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LPG remains committed to finding solutions to TR4

27/06/2022

TR4 – three seemingly harmless symbols that, when put together, spell deadly consequences for those in the business of growing and selling bananas across the globe. The letters stand for Tropical Race, and the number 4 refers to the strain of the disease, which is known as Panama disease and is now in the fourth permutation since its discovery in the early 20th century.

Tropical Race 4 is technically known as Fusarium wilt – a fungal disease caused by the common soil pathogen Fusarium oxysporum and inducing characteristic wilting of the host plant’s leaves. This is because the fungal spores penetrate their host through its roots then reproduce in the infected plant’s vascular system – the system of veins and vessels through which the plant takes up and circulates nutrients. Eventually, these vessels become clogged, inhibiting the flow of nutrients which causes the leaves to wilt and leads to the plant’s eventual death. This rather bleak series of events is perfectly engineered as only nature can to provide a continual source of food for the fungus, which feeds on dead and decaying plant matter (though not fruit, which remain uninfested). Fusarium dines out on its first host before repeating the fatal exercise with the neighbours, spreading its soil-inhabiting spores by hitching a ride on planting equipment or surfing the irrigation system.

The first strain of the disease, TR1, ravaged the banana plantations of Central America during the forties and fifties in an outbreak that all but wiped out the Gros Michel cultivar, which was the main variety of banana cultivated commercially at the time. Subsequently the Cavendish cultivar took over to dominate the global market, as it could be grown in the same soil as its predecessor Gros Michel without being infected, leading to the assumption that this variety of banana was resistant to Panama disease. Alas, it was not to be – in 1997, the new TR4 strain was first detected in Australia’s own Darwin, where within ten years it had wiped out eight of the Northern Territory’s nine commercial banana farms operating at that time, all of which were farming Cavendish bananas. Thus, the Cavendish stronghold fell to the Panama enemy (the Panenemy), which has since marched on Queensland, where it was first detected in 2012. There are now five farms known to be infected in the Tully region, located about 80km south of Innisfail (home to LPG’s own ABC and IBFC) in tropical north Queensland. The disease has also spread rapidly throughout Southeast Asia and beyond – from Malaysia and Sumatra to Laos, Vietnam, Taiwan, Borneo, Indonesia, mainland China, Philippines, Jordan, Mozambique, Pakistan, Lebanon, Oman and India.

But you may be wondering, what about the Northern Territory’s ninth commercial farm – that lone survivor of Panama’s 1997 re-emergence in new TR4 armour – what happened to it? That farm is in fact LPG’s own Darwin Fruit Farms. Since TR4 ripped through the region, DFF has been working with the Queensland University of Technology (QUT) on developing a banana cultivar that is truly resistant to the disease. The crisis has also given rise to new farming strategies based on a shorter lifespan – banana plants, which can continue producing fruit for as many as 20 cycles, now produce for just two before being plowed back into the ground. That site is then left untouched for a few years to minimise the build-up of fungal spores in the soil. Darwin’s warmer temperatures make for stellar bananas with vibrant yellow skin, which remain completely unaffected by the disease – the problem is that if the spores are allowed to build up and infect the banana plants, it can wipe out as much as 50% of the entire crop before the plants even manage to produce a single yellow finger.

There is no defence against the fungus or cure once infected – the only real hope is to develop a cultivar that is truly resistant to Panama disease. To this end, QUT have been running trials of potentially resistant plants on infected soils since 2011 – some of which DFF have hosted. In the meantime, heavy quarantine measures on sites where TR4 is detected and restrictions on plant movement between states aim to prevent the spread of the disease. If left unmanaged, Panama TR4 would wreak even more devastation on the country’s banana production and the industry around it – killing plants, ruining livelihoods and taking Australia’s favourite fruit off the menu. As ever, the only solution lies in cooperation, and LPG remains committed to the cause.

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