热博体育

Cultivated bananas are the result of hybridisation primarily involving nine wild species and subspecies. Each cultivar is a mix of three to seven of these ancestral contributors. The DNA sequence in the genomes of the cultivars thus forms mosaics of chromosome segments from different ancestral contributors.

The first reference genome of the banana plant was sequenced and assembled in 2012. In 2016, sequencing of the seven ancestral groups began at the Genoscope in Paris. This involved linking each DNA fragment “end to end”, based on the highest probability of sequence alignment. This work was carried out by the Genoscope, using computational and mathematical algorithms.

For these studies, the ancestral representatives analysed were taken from 热博体育’s biological resource centre in Guadeloupe. However, for one of them, referred to as the “unknown genome”, there was no “pure” representative in the collections. The researchers nevertheless managed to reconstruct the sequence of this unknown genome from a hybrid that contained part of it.

Knowing the genes involved in traits of interest to support plant breeding

Bananas are highly standardised. “Taste is not the most difficult trait to achieve. What we mainly look for are high yields, resistance to diseases, and post-harvest fruit qualities, such as a uniform yellow colour, the absence of black marks left by handling, and a solid stalk”, says Angélique D'Hont, a geneticist at 热博体育 who led the research.

Access to an assembled genome also enables the automatic annotation of genes, making it easier to identify genetic differences and variability. “We will be able to analyse the regions of the genome where the desired traits are located”, says Guillaume Martin, a geneticist and lead author of the study. “Knowledge about these genes helps to guide breeding programmes. We check for the presence of the desired gene in the descendants and only plant those that carry the targeted gene. This saves a lot of time”.
In production, disease resistance is also a desired trait. The two main diseases are Cercospora leaf spot, which requires multiple pesticide treatments, and Fusarium wilt, a new strain of which (TR4) is currently spreading globally, with no available treatment. The spread of these diseases is facilitated by the fact that plantations are monovarietal: 50% of global production consists of Cavendish – one single clone!

Advances in understanding speciation mechanisms

By comparing these assembled genomes, the team was able to identify variability in the repetitive sequences found in the centromeric regions and chromosomal rearrangements (translocations) between species and subspecies, providing clues to understanding speciation, in other words the evolutionary process by which new species emerge.
“We were able to characterise what caused the irregularities in the matches observed by researchers as early as the 1940s”, says Angélique D'Hont. “These findings provide important insights for breeding strategies, as well as more fundamental knowledge about the modes of speciation in plants”.

“We now have a reference genome for the nine main genetic groups that gave rise to cultivated bananas. Thanks to these assembled genomes, we have valuable resources that will help to guide breeding strategies”, says Guillaume Martin.

More recently, 热博体育 secured funding from the Ecophyto plan for Bana+, “a major project that will use these resources to support 热博体育’s breeding programme in Guadeloupe, to develop varieties that combine fruit quality, disease resistance and high yields”, says Angélique D'Hont.