New test helps product screening for Chalara management

New test helps product screening for Chalara management

Multiple fungal organisms are known to cause Crown end rot (CER) in bananas. The following research is focused on the more serious form of CER commonly known as Chalara where the rot extends into the fruit (caused by Thielaviopsis musarum). Disease symptoms are typically observed in the supply chain during cooler periods of the year (winter). Chalara is sporadic in occurrence, making it difficult to conduct research trials with the disease. Department of Agriculture and Fisheries researchers have now developed an inoculation technique that mimics the development of Chalara in the supply chain, enabling researchers to screen and evaluate alternative management options.

There are two post-harvest fungicides currently registered for use in Australia to help manage CER. Although these treatments are effective against the fungi that cause CER, growers have expressed a need for non-chemical options for managing the disease, particularly those with organic status.
The inoculation technique has now been used to determine efficacy of the currently registered fungicides, alternative fungicides and biological products.

Results

Overall, the inoculation technique developed is rapid and reliable and the results are reproducible. Even though the technique was specific for Chalara (T. musarum), crown mould assessments were also obtained. Ideally a successful test product should have efficacy against T. musarum and the range of fungi that cause crown mould.

Prior to conducting this research there was only anecdotal evidence that the current registered projects had efficacy against T. musarum, but this has now been confirmed, with both Tecto® and Protak® effective in halting the development of Chalara. Results also showed that some biological products are capable of managing Chalara and reducing levels of crown mould.
Participating companies have been supplied the results for their products. They can use the results to support registration applications and/or determine which products are worth investing in further trials. It is hoped this work will lead to product registration adding alternative management options for growers.
Crown end rot
Fruit inoculated in suspension of T. musarum (concentration is 1 million spores per ml).
Crown end rot
Fruit artificially inoculated with T. musarum. This photo was taken one week after inoculation, following storage and ripening under near commercial conditions.
Crown end rot
One alternative fungicide and one biological product provided excellent management of T. musarum. Photo taken of alternative fungicide.

Remember...

Before using any chemicals, always check the current registration status and read the product label. Label and permit details can be accessed via APVMA website: www.apvma.gov.au
This work was undertaken as part of the ‘Enhancing the outcomes of BA13011-Crown end rot investigations’ funded as part of Department of Agriculture and Fisheries’ Horticulture and Forestry Science development funding. 

Alternative post-harvest product testing

Alternative post-harvest product testing

Research has shown that a range of farm management practices have some incremental influence on disease management of crown end rot (CER), from site selection to irrigation practices through to packaging and dispatch.  Specifically, good field and shed hygiene practices help reduce fungal spores making it easier and more effective for post-harvest fungicides to do their work. However, to reduce reliance on fungicide use and address issues associated with chemical resistance, research into potential alternative post-harvest treatments are being investigated. 

Twelve post-harvest treatments including disinfectants, biological/organic treatments and alternative fungicides have been screened using clusters of bananas and observing the natural development of CER symptoms. 

Crowns of each of the clusters were dipped in various treatments (for 30 seconds or 3 minutes), then ripened under standard ripening conditions. Once the fruit was ripened, the symptom development of CER was rated on a scale of 0-7 (7 being the most severe). 

 
Preparing to dip fruit
Preparing to dip fruit.
The crown of clusters being dipped in the various treatments
The crown of the clusters being dipped in the various treatments.

What are the results so far?

This initial screening has indicated that one fungicide (Fungicide B in the table below) appears to be better at managing some of the CER organisms than the currently registered fungicides.

The treatments that showed promise in this initial screening trial require further investigation on larger quantities of fruit and fruit from different production regions. This will help determine if they would be suitable candidates for post-harvest treatment in a commercial setting.
 
Some of the poorer performing treatments, including a biological product that caused severe fruit burn, will not be further investigated.
 
Severe burn was observed on one of the biological treatments
Severe burn was observed on one of the biological treatments.
Fungicide B treatment with no visible fungal growth on the crown surface
Fungicide B treatment with no visible fungal growth on the crown surface.
The water only treatment with obvious fungal growth on the crow
Water only treatment with obvious fungal growth on the crown.

The table below provides a summary of the performance rating of each of the post-harvest treatments tested. 

If you would like more information on this trial contact the better bananas team at betterbananas@daf.qld.gov.au or 13 25 23.

This work is funded as part of the Cause and management of crown rot of banana project (BA13011). This project is funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland 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.

Host research using Panama disease race 1

Host research using Panama disease race 1

Understanding what species are capable of hosting the fungal organism that causes Panama disease will help inform how weeds and ground covers are managed in areas infested with the disease. 

Work in Far North Queensland has used Panama disease race 1 as a surrogate for tropical race 4. Field surveys conducted in the region have identified plant species common to banana plantations that may act as potential alternative hosts. In this context, a host is defined as a plant in which the fungus can survive, often without obvious disease symptoms apparent.

Weed and ground cover species were collected from farms in Far North Queensland with a history of race 1 infection. In total 115 samples from 20 different plant species were analysed for the presence of the fungal organism (Fusarium oxysporum f.sp cubense) that causes Panama disease race 1. 

Roots from each of the plant samples were washed to dislodge excess soil before being surface sterilised. Segments of roots were placed in Fusarium selective media, and incubated for 3-5 days to allow fungal growth. The recovered populations were sent to a specialist diagnostic lab in Brisbane for formal identification. 

Race 1 was found living within four different species commonly found co-habiting Far North Queensland banana farms. These species were, spiny spider flower (Cleome aculeata), Youngia japonica, crowsfoot grass (Eleusine indica) and summer grass (Digitaria ciliaris).

Spiny Spider
Spiny spider flower
Summer grass
Summer grass
Youngia japonica
Crowsfoot grass

Please note...

Panama disease race 1 (R1) was used as a surrogate for Panama disease tropical race 4 (TR4), as access to TR4 infested banana properties in Queensland is restricted.

This trial was funded as part the Fusarium Wilt Tropical Race 4 – Biosecurity and Sustainable Practices project (BA14013). This project was funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland 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.

Host research using Panama disease subtropical race 4

Host research using Panama disease subtropical race 4

Understanding what species are capable of hosting the fungal organism that causes Panama disease, will help inform how weeds and ground covers are managed in areas infested with the disease. Using Panama disease subtropical race 4 (SR4) as a surrogate for Panama disease tropical race 4 (TR4), a glasshouse experiment was conducted in Brisbane to investigate potential alternative hosts of the fungus. In this context, a host is defined as a plant in which the fungus can survive, often without obvious disease symptoms apparent.

The glasshouse experiment included 18 species identified as being the most common species co-habiting Far North Queensland banana farms, or were regarded as high risk due to their presence on TR4 infested farms in the Northern Territory and Far North Queensland. The plants were inoculated with SR4, and their roots were analysed for the presence of the fungus after a period of 3 months. The roots from each of the plant samples were washed to dislodge excess soil before being surface sterilised. Segments of roots were placed in Fusarium selective media, and incubated for 3-5 days to allow fungal growth. The recovered populations were sent to a specialist diagnostic lab in Brisbane for formal identification.

Panama disease subtropical race 4 was recovered from all 18 species. The fungal organism that causes the disease was recovered from more of the sample plants of some species than others. Although the experiment showed that all species had the potential to host SR4, the differences in the frequency in which it was recovered suggests that some species more readily host the fungus than others do.  
Weeds included in glasshouse trials

Please note...

Panama disease subtropical race 4 (SR4) was used as a surrogate for tropical race 4 (TR4), as  SR4 is more closely related to TR4 than other races of the disease.

As seen in the figure above, Mullumbimby Couch had the highest disease recovery, with SR4 recovered from 80% of samples. Whereas Pinto Peanut had the lowest recovery, with approximately 16% of samples recovering SR4.
This trial is part of the Fusarium Wilt Tropical Race 4 – Biosecurity and Sustainable Practices project (BA14013). This project was funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland 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.

Guide to crown end rot identification

Guide to crown end rot identification

Thielaviopsis musarum (commonly known as Chalara).
  • Rot extends beyond the crown and into the fruit (rapid development).
  • Usually limited to a few clusters.
  • Occurs randomly and mostly reported during winter and spring.
Thielaviopsis musarum
Fusarium equiseti-incarnatum species complex.
  • Gives a fuzzy/fluffy appearance on cut crown surface.
  • Usually causing cosmetic damage but incidence is often reported as high.
  • Reported to be worse during summer/spring. 
Fusarium equiseti-incarnatum species complex
Musicillium theobromae
  • Appearance not as fuzzy/fluffy as the above organism.
  • High incidence reported.
  • Reported to be worse during summer/spring.
Musicillium theobromae
Colletotrichum musae
  • Limited fungal growth apparent and sometimes orange spore masses are observed.
  • Rot can extend below the crown.
  • Low incidence reported.
Colletotrichum musae

Please note...

The above information is a guide only, as multiple organisms may be involved and simultaneously cause symptoms.  

If you notice any crown end rot symptoms or want further information, contact the better bananas team at betterbananas@daf.qld.gov.au or 13 25 23. 

This work is funded as part of the Cause and management of crown rot of banana project (BA13011). This project is funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland 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.

Resistance to current post-harvest chemical trials

Resistance to current post-harvest chemical trials

Lab testing used to indicate whether a fungal organism has developed resistance to a particular post-harvest fungicide is commonly termed ‘sensitivity testing’. Sensitivity testing has been carried out on the two registered post-harvest products (prochloraz – Protak® and thiabendazole – Tecto®), against each of the four fungi known to be responsible for causing crown end rot (Fusarium spp., Colletotrichum musae, Musicillium theobromae and Thielaviopsis musarum, commonly known as Chalara). 
The fungal organisms listed above were collected from both Cavendish and Lady Finger fruit and from different growing regions including the coastal production area of Far North Queensland, the Atherton Tablelands and northern New South Wales.  Where possible the fungi were also sourced from fruit that had not been exposed to commercial management practices (backyard production) in order to provide a suitable comparison.

These results show that it may be necessary to change your post-harvest treatment products, depending on the organism/s you are having issues with and the location of your farm.

If you would like more information on this trial contact the better bananas team at betterbananas@daf.qld.gov.au or 13 25 23.
This work is funded as part of the Cause and management of crown rot of banana project (BA13011). This project is funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland 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.

Time in supply chain studies

Time in supply chain studies

The length of time bananas spend in the supply chain can have a significant impact on the development of crown end rot (CER). 
Researchers conducted a simulation experiment, where Cavendish (Williams) and Lady Finger clusters were held 1, 2, 3 and 4 weeks prior to being ripened. The fruit for the experiments was sourced from a commercial property and all fruit was treated with a post-harvest chemical (prochloraz). To ensure a fair comparison, fruit from different positions in the bunch (top, middle and bottom hands) were assessed in case this was also a contributing factor. Once the fruit was ripened, the symptom development of CER was rated on a scale of 0-7 (7 being the most severe).

As seen in the graph below, the experiment with Cavendish fruit revealed fruit held longer within the supply chain resulted in relatively more severe symptoms of CER than fruit that would generally move through quicker. However, the overall symptom development was low as you can see in the graph below. 

Crown end rot ratings from the Cavendish time in supply chain simulation experiment (values with different letters are significantly different to each other)

As seen in the figure below, the simulation experiment using Lady Fingers showed similar results to Cavendish fruit in that fruit held for longer prior to ripening produced more severe symptoms of CER. However the overall symptom development was low as you can see in the graph below. 

Crown end rot ratings from Lady Finger time in supply chain simulation experiment (values with different letters are significantly different to each other)

If you would like more information on this trial contact the better bananas team at betterbananas@daf.qld.gov.au or 13 25 23.

This work is funded as part of the Cause and management of crown rot of banana project (BA13011). This project is funded by Hort Innovation, using the banana research and development levy, co-investment from the Queensland 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.

Crown end rot

What is it?

Crown end rot (CER) of bananas is a serious cause of post-harvest quality loss for banana fruit. As the name suggests, the rot begins at the cut surface of the crown, and depending on the severity, can extend down the neck of the fruit and into the fingers. There are several fungi that can cause CER symptoms and the visual appearance of those symptoms may indicate what fungal organism is responsible. However, multiple fungi can simultaneously cause symptoms, so it can be difficult to distinguish the difference with the naked eye.

The following fungi can cause crown end rot in bananas:
  • Fusarium equiseti-incarnatum species complex
  • Musicillium theobromae
  • Colletotrichum musae
  • Thielaviopsis musarum (commonly known as Chalara). 
Crown end rot extending into banana fruit.

More info...

Click here for more information and photos of the symptoms typically associated with each fungal organisms.

How do you manage crown end rot?

Currently, the most effective management strategy for CER is the application of post-harvest fungicides. Products containing thiabendazole (e.g. Tecto®) and prochloraz (e.g. Protak®) are registered for post-harvest use in bananas.

Recent research has indicated that some of the organisms that cause CER are less sensitive to thiabendazole based products, particularly in the coastal regions of Far North Queensland. These organisms remain more sensitive to products containing prochloraz.  Simulation studies have also shown that the longer banana fruit is held in the supply chain before ripening, the greater the risk of developing more severe symptoms of CER. Research has also investigated alternative post-harvest products. 

See below for more information on this research.

More info...

This work is funded as part of the Cause and management of crown rot of banana project (BA13011). This project 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, non-for-profit research and development corporation for Australian horticulture.