Simple Sequence Repeat Markers Reveal Genetic Diversity Within and among Landrace Collections of Citron and Dessert Watermelon from South Africa

A BSTRACT . Genetic diversity analysis is fundamental for effective breeding and genetic conservation. The objective of this study was to determine the genetic diversity present among dessert watermelon ( Citrullus lanatus var. lanatus ) and citron watermelon ( C. lanatus var. citroides ) landraces widely grown in South Africa and to select genetically diverse and complimentary genotypes for strategic breeding or conservation. Thirty-one dessert watermelon and 34 citron watermelon landraces were genotyped using 10 polymorphic simple sequence repeat markers. The number of alleles detected per marker ranged from 2 to 23 alleles, with a mean of 13.5 alleles. A total of 135 putative alleles were amplified from sampled watermelon populations. Number of effective alleles ranged from 1.99 to 10.88 alleles with a mean of 5.83 alleles. The mean observed and expected heterozygosity were 0.50 and 0.79, respectively. The mean polymorphic information content was 0.79. Cluster and principal coordinate analyses grouped the two watermelon populations into two separate clusters. The two populations were genetically differentiated with low gene flow, suggesting the presence of high genetic differences between the two populations. Overall, the study established the existence of considerable genetic diversity among South African grown dessert and citron watermelon landraces. Unique dessert watermelon landraces such as SWM-39, SWM-24, SWM-01, SWM-40, SWM-18, SWM-36, and SWM-26; and citron watermelon genotypes including WWM-24, WWM-37, WWM-28, WWM-34, WWM-02, WWM-22, WWM-50, and WWM-36 were selected based on their high dissimilarity index. These could be useful for breeding and systematic conservation.

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