Small Calcutta 4 banana plants being screened for STR4 resistance in a glasshouse. Picture: Dr Elizabeth Aitken
Scientists have pinpointed crucial genetic resistance to a fungal disease which threatens the global banana supply in a wild subspecies of the fruit.
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In a valuable step forward for banana breeding programs, Dr Andrew Chen and Professor Elizabeth Aitken from the University of Queensland have identified the genomic region which controls resistance to Fusarium wilt Sub Tropical Race 4 (STR4).
“Fusarium wilt – also known as Panama disease – is a destructive soil-borne disease which impacts farmed Cavendish bananas worldwide through its virulent Race 4 strains,” Andrew says.
“Identifying and deploying natural resistance from wild bananas is a long-term and sustainable solution to this pathogen that wilts and kills the host plant leaving residue in the soil to infect future crops,” he says.
“We’ve located the source of STR4 resistance in Calcutta 4 which is a highly fertile wild diploid banana by crossing it with susceptible bananas from a different subspecies of the diploid banana group.
A Calcutta 4 fruit showing the seeds that make it ideal breeding stock. Picture: Dr Elizabeth Aitken
“After exposing the new progeny plants to STR4, we examined and compared the DNA of the ones which succumbed to the pathogen and those that didn’t.
Professor Elizabeth Aitken and Dr Andrew Chen with tissue culture banana plants grown by crossing Calcutta 4 with a susceptible banana subspecies.
“We also mapped STR4 resistance to chromosome 5 in Calcutta 4. This is a very significant finding; it is the first genetic dissection of Race 4 resistance from this wild subspecies.”
The complex and challenging School of Agriculture and Food Sustainability project took five years to complete.
Fusarium wilt – also known as Panama disease – is a destructive soil-borne disease which impacts farmed Cavendish bananas worldwide through its virulent Race 4 strains.
Each generation of banana crosses needed to be grown for at least 12 months before it could be challenged, examined and then used for further breeding once it flowered.
The team used a combination of forward genetics (population development and disease screening), genome sequencing and bulked segregant analysis.
Andrew says he discovery will help develop Fusarium wilt resistant commercial banana varieties.
A banana plantation affected by Fusarium wilt in Nanning, China. Picture: Dr Andrew Chen
“While Calcutta 4 provides crucial genetic resistance, it isn’t suitable as a commercial cultivar because it doesn’t produce fruit which are good to eat,” he says.
“The next step is to develop molecular markers to track the resistance trait efficiently so plant breeders can screen seedlings early and accurately before any disease symptoms appear.
“This will speed up selection, reduce costs and hopefully ultimately lead to a banana that is good to eat, easy to farm and naturally protected from Fusarium wilt through its genetics.”
STR4 affects bananas in subtropical regions around the world. It is a genetic variant of Tropical Race 4 (TR4) which is found in Australia.
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