Citrus scion/rootstock combinations show tolerance to huanglongbing

March 28, 2016
'Hamlin/Kinkoji' (left) and 'Sugar Belle/Sour Orange' (right), two of the citrus trees in the study. 'Sugar Belle/Sour Orange' showed the greatest growth rates and canopy volume among the trees studied. Credit: Photo courtesy of Ed Stover.

The citrus disease huanglongbing (HLB) is endemic in Florida, where it is estimated that more than 80% of citrus trees are currently infected. Largely as a result of this devastating disease, Florida citrus production in 2014-15 was the lowest recorded in the past 50 years. Sweet orange and grapefruit, which account for more than 95% of Florida citrus production, appear to be especially compromised by HLB. Understandably, there is an urgent need to identify citrus varieties that can resist the widespread disease. A new study in HortScience identified some scion/rootstock combinations that show potentially valuable tolerance to huanglongbing.

Ed Stover, Sharon Inch, Matthew Richardson and David Hall from the USDA Agricultural Research Service said that, although there are no commercial varieties with strong HLB resistance, some field tolerance has been seen in that were exposed to the disease after they reached maturity. To learn more, the researchers studied tolerance to HLB under field conditions for newly planted trees of scion/rootstock combinations. The trial included 20 trees each of 'Hamlin/Kinkoji', 'Hamlin/Cleopatra', 'Temple/Cleopatra', 'Fallglo/Kinkoji' and 'RubyRed/Kinkoji' with 10 imidacloprid-treated and 10 nontreated trees of each scion/rootstock. An additional 10 trees each of 'Sugar Belle/Sour Orange' and 'Tango/Kuharske' were included, all receiving imidacloprid. Trees were planted at the U.S. Department of Agriculture research farm in Fort Pierce, Florida, and were analyzed over 5 years.

All of the trees had symptoms of HLB and tested positive for the Candidatus Liberibacter asiaticus (CLas) bacterium by 20 months after planting. Despite becoming infected by CLas, the trees continued to grow and all scion/rootstocks displayed increasing fruit production (although production was "very low" in 'Hamlin/Kinkoji', 'Hamlin/Cleopatra' and 'Ruby Red/Kinkoji'). "It is noteworthy that the most pronounced HLB symptoms and higher early pathogen titer, which are the two criteria most widely used in assessing HLB resistance, were not associated with the greatest suppression of growth and cropping, and focus on early symptomatic traits may obscure important disease tolerance," the authors said.

'Sugar Belle/Sour Orange', 'Tango/Kuharske' and 'Temple/Cleopatra' exhibited the greatest growth rates and canopy volumes, while the slowest growth rates and canopy volumes were seen in 'Ruby Red/Kinkoji'. Although it had the greatest rate of growth, 'Sugar Belle/Sour Orange' had the highest percentage of leaves showing mottle.

"It remains to be seen whether the HLB tolerance in some scion/rootstock combinations permit reasonable production of fruit of commercial quality," the authors said, "but it is promising that several mandarin hybrid/rootstock combinations displayed markedly greater growth and cropping compared with sweet orange/rootstock and grapefruit/rootstock combinations under very high HLB pressure."

Explore further: Fighting back against citrus greening

More information: HortScience,

Related Stories

Fighting back against citrus greening

January 25, 2013

U.S. Department of Agriculture (USDA) scientists in Fort Pierce, Fla. are helping citrus growers and juice processors address the threat posed by Huanglongbing (HLB), a disease that is costing the citrus industry millions ...

Phloem production in Huanglongbing-affected citrus trees

March 26, 2014

Citrus Huanglongbing (citrus greening disease) is highly destructive and fast-spreading, contributing to a reduction in crop yields in Florida and threatening the future of the citrus industry worldwide. Once infected, trees ...

UF creates trees with enhanced resistance to greening

November 23, 2015

After a decade of battling the highly destructive citrus greening bacterium, researchers with the University of Florida's Institute of Food and Agricultural Sciences have developed genetically modified citrus trees that show ...

Recommended for you

Blueprint for shape in ancient land plants

December 9, 2016

Scientists from the Universities of Bristol and Cambridge have unlocked the secrets of shape in the most ancient of land plants using time-lapse imaging, growth analysis and computer modelling.

Protein disrupts infectious biofilms

December 8, 2016

Many infectious pathogens are difficult to treat because they develop into biofilms, layers of metabolically active but slowly growing bacteria embedded in a protective layer of slime, which are inherently more resistant ...

An anti-CRISPR for gene editing

December 8, 2016

Researchers have discovered a way to program cells to inhibit CRISPR-Cas9 activity. "Anti-CRISPR" proteins had previously been isolated from viruses that infect bacteria, but now University of Toronto and University of Massachusetts ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.