Banana improvement in the Pacific Islands

• Department of Agriculture and Forestry, Tonga
• Ministry of Agriculture, Forests, Fisheries and Meteorology, Samoa
• Ministry of Agriculture, Cook Islands

The banana is a very important basic food and revenue source for countries throughout the tropical world. It is the third most important agricultural commodity in Samoa and Tonga, and an important fruit crop in Queensland. However, banana production in many Pacific island countries and Australia is threatened by diseases, in particular the fungal diseases black Sigatoka and Fusarium wilt (race 4) and the viral disease bunchy top.

Black Sigatoka leaf disease has already caused serious problems in many Pacific island countries. It can be controlled with fungicides, but this is expensive, and many developing countries do not have the necessary money, equipment or expertise. Black Sigatoka disease is present in Papua New Guinea (PNG) and on islands in Torres Strait - not far from major banana-growing areas in Australia. Resistant cultivars are required urgently.

Fusarium wilt (race 4) is a serious threat to banana production in many countries and occurs in Taiwan, the Philippines, South Africa and Australia. This is the first race of Fusarium wilt capable of attacking the Cavendish group, which includes the major commercial cultivars grown throughout the world. The only satisfactory control is to use resistant cultivars, but to date there are no commercially acceptable resistant clones. The disease is not known to occur on Pacific islands, but spread may be expected with the steady increase in tourism and improvement in communications.

Banana bunchy top virus (BBTV) is widespread. It occurs in Australia, Samoa and Fiji, and is a major factor in the decline of the banana industry in Tonga. The supply of virus-tested is an essential requirement of any banana plant distribution scheme in the Pacific region.

This project - a continuation of the banana improvement research conducted by ACIAR in the Australia-Pacific region - will identify, differentiate and screen banana plants affected by various forms of Sigatoka and Fusarium wilt diseases in order to evaluate the disease-resistant status of cultivars in the cooperating countries and assess requirements for improved cultivars. It has two approaches: selection, importation and redistribution of material from international collections, somaclonal generation schemes and breeding projects; and investigation of the processes and opportunities for breeding offered by the in-vitro techniques of mutagenesis and ploidy alteration. There is a strong plant pathology input for disease identification and screening, and a high tissue culture component for multiplication, progeny development, quarantine and distribution activities.

In Australia, experienced scientists at the Plant Pathology Branch of the Queensland Department of Primary Industries will undertake all aspects of tissue culture propagation and in-vitro breeding research. They will:

. screen germplasm for reaction to Fusarium wilt and investigate ways of differentiating races of the pathogen;
. study forms of Sigatoka disease; and
. develop monoclonal antibodies for detecting BBTV in serological tests. A collaborator at the Queensland University of Technology will develop DNA probes for BBTV detection.

Australian scientists will visit the cooperating countries regularly to provide assistance in all aspects of the project.

Earlier in the program, collaborators in South Pacific countries collected disease specimens for identification and use. Now they are evaluating banana clonal selections in the field for cultural performance, disease resistance, and the suitability of the fruit for local consumption and export. A range of locally available cultivars has already been assessed in Tonga, the Cook Islands and Samoa, and cultivars highly resistant to black Sigatoka disease have been identified in Tonga.

The banana improvement program in the Pacific Islands will, in the short term, give developing countries the opportunity to improve or expand their range of cultivars from pathogen-tested progeny derived from world- wide collections, for both domestic consumption and export. In the medium term, improved cultivars arising from both conventional and unconventional breeding schemes will provide additional germplasm with added disease resistance. Pest and disease control represents 25-50% of total costs in banana production in Pacific countries. Resistant cultivars will reduce production costs and improve both the level and the stability of production. The identification of cultivars with resistance to the Sigatoka diseases and Fusarium wilt will also make a substantial contribution to the Australian industry.