Understanding Strain Diversity in Fusarium oxysporum f. sp cubense and History of Introduction of 'Tropical Race 4' to Better Manage Banana Production

Fusarium wilt of banana is caused by 35 different strains or genotypes of Fusarium oxysporum f. sp. cubense. VCG 01213, so-called 'tropical race 4', is just one of six distinct strains that can attack Cavendish, but it is much more aggressive on Cavendish than strains known earlier in Australia and South Africa. New plantations established in the 1990s in peninsula Malaysia and Sumatra soon succumbed. VCG 01213 was later found to be common in village banana plants in those areas. It is only one of eight strains present in the villages. It is not a new mutant strain but is only newly recognised as unique. The combination of many strains and many different cultivars in mixed plantings allows sufficient banana production for home use. Yet attempts to grow Cavendish in plantation fail within a few years of establishment. Commercial Cavendish production in Taiwan, where strain VCG 01213 is present, is possible only by planting partially resistant Cavendish mutants in rotation with paddy rice and ratooning only twice. Even so, losses continue and costs are high. Permanent commercial plantations are no longer economic in areas where VCG 01213 is found. However, surveys indicate this pathogen is not ubiquitous. VCG 01213 was recently introduced into the Northern Territory of Australia, where eradication was attempted. This involved investigation of source, elimination of entire banana fields, isolation of sites, no replanting and tight quarantine. The situation here is not confounded by 'village banana plants' and is simplified by isolation and distance from the country's main banana-growing areas. In the Philippines and China, the disease now occurs in plantations situated within large areas of commercial banana production. The threat was at first not taken seriously and strain identification was delayed. Spread has occurred very rapidly in South China and less so in the Philippines. The VCG 01213 pathosystem is virtually unstudied, and its biology and epidemiology unknown. The results of experimental studies in Sumatra on incidence, treatment with endophytes and antagonists, cassava rotation, timing of infection, root invasion and breeding for resistance are reported. Rotation with cassava appears promising.