Research to contain banana wilt infection

In less than a decade the Fusarium fungal pathogen has devastated the Northern Territory’s banana industry, although tough quarantine measures have so far protected the economically critical Queensland industry.

Fusarium wilt is a disease common to many horticultural industries; the form that strikes bananas is commonly known as Panama disease. The first major impact of this disease was observed in Panama (Central America), where between 1890 and the mid-1950s it destroyed 40,000 hectares of banana plantations with the variety ‘Gros Michel’ banana.

A Northern Territory Primary Industry group researcher and CRC for National Plant Biosecurity PhD candidate, Rachel Meldrum, says relatively little is known about the Fusarium strain causing the problem in the Northern Territory. She says tropical race 4 of Fusarium oxyporum f. sp. cubense (Foc TR4) was detected in the Northern Territory in 1997, although the exact source of the infection remains unknown.

It was identified in a banana farm on the outskirts of Darwin and is genetically similar to the strain that devastated ‘Cavendish’ plantations developed for export in south-east Asia in the early 1990s. “The industry here was looking to expand at the time, to fill an offseason niche in production,” Ms Meldrum says.

“Production peaked in 2000, with 7,000 tonnes of production valued at $13 million. But by 2009 the industry was reduced to one-third of its original value, worth about $4 million, and most of the major growers in the Territory had left the industry,” she says.

Ms Meldrum’s PhD project aims to create a better understanding of the Foc TR4 pathogen and how it spreads, and to develop more effective control strategies.

She says there are four races of Fusarium oxyporum f.sp. cubense (Foc) known to exist, and three are pathogenic to bananas. Race 1 causes disease in ‘Lady Finger’ and ‘Gros Michel’ varieties and race 2 affects ‘Bluggoe,’ a cooking banana variety.

Race 3 is pathogenic to decorative floral and landscaping plants of the Heliconia species.

Foc Tropical race 4 is pathogenic to all commercial banana cultivars, including Cavendish, which make up 95 per cent of the $350 million Australian crop.

Race 4 is further divided: subtropical and tropical race 4. While all races of Foc are important to the Australian banana industry, the threat of Foc tropical race 4 is considered the greatest; it kills otherwise healthy plants quickly and can spread rapidly on plantations.

“We know it is a soil-borne pathogen, so we already have some recommendations for growers about steps they can take to prevent it spreading,” Ms Meldrum says.

Chief among these is the use of tissue-cultured banana plants to prevent the spread of infection. Ms Meldrum says that while it is possible for banana growers to regenerate their primary banana plants from suckers or daughter plants, the transportation of soil adhering to the plant can also transfer the pathogen.

Ms Meldrum is also investigating the role of the banana borer weevil as a possible disease vector. The borer is not a big problem for growers, particularly once banana plants are well established, but it can travel 30 metres in a day and has the potential to transfer infected soil between plants and crops.

Greater control of the borer may help eliminate one potential source of spread. Other quarantine measures being implemented include fencing for banana plantations to prevent wild animals transferring disease through the transfer of soil, and the use of washdown facilities and chemical washes.

As part of her research Ms Meldrum hopes to learn more about the epidemiology of the Foc TR4 pathogen, including how long it survives in the soil. “It is believed to survive in the soil for decades and we need to work out how it survives – does it use alternative host plants, or does it have hard spore cases that protect it?”

Tests are being conducted on two weeds common in the Northern Territory – Mission Grass and Gamba Grass – as possible alternative host plants that may be allowing the pathogen to survive long periods in the soil. Farmers also commonly grow sorghum as a cover crop on cleared land and this will also be tested as a possible host for Foc TR4.

Ms Meldrum says some banana species and cultivars with resistance to TR4 have been identified. However, none are acceptable as a commercial replacement for the Cavendish cultivars. “Our best long-term response may be to improve resistance in the commercial varieties,” she says.

To show its support to the banana industry, the Cooperative Research Centre for National Plant Biosecurity is providing sponsorship for the ninth Australian Banana Industry Congress at the Hyatt Regency on the Sunshine Coast from 1-4 June 2011. For more information, visit the banana congress website.