Bananas and plantains are important food and cash crops throughout the humid tropics. The banana (Musa spp.) evolved and became domesticated in Southeast Asia and the Pacific, as did most of its pests and pathogens. Thus, any research that contributes to the solution of important problems affecting its culture, particularly the high cost of disease control, has considerable scientific interest.

The most important diseases include the three Sigatoka types - yellow Sigatoka, black Sigatoka and black leaf streak. The last two (caused by particularly closely related fungal pathogens) may yet prove identical; they have developed more recently and attack with greater virulence than the yellow form. They are also more difficult and expensive to control, requiring significant increases in fungicide applications (up to 20 sprayings a year). Moreover, they attack plantains as well as bananas. Another recent threat has come from the appearance of at least one new race of the soil fungus Fusarium oxysporum that can attack Cavendish bananas, which were previously considered resistant to fusarium wilt.

This project seeks to identify and obtain disease-resistant banana varieties for cultivation in collaborating countries. it will involve methods of identifying and differentiating between the forms of the diseases - to determine resistance status and for use in the plant improvement program. In that program, the team will select, import and redistribute material from international collections, somaclonal generation schemes and ongoing breeding projects, and will investigate in vitro techniques for mutagenesis and ploidy alteration. They will use tissue culture for multiplication, progeny development, quarantine and distribution.

For research on the Sigatoka diseases, the team will first develop specific procedures needed for rapid mass screening of seedlings and plantlets produced in vitro. They will then introduce potential commercial clones, developed by breeding or somaclonal work and considered resistant elsewhere, for assessment in the glasshouse and later in the field in the Pacific islands. Experiments in northern Queensland with resistant and susceptible lines should determine whether resistance to black Sigatoka implies resistance to yellow Sigatoka also. Determination of the pathogen's range of variability in areas with great host genetic diversity (wild species and primitive and modern cultivars) should also contribute to other studies seeking to clarify relations between the three forms.

The project will establish a set of differentials, comprising both true seeded and clonal types, to distinguish pathogen groups, and will determine diploids that can act as differentials for use in genetic studies of relative virulence and resistance.

Research on fusarium wilt will follow a similar pattern of developing screening methodologies, then evaluating germplasm (especially for resistance to Race 1 and Race 4). Identification of differential banana varieties will help to clarify the number of races of Fusarium oxysporum, together with their distribution.

Banana micropropagation will be used primarily to multiply promising clonal material for distribution and evaluation in different countries. Some research will also concern methods for rapid screening. Because of the problem of off-types, the team will seek to develop improved tissue culture techniques to facilitate manipulation of the banana plant in micropropagation. They will also attempt to develop mutation breeding techniques and use these to generate variability in Musa spp.

In addition to upgrading the knowledge of the banana disease status of the region and its relation with the rest of the world, the project should improve and/or expand the cultivar range, increasing self-sufficiency and in some cases the export potential. It should also provide a basis for joint work, exchange of technology and of genetic material and ongoing scientific collaboration between the countries of the region.

ACIAR's work is closely linked with banana improvement studies being undertaken in other countries through the International Network for Improvement of Banana and Plantain (INIBAP).