New varieties were screened against Fusarium wilt Race 1 in the Australian subtropics and tropics as part of the ‘Banana Plant Protection Program’ project. Here we look at several promising varieties which were identified.

By Jeff Daniells, Mike Smith, David Peasley, Wayne O’Neill and Andre Drenth

THE DISEASE

Fusarium wilt of bananas, otherwise known as Panama disease, is by no means a new disease of bananas having plagued the subtropical Lady Finger industry in Australia since early in the 20th Century.

Initially only Race 1 of the pathogen—to which Cavendish is typically resistant—was known. Subtropical Race 4 began to cause losses in Cavendish grown in southern production areas in the 1970s and tropical Race 4 (TR4) was detected in the Northern Territory in 1997.

However, it is only since the 2015 TR4 incursion in North Queensland that the quest to find resistance for this strain of the Panama disease has become urgent.

These days the Lady Finger industry is mostly split between NSW and the Atherton Tablelands with an overall gross revenue of about $30 million per year.

In NSW the variety  represents about half of the total banana production area.

Race 1 has to date only caused minor problems for Lady Fingers on the Atherton Tableland because of both limited distribution of the pathogen and warmer winters resulting in less stress than the subtropics.

The niche variety Ducasse is also seriously affected by Race 1. Most growers of Ducasse on the wet tropical coast are affected.

As a result, there has been a shift in production to NSW which now represents a majority of the area under Ducasse.

The strategic levy investment project Banana Plant Protection Program (BA10020) is part of the Hort Innovation Banana Fund.

The project developed a rigorous screening program for Panama wilt which included multiple screenings at different sites.

New varieties were screened against Race 1 (VCG 0124) in the subtropics at Duranbah, northern NSW as well as on grower’s properties in the tropics at East Palmerston and South Johnstone in North Queensland, while screening for TR4 was conducted in the Northern Territory and overseas through a collaboration with Wageningen Agricultural University.

The subtropical banana industry has struggled for many years due to inability to compete successfully in the wider Australian market with fruit from the tropics.

Product differentiation is seen as a solution and alternative varieties are one means of achieving greater market share.

Due to the widespread occurrence of Race 1 in subtropical production areas, resistant varieties are eagerly sought by many growers.

VARIETIES EVALUATED

At the commencement of the project in 2011 there were several previously imported varieties that had just cleared quarantine and were ready for evaluation.

These included several Cavendish and Gros Michel selections and hybrids from the Honduran breeding program. More background information and results from other aspects of
the evaluations can be found in past editions of Australian Bananas.

FUSARIUM WILT SYMPTOMS

Like TR4, Race 1 Panama disease is characterised by yellowing of the margins of older leaves followed by necrosis.

Leaves eventually collapse leaving a skirt of dead leaves. Pseudostem splitting can occur.

Cutting through the pseudostem reveals dark brown to black discolouration of the water conducting tissues.

SCREENING PROCEDURE 

A subtropical screening site in northern New South Wales and two tropical sites around Innisfail were selected for disease screening.

To ensure relatively uniform disease inoculum pressure, the Duranbah trial site was artificially inoculated with Race 1 (VCG 0124) at planting.

At the two grower properties in North Queensland previous cropping of the blocks had included Ducasse bananas severely affected by Race 1.

Plants were inspected at regular intervals during growth with disease symptoms and death of plants recorded. Discolouration of the cut rhizome due to disease was rated at bunch harvest.

RESULTS

There are various ways to categorize the reaction of varieties to the disease.

Here we have attempted to integrate our findings into a simplified format for ease of interpretation. Essentially we have three categories:

• Very susceptible (VS)—Severe symptoms with >50% of plants not producing a bunch. Clearly not commercially feasible.
• Intermediate (I)—Typically many plants with mild disease symptoms but most producing a commercial bunch. With the right environment/crop management to lower inocula levels these should be commercially feasible.
• Resistant (R)—Plants show no sign of disease under most circumstances.

DISCUSSION

• Not surprisingly all of the Cavendish selections tested were resistant to Race 1. Due to limited space/plant availability/expectation of resistance most of the Cavendish were not
  tested in the tropics.
• The Gros Michel selections from Cuba (IBP series) were all very susceptible in both the tropics and subtropics despite them reportedly being resistant in Cuba. Results from overseas evaluations may not hold true in our production areas—thus the need for evaluation in our own regions. It appears that there may have been insufficient disease pressure in the Cuban trials.
• Surprisingly the semi-dwarf Gros Michel, Highgate, was resistant in North Queensland. This is encouraging because it is a further example that resistant selections can be located amongst closely related banana types.
• Hom Thong Mokho and High Noon were resistant in the tropics but intermediate in the subtropics. Disease reactions obtained in the subtropics are not always the same as for the tropics. This is mostly due to cold stress experienced in the subtropics leading to breakdown of resistance. Stresses due to other extremes of environment can also contribute.
• There is much emphasis on seeking TR4 resistance given the threat of its further spread. But it must be remembered that any new varieties need to also have Race 1 resistance given its already widespread distribution.
• Having demonstrated TR4 resistance does not imply that a variety will automatically be equally resistant to Race 1. There are indications from the Northern Territory screening work that Dwarf Ducasse has an intermediate reaction to TR4 whilst it is very susceptible to Race 1.
• Screening for Race 1 resistance in the subtropics and tropics is continuing in the new project—‘Improved Plant Protection for the Banana Industry’ (BA16001).

* The contributors; Jeff Daniells, Mike Smith and Wayne O’Neill, QLD  Department of Agriculture and Fisheries, David Peasley, Peasley Horticultural Services, and Andre Drenth, University of Queensland. 

* This project has been funded by Hort Innovation, using the banana research and development levy and contributions from the Australian Government. Hort Innovation is the grower owned, not-for-profit research and development corporation for Australian horticulture.