Bananas and Black Sigatoka

Banana production is threatened by various fungi. One of them, Pseudocercospora fijiensis, causes the feared black Sigatoka disease. The fungus is air-borne and occurs worldwide. It affects the leaves of banana plants in all sorts of plantations and results in huge yield losses. The disease also reduces the quality of the fruit, causing premature ripening. The bananas can then no longer be exported and growers lose their income. The Cavendish banana, the most commonly grown banana variety worldwide, is especially susceptible to the black Sigatoka fungus.
Farmers, who can financially afford it, use fungicides or crop protection products to manage black Sigatoka. The effectiveness of these products often quickly reduces, which means that most commercial plantations have to spray increasingly often – over 50 times a year is becoming a common practice. This has a major impact on the environment of the plantations and costs the banana sector some 400 million dollars a year.

Scientists from Wageningen University (The Netherlands) have now unravelled the DNA of Pseudocercospora fijiensis. Gert Kema, Professor at Wageningen University said: “Thanks to the sequencing of the DNA of the Pseudocercospora fungus we are now gaining a greater insight into the interaction between the fungus and the banana plant. This provides us with leads for increasing the sustainability of banana cultivation. For example, the insights offer us opportunities to develop a banana plant that is suitable for production and export, and which is also resistant against black Sigatoka.”
This fresh understanding of the DNA of the black Sigatoka fungus is also providing new information that is useful in the development of more effective and, hopefully, less environmentally unfriendly crop protection products. This could reduce the amount of spraying which, in turn, would improve the quality of life of the people working in the plantations and those who live in the immediate surroundings.

The research has helped identify the segment of DNA of the fungus that forms the basis for a so-called effector: a substance in the fungus that generates a resistance reaction in the wild banana variety Calcutta 4[1]. This wild banana has a receptor which recognizes the fungal substance. In other words, thanks to the receptor the wild banana plant ‘knows’ when it is being attacked and then encapsulates the fungus, preventing the leaves from being colonized further.

The scientists also discovered that tomato plants recognize the substance of the black Sigatoka fungus via a receptor[2]. The wild Calcutta 4 banana and the tomato apparently resemble each other genetically in this regard. A great deal is already known about the tomato receptor, and the gene for the receptor is also available. It would be relatively simple to build these tomato genes into the DNA of banana in order to develop resistant banana plants.

[1] Arango Isaza et al: Combating a Global Threat to a Clonal Crop: Banana Black Sigatoka Pathogen Pseudocercospora fijiensis (Synonym Mycosphaerella fijiensis) Genomes Reveal Clues for Disease Control in PLoSGenetic 2016 
[2] Stergiopoulos et al: Tomato Cf resistance proteins mediate recognition of cognate homologous effectors from fungi pathogenic on dicots and monocots in Proceedings of the National Academy of Sciences of the USA - 2010

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