Characterization of watermelon local cultivars from Southern Tunisia using morphological traits and molecular markers

In Southern Tunisia, local cucurbitaceous genetic diversity is threatened by the introduction of many commercial varieties. In the present study, the genetic diversity of local Tunisian watermelon cultiavrs and two commercial varieties (Giza and Sugar-baby) was studied using morphological traits and RAPD markers. The morphological analysis showed an important diversity among the studied watermelon cultivars. The principal component analysis based on 15 morphological traits explained 67.85% of the total variation and showed a clear classification of the cultivars into several groups. Geographical origin was correlated with seed weight and thickness of pericarp parameters. RAPD primers generated 86 reproducible bands, of which 85 were highly polymorphic. The AMOVA showed significant inter-population differentiation (28%). The principal coordinate analysis indicated that commercial varieties are significantly different from the local cultivars. The commercial varieties have the highest PhiPT when compared to the local cultivars. No correlation between the RAPD markers and the geographical origin of the watermelon cultivars was found. However, a significant correlation was found between RAPD markers and some fruit characteristics such as seed weight and fruit acidity. The results obtained from this study provide new data about the genetic diversity of Tunisian watermelon local germplasm, which constitue the first step for the establishment of a core collection of the Tunisian watermelon germplasm and would be useful for the preservation of these local resources and their use in future breeding programs.