Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2008
Publication Date: 4/16/2009
Citation: Kousik, C.S., Adkins, S.T., Turechek, W., Roberts, P.D. 2009. Sources of Resistance in U.S. Plant Introductions to Watermelon Vine Decline Caused of Squash Vein Yellowing Virus. HortScience. 44:256-262.
Interpretive Summary: Watermelon is an important crop grown in forty-four states in the US. About 47% of the watermelon in the US is grown in four southeastern states (FL, GA, SC and NC). Many different pests and diseases attack watermelon plants causing extensive damage. In recent years a new and emerging disease called as watermelon vine decline that is incited by a newly described virus has been causing havoc in watermelon production in southern parts of Florida. The newly described virus causing this problem in watermelon production is called Squash Vein Yellowing Virus (SqVYV) and is transmitted from plant to plant by a small insect called whitefly. This viral disease has already caused over $60 million in losses to watermelon growers in Southwest Florida. This newly described virus has the potential to become a serious pest all over southeastern US and may be other states where watermelons are grown. The USDA ARS maintains a large collection of over 1,800 accessions of watermelon that were collected from different regions of the world. In this study we tested a representative core collection of over 200 wild watermelon accessions for their reaction to squash vein yellowing virus in the greenhouse and field. None of the plants from the wild watermelon collection were completely immune to the virus. However, we identified several watermelon accessions with moderate levels of resistance to the virus. These wild watermelons will be useful as a source for plant breeders for enhancing SqVYV tolerance in watermelon cultivars. Because only moderate resistance was identified, it will be necessary to combine this resistance with other known strategies to manage the whitefly, thus managing this serious disease plaguing south Florida watermelon.
Technical Abstract: Watermelon vine decline (WVD) caused by the whitefly-transmitted (Bemisia tabaci) Squash vein yellowing virus (SqVYV; genus Ipomovirus, family: Potyviridae) has become a major limiting factor in watermelon (Citrullus lanatus) production in southwest and west-central Florida in recent years. Symptoms of WVD typically occur at or just prior to harvest and are manifested as a sudden decline of the vines, often with a reduction in fruit quality. WVD is estimated to have caused more than $60-$70 million in losses in Florida since its occurrence. We evaluated 218 plant introductions (PI) belonging to the watermelon core collection for resistance to SqVYV by mechanical inoculations of seedlings in a greenhouse. None of the PI were immune to SqVYV, but, several PI showed tolerance to SqVYV and were further evaluated in two greenhouse and two field trials (2006 & 2007). Though, disease developed on all the select PI, disease progress was significantly slower compared to the susceptible checks. Two Citrullus colocynthis PI (PI 386015 and PI 386024) had significantly less disease compared to the susceptible commercial watermelon cultivars Mickey Lee and Crimson Sweet (C. lanatus). Moderate resistance was also observed in several Citrullus lanatus var. lanatus PI (PI 482266 and PI 392291). A Praecitrullus fistulosus PI (PI 381749) was also resistant to SqVYV compared to the susceptible checks. Variability in the resistant reaction to SqVYV within most PI was observed. Identification of sources of resistance to SqVYV in this study suggests that watermelon germplasm with moderate resistance can be developed by careful screening and selection of individual resistant plants within these PI for use in breeding programs.