Breeding for watermelon chlorotic stunt viral disease resistance in watermelon

The white fly transmitted watermelon chlorotic stunt virus (WmCSV) is the causal agent of the most devastating disease of watermelons (Citrullus lanatus) across many African and Middle Eastern countries including Sudan. Commercial cultivars collected from around the world proved susceptible to the disease especially during the hot dry summers and in severe situations the disease may cause complete damage of the crop. In search for sources of resistance, 27 cultivars and hundreds of landraces of C. lanatus were initially screened; however, none had sufficient levels of field resistance. Efforts were then expanded to include wild relatives of watermelon such as C. colocynthis. Large variability was noticed within the highly bitter white fleshed C. colocynthis in fruit size, external colour, disease and insect resistance and drought tolerance. Out of the screened collection, two accessions; C114 and Grift, were found to be highly resistant to WmCSV. The identified resistance in the wild resources was transferred by backcrossing to two of the widely cultivated watermelon cultivars; Crimson Sweet and Peacock. Both donors were readily crossable with commercial cultivars and hybrids (F1s) were fertile and no genetic barriers were noticed along the entire process of advancement of backcrossing generations.