GENETICS AND GENETIC IMPROVEMENT OF DISEASE RESISTANCE AND QUALITY TRAITS IN WATERMELON, BROCCOLI, AND LEAFY GREEN BRASSICAS
Location: Vegetable Research
Title: USVL-220, A Novel Watermelon Breeding Line
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 4, 2010
Publication Date: January 15, 2011
Citation: Levi, A., Thies, J.A., Simmons, A.M., Harrison Jr, H.F., Hassell, R., Keinath, A. USVL-220, A Novel Watermelon Breeding Line. HortScience. 46(1):135–138. 2011.
Interpretive Summary: Watermelon is a major vegetable crop with an annual farm production value of over $430 million. Because of many years of cultivation and selection for watermelon with desirable fruit qualities, many of the watermelon cultivars in North America have the same genetic background. As a result, they are susceptible to a large number of diseases and pests. In this study, we designed a breeding scheme to broaden the genetic base of watermelon cultivars by crossing them with a wild type watermelon that thrives in the deserts of North Africa, the Middle East, and southern and central Asia (Afghanistan). This desert watermelon is called Citrullus colocynthis, and is known to be drought resistant. It is also known to be resistant to whiteflies, spidermites, and viruses that cause serious damage to the watermelon crop. Our breeding experiments produced a new watermelon breeding line (USVL-220) that contain genes from the desert watermelon, and has desirable fruit qualities. This breeding line can be useful for plant breeders and seed companies in their efforts to develop watermelon cultivars that have broad genetic base and are resistant to diseases and pests.
A novel watermelon breeding line was developed at the USDA, ARS, U.S. Vegetable Laboratory, Charleston, South Carolina. This breeding line contains the nuclear genome of cultivated watermelon (Citrullus lanatus var. lanatus) and the chloroplast and mitochondrial genomic background of the desert species C. colocynthis. USVL-220 has elongated-oval shaped fruits with green dappled rind (rind thickness = 0.7-0.8”) (Fig. 2). In field trials (2008-2009), USVL-220 plants produced 1.8 large fruits (13.0-15.5” long and 6.7-7.9” width) per plant, comparable with Charleston Gray and Jubilee (1.8 and 2.0 large fruits per plant, respectively). The mature fruits have red flesh color with sweet flavor, and 8.5-11.0% solid soluble content. The flesh is firm with slightly crispy texture and does not exhibit hollow heart. Mature fruits are ready for harvest in mid-late season (76-78 days post planting). The fruit contains brown seeds (7.0 mm long and 4 mm width). USVL-220 is moderately susceptible to southern root-knot nematode (Meloidogyne incognita) with an average root gall index of 3.4 on a scale of 1.0 to 5.0, where 1.0 = no galls and 5.0 = greater than 80% of root system galled. USVL-220 may be useful for scientists and plant breeders interested in enhancing watermelon cultivars with cytoplasm (chloroplast and mitochondrial genomes) of wild watermelon species. This breeding line may be used for examining the effect of the desert species C. colocynthis cytoplasm on photosynthesis and respiration, on disease resistance in watermelon and possibly on yield. In breeding programs, USVL-220 should be used as a maternal parent to retain the C. colocynthis cytoplasm.