Assessment Of Genetic Variations Within And Between Populations Of Marama Bean [Tylosema Esculentum (Burchell) Schreiber] Based On Microsatellites (Ssrs) And Intergenic Spacer Length Variatio

ABSTRACT

Tylosema esculentum (Burchell) L. Schreiber is a herbaceous perennial drought

tolerant legume that is endemic to the arid and semi-arid zones of southern Africa. Its

agronomic potential is on the basis of its seed’s nutritional composition that is

comparable with soybean and peanut, the two mostly consumed legumes. In this

study SSR markers were used to assess genetic diversity in natural populations of

marama in the Namibian germplasm. Additionally, in the present study, the

intergenic spacers (IGS) region of the large ribosomal DNA gene was amplified to

assess length variation in marama bean. In the present study two to four alleles per

primer pair were amplified from the 332 marama individuals among 11 populations.

The study revealed that substantial genetic variation exists in marama populations

and most of this variation (66.5%) occurred within populations. The direct-count

heterozygosities showed a substantial variation of 0.51 among populations. The

mean Shannon diversity index for eleven marama populations assessed in this study

estimated a higher genetic diversity in marama with a mean total diversity of (Hʹ

=

1.526). There were no significant differences (p > 0.05) in the mean genetic diversity

between populations. However, there were significant differences in the mean

genetic diversity attained by different SSR primer pairs (p < 0.05). Assessment of

length variation in marama bean has disclosed a high intraspecific genetic variation

(Hʹ= 1.700) in the nuclear ribosomal DNA repeat units in marama bean. There was

no clear indication of population differentiation between the marama populations.

This study is the first to document genetic variation present in marama ecotypes in

the Namibian germplasm using SSR markers. The evaluation of genetic variation for

marama is important for identification of the best strains, for the selection of the

genetically diverge parent plants for marama genetic mapping and domestication.

This study confirmed the usefulness of SSR in providing a quick and reliable method

of assessing genetic variation in plant populations.

Keywords: microsatellite, SSR, marama bean, Tylosema esculentum, genetic

diversity, rDNA, IGS, length variation