Developing new resistant varieties
Goldfinger mutagenesis trial

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The top five selections out of the original 630 Goldfinger variants grown at South Johnstone have been identified for consumer acceptance evaluation. 

Goldfinger overview

Goldfinger (FHIA-01) which was bred by the Honduran Foundation for Agricultural Research (FHIA) is a non-Cavendish dessert banana variety that is highly resistant to Panama disease tropical race 4. 

Variety evaluation work previously conducted at South Johnstone has shown the agronomic performance of Goldfinger rates relatively well when compared to Williams. Average bunch weight of plant crop was heavier for Goldfinger at 34.3 kg compared to Williams 30.5 kg. However, the variety had a longer cycling time at 14.4 months from planting to harvest, compared to 12.4 months for Williams. Although it is a reasonably productive variety, improvements are sought in fruit quality characteristics. 

Goldfinger trial block at the South Johnstone Research Station (January 2018)
20 Goldfinger selections included in second stage trial block (July 2020)

Trial progress

Mutagenesis

Mutagenesis, which is a breeding technique using gamma irradiation to promote changes in tissue cultured plants, has been applied to the cultivar Goldfinger. The aim is to develop an improved variety which retains its tolerance to the disease and has improved fruit quality characteristics. 

The first step in this process was to determine how much gamma irradiation to use on this variety. Too much irradiation can severely damage or kill the plant, and too little may not induce sufficient changes to the plants.

Experiments, known as dose response trials, have been conducted at the Maroochy Research Station and the sufficient dosage for Goldfinger was determined.

Initial screening

630 irradiated Goldfinger plants were sent to South Johnstone Research Station, in two batches during June and August 2017 where they were held in the glasshouse prior to planting.

They were planted in the field in September and November 2017 respectively. Goldfinger plants which hadn’t been irradiated were also planted as control plants to compare against.

Irradiated plants in the field showed considerable variation in vegetative characteristics. This variation is mostly related to degree of dwarfness/plant height, pigmentation of pseudostem/leaf stalk and midribs, leaf uprightness/droopiness and minor leaf deformities. Also some of the irradiated plants have gross plant/leaf deformities and extremely slow growth. About 13% of the irradiated plants were in this reject category. 

Harvest of both the September and November 2017 plantings were completed by the end of 2018. The photos above show the very large range in bunch and fruit characteristics which have been obtained by irradiation. Yes they have all come out of Goldfinger!

Postharvest assessments also revealed diversity in the eating quality of the Goldfinger variants. Several had qualities considered to be ‘improved’ and ‘better’ than the standard Goldfinger, including increased sweetness and firmness. Taste-testing sessions held amongst the staff at the research station were used to gauge consumer acceptance of these variants.  

Twenty better tasting Goldfinger variants, which rated highly in the agronomic and post-harvest assessments were selected for a second stage of testing. 

Example of tissue culture that undergoes gamma irradiation treatment
Gammacell chamber used to apply gamma irradiation to banana tissue culture
Taste test survey
Postharvest quality assessments use the Brix scale to measure the sugar content of fruit

Examples of variation

Normal Goldfinger bunch (unirradiated).

Goldfinger bunches (irradiated) – Variations as a result of mutagenesis.

Left is control that didn't undergo mutagenesis. Variant on the right has undergone mutagenesis and shows dwarfism and more upright leaves.
Left is control that didn't undergo mutagenesis. Variant on right shows changes to plant pigmentation as a result of mutagenesis.

Screening of top 20 selections

Following the selection of the top 20 variants, sucker and bit material from the original trial was planted in September and October 2019.
Bunches of the 20 variants began to emerge from the more established plants in March 2020 and continued throughout the year; the final harvest was performed in January 2021. Data was again collected on both agronomic performance and eating characteristics to substantiate the findings from the first investigation.
The taste panelling occurred once a week, with a maximum of six variants tasted in one session (including a Goldfinger and a Lady Finger ‘Dwarf Rossi’ as control samples to compare against). Panellists included colleagues who volunteered to taste the fruit under ‘controlled’ conditions at the research station and the family members and friends of those who took fruit home.
Each variant was tasted 3 – 4 times over the six-month trial period, except for variant 423 (which was only tasted twice due to late bunch emergence). Taste preference was ranked on a hedonic scale, which included the following categories: 1 = dislike extremely, 2 = dislike very much, 3 = dislike moderately, 4 = dislike slightly, 5 = neither like nor dislike, 6 = like slightly, 7 = like moderately, 8 = like very much, and 9 = like extremely.
Dwarf Rossi, the Lady Finger comparison, scored the highest overall rating (at 6.8) of all the varieties included in the taste panelling (Figure 1), corresponding with 77% of respondents indicating they would purchase it if it were commercially available (Figure 2). This was closely followed by variant 521, which was the best performer out of all the Goldfinger variants with an average rating of 6.5.
Figure 1: The average overall rating given to the variants across several taste panels (where 1 = dislike extremely, 5 = neither like nor dislike, and 9 = like extremely). The bars represent the standard error of the mean. Dwarf Rossi is a Lady Finger-type control included in the panelling as a reference variety
Figure 2: The percentage of respondents in the taste panelling who answered ‘yes’ (green) or ‘no’ (red) to the question, 'If this product was commercially available, would you choose to purchase it?' The remaining category (blue) are the instances where the question was left unanswered
Several comments were made that this variant had similar eating characteristics to a Lady Finger. The Goldfinger control was rated poorly, 4.7 on average, with 255 the only variant below it at 3.7. Variants 211, 544, 144 and 903 joined 521 in making up the five selections given the highest overall eating experience rating, and which also had the greatest number of people answer ‘yes’ to the question: ‘if this fruit was commercially available, would you choose to purchase it?’
The plant heights of all the selected variants were not significantly different from the 3.1 m Goldfinger average. The total fruit yield was also comparable to the average Goldfinger bunch (27.3 kg) for three of the selected variants, while the other two were 15-20% lower.
There were a couple of variants with undesirable characteristics which had gone undetected in the original selection of top performers. For example, several plants from one variant had severely fused fingers – to the point where several hands in a bunch were unusable.
Another variant had fruit which retained a green-tinge upon ripening. The relatively tall (3.5m) and thin pseudostem (54cm) of another contributed to two of the ten plants snapping before bunch maturity; its brittle pseudostem also made harvesting difficult. Such issues prevented these three variants being pursued further. 

Further screening and consumer and sensory evaluation of top 5 performers

Plants were nurse-suckered in December 2020 and the first bunches began emerging in June 2021. Agronomic data will again be collected from all variants, but only fruit from the top five performers will be sent down for consumer and sensory evaluation at DAF’s Coopers Plains facility in Brisbane later in the year. 

Here, a much larger tasting panel will be engaged to assist in identifying which variants are the most well-received by consumers and have the best market prospects for the future. Planting material is also in the process of being sent to the Northern Territory, where field trials will confirm if the variants have retained Panama disease resistance before they are included in DAF supervised pre-commercialisation trials.

Normal Goldfinger bunch (unirradiated)

Bunches of the five variants selected to progress into the next phase of the investigation

Goldfinger variety research features on ABC's Catalyst program

Check out ABC’s Catalyst story on banana production and the work that’s underway to find a new variety; a variety that can match our love for Cavendish while also having good pest and disease resistance. Paul West speaks with Cameron Mackay and banana researchers Jeff Daniells and Stewart Lindsay to find out more. 

More information...

This Goldfinger work was initiated as part of the Fusarium Wilt Tropical Race 4 Research Program (BA14014). At the close of BA14014 funding has been provided through the project Improved Plant Protection for the Banana Industry (BA16001) for continuation of the evaluations.   This project has been funded by Hort Innovation, 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.