FUSARIUM WILT: THE BANANA DISEASE THAT REFUSES TO GO AWAY

Abstract

Fusarium wilt, also known as Panama disease, is the most important lethal disease of banana. This workshop began with a summary of the early history of, and research on, this important disease. Its current status and recent developments were then highlighted for different regions. The causal soilborne fungus, Fusarium oxysporum f. sp. cubense (Foc), is found in most banana-producing regions and is phylogenetically diverse. Pathotypes (“races”) that affect different groups of cultivars have been useful for describing host reactions and new disease outbreaks, even though races 1 and 2 are heterogeneous (i.e. numerous clonal lineages and vegetative compatibility groups or VCGs have been identified). In contrast, populations of the pathogen that affect the Cavendish subgroup are fairly well defined and are separated into subtropical race 4 (SR4) (VCG 0120 and related VCGs) and tropical race 4 (TR4) (VCG 01213-01216). Although SR4 and TR4 affect many of the same cultivars, they interact significantly with temperature: TR4 kills plants in the tropics, but SR4 only affects plants that have been predisposed to disease by cold temperatures (in areas with pronounced winters). TR4 is decimating Cavendish monocultures in southern Asia and would affect 85% of global production were it disseminated more widely. Measures are needed to diagnose, interdict and manage TR4 and other variants of Foc worldwide. To that end, recent research to interdict, understand and manage this disease was discussed. The workshop concluded with an open forum/discussion on results that were presented during the symposium and on key issues and data gaps that should be addressed by future work. INTRODUCTION Fusarium wilt (Panama disease) is the most significant vascular wilt disease of banana (Ploetz, 1990; Ploetz and Pegg, 2000; Stover, 1962). Simmonds (1966) ranked it as one of the six most destructive plant diseases. This notorious reputation stems from damage it caused in the first export trades, which were based on ‘Gros Michel’ (AAA). Extreme susceptibility to Fusarium wilt, the use of infected suckers to establish new plantings and the practice of monoculture doomed ‘Gros Michel’ and led to its eventual replacement by the Cavendish clones. Interested readers are referred to Stover’s (1962) monograph for a comprehensive early history of the disease, and to a recent retrospective on the ‘Gros Michel’ epidemics and on the political intrigue and social upheaval that surrounded the early trades (Ploetz, 2005). Fusarium wilt was first reported in Australia. Bancroft (1876) speculated that a fungus caused the disease and recognised that suckers that looked healthy could harbour the disease. Smith (1910) was the first to isolate the pathogen, which he called Fusarium cubense, from banana, and Brandes (1919) was the first to complete Koch’s postulates. During the ensuing decades, almost all first reports of the disease in an area were on ‘Gros Michel’ (Stover, 1962). Wollenweber and Reinking (1935) recognised that F. cubense was a variant of the common soilborne fungus, Fusarium oxysporum. Soon after, their F. oxysporum var. cubense was renamed F. oxysporum f. sp. cubense (Foc) by Snyder and Hansen (1940). Although Snyder and Hansen’s name is still used to designate this pathogen, research over the last decade indicates that it is represented by at least three Proc. Int’l ISHS-ProMusa Symp. on Global Perspectives