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New form of Fusarium wilt could pose threat to watermelon crop

It’s too bad that one of summer’s
most enjoyed simple pleasures – the watermelon – can be such a pain to
grow. Melon growers are beset by numerous problems related to disease,
weather, pests and the quest for fruit uniformity.

Scientists have identified a new, more aggressive race of the fungus that causes Fusarium wilt in watermelon and 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.

It’s too bad that one of summer’s most enjoyed simple pleasures – the watermelon – can be such a pain 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 U.S. Department of Agriculture and the University of Maryland (UM) 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.

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.

Bruton and Fish found the new race, dubbed “Race 3,” while monitoring watermelon plants in fields in Oklahoma. Bruton saw that a new, different-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.