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New viruses detected in watermelon in South Florida

By: Pamela Roberts

Plant pathologist, South Florida Research and Education Center, Immokalee

Whitefly transmitted viruses are the major limiting disease problem for growers in South Florida. In the past few decades, these transmitted viruses have been Squash vein yellowing virus (SqVWV), Cucurbit leaf crumple virus (CuLCrV), and Cucurbit yellow stunting disorder virus (CYSDV). Management of these viruses has been through an integrated approach but with a heavy reliance on insecticides to control whiteflies.

In Spring 2021, two previously unknown viruses were identified in watermelon from Texas and South Florida. The two new viruses, Watermelon crinkle leaf-associated virus-1 (WCLaV-1) and WCLaV-2, are a completely different virus type unrelated to SqVYV, CuLCrV, CYSDV or other potyviruses such as Watermelon mosaic virus. Another whitefly vectored virus, Cucurbit chlorotic yellows virus, was also detected for the first time in Florida in Spring 2021, but this virus has been long established in California and Arizona. In total, the viruses now found in watermelon in South Florida include four whitefly transmitted, several aphid transmitted Potyviruses, and the two new viruses, WCLaV-1 and WCLaV-2.

From surveys and samples submitted to the diagnostic clinic in spring and fall 2021, we determined that WCLaV-1 is the predominant virus in watermelon in South Florida. This raises the question, do these new viruses affect fruit quality and yield? Leaf symptoms associated with WCLaV-1 and WCLaV-2 seem to be deformation, crinkling, and mild mottling, but these symptoms are quite similar to those caused by the other viruses. In fact, the new viruses were initially suspected because symptomatic samples submitted for virus testing were negative for the other viruses. The mode of transmission for WCLaV-1 and WCLaV-2, as yet unknown, is fundamental to devising any potential management programs. The same type of virusesinfecting humans, animals, or other plants are vectored by arthropods such as ticks, planthoppers, and thrips. While this does not rule out whitefly as a potential vector it raises the possibility that another insect is the vector.

Going forward, we will continue testing for all the viruses, begin testing insects for detection of the new viruses, and examine fruit quality infected with WCLaV-1 and WCLaV-2 in efforts better understand the impact of these viruses to watermelon production.

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