Subtropical banana research and resources

Silicon innovation trial

Posted on 2023-06-02 by Better Bananas

Using silicon fertilisers to improve Lady Finger tolerance to Panama disease race 1

By Stephen Norman

Background

Fusarium oxysporum f. sp. cubense (Foc) race 1 (Panama disease race 1) has been present in the north of New South Wales from the Tweed region south to Coffs Harbour for several decades and has had a devastating impact on growers of susceptible varieties in these areas.

Considered endemic in NSW, Panama disease race 1 is widely distributed across the region and has made it extremely difficult for Lady Finger growers to continue to produce this variety. As there are no control options for Panama disease race 1, the only alternative is to switch to growing those varieties that are resistant.

About the trial

The trial location is within the Tweed Valley of New South Wales and was planted in December 2021. A complete cycle of planned silicon treatment application has been carried out in collaboration and support with the grower. A new round of treatments will begin in late November 2022.

As most NSW growers agree, 2022 was a challenging year due to the extended wet and cold periods. A combination of the sub-optimal growing conditions and isolated severe weather events has significantly slowed the growth of the bananas within the trial. The slowed growth reduced the infection rate, resulting in a lag of external symptoms. Our ability to record adequate data for early interpretation has been delayed. As the hotter months begin and growth rates increase, our ability to make accurate observations has improved.

Samples were taken in late September 2022 of suspect disease in plant tissue across the trial. It has been confirmed that Panama disease race 1 has infected the plants uniformly within the trial. This is good news for the trial efficacy. Uniform infection is paramount to measuring the silicon application’s effectiveness and its potential to improve tolerance to Panama disease race 1.

Latest update

Until March 2023, no external symptoms of Fusarium wilt were present, including the non-treated treatments (no silicon applied) within the trial.

More information will be made available as the trial progresses.

This trial is a joint initiative between the NSW Department of Primary Industries, Southern Cross University, the University of Queensland, Agripower Australia and the Australian Banana Growers’ Council.

This information has been prepared as part of the National Banana Development and Extension Program (BA19004) which is funded by Hort Innovation, using the banana industry research and development levies and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture. The Queensland Government has also co-funded the project through the Department of Agriculture and Fisheries.

Why is Banana Bunchy Top Disease so hard to eradicate?

Posted on 2023-03-03 by Better Bananas

Why is banana bunchy top disease so hard to eradicate?

By Dr. Kathy Crew and Dr. John Thomas

Banana bunchy top disease (BBTD) occurs in many locations throughout northern NSW and southern Queensland. The disease was first recognised in Australia in 1913 and by the mid-1920s had devastated the Australian industry, which was based in this region at that stage, causing losses of 90 to 95% of production. The research work of Charles Magee at the time revealed that the disease was caused by a virus (banana bunchy top virus, BBTV) which was transmitted by the banana aphid and in infected planting material. He devised a successful control program which enabled the resurrection of the industry. His strategy of inspection, destruction of infected plants, use of clean planting material, and quarantine remains the basis of BBTV control to this day.

However, despite the generally low incidence of BBTD in the region today, occasional flare-ups still occur, and the virus has rarely been eradicated from a district. Despite the low incidence in many subtropical plantations, the virus remains a potential threat to the banana industry. Why is this so?

In his research, Magee was only able to transmit the virus by aphids when they fed on a symptomatic leaf. Excellent subsequent epidemiological and computer modelling work by Rob Allen predicted that aphids were only likely to spread the virus after about four new leaves had been formed on the newly infected plant. This allowed enough time for the infected plant to develop symptoms and for the aphid vector to acquire enough virus to be infective. The BBTD control program is based on inspection intervals timed to allow the location and eradication of most infected plants within this window.

The strategic levy investment project “Understanding the role of latency in Banana Bunchy Top Virus symptom expression” (BA19002) is part of the Hort Innovation Banana Fund. As part of BA19002, we have been studying an outbreak of BBTD on a plantation in northern NSW where the disease persists at a high level, despite the control program.

By selecting “hot spot” areas in the plantation and carefully inspecting all plants in the area individually, stem by stem, we have shown that the inspectors’ high rate of positive identifications (>80%) is being maintained here. However, using laboratory tests on leaf samples from these plants, we found that BBTV was detectable in some recently infected plants before they showed symptoms. In other plants, the virus was detected in the symptomless leaf formed immediately prior to the first leaf to show symptoms.

This should not be a concern for disease spread if the virus was not transmitted from these symptomless, but infected, leaves. However, to our surprise, when we fed aphids on these leaves, the virus was transmitted to healthy banana plants. Furthermore, the rate of virus transmission was similar regardless of whether the aphids fed on infected leaves with symptoms or without symptoms.

The map shows a survey area where symptomatic (red) and pre-symptomatic (yellow) plants were located amongst the healthy (green) plants. We found that the virus was transmitted from thirteen symptomless leaves, eight of which remained symptomless over the whole three-week observation period.

Our next step is to determine whether these infectious, asymptomatic leaves are produced by BBTV-infected plants year-round or in a seasonally dependent pattern.

This plantation was poorly managed, with limited de-leafing, providing a sheltered environment for the banana aphids to multiply. De-suckering was also limited, thus providing more susceptible young plants (favoured by the aphid) that are often obscured by the dead leaf skirts. We suspect that the higher aphid numbers along with the higher number than expected of infection sources present as symptomless, infected leaves and obscured, infected suckers, combine to promote and prolong the epidemic.

Remember

• BBTV-infected plants can be infectious prior to development of leaves with symptoms.
• Removing newly infected plants promptly slows the spread of the virus.
• Four-week inspection cycles during the summer months in high disease pressure situations can reduce but may not completely suppress the outbreak.
• Any reductions in inspection frequency will allow the epidemic to take off.
• Plantations need to be well-maintained to limit aphid vector numbers.
• Grower participation in detection and eradication between formal inspections is likely to have a significant beneficial
impact on control.

More information

This research has been funded as part of the Improved Plant Protection for the Banana Industry Program (BA19002), which is funded by Hort Innovation, using the banana research and development levy, co-investment from the Department of Agriculture and Fisheries and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

Support for the establishment of research sites and identification of infected plants has also been provided through Hort Innovation Project BA21003 “Multi-pest surveillance and grower education to manage banana pests and diseases”.

Banana bunchy top disease

Posted on 2023-02-27 by Better Bananas

Banana bunchy top disease

Banana bunchy top is considered the most serious viral disease of bananas worldwide

Banana bunchy top disease (BBTD) reduces the growth of banana plants and causes bunching of newly emerged leaves (Figure 1). Infected plants rarely produce fruit and are a source of inoculum for further spread, which can lead to serious commercial losses if not promptly eradicated. The disease is caused by a virus (banana bunchy top virus, BBTV) and affects all banana varieties. Unfortunately, there is no cure for the disease, once a plant becomes infected it must be destroyed as all parts of the clump/stool/mat are also infected.

BBTV is spread two ways, by banana aphids and infected plant material

BBTV is transmitted by a small black insect (1.5–2.0 mm long) called the banana aphid Pentalonia nigronervosa (Figure 2 & 3). Aphids that feed on infected plants can carry the virus spreading it to healthy plants as they feed. Aphids can carry the virus for several weeks and may cover large distances when blown by the wind. The virus can also be spread to new areas from infected planting material. It’s important to note that plants can be infected with the virus without showing symptoms. It’s always recommended that you source tissue cultured planting material from a Quality Approved Banana Nursery (QBAN) to minimise the risk of introducing serious pests and diseases onto your farm, such as Panama disease, BBTV, banana weevil borer and many more. Click here for a list of QBAN accredited nurseries.

New research discovers new findings on virus transmission and explains why this disease is so hard to eradicate.
Click here for more information.

Control and containment activities continue to play an important role in limiting the spread of BBTV within Australia.

Banana bunchy top disease was first discovered in Australia over a century ago in the Tweed River region, located on the New South Wales and Queensland border. To date the disease has been successfully contained within the Bunchy top zone of South East Queensland and northern New South Wales. The banana growing regions of Far North Queensland, Northern Territory and Carnarvon in Western Australia remain free of the virus. However, it’s important for banana growers across all production regions to be on the lookout for BBTD symptoms.

What to look out for?

Early symptoms of BBTD can be difficult to detect to the untrained eye. If you have stunted or unthrifty banana plants, examine the leaf lamina of the newest banana leaves for short dark green on lighter green dot-dash lines starting from, and sometimes extending or ‘hooking’ into, the mid-rib (Refer to photos below). You can see them best if you hold the leaf up to the light and look through from the underside of the leaf. There may also be dark green stripes running along the mid-rib. Plants with advanced infection have stunted looking leaves and a bunched appearance (bunchy top). If bunches are present, they may be small and deformed.

Do not cut or disturb plants or move plant material off your property as this can spread the disease.

Key symptoms

Dark green on lighter green, dot-dash flecks (sometimes called Morse code streaking/patterning) on leaves.
Dot-dash flecks are initially visible along the lower edge of the leaf’s midrib, then progress to the leaf veins adjacent to the midrib, and gradually becoming more prominent across the leaf blade.
Eventually dot-dash flecks can form into irregular streaking.
Leaf flecks and streaking are most visible when viewed from the underside of leaves.
Flecks in veins can form a characteristic ‘hook’ shape at the point where the midrib meets the leaf blade.
Vein-flecking can also be seen on the petioles and in the leaf sheaths of stems.
Growth of the whole plant is reduced and emerging leaves develop a choked or ‘bunched” appearance.
Affected leaves often appear more upright with pale yellow margins, and may have wavier leaf edges than normal.

Image of advanced BBTV symptoms in a banana plant. Shortening and bunching up of new leaves with yellow margins (photo courtesy of Australian Banana Growers Council)

Image of advanced BBTV symptoms in a banana plant. Stunted growth and emerging leaves develop a choked or ‘bunched’ appearance

Dark unbroken stripes along the leaf midrib (not always present) (photos courtesy of Australian Banana Growers Council)

Dark green on lighter green, dot-dash flecks (sometimes called Morse code streaking/patterning) on leaves (photo courtesy of Australian Banana Growers Council)

Do your staff keep an eye out for Banana bunchy top?

ABGC have produced the following video on how to detect Banana Bunchy Top Virus symptoms in commercial plantations.

How to report

It’s important for banana growers across all production regions to be on the lookout for BBTD symptoms.
Growers or members of the public that suspect BBTD must immediately notify their state’s biosecurity agency or through the bunchy top hotline 1800 068 371. Early detection and destruction are critical to limit its spread. Strict quarantine restrictions remain in place to prevent the movement of contaminated planting material.

Surveillance and containment work within the known bunchy top zone is continuing as part of Hort Innovation’s ‘Multi-pest surveillance and grower education to manage banana pests and diseases’ project, led by the ABGC. This important work is aimed at controlling and containing the disease within the known BBTV zone, supporting the commercial industry within this zone and aims to prevent its spread to other commercial growing regions within Australia. Click here to read more information about this project.

Currently, there is no cure for BBTV and there are no known resistant banana varieties. Control is only achieved through the destruction of infested plants and banana aphids. Early detection and destruction are critical to limit the spread of BBTD.

Latest research update

Click here to read about the latest new research that helps explain why banana bunchy top disease is hard to eradicate.

More information

In collaboration with ABGC, this information has been compiled by the National Banana Development and Extension Program (BA19004). This project has been funded by Hort Innovation, using the banana research and development levy, co-investment from the Department of Agriculture and Fisheries and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.