This native lime’s genome could be key to stopping a damaging citrus disease

A native, bumpy-looking lime has had its moment in the spotlight this week, after an Australian research team created a comprehensive genomic map of the fruit.

This is particularly exciting, as the fruit (Citrus australis) is resistant to a devastating citrus disease called Huanlongbing (HLB), meaning that these genes could hold the key to making genetically modified citrus resistant to the disease.

“People have been trying to control this disease using chemicals and other methods but there’s been no permanent solution,” says first author on the new paper, University of Queensland plant geneticist Upuli Nakandala.

“One option available is to develop resistant cultivars, and the first step towards that is identifying these important resistant genes in Australian citrus.”

The citrus, known as the Australian round lime, Dooja, Gympie Lime or Native lime, is the first of six native lime species to be genetically sequenced by the team.

HLB is a disease caused by the bacterial genus Liberibacter, which stops citrus from ripening and generally causes trees to decline. Currently, the disease has been reported in all citrus-growing regions in Asia except Japan, as well as Brazil, Florida and Mexico. 

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Huanglongbing causes colour inversion on oranges in Texas. Credit: USDA photo by David Bartels

There’s currently no cure, but some of Australia’s native limes are resistant, meaning their genes could be used to create immunity in other citrus. 

“Recently, a novel class of small antimicrobial peptides (SAMPs) were isolated from C. australasica and other close relatives which can suppress the growth of HLB causing bacteria and promote host immunity in citrus,” the team write in their new paper.  

“However, SAMPs have not yet been identified in C. australis or other Australian wild limes which are resistant to HLB.”

There’s still a long way to go before the Australian round lime could be used for stopping HLB, but genome sequencing – particularly the chromosome level sequencing that the research team did – is an important first step.

“Sequencing the genomes of plants, particularly these tree crops will give us a new platform for genetic improvements and better management of their production into the future,” said Professor Robert Henry.

“We have the climate and the crops here that put us in a great position to make an important contribution to international efforts to solve this devastating disease problem.”

The research has been published in Horticulture Research.

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