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Significance

Cucurbits (Family Cucurbitaceae) provide humans and animals with numerous edible products and seeds that are rich in oil and protein. The flesh is an important source of carbohydrates and water for many people of the tropical and semiarid regions of the world. Cucurbit production experienced a tremendous growth in the last decade, up 90% worldwide. Approximately 160,000,000 metric tons of watermelons, cucumbers, melons, squashes, and pumpkins were harvested worldwide in 2002. Watermelons represent one half of the total production (80,000,000 metric tons) and melons (muskmelon, cantaloupe, honeydew) make up another 15% (25,000,000 metric tons). The United States ranks 4th in world production of watermelon (1,900,000 metric tons), while China is the world leader with over 40,000,000 metric tons harvested annually. Over 80% of the watermelons produced in the U.S. come from just six states (FL, CA, TX, GA, AZ, and IN).

Fusarium wilt of watermelon has been an important factor in watermelon production in the U.S. since the late 1800’s. The disease was first described by E. F. Smith in 1894 from South Carolina and was only the second Fusarium wilt disease described (Fusarium wilt of cotton was the first). The disease now occurs in all watermelon growing regions of the world and on every continent except Antarctica. It is the most economically important disease of watermelons throughout the world. While there are no economic loss data due specifically to Fusarium wilt, significant losses continue in many areas of the world, including the U.S. Fusarium wilt causes economic losses in various ways. First, and most obvious, is a direct loss in yield (harvested fruit) because the plant dies. In cases where fields are heavily infested with FON and susceptible varieties are grown, losses may approach 100%. Second, and less obvious but very important, is the loss in marketable yield i.e., fruit that is formed but can not be sold because they are too small, misshapen, low in sugars and soluble solids, or may be cracked or sunburned. There also are hidden losses resulting from increased costs associated with roguing or replanting dead plants, fumigation or other soil treatments, and fuel and labor. Lastly, there are considerable costs associated with renting and preparing new land for production once an existing field becomes unusable because it is infested with FON.

While race 1 of FON is widespread throughout the world, race 2 has a more limited distribution, but is of great concern because of its ability to attack all current commercial varieties and hybrids. Race 2 was first described in Israel in 1976 and in the U.S. in 1985. It has since been identified in six states in the U.S. and a handful of other countries, including Cyprus and Tunisia. In the US, 50% of watermelon production is from states where race 2 has been detected. While the spread of race 2 around the world has been slow, its potential introduction into other major watermelon producing countries i.e., China, Turkey, Iran, etc. is of concern. Additionally, there is the concern that other new races will emerge.

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