The world’s favourite fruit needs a genetic boost
The Cavendish variety of banana is under threat from a range of fungal diseases, writes UQ's Professor André Drenth
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The world’s most popular banana variety, the 'Cavendish', is not the result of a breeding program but rather was found by a prehistoric farmer in an Asian rainforest.
Ever since, Cavendish has been vegetatively propagated using small suckers sprouting from the base of the mother plant and, more recently, tissue culture processes, to form the basis of our global banana export industry.
More than 40 per cent of bananas grown globally belong to this single variety.
Within Australia, over 95 per cent of bananas grown in commercial plantations are of the Cavendish variety.
The majority of banana production is located in North Queensland, which produces more than 95 per cent of Australia’s bananas, with a gross value of production close to $600 million.
Although farmers select for shorter plants and better bunch characteristics, over time no significant genetic gain in the global banana industry has occurred.
A banana plantation in Atherton, Far North Queensland. Image: Getty Images/Wendy Townrow
A banana plantation in Atherton, Far North Queensland. Image: Getty Images/Wendy Townrow
Cultivating a single variety on a such a large global scale has led to a very high level of genetic vulnerability.
The Cavendish variety is currently under threat from a range of fungal diseases, most notably Black Sigatoka and Fusarium Wilt Tropical Race 4 (TR4), to which it has no resistance.
Black Sigatoka has spread widely. Almost one-third of the cost of growing Cavendish depends on the control of this disease using fungicides, which in some countries are applied each week.
Luckily, Australia is free from Black Sigatoka.
The other disease, Fusarium with TR4, is spreading across the world and is presently in North Queensland, where it is under active containment since first being identified in 2015.
The most obvious solution to these problems is to breed bananas resistant to these diseases – but this is easier said than done.
The first problem is that the bananas we eat are sterile because they result from fruit formation without fertilisation.
Cavendish bananas are also triploid, and both male and female are sterile.
In contrast, wild bananas are diploid, and produce lots of seed, making them unsuitable for consumption.
Native or wild bananas of different Musa species or subspecies occasionally fertilise each other.
Then you end up with an infertile fruit lacking seed and they are the ones we can eat.
Bananas are enjoyed around the world. Image: Getty Images/pixdeluxe
Bananas are enjoyed around the world. Image: Getty Images/pixdeluxe
It’s similar to how you produce a mule from a horse and a donkey, where the offspring is sterile.
The second problem is that not many fundamental genetic studies have been done on bananas, despite them being one of the top ten food crops in the world today.
In terms of other crop industries, bananas are still in the predomestication phase and can be considered as an orphan crop suffering from a fertility crisis.
Very little basic research has been done on bananas, which was typical for crops grown by smallholders in the tropics.
We have not really domesticated bananas; we’re still just using material from the wild.
Although there is a lot of diversity within the Musa genus, very little as yet has found its way into the hands of the consumer.
Genetic improvement is needed to be able to effectively control plant diseases that threaten the cultivation of the Cavendish banana.
After a century of plant breeding, less than five per cent of the world’s bananas actually come from a breeding program.
To investigate the reasons behind this situation and the challenges involved in developing new banana varieties, I – together with Professor Gert Kema from Wageningen University – have edited a book on germplasm and genetic improvement of bananas, which was recently published by Burleigh-Dodds in the United Kingdom.
This volume is part of the three-part Achieving Sustainable Cultivation of Bananas series.
The first volume in the series, published in 2018, was on banana cultivation techniques.
The second volume, published in 2020, deals with germplasm and genetic improvement.
Volume three will cover the diseases and pests of bananas.
Volume two aims to cut across boundaries of botany, taxonomy, genetics, floral biology, molecular genetics, cytogenetics, genetic modification and plant breeding.
A lot of information is scattered among hundreds and hundreds of research papers, so what we try to do is what I call 'write what needs to be written'.
It’s really about bringing all these diverse issues together and identifying key trends in a single easy-to-understand format.
The book contains information relevant for banana researchers, industry leaders and investors.
Professor André Drenth is a Professorial Research Fellow at UQ's Centre for Horticultural Science. He obtained a master's degree in Plant Breeding from Wageningen Agricultural University in the Netherlands, before completing a PhD jointly at Wageningen and Cornell University, USA, on the population biology of Phytophthora infestans, the causal agent of late blight on potatoes.
Prior to his current role as Principal Research Fellow at UQ's Queensland Alliance for Agriculture and Food Innovation (QAAFI), Professor Drenth worked as a plant pathologist for the Cooperative Research Centre (CRC) for Tropical Plant Pathology in Brisbane from 1994 to 2000 and was program leader of the Disease and Pest Prevention Program in the CRC for Tropical Plant Protection from 2001 to 2006.
From 2006 to 2011, his position was supported by Queensland’s Department of Primary Industries and Fisheries and UQ, and was focused on research and delivery of innovative solutions to reduce disease losses in tree crops in horticulture and forestry.
Researcher profile: qaafi.uq.edu.au/profile/357/andre-drenth
Phone: 07 3443 2460
Email: a.drenth@uq.edu.au
Last updated: 23 July 2021
Professor André Drenth. Image: The University of Queensland.
Professor André Drenth. Image: The University of Queensland.
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