French agricultural research and international cooperation organisation CIRAD has completed sequencing the sugarcane genome, unlocking the genetic map of the last major cultivated plant.

The sugarcane genome had so far proved challenging to researchers due its extreme complexity, comprising 10-12 copies of each chromosome, compared with the human genome, which only had two, CIRAD said on 10 July.

The CIRAD team refined its approach based on the 20-year-old discovery of collinearity – or high similarity caused by numerous genes occurring in the same order in both genes – between sugarcane and sorghum.

The parallelism between the two plants allowed the team to use the sorghum genome as a template to assemble and select the sugarcane chromosome fragments to sequence.

“Thanks to this novel method, the reference sequence obtained for a cultivar from Réunion, R570, is very good quality,” said CIRAD geneticist Angélique D’Hont, who coordinated the study.

The reference sequence was a crucial step to fully sequencing the sugarcane genome and to analysing the variations between different sugarcane strains more accurately.

D’Hont, who had the same experience with the banana genome in 2012, said that having a reference sequence for a species “radically changed” all the genomic and genetic approaches for that species.

With its genome now unlocked, CIRAD said it would now be possible to modernise the methods used to breed sugarcane varieties and to bring them to the age of molecular biology.

Until now, sugarcane cultivar breeding programmes had been restricted to hybridisation and extremely slow and laborious field assessments.

With the reference sequence, molecular screening techniques for sugarcane could be developed to supplement field trials, enabling the creation of new varieties for wider applications, said CIRAD.

Sugarcane was the source of nearly 80% of the world’s sugar and had also become a frontrunner in ethanol and biomass production.