Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 2, 2006
Publication Date: December 4, 2007
Citation: Thies, J.A., Levi, A. 2007. Characterization of watermelon (citrullus lanatus var. citroides) germplasm for resistance to root-knot nematodes. Journal of Nematology. 42:1530-1533. Interpretive Summary: Watermelon is an important crop in many parts of the world. Watermelon production in the U. S. has increased from 1.2 M tons in 1980 to 2.2 M tons in 2004 with an at-farm value of $310 million. Root-knot nematodes are microscopic worms that occur in many field and garden soils. Nematodes invade the roots of watermelon and most other vegetable crops, causing extensive damage to the roots. Consequently, growth of the watermelon plant is stunted, and watermelon fruit quality and yield are reduced. Wild species of watermelon that grow in Africa and Asia have wide genetic diversity and are known to possess resistance to a broad range of pests and diseases. ARS scientists evaluated plants of the different wild watermelon species and identified a few wild types that are resistant to nematodes. Plant breeders will cross pollinate these resistant plants with susceptible cultivated watermelon in order to develop resistant cultivated watermelon. Planting resistant watermelon varieties would reduce the need for pesticides to control nematodes in watermelon.
Technical Abstract: Root-knot nematodes (Meloidogyne arenaria, M. incognita, and M. javanica) cause extensive damage to watermelon and resistance to these root-knot nematode species has not been identified in any watermelon cultivar. Twenty-two U. S. Plant Introductions (PI) of Citrullus lanatus var. citroides, previously identified as moderately resistant to M. arenaria race 1, were evaluated in greenhouse tests for resistance to M. incognita race 3 and M. arenaria race 2. Overall, the C. lanatus var. citroides PIs exhibited low to moderate resistance to both M. incognita race 3 and M. arenaria race 2. The C. lanatus var. citroides PI 482303 was the most resistant with gall indices of 1.77 for M. incognita race 3 and 2.10 for M. arenaria race 2, respectively (1 = 0 to 3% root system galled; 5 = more than 80% root system galled). These results demonstrate that there is a significant genetic variability within C. lanatus var. citroides for reaction to M. incognita and M. arenaria race 2, and a few Citrullus lanatus var. citroides PIs may be a source of resistance to root-knot nematodes.