20 Years Of Research Benefits Banana Growers Globally

Fusarium is a soil-borne fungus that has hundreds of forms, not all causing crop diseases. However, there is a large range of plants, including many fruit and vegetable crops, that are affected by disease-causing forms of Fusarium. The resulting disease is Fusarium wilt, which is also known as Panama disease when it occurs in bananas. There are around 24 strains of Fusarium that can cause wilts in bananas, but it is the Tropical Race 4 strain that is detrimental to Cavendish bananas.

The fungus invades the roots and moves into the banana plant's water and nutrient transport system. As the fungus grows it clogs this system - preventing nutrients and water from moving upwards - causing the plant to die. The fungus then moves into the plant tissue where it produces chlamydospores, a type of tough, long-lasting spore that helps the fungus survive. As the dying leaf material collapses to the ground, these spores are released into the soil, adding to the already present fungi population. The spores can exist in the soil for decades.

Of more than 1,000 varieties of bananas (including plantain), Cavendish is grown in more than 20 countries and represents almost half the annual production at around 50 million tonnes globally. The Philippines, and to a lesser extent Indonesia, export Cavendish bananas, although many other varieties are eaten locally. Australia produces more than 350,000 tonnes of Cavendish a year for the domestic market.

Preliminary ACIAR-supported research in Indonesia aimed to identify and understand the spread of Fusarium wilt. It was during this period (2004 to 2008) that researchers identified the dominance of TR4 among the many forms of Fusarium affecting commonly grown banana cultivars.

'What was evident is that some banana growers in Indonesia were able to manage the spread of TR4 on their farms, so the question was: what were they doing differently?' said Dr Pattison. This led to the next phase of ACIAR-supported research to mitigate the threat of banana Fusarium wilt.

This project found that some soil physical, biochemical and biological properties may influence suppression of Fusarium wilt.

'Some farmers were able to keep the Fusarium wilt under control by improving their production practices such as using clean planting materials, diverse cropping systems and farm hygiene,' explained Dr Pattison. 'While we didn't understand at the time the mechanics of why it worked, we could see the benefit and developed management tools and extension programs with Indonesian representatives.'

Banana Fusarium wilt was first reported in the Philippines in 2005, with similar devastating effects to those experienced in Indonesia.

Building on lessons from the Indonesian research, ACIAR supported a project in the Philippines to help farmers and authorities tackle Fusarium wilt. The key challenge was to adapt practices that had worked in smallholder trials in Indonesia to the very different conditions of large-scale Cavendish banana plantations geared for export.

In the Philippines, production relies heavily on smallholder growers, many of whom are contract growers supplying export markets. The contractual arrangements often limit growers' ability to change farming practices, creating barriers to adopting new disease-management strategies.

To address this, Australian and Filipino researchers worked with local agriculturists to establish demonstration farms showcasing integrated management practices. These sites provided proof that Fusarium wilt could be contained. Growers with the flexibility to adapt are beginning to see real benefits - helping them remain viable participants in the country's valuable banana export industry.

Australian growers have drawn on knowledge from Indonesia to contain TR4 outbreaks.

TR4 in Australia was first detected in 1997 in Darwin, all but wiping out banana production in the Northern Territory. However, by adopting biosecurity practices, Fusarium wilt was contained in the NT for almost 20 years.

In 2015, Fusarium wilt was discovered in Far North Queensland, and growers quickly initiated on-farm biosecurity measures. Based on the lessons learnt from the previous 10 years of ACIAR-supported Fusarium wilt research in Southeast Asia, protocols and information packages were made available to the Far North Queensland banana growers.

Ms Leanne Erakovic, CEO of the Australian Banana Growers' Council (ABGC), said TR4 has the potential to devastate Australia's $700 million banana industry. With strong grower commitment, government investment and industry leadership, the disease has largely been contained to a small number of farms in Far North Queensland. The early adoption of biosecurity measures has meant that Australia is one of the few regions where TR4 has been contained.

'Australia's TR4 program - now called Grower Support (Biosecurity) - was established by the Queensland Government in response to the detection of the disease,' said Ms Erakovic. 'Now delivered by ABGC, biosecurity awareness forms the cornerstone of the program. Research into resistant varieties, soil health and long-term farming practices is critical to the future of the industry.

'The research undertaken through ACIAR and Queensland Department of Primary Industries forms the basis of the Grower Support program. We are all striving to support growers and give them practical tools to manage risk. To do that we have a strong relationship with the research community and our growers to give the best possible outcomes.'

During the research in the Philippines, it became clear that tiny organisms in the soil affect the disease. Current ACIAR-supported research, led by the Queensland Department of Primary Industries, is investigating the role soil health plays in the prevalence of Fusarium wilt in bananas (HORT/2018/192, HORT/2022/178). This research is underway in Australia, Laos, the Philippines, Malaysia and Indonesia.

Dr Paul Dennis, Associate Professor in the School of the Environment at the University of Queensland, said biosecurity and sanitation were important tools to assist growers in controlling the disease when it is first detected. However, these do not control or mitigate the underlying fungi present in the soil.

'By understanding the behaviour and ecological preferences of a fungi, we can begin to characterise which soil biome factors can control Fusarium,' explained Dr Dennis.

To better understand this, Dr Dennis's team has analysed soils in Far North Queensland taken from natural tropical forests, grasslands, sugarcane and banana plantations.

'Microorganisms in soils from rainforests and grasslands are twice as numerous as those in sugarcane and banana farms and help to suppress Foc as it is spread from one area to another,' he said.

'Something about how banana soils are managed makes them highly conducive to Fusarium fungi in general and appears to decrease predators of the fungi - such as fungal feeding nematodes - which no doubt makes it easier for Foc to colonise.'

Researchers are now assessing how groundcovers, mulch, the application and timing of nutrients, irrigation and crop rotations could help native microorganisms compete with Fusarium.

'As the biology of soils differs between locations, we pay special attention to a subset of 'core' microorganisms that persistently associate with bananas irrespective of where they are grown,' said Dr Dennis.

'While these 'core' microorganisms typically represent a tiny fraction of the species present, they are by far the most dominant, comprising up to 80% of the individuals present.

'We have identified and isolated these 'core' microbes in Australia, Asia and Africa, and are learning what they do and how to manage farms to help them promote healthier and well-nourished banana plants. This provides growers with options to manage disease by enhancing the defences already present in nature.'

A 2014 ACIAR evaluation of the impacts (IAS105) of early TR4 research projects showed substantial returns on the investment for Australian growers, in the order of $70 for every $1 invested. It concluded that 'the knowledge has been positively applied, informing the quick detection and containment of Fusarium outbreaks, particularly in Australia'.

In the Philippines, research had provided 'a strong foundation for on-going local research and management for local growers well into the future'.

ACIAR Research Program Manager, Horticulture, Dr Sandra McDougall said the research capacity ACIAR could provide to partner countries meant it could share knowledge and provide access to resources they might not otherwise be able to reach.

'For Australian researchers, while they may be familiar with the disease in the laboratory, the ability to see it firsthand in a local growing environment, such as Indonesia or the Philippines, gives a deeper appreciation of the scope and scale of the research,' added Dr McDougall.

Since the initial research in Indonesia and the Philippines, ACIAR has supported TR4-related projects in Laos, Mozambique, South Africa and Tanzania. Pakistan has also expressed interest in gaining assistance, based on the learnings that the ACIAR projects have provided in the Southeast Asian region.