Genetic diversity among watermelon ( and ) accessions

Genetic diversity was estimated among 42 U.S. PlantIntroduction (PI) accessions of the genus (of these, 34 PIs are reported tohave disease resistance), and 5 watermelon cultivars, using 30RAPD primers. These primers produced 662 RAPD markers that could berated with high confidence. Based on these markers, geneticsimilarity coefficients were calculated and a dendrogram wasconstructed using the unweighted pair-group method witharithmetic average (UPGMA). The analysis delineated threemajor clusters. The first cluster consisted of a group of fivewatermelon cultivars, a group of . var. accessions, and a group of . var. accessions that contained some . var. genes. The second cluster consisted of the . var. accessions, while the third cluster consisted of the. accessions.The two . clustersdifferentiated from each other and from the . cluster at the level of 58.8%and 38.9% genetic similarity, respectively. Assessment ofgenetic diversity among accessions that have been reported to havedisease resistance indicated that resistance to either anthracnose,downy mildew, powdery mildew, or watermelon mosaic virus is foundamong all major groups of PIs.Additionally, resistance to gummy stem blight or Fusarium wilt mayexist among . var. PIs. This study demonstrates thatmolecular markers can be useful in assessing genetic diversity, andin sorting PIs into phylogeneticgroups prior to their evaluation for disease or pestresistance.