Submitted to: HortScience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/22/2002
Publication Date: 12/1/2003
Citation: Thies, J.A., Levi, A. 2003. Resistance of watermelon germplasm to the peanut root-knot nematode (Meloidogyne arenaria race 1). Hortscience. 38(7):1417-1421. Interpretive Summary: Watermelon (Citrullus lanatus) is an important vegetable crop in the U.S. and world-wide. Root-knot nematodes (Meloidogyne arenaria, M. incognita, and M. javanica) are serious pests of watermelon in the southern U.S. Root-knot nematodes are currently controlled in watermelon by pre-plant fumigation of soil with methyl bromide or by use of other nematicides. However, because methyl bromide is an ozone-depleting substance, it's use will be phased out in the U.S. in 2005. Thus, it is urgent that alternative methods to methyl bromide are discovered that are safe and effective for managing root-knot nematodes in watermelons. We searched for resistance to root-knot nematodes in the U.S. Citrullus (watermelon) germplasm collection, which contains many wild types of watermelon. In greenhouse studies, we demonstrated that there is significant genetic variability within the U.S. Citrullus collection for resistance to the peanut root-knot tnematode, M. arenaria race 1. We also discovered that the C. lanatus var. citroides portion of the collection is a potential source of resistance to the peanut root-knot nematode. Thus, future searches for resistance to this and other root-knot nematode species should focus on C. lanatus var. citroides.
Technical Abstract: Watermelon (Citrullus lanatus) is an important vegetable crop in the U.S. and world-wide. Root-knot nematodes (Meloidogyne arenaria, M. incognita, and M. javanica) are serious pests of watermelon in the southern U.S. All available accessions of C. colocynthis (21) and C. lanatus var. citroides (88), and approx. 10 percent of the C. lanatus var. lanatus (157) accessions from the U.S. Citrullus germplasm collection were evaluated for resistance to M. arenaria race 1 in greenhouse tests. 'Charleston Gray', 'Crimson Sweet', and 'Dixie Lee' were included as check cultivars in all tests. The checks and nearly all C. lanatus var. lanatus accessions were very susceptible; root gall severity indices (GI) ranged from 8.1 to 9.0 and from 4.0 to 9.0, respectively. Likewise, all C. colocynthis accessions evaluated were highly susceptible (GI = 8.0 to 9.0). However, some C. lanatus var. citroides accessions appeared to be moderately resistant (GI = =3.0 to 9.0). These results demonstrate that there is significant genetic variability within the U.S. Citrullus germplasm collection for reaction to M. arenaria race 1 and also identify the C. lanatus var. citroides accessions as potential sources of resistance to M. arenaria race 1.