Fusarium wilt on watermelons. Image courtesy Benny Bruton, ARS.

New Form of Fusarium Wilt Could Pose Threat to Watermelon Crop

By Erin Peabody
August 14, 2006

It’s too bad that one of summer’s most enjoyed simple pleasures--the watermelon--can be such a bear to grow. Melon growers are beset by numerous problems related to disease, weather, pests and the quest for fruit uniformity. But now, unfortunately, a new threat has emerged--one that may cause growers to wince even more.

In separate studies, scientists with the Agricultural Research Service (ARS) in Lane, Okla., and at the University of Maryland (UM) in Salisbury have identified a new, more aggressive race of the fungus that causes Fusarium wilt in watermelon.

This disease is one that all melon farmers dread seeing. It can attack plants at any stage of growth, leaving young seedlings lifeless, or mature plants fruitless with nothing to show but shriveled and yellowing leaves.

Watermelon grafted onto Cucurbita rootstock. The resulting watermelon plant will gain resistance to Fusarium wilt and enhanced fruit quality from the graft. Click the image for more information about it.

ARS scientists Benny Bruton and Wayne Fish, together with UM’s Xin-Gen Zhou and Kathryne Everts, discovered a new race of the fungus Fusarium oxysporum that causes Fusarium wilt. Their findings were presented last week at the joint meeting of the American Phytopathology Society and Mycological Society of America, in Quebec City, Canada.

Bruton and Fish, who work at the ARS South Central Agricultural Research Laboratory in Lane, found the new race, dubbed “Race 3,” while monitoring watermelon plants in fields near their Oklahoma laboratory. Bruton saw that a new, differently-acting fungus was plaguing plants thought to be resistant to Fusarium.

Three distinct races of Fusarium are known to cause wilt in melons. Plant breeders have developed watermelon varieties that can fend off Races 0 and 1 fairly well. And, luckily, Race 2--for which there are no resistant commercial cultivars--isn’t competitive in the soil environment.

According to Bruton, the same is likely true for the new, more virulent Race 3. But he’s got a solution. He and colleagues have found that grafting watermelon onto sturdy squash or gourd rootstock is an effective way of controlling Fusarium wilt. Those rootstocks are resistant to the Fusarium races that attack watermelon.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.