What assistance is resistance?

New banana varieties developed for TR4 resistance are already being trialled in Australia, with others in the pipeline. Jeff Daniells, Stewart Lindsay, Mike Smith, Sharon Hamill and Tony Pattison report on what’s here, what’s on the way and what’s the potential.
The Panama disease Tropical Race 4 (TR4) outbreak in North Queensland has immediately increased focus on the Australian banana industry’s ongoing research work into disease-resistant varieties.

With Australia’s major banana variety, Williams Cavendish, under threat from the banana plant disease, growers are asking: “What resistant varieties available?” “How good are they?”  “Which ones should we plant?” Where can we get them?” and “What other plants are in the pipeline?”

The Australian banana industry’s Banana Plant Protection Program (BPPP) has established relationships with banana plant breeding programs around the world.

Already, seven Cavendish varieties and five non-Cavendish developed for TR4 resistance have been trialled in Australia with some of these commercially available.

Growers have already had a chance to see these plants on the industry’s trial blocks and some growers have already accessed some of the varieties to trial on their own farms.

Varieties on the way include three new Cavendish varieties from Taiwan, now undergoing quarantine in Australia. Negotiations are underway for other varieties from mainland China and the Philippines and there are others being developed elsewhere, including the Honduran breeding program.

It’s timely to review some of these varieties and their agronomic attributes and to look ahead to what’s in the pipeline.

Given that the resistant varieties generally have lower yields than Williams Cavendish, it’s also timely to look at the possible scenarios when use of resistant varieties will be most beneficial to the Australian banana industry.

Cavendish domination

Williams Cavendish has been the dominant variety in Australian banana growing for more than 50 years. The fruit’s excellent agronomic and taste attributes have earned it market dominance and, worldwide, Cavendish is also the major variety.

Cavendish bananas are sold as a commodity product with relatively limited product differentiation in the marketplace. Despite efforts to diversify varieties grown, the market situation has changed very little in the past 25 years.

The reasons for this were researched in a banana industry project New and alternative banana varieties designed to increase market growth (BA09041). A final report by Jeff Daniells and others was completed in 2011.

Among the reasons found for the dominance of Cavendish was the simplicity of having one main variety to manage in a relatively complex supply chain. The focus on one variety makes possible very successful mass marketing.

Perhaps the arrival of TR4 in North Queensland may be the impetus for some change in this arena.

The new varieties

In answer to growers’ questions about the new resistant varieties available, here is a summary of the Cavendish and non-Cavendish varieties now available.

We currently have seven Cavendish varieties in Australia showing varying degrees of resistance (best described as partial resistance or tolerance).

The varieties are shown in the accompanying table. Two were also rated in an agronomic trial (see story, Page 26).

Depending on the variety and growing circumstances, varying proportions of these plants will succumb to the disease eventually.

Most of the varieties listed in the table can be released and multiplied but not all have been fully evaluated or recommended and are awaiting TR4 resistance screening in the Northern Territory. Screening has been delayed due to the Banana Freckle eradication program requiring the removal of banana plants in parts of the NT until mid-2016.

There are limited plants of these varieties from which to source suckers for commercial production. Some growers have already obtained plants of DPM25, Formosana, CJ19 and GCTCV 119 under a Material Transfer Agreement for evaluation on their properties. This has allowed growers to assess the plants’ prospects.

DPM25, the variety developed by the then Queensland Department of Primary Industries (now known as the Queensland Department of Agriculture and Fisheries), was released commercially this year.

Unfortunately, many of these varieties have agronomic or postharvest defects. One of the varieties, Formosana, is quite prone to high levels of offtypes in tissue
culture plantings. This must be taken into consideration when interpreting its performance.

Some of these varieties are reported on in this edition of Australian Bananas as well as previous editions – see Australian Bananas Vol 41 pp 26-27, Vol 38 pp 14-15 and Vol 30 pp 30-31. 

And the non-Cavs

There are just a few non-Cavendish varieties that we know of that have resistance or tolerance to TR4.

They include five hybrids from the Honduran breeding program, amongst them Goldfinger (FHIA-01), FHIA-18 (‘Bananza’) and FHIA-25 (cooking type).

Despite their high productivity, any prospects they have can only be described as niche. Goldfinger has already been released and can be obtained for commercial production. However, the variety has not so far achieved commercial success.

QDAF holds the FHIA licence in Australia for the other hybrids, so a commercial partner would be required to manage the FHIA lines if commercialisation is sought.

Other varieties with tolerance include Pisang Ceylan and Ducasse but their prospects also remain niche as far as the Australian market is concerned. It should be noted that Ducasse is highly susceptible to Fusarium wilt race 1 in the tropics and subtropics, as is Pisang Ceylan in the subtropics.

In overseas trials, plantains (like the Horn Plantain and Dwarf French Plantain we have in Australia) have shown some tolerance to TR4. Lady Finger, Pacific Plantain and Dwarf Red Dacca were all very susceptible in the NT screening trials.

Sucrier has not been screened against TR4 in the NT but the pathogen has been recovered from diseased plants of this variety in South East Asia.

In the pipeline

So far, there are six more Cavendish varieties identified as having potential from breeding programs in Taiwan, China and the Philippines. There is also potential for new hybrids from the FHIA breeding program in Honduras.

Of the six identified Cavendish varieties, three are now in Australia undergoing the required quarantine holding period.

These are from the Taiwan Banana Research Institute (TBRI) and are the Tai Chiao varieties numbered 3, 5 and 7. They were imported from Taiwan last August.

The Tai Chiao varieties are partially resistant, but we understand have much improved agronomic characteristics compared to Formosana.

Any potential future commercialisation of these lines will be subject to licensing and commercialisation to protect the intellectual property of the TBRI.

There are ongoing negotiations with breeding programs in China and the Philippines to trial in Australia selections of the other three Cavendish varieties showing tolerance to TR4. These include the Cavendish selections ZJ4 and ZJ6 and GCTCV 219.

We continue to seek the new Cavendish hybrids developed in the Honduran breeding program for evaluation in Australia – negotiations are ongoing.

These hybrids potentially offer not only resistance to TR4 but also to major leaf diseases. While TR4 is the major issue now faced by the Australian banana industry, we must not lose sight of other issues that the banana industry may face.

There are other hybrids from CIRAD (the French program – Centre de Cooperation Internationale en Recherche Agronomique pour le Developpment) and from elsewhere which are currently undergoing quarantine. However, whether they have resistance is totally unknown with TR4 disease screening required.

What about GM?

The Queensland University of Technology (QUT) has been screening genetically modified (GM) Cavendish against TR4 in the Northern Territory.

Verbal reports from QUT are that the results to date, in terms of TR4 resistance, have been encouraging.  However, should the work prove successful there remains the bigger hurdle of obtaining permission to commercially grow the plants in Australia, along with convincing consumers to purchase them.

There is currently no fresh GM fruit and vegetables in the Australian marketplace and a consumer reluctance to accept it raises questions about the prospects for the introduction of a locally-grown GM banana. Research will be ongoing in this area but it would seem no GM variety would be ready for possible commercialisation for quite a few years yet.

Use of resistant plants

As part of growers’ consideration of the current resistant varieties available in Australia, growers should consider that the Cavendish selections mentioned above only have partial resistance.

If the pathogen is already present on a property, some plants of these varieties could be expected to become diseased in the plant crop. As progressive cycles of disease infection occur, the disease inoculum can build in the plantation, causing disease in more and more plants in successive crops.

Overseas experience suggests that only one to three crops may be possible before the need for fallowing and eventual replanting.

Therefore, growing such partially resistant varieties will contribute to a build up of disease inoculum in the region, potentially increasing the risk of disease spread to clean properties.

For this reason, one possible scenario is that banana cropping on infested sites will not be permitted but this would likely depend on the eventual number and distribution of infested properties.

If a property does not have the pathogen present, it should be noted that these Cavendish varieties are not as productive/profitable as the standard Cavendish varieties Williams or Grande Naine – yield reduction of 20 per cent or more is typical along with other possible defects.

Many of these lines also have different post-harvest handling requirements compared to Williams Cavendish which would require segregation at ripening and distribution centres.

Also, growers should be aware that thinking a variety is resistant may lead to a false sense of security meaning insufficient attention is paid to biosecurity measures necessary to keep the pathogen out for as long as possible.

Worst-case scenario

So, it is possible that the biggest potential for the new varieties to play a significant role in longer-term industry production may only occur under a scenario where TR4 has spread rapidly to many production regions.

Experience with Fusarium wilt of bananas overseas has typically been that Cavendish rules the market and the resistant varieties are a last resort. So, unless a truly resistant variety is found with essentially the same yield and marketing characteristics, production of the susceptible variety continues by moving to clean sites. This happens until no clean production sites remain and there is no alternative but to switch to a partially resistant or resistant variety.

The Australian banana industry will need to consider what the best options are for a property once it becomes infested and the economics of the different options will require scrutiny.

It remains clear that containment is a top priority and regions not currently infested must be protected with a very high level of biosecurity.

219 – the latest model

The Cavendish variety GCTCV 219 is an enhanced selection bred in the Philippines out of GCTCV 119. It has better agronomic characteristics than 119 and the fruit is sweeter than Williams. Fruit of the variety has recently gained acceptance in Japan where it is sold as premium Cavendish and tagged as ‘sweeter banana / elegant taste banana’. It is sold as packaged small clusters, further distinguishing it from the standard commodity product.

While this market is best described as a niche opportunity, the higher value derived in the marketplace helps to maintain profitability in spite of the lower productivity of 219.

Quarantine process

Typically, once plants arrive in Australia from overseas they will take 18 months to two years to traverse the quarantine process.

Even though some growers desperately want resistant varieties we cannot fast track the quarantine process without running the risk of introducing additional exotic pests and diseases which would only make matters worse.

Once they have successfully passed through quarantine they will be screened for resistance to TR4 which could be expected to take at least a further two years. Other aspects of agronomy and postharvest handling will occur simultaneously.

Not all of the imported varieties can be expected to suit Australian growers. What may be promising varieties overseas will still need research in Australia on production, postharvest, supply chain and marketing to ensure that banana sales are not jeopardised by a poor quality product.

Getting plants

Some varieties with tolerance and resistance to TR4 are available with no intellectual property processes being necessary (DPM25, Goldfinger and Formosana). The others may require material transfer agreements to be in place. Commercial quantities are not currently available of most of the varieties mentioned in this article. Sharon Hamill, Senior Principal Scientist at the Queensland Department of Agriculture and Fisheries’ Maroochy Research Station can provide more information (phone 07 5453 5942). See Sharon’s article on tissue culture in this edition, Page 33.

Farming with TR4

In our (Daniells and Lindsay) paper ‘Tropical Race 4 Fusarium Wilt – what If?’ presented at the 2009 Australian Banana Industry Congress, we made it clear that “once TR4 occurs on a property it would not be business as usual”.

This included aspects of crop management which would need to be modified to allow sustainable production of tolerant varieties.

It is unlikely that plantings would be viable much beyond first ratoon as disease builds up in the crop. Considering the need for significant fallowing to help reduce inoculum pressure following cropping, a much larger property area would be required to sustain the same total area of bananas at any one time – doubling it in some cases.

Other crop management measures recommended in the deployment of tolerant varieties are to minimise waterlogging and soil compaction, modest levels of nitrogen fertiliser application and killing of diseased plants without delay to minimise disease inoculum levels.

Stewart Lindsay has reported previously on commercial production of Cavendish bananas in the presence of TR4 in Indonesia (2011 Winter edition Australian Bananas Vol 33 pp 38-39). By employing such crop management strategies it should be possible to grow tolerant varieties in a diseased site for at least one, or even several, crops depending on the variety and location in question.