Black Sigatoka, fungicides, and the risk to the world's banana crop.

[NNadir]

A fascinating tale about an important food crop:

Reviewed feature article
Ploetz, R.C. 2001. Black Sigatoka of Banana. The Plant Health Instructor.
DOI: 10.1094/PHI-I-2001-0126-01.
The most important disease of a most important fruit

Origins and importance of banana as a food crop Banana is one of the most fascinating and important of all crops. It is a large monocotyledenous herb that originated in Southeast Asia. Virtually all of the cultivars that are grown are thought to have been selected as naturally occurring hybrids in this region by the earliest of farmers. In fact, Norman Simmonds proposed that banana was one of the first crops to be domesticated by man. In writing of the beginnings of agriculture in Southeast Asia, he concluded, "It seems a reasonable assumption that the bananas evolved along with the earliest settled agriculture of that area and may therefore be some tens of thousands of years old..."

...Banana is now one of the most popular of all fruits. Although it is viewed as only a dessert or an addition to breakfast cereal in most developed countries, it is actually a very important agricultural product. After rice, wheat and milk, it is the fourth most valuable food. In export, it ranks fourth among all agricultural commodities and is the most significant of all fruits, with world trade totaling $2.5 billion annually. Yet, only 10% of the annual global output of 86 million tons enters international commerce. Much of the remaining harvest is consumed by poor subsistence farmers in tropical Africa, America and Asia. For most of the latter producers, banana and plantain (which is a type of banana) are staple foods that represent major dietary sources of carbohydrates, fiber, vitamins A, B6 and C, and potassium, phosphorus and calcium...

... leaf spot disease is the most important of these problems. Black Sigatoka, which is also known as black leaf streak, causes significant reductions in leaf area, yield losses of 50% or more, and premature ripening, a serious defect in exported fruit. It is more damaging and difficult to control than the related yellow Sigatoka disease, and has a wider host range that includes the plantains and dessert and ABB cooking bananas that are usually not affected by yellow Sigatoka...

...In export plantations, Black Sigatoka is controlled with frequent applications of fungicides and cultural practices, such as the removal of affected leaves, and adequate spacing of plants and efficient drainage within plantation. In total, these are very expensive practices. For example, fungicide application includes the use of airplanes or helicopters, permanent landing strips and facilities for mixing and loading the fungicides, and the high recurring expense of the spray materials themselves. In total, it has been estimated that the costs of control are ultimately responsible for 15-20% of the final retail price of these fruit in the importing countries. Their great expense makes them essentially unavailable to small-holder farmers who grow this crop, it is these producers who are affected most by this important disease...

Given the high expense of fungicides, their unavailability for subsistence farmers, and the recurring problem with fungicide resistance in the export plantations, it is clear that genetic resistance to black Sigatoka would be most useful. If resistant, agronomically acceptable cultivars were available, they would provide the best solution to this problem in export and subsistence situations alike.

...Unfortunately, resistance to black Sigatoka among pre-existing banana genotypes is poor. The Cavendish cultivars that are used for export are so susceptible that nothing short of intensive fungicide application will control the disease in most areas. Resistant cultivars that could be used in subsistence situations are available, but they are usually less productive or desirable than those that are susceptible. This situation has begun to change as a result of new, resistant hybrids that are being developed by the banana breeding programs (http://www.promusa.org ).

http://www.apsnet.org/education/feature/banana/