Five year programme finds Sub Tropical Race 4 resistance associated with chromosome 5 in wild diploid banana Calcutta 4

Scientists from the University of Queensland (UQ) have pinpointed crucial genetic resistance to Fusarium wilt Sub Tropical Race 4 (STR4) – a fungal disease which threatens the global banana supply – in a wild subspecies of the fruit.  

Professor Elizabeth Aitken and Dr Andrew Chen with tissue culture banana plants grown by crossing Calcutta 4 with a susceptible banana subspecies.

Elizabeth Aitken and Andrew Chen with tissue culture banana plants grown by crossing Calcutta 4 with a susceptible banana subspecies

Image: The University of Queensland

In a valuable step forward for banana breeding programmes, Andrew Chen and Elizabeth Aitken have identified the genomic region that controls resistance STR4 by crossing a wild diploid banana with susceptible bananas from a different subspecies.  

“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,” Chen explained.  

“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. 

“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.” 

Through this process, the researchers were able to map 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,” Chen said.  

The UQ School of Agriculture and Food Sustainability project took five years to complete as 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. 

Chen said the discovery will help develop Fusarium wilt resistant commercial banana varieties. 

“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 said. 

“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.” 

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