High levels of RAPD and SSR marker diversity in landraces of watermelon (Citrullus lanatus) in southern Africa
2011
Mujaju, C. | Werlemark, G. | Garkava-Gustavsson, L. | Nybom, H.
Previous studies have reported relatively low levels of genetic diversity in cultivated watermelon. The investigated material has, however, consisted mainly of US plant introductions and modern watermelon cultivars linked to breeding programmes for disease resistance. By contrast, germplasm maintained in the putative centre of origin in southern Africa, could be expected to display considerably higher variability. Three different sampling strategies have been used to collect plant material of both wild and cultivated forms of cow-melons (Citrullus lanatus var. citroides) and of sweet watermelons (C. lanatus var. lanatus, only known from cultivation); (1) in-depth sampling in the fields of one village in Zimbabwe, (2) medium-scale sampling across the water-melon growing districts in Zimbabwe, and (3) broad-scale sampling across southern Africa (Botswana, Namibia, South Africa, Zambia and Zimbabwe). Two molecular markers have been, random amplified polymorphic DNA (RAPD) and simple sequence repeats (SSR) also known as microsatellite DNA. Similarity matrices obtained with RAPD and SSR, respectively, were highly correlated, suggesting that for some applications, the less demanding RAPD can be a useful alternative, especially in developing countries. Considerable amounts of genetic diversity was found at all levels, including within-accessions (half-sib families), and sweet watermelon accessions appear to contain almost as much variability as cow-melon accessions.
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