The Banana Fusarium Wilt, Tropical Race 4, and Efforts to Combat the Disease

The banana crop that ranks among the world's top ten staple foods is now threatened by a new race of the soil-borne pathogen, Fusarium oxysporum, f. sp. cubense (Foc), that causes the Fusarium Wilt disease. The combined annual production of bananas and plantains across the globe is 155 million metric tons with over 400 million people relying on bananas and plantains for food security and for income (Kema et al., 2021). About 84% of the banana crop is produced by smallholder farmers and supplied to domestic markets, while 16% of the global banana production that accounts to about 25 million metric tons is exported from tropical areas to countries in temperate zones (FAOSTAT 2020; data for 2018). Predominant in banana cultivation is the Cavendish variety which represents roughly 50% of the global production and is important both for domestic and export markets. The export banana market is almost exclusively (99%) constituted by this variety grown under monoculture conditions in large plantations. Fusarium Wilt is considered the most important lethal disease of banana and is believed to have originated in Southeast Asia although its first report came from Australia in 1876 (Ploetz, 2006). Early reports of the disease in any given country were on damage in export plantations of the variety, Gros Michel, which was the basis of export trade in banana until the mid-twentieth century (Ploetz 2015). The disease was caused by Fusarium oxysporum f.sp. cubense (Foc), Race 1, and it invaded banana growing countries in Central and South America destroying plantations wreaking havoc on the export industry. The variety, Gros Michel, was susceptible to Race 1, and throughout the banana belt, production was eliminated or became increasingly difficult. The banana industry tried to hold on to Gros Michel during the first half of the twentieth century by shifting cultivation to escape the pathogen at huge socioeconomic and environmental costs. With increasing losses and reduced availability of pathogen-free soil, the banana industry turned to the Cavendish variety which was identified to be resistant to Race 1. This led to the disappearance of the disease for a while until the 1990s when Cavendish began to succumb to a new race of F. oxysporum f. sp. cubense, tropical race 4 (TR4), first in Southeast Asia and then Australia. For more than twenty years TR4 remained restricted to Southeast Asia and the Northern Territory of Australia. However, recent reports confirm its presence in Jordan, Oman, Mozambique (2013), Lebanon, Pakistan (2015), Queensland in Australia (2015), Vietnam, Laos, Myanmar, Israel (2018), Mayotte, Indonesia, Colombia, Thailand, Turkey (2019) and Peru (2021). Although estimates are not available at the global level, figures for some countries indicate that in 2019 Foc TR4 affected some 15,700 ha of banana plantations in the Philippines out of a total of 440,000 ha and 70% of the plantations in Guangdong provinces and Hainan in China (Aquino et al., 2013a; Chen et al., 2013). Annual economic losses caused by Foc TR4 have been estimated at US $121 million in Indonesia, US $253 million in Taiwan, and US $14 million in Malaysia (Aquino et al., 2013b). Currently Foc TR4 is reported in 27 countries across the world affecting thousands of hectares.