SINGAPORE – The Robusta bean often used to brew cheaper cups of coffee – like the traditional Nanyang kopi – can save the more premium Arabica from a fungal disease. 

For generations, Arabica plants, from which about 60 per cent of all coffee is produced, have been ravaged by an incurable fungal disease called coffee leaf rust.

Agriculture institutes in coffee-producing regions have been using selective breeding to confer the Robusta traits to Arabica plants, after a rust-resistant plant hybrid was found in Timor, Indonesia, in the 1920s.

Now, recent international research co-led by Nanyang Technological University (NTU) could optimise the breeding process. The study involved mapping the genomes of various coffee varieties, and the researchers zeroed in on the specific Robusta genes that are resistant to coffee leaf rust.

“For the Timor hybrid descendants, in every generation the hybrids have been crossed with an Arabica variety, the offspring’s Robusta content gets smaller and smaller,” said Assistant Professor Jarkko Salojarvi from NTU’s School of Biological Sciences, who led the research team.

Through identifying the resistant genes, the researchers found a means to enable more efficient targeted breeding of resistant plants, similar to targeted therapies against human diseases.

The study was done with Nestle and two universities in the United States and France.

When the coffee-hunting fungus attacks Arabica coffee plantations, it leaves brownish-orange spots on the leaves – much like rust on steel.

The Arabica leaves then wither and die off. Leaf loss lowers the amount and quality of coffee berries harvested, leading to great economic losses for farmers in Latin America and other places.

In 2020, the disease spread to Hawaii for the first time, and a 2015 outbreak in the Mexican state of Oaxaca caused a 50 per cent loss in yields.

While farmers have used fungicides as well as pruning and weed management to drive out the pesky fungus, the best way to control it is through the use of resistant cultivars, said Dr Luiz Filipe Pereira, a researcher at the Brazilian Agricultural Research Corporation (Embrapa).

Since the 1970s, the Arabica-Robusta hybrid from Timor and its descendants have been cross-bred with the preferred Arabica plants to create rust-resistant varieties.

While Robusta beans are considered inferior to Arabica beans in terms of flavour, they ar...