Genetic Structure Analysis Of Wild Rice Populations (oryza Longistaminata) From Kwale District Of Kenya Using Microsatellite Markers
Abstract
The most agriculturally important wild rice species found in Kenya is Oryza longistaminata,
which can act as a source of useful traits for improvement of cultivated rice. Knowledge of the
amount of genetic diversity in natural populations is needed for development of good strategies
for in-situ and ex-situ conservation so as to sustain this diversity and prevent it's erosion through
man made activities. Likewise the genetic diversity and genetic structure of these populations
can act as a pointer to whether gene flow from cultivated rice species has occurred and the
consequences of gene flow if transgenic rice is introduced. The genetic structure and genetic
diversity of natural populations of Oryza longistaminata on a fine scale has not been well
documented. Microsatellite loci were used to unravel the fine scale genetic variation within and
between populations of Oryza longistaminata from Kwale District of Kenya. To better estimate
the genetic diversity and structure of the Kwale populations a total of 244 individuals from ten
discretely distributed populations were analysed using five Oryza saliva microsatellites (SSRs).
To estimate the differentiation and the 'connectivity among the populations the study relied on
Wright's (1951) FST and FST estimator (8) while the effective number of alleles (Ae), the
observed heterozygosity (Ho), ex~e~ted heterozygosity (H~) and Shannon's index were used to
demonstrate the level of population genetic diversity and locus genetic diversity. FSTwas used to
indirectly estimate gene flow through its link with effective number of migrants (Nm) i.e.[ Nn =
(1/4)(I-FsT)/FsT). Microsatellite genotyping resulted in a tptal of 40 alleles and an average of 8
alleles per locus which revealed high polymorphism. The genetic diversity indices indicated the
observed heterozygosity is higher than expected heterozygosity resulting to a general increase in
diversity within populations i.e. mean (F1s = -0.14023). The fixation index (FST= 0.4049) shows
considerable population differentiation while FSTestimator (8 = 0.42331) is also proportionally
high and significant (P < 0.05). The gene flow (Nn = 0.3629) is quite low which could have
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influenced the differentiation through isolation by distance. In general the parameters reveal high
levels of variation in the populations of Oryza longistaminata and this diversity is higher within
the populations than between populations. The increased diversity suggests that alleles from
cultivated rice may have introgressed into wild rice as cultivated rice in this region grows
sympatrically with Oryza longistaminata. There is therefore need to consider identifying a safe
distance between Oryza longistaminata populations and cultivated transgenic rice to avoid
contamination and erosion of the inherent diversity.
Citation
Master of Science in biotechnologyPublisher
University Of Nairobi college of biological and physical science