci, and the
only important factor is the total number of alleles.
In genetic relationship analysis, the African marigold
and the French marigold were separated into different
clusters with the highest genetic distance. Accordingly,
the highest bootstrap value was at the major node that
separated the African marigold cluster from the French
marigold cluster. This indicated that the association was
strong. The set of SSRs used in this study could also classify
commercial varieties and Thai landraces of African
marigold. This indicates that the SSR markers are effective
for classifying populations and for analysing the genetic
relationship. Moreover, the markers can be used to classify
most commercial varieties of African marigold,
although the markers could not differentiate the varieties
‘Bali’ and ‘Narai’, which share the same female parent.
The SSR markers were able to identify almost all the
samples, except FM04 and FM05, which have the same
morphological traits and were collected from the same
area and therefore possibly have the same genotype.
However, the markers are effective at identifying
individual marigolds. These SSRs will be useful in genetic
differentiation of marigolds that have not been reported
elsewhere, but only in related taxa such as sunflower
(Heesacker et al., 2008).