786

Agnote

No: I51

November 2006

Fusarium Wilt of Bananas (Panama Disease)

(Fusarium oxysporum f. sp. cubense)

A. Daly, Diagnostic Services and G. Walduck, Crops, Forestry and Horticulture, Darwin

BACKGROUND

Fusarium wilt (Panama disease) is a de structive fungal disease of banana plants. It is caused by Fusarium

oxysporum f. sp. cubense (Foc ). It first became epidemic in Panama in 1890 and proceeded to devastate the

Central American and Caribbean banana industries that were based on the ‘Gros Michel’ (AAA) variety in the

1950s and 1960s. Once Foc is present in the soil, it cannot be eliminated.

There are four recognised ra ces of the pathogen which are separated ba sed on host susceptibility. Race 1,

which was responsible for the epidemi cs in ‘Gros Michel’ plantations, also attacks ‘Lady Finger’ (AAB) and

‘Silk’ (AAB) varieties. Race 2 affe cts cooking bananas such as ‘Bluggoe’ (ABB) and race 4 is capable of

attacking ‘Cavendish’ (AAA) as well as the other variet ies of banana affected by races 1 and 2. These three

races have been present on the east coast of Australia fo r many years and race 1 is present in WA. Race 4

is further divided into ‘sub-tropical’ and ‘tropical’ stra ins. ‘Tropical’ race 4 is a more virulent form of the

pathogen and is capable of causing disease in ‘C avendish’ growing under any conditions, whereas ‘sub-

tropical’ race 4 generally only causes disease in plant s growing sub-optimally (cool temperatures, water

stress, poor soil). Race 3 affects Heliconia spp., a close relative of banana, and is not considered to be a

banana pathogen.

‘Tropical’ race 4 was discovered in Darwin’s rural area in 1997 and has since spread to most banana

growing areas of the Top End.

DISEASE SYMPTOMS

Fusarium wilt of banana can be described as a “classic” vascul ar wilt disease. It invades the vascular tissue

(xylem) through the roots caus ing discolouration and wilting.

Externally, the first obvious signs of disease in most varieties are wilting and a light yellow colouring of the

lower leaves, most prominent around the margins. They eventually turn a bright yellow colour with dead leaf

margins (Figure 1). As the disease advances, more of the leaves become yellow and die. A “skirt” of dead

leaves often surrounds the pseudo-stem. In the advanc ed stages of disease, affected plants may have a

spiky appearance due to prominent upright apical leaves in contrast to the skirt of dead lower leaves

(Figure 2).

Internally, symptoms first become obvious in the xylem (water conducting) vessels of the roots and the

rhizome. These turn a reddish-brown to maroon colour as the fungus grows through the tissues (Figure 3).

Occasionally, the discolouration first appears yellow in plants showing early stages of infection (Figure 4).

When a cross-section is cut, the disc olouration appears in a circular pattern around the centre of the rhizome

where the infection concentrates due to the arrangem ent of the vessels (Figure 5). As symptoms progress

into the pseudo-stem, continuous lines of discolourati on are evident when the plant is cut longitudinally

(Figure 3). The infection may travel all the way up to t he top of the pseudo-stem. In severe cases it may even

enter the leaf petioles and the pedunc le (bunch stalk) of bunched plants. However, infection has not been

shown to progress into the fruit.© Northern Territory Government, 2006 Page 2 of 5

Figure 1. Figure 2.

Figure 3. Figure 4.

Figure 5.

Figure 1. Plant showing early symptoms of Fusarium wilt

Figure 2. Plant showing advanced symptoms of Fusarium wilt

Figure 3. Reddish-brown to maroon staining of vessels in the pseudo-stem

Figure 4. Yellow staining of xylem vessels in the pseudo-stem

Figure 5. Reddish-brown to maroon staining of the vessels in the rhizome© Northern Territory Government, 2006 Page 3 of 5

DISEASE CYCLE

Spores of Foc in the soil germinate and grow towards the nearby roots of banana plants in response to

chemical compounds exuded from the roots. Infecti on takes place on the secondary and finer roots and

proceeds into the larger, primary roots through the xylem vessels before entering the rhizome. The primary

roots and the rhizome do not appear to be infected direct ly by the pathogen. The xylem network consists of a

series of individual vessels with perforated end walls through which the sap flows. Movement of the spores

with the sap flow is blocked temporarily when th ey become lodged at the end walls. The spores then

germinate and hyphae grow through the perforations into adjoining vessels where further spores are

produced. The plant is often able to prevent infection from successfully travelling to and entering the rhizome

by the production of gels and tyloses (a resistance mechanism) to seal off the infection. However, multiple

infections occur during the life of a plant and invariably one or more lead to its complete invasion. The

virulence of ‘tropical’ race 4 on ‘Cavendish’ bananas su ggests that the resistance mechanisms employed by

the plant against this strain are not as effective as for ‘sub-tropical’ race 4. This strain generally only causes

serious losses in a plantation where the plants are under stress.

Formation of resting

spores in

dying plant

Death of plant and return of resting spores to soil

Infected planting material

Infection of young

fleshy roots and wounded roots

Germination of resti ng

spores in soil

Mov ement up xylem

Infection from root to

root contact

Colonisation of

plant and spore formation

Figure 6. Disease initiation and life cycle of Foc in a banana plant© Northern Territory Government, 2006 Page 4 of 5

PATHOGEN DISPERSAL

Foc can be spread unknowingly over long distances onto new plantations when infected rhizome bits and

suckers are used for planting material. The use of tissue cultured plantlets from a certified source guarantees

planting material free from the disease. Spread can also occur over long distances in infested soil adhering

to vehicles and footwear. There is reason to believe t hat infested soil adhering to the feet of animals is

another way by which spread occurs. The fungus can move over short distances within an infected area of a

property through the interconnecting netw ork of roots and in surface water.

DISEASE CONTROL

Once a property becomes contaminated with Foc, the only option for continued long-term production is

replacement of the susceptible variety with a resistant one. Foc cannot be controlled using fungicides and

cannot be eradicated from the soil using fumigants. Re search conducted in Darwin has identified a number

of resistant varieties. However, whilst their resistance genes may be useful in future breeding or gene

transfer programs, none are suitable as immediate repl acements for the ‘Cavendish’ variety. Currently, the

best option for managing the disease and extending the prod uctive life of a plantation is to minimise spread

from known infected areas by restricting movement of people and machinery, animals and water flow within

the infected areas. When infected plants are detected, it is best to disturb the area as little as possible and

not to cut the plant down. A heat shield, such as corrugated iron, can be erected around the infected and

adjacent plants which are then burned. This practice destr oys the inoculum in the infected plants (and some

in the soil) which would otherwise be released into t he soil and add to disease spread as the plant decays.

Machinery, tools and footwear that have come in c ontact with infested soil or diseased plants should be

sanitised using a detergent-based product known as Farmcleanse®.

Better management practices

• Do not allow unauthorised vehicles to be driven around the farm and shed area. Vehicles should be

driven to a designated area.

• No vehicles or equipment should be allowed to leave or enter the farm beyond the designated area

without inspection and approval by management. Machinery and equipment should be treated with a

sanitary solution such as Farmcleanse® which can be obtained from your local agricultural chemical

dealer.

• Footwear, which may have contacted banana plants or soil around banana plants elsewhere, should

not be worn on the farm.

• No agricultural vehicles, tools (including shov els, knives and ladders) or equipment should be

removed from, or brought on to, the farm without prior approval from management.

• When staff show visitors around the farm, it is t heir responsibility to adhere to all farm procedural

guidelines.

• Do not take on to or off the farm any soil or banana material except banana fruit supplied from the

packing shed.

• Field staff should make themselves familiar with Fusarium wilt information material in order to

recognise the disease symptoms and comply with all updated, additional procedural guidelines or

regulations.

In the NT, restrictions are placed on movement of banana material. Know the quarantine

requirements for importing planting material into the NT and between the Declared NT Banana

Protection Areas.© Northern Territory Government, 2006 Page 5 of 5

WHAT TO DO WHEN SUSPECT PLANTS ARE FOUND

• Cordon off the area containing the suspect plant(s ) and the plants immediately adjacent to prevent

movement of field staff and machinery through the area. If possible, immobilise any machinery and

other equipment that has come in contact with the ground surrounding the affected plant(s).

• Immediately suspend movement of machinery and equipment off the property that has been used in

the field.

• Contact the Department of Primary Industry, Fish eries and Mines to arrange an officer to visit to

collect samples and advise on decontamination procedures.

CONTACT THE DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES

FOR FURTHER INFORMATION AND ADVICE:

Suspected diseased plants:

1800 084 881 (Free call)

Banana plant import requirements:

(08) 8999 2088

Please visit us at our website:www.nt.gov.au/dpifm

Department of Primary Industry, Fisheries and Mines

© Northern Territory Government, 2006

ISSN 0157-8243

Serial No. 786

Agdex No. 234/633

Disclaimer: While all care has been taken to ensure that information c ontained in this Agnote is true and correct at the time of

publication, the Northern Territory of Australia gives no warrant y or assurance, and makes no representation as to the accuracy of any

information or advice contained in this publication, or that it is suitable for your intended use. No serious, business or inve stment

decisions should be made in reliance on th is information without obtaining independent/o r professional advice in relation to your

particular situation.