The bananas that we commonly find in supermarkets are under threat of functional extinction due to the disease Fusarium wilt of banana (FWB) caused by a fungal pathogen known as Fusarium oxysporum f.sp. cubense (Foc) tropical race 4 (TR4). However, recent research conducted by an international team of scientists led by the University of Massachusetts Amherst has shed light on this issue. The research revealed that Foc TR4 did not evolve from the strain that wiped out commercial banana crops in the 1950s. It also found that the virulence of this new strain may be caused by accessory genes associated with the production of nitric oxide. This discovery opens up new possibilities for treatments and strategies to slow down, if not control, the spread of Foc TR4.
The Gros Michel banana, a popular variety in the past, is now functionally extinct due to the first Fusarium outbreak in the 1950s. The Cavendish banana, a disease-resistant variety bred in response to the Gros Michel extinction, became the dominant commercial banana crop for the next few decades. However, by the 1990s, another outbreak of banana wilt began, spreading rapidly from South-East Asia to Africa and Central America. This new outbreak of banana wilt has been the focus of research for the past 10 years, leading to the discovery of the role of accessory genes associated with the production of nitric oxide in the virulence of Foc TR4.
Through sequencing and comparing 36 different Foc strains collected from around the world, including those that attack Gros Michel bananas, researchers were able to identify the specific genes responsible for the virulence of Foc TR4. The team discovered that Foc TR4 uses accessory genes for both the production and detoxification of fungal nitric oxide to invade the host. While the exact mechanisms of how these genes contribute to disease infestation in Cavendish bananas are not yet fully understood, the research has shown that eliminating genes that control nitric oxide production can greatly reduce the virulence of Foc TR4.
The identification of these accessory genetic sequences presents new opportunities for developing strategies to mitigate or even control the spread of Foc TR4. However, the ultimate issue facing commercial banana crops is the practice of monocropping, which lacks diversity and makes the crop vulnerable to pathogens. Researchers suggest trying different banana varieties available in local specialty food stores to support diversity and reduce the risk of disease outbreaks. Funding for this research was provided by various organizations, including the U.S. National Science Foundation and the U.S. Department of Agriculture, highlighting the importance of addressing the threat to banana crops.