Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/6/2001
Publication Date: 5/3/2001
Citation: Levi, A., Thomas, C.E., Keinath, A.P., Wehner, T.C. 2001. Genetic diversity among watermelon (citrulus lanatus and citrullus colocynthis) accessions. Genetic Resources and Crop Evolution. 48:559-566. Interpretive Summary: Watermelon accounts for 2% of the area devoted to vegetable production throughout the world. In the U.S. watermelon production has been increasing from 1.2 M tons in 1980 to 2.1 M tons in 1998, with an at the farm value of $287 million. A large number of watermelon varieties have been developed in the U.S. during the last century, most of these varieties are closely related and susceptible to various diseases that cause significant damage to the crop. Therefore, there is need to develop new watermelon cultivars that are resistant to diseases and pests. The cultivated watermelon is related to wild species found in Africa, Asia, and the Mediterranean region. These species may be an essential source of genes to confer disease and pest resistances in cultivated watermelon. Thus, we conducted experiments to assess the genetic diversity among these species using DNA analysis. The results of our study indicate that these wild species have a broad genetic base that may be useful for genetic improvement of the cultivated watermelon. Therefore, we should increase efforts in collecting and preserving seeds of these wild species, and in using them in watermelon breeding programs.
Technical Abstract: Genetic diversity was estimated among 42 U.S. Plant Introduction (PI) accessions of the genus Citrullus (of these 37 PIs are reported to have disease resistance), and 5 watermelon cultivars, using 30 RAPD primers. These primers produced 662 markers that could be rated with high confidence. Based on these markers, genetic similarity coefficients were calculated and a dendrogram was constructed using the unweighted pair- group method with arithmetic average (UPGMA). The analysis delineated three major clusters. The first cluster consisted of a group of five watermelon cultivars, a group of C. lanatus var. lanatus accessions, and a group of C. lanatus var. lanatus accessions that contained some C. lanatus var. citroides genes. The second cluster consisted of the C. lanatus var. citroides accessions, while the third cluster consisted of the C. colocynthis accessions. The two C. lanatus clusters differentiated from each other and from the C. colocynthis cluster at the level of 58.8% and 38.9% genetic similarity, respectively. The results in this study indicate that Citrullus PIs with resistances to the same diseases may be closely related. Thus, molecular markers may be a useful tool in the development of core collections of Citrullus PIs with disease resistance.