The devastating disease Huonglongbing, or citrus greening, looms darkly over the United States, threatening to wipe out the nation’s citrus industry, whose fresh fruit alone was valued at more than $3.4 billion in 2012.
Recently, however, a research team led by a University of California, Davis, plant scientist used DNA sequencing technologies to paint a broad picture of how citrus greening impacts trees before they even show signs of infection, offering hope for developing diagnostic tests and treatments for the currently incurable disease.
“Florida is seemingly in the death grip of citrus greening, and many experts believe it is just a matter of time before the disease appears full force in California,” said plant molecular biologist Abhaya Dandekar, lead author on the study.
The new findings indicate that the bacterial disease interferes with starch and sugar metabolism in young and mature leaves and fruit, while also wreaking havoc with hormonal networks that are key to the trees’ ability to fend off infections. Study results will be reported Sept. 25 in the journal PLOS ONE.
“Because the disease has a long latent phase during which there are no symptoms of infection and the bacteria are resistant to being grown in the laboratory, the only option for halting transmission of citrus greening has been to apply chemical pesticides to control the insect that spreads the bacteria,” Dandekar said.
About citrus greening
HLB, or citrus greening, is the most destructive citrus disease worldwide. It is caused by three species of the Candidatus Liberibacter bacteria, including Candidatus Liberibacter asiaticus, which is known by the abbreviation CaLas. These bacteria are carried from tree to tree by two species of the citrus psyllid, a winged insect that is about one-eighth of an inch long and attaches itself to the underside of the trees’ leaves.
As the citrus psyllid feeds on a leaf, it can pick up the bacteria from a diseased tree and introduce the bacteria to a non-infected tree. These disease-causing bacteria reside in the tree’s phloem — the vascular tissue that carries vital nutrients throughout the tree.
The disease affects most citrus species, causing yellowing of shoots, blotchy and mottled leaves, lopsided and poorly colored fruit and loss of viable seeds. The fruit of diseased trees is hard, misshapen and bitter, and the infected trees die within a few years.
Other than one infected backyard tree found in 2012 in the Southern California community of Hacienda Heights, the disease has not been detected in California. However the citrus psyllid that transmits the bacteria was first found in California in 2008 and has since been identified in San Diego, Imperial, Riverside, San Bernardino, Orange, Los Angeles, Ventura, Santa Barbara, Kern and Tulare counties, resulting in quarantines and restricted areas.
The new study
In this new study, the researchers studied four categories of healthy and diseased citrus trees, with the goal of better understanding how HLB affects trees physiologically during the very early stages of infection.
“Earlier sequencing of the CaLas bacteria genome showed that there were no toxins or enzymes that would destroy plant cell walls, or specialized secretion systems associated with citrus HLB,” Dandekar said.
“Because these factors, which normally accompany plant diseases, were not present, we suspected that the disease was causing metabolic imbalances or interfering with nutrient transport in the infected trees,” he said.
The researchers used gene sequencing technology to study the “transcriptome,” which is the collection of RNA found in the tree leaves and fruit.
Their analysis confirmed that in infected trees, HLB disease caused starch to accumulate in the leaves, blocking nutrient transport through the phloem and decreasing photosynthesis. They also found that normal metabolism of sucrose, a sugar also key to photosynthesis, was disrupted.
Furthermore, the researchers discovered that HLB interfered with the regulation of hormones such as salicylic acid, jasmonic acid and ethylene, which are “the backbone” of the plant innate immune response. And they found that infected trees also had changes in the metabolism of important amino acids that serve as a reservoir for organic nitrogen in many plants. The nitrogen is required to stimulate the plant immune response.
Cause for hope
The researchers anticipate that these discoveries will lead the way to new tests for detecting the bacteria and thus the presence of HLB in orchard trees.
They also suggest that it may be possible to develop several short-term treatments for infected trees. Such therapeutic procedures might rely on using hormones and other small molecules to restore the infected tree’s normal metabolism or boosting the tree’s innate immune response to effectively fight the infection.
The Latest Bing News on:
Citrus greening
- Florida citrus sector urges signing of greening research fundson April 26, 2024 at 1:06 pm
During the 2024 legislative session, the Florida Legislature approved a budget that would provide the citrus industry with $47 million to support the state's signature crop.
- Asian citrus psyllid spreading devastating disease to citrus treeson April 22, 2024 at 5:19 pm
The Asian citrus psyllid is a sap-sucking bug that can spread a devastating disease to citrus trees. If the Asian citrus psyllid were to get on a healthy citrus tree, it could kill it in no time.
- Miracle cure or wishful thinking? Proposed treatment for citrus greening gets mixed reviews from growerson April 20, 2024 at 5:59 am
Research using oak leaves on citrus trees to combat citrus greening has been fruitful so far. Some growers say it’s been a lifesaver, but others say it’s not enough.
- Miracle cure or wishful thinking? Proposed treatment for citrus greening gets mixed reviews from growerson April 17, 2024 at 3:39 am
Research using oak leaves on citrus trees to combat citrus greening has been fruitful so far. Some growers say it’s been a lifesaver, but others say it’s not enough. When Ben Bateman first ...
- Florida's citrus industry slated for another rough yearon April 12, 2024 at 5:08 am
The industry has struggled for years with deadly citrus-greening disease and was dealt another blow when Ian made landfall in September 2022 in Southwest Florida and barreled through major citrus ...
- Florida’s citrus forecast turns sour as growing season come to a closeon April 11, 2024 at 6:36 pm
Florida’s citrus industry got some bitter news Thursday as it enters the final months of the 2023-2024 growing season.
- Florida citrus forecast takes a hiton April 11, 2024 at 5:00 pm
The industry has struggled for years with deadly citrus-greening disease and was dealt another blow when Ian made landfall in September 2022 in Southwest Florida and barreled through major citrus ...
- Expert tells Rancho Bernardo gardeners how to protect citrus trees from deadly diseaseon April 3, 2024 at 2:25 pm
Ross said Huanglongbing — HLB for short, also known as citrus greening disease — has been in other parts of the world, but is relatively new to California. Spread by the Asian citrus psyllid ...
- Florida growers eye agroecology solution to devastating citrus diseaseon April 2, 2024 at 4:59 pm
Virtually all of Florida’s citrus groves have been infected with citrus greening disease, also known by its Chinese name Huanglongbing, since the early 2000s. Despite billions of US dollars put ...
- A New Technology Is Helping To Save The Florida Citrus Industry With A ‘Shot In The Arm’on September 29, 2023 at 6:59 am
According to Invaio’s Founding CEO, Ignacio Martinez, “Invaio’s Trecise™ technology offers a real breakthrough in the fight against citrus greening and is the first of many treatments we ...
The Latest Google Headlines on:
Citrus greening
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Huonglongbing
- Asian citrus psyllid spreading devastating disease to citrus treeson April 22, 2024 at 11:01 am
The Asian citrus psyllid is a sap-sucking bug that can spread a devastating disease to citrus trees. If the Asian citrus psyllid were to get on a healthy citrus tree, it could kill it in no time.
- Miracle cure or wishful thinking? Proposed treatment for citrus greening gets mixed reviews from growerson April 20, 2024 at 5:59 am
Research using oak leaves on citrus trees to combat citrus greening has been fruitful so far. Some growers say it’s been a lifesaver, but others say it’s not enough.
- Farmland values increase at slower rate with tighter profitson April 19, 2024 at 11:00 pm
Farmers could see a leveling off in farmland values and cash rents — and even declines in coming years — if farm profit margins remain tight or negative.
- Discovery speeds orange pushon April 18, 2024 at 6:00 pm
It’s one thing for a hybrid citrus tree to tolerate citrus greening disease -- Huanglongbing -- and quite another if it also produces orange-like fruit, especially if the juice makes ...
- Advancing citrus cultivation: The superior tolerance and growth vigor of 'Shuzhen No.1' rootstockon April 16, 2024 at 10:31 am
Citrus is the world's most economically significant fruit crop, but it faces various environmental adversities that restrict its distribution. Grafting is a crucial factor in enhancing citrus ...
- New California Citrus Breeding Program on the Grow With Fundingon April 12, 2024 at 8:16 am
The California citrus breeding program will focus on fresh market citrus. Funding will go toward research and development of high-quality, superior citrus selections well suited to California growing ...
- Expert tells Rancho Bernardo gardeners how to protect citrus trees from deadly diseaseon April 3, 2024 at 2:25 pm
Ross said Huanglongbing — HLB for short, also known as citrus greening disease — has been in other parts of the world, but is relatively new to California. Spread by the Asian citrus psyllid ...
- HLB Grower Web Toolon November 22, 2023 at 1:49 pm
Enter details for your grove below. The default values shown in the enter boxes are based on a recent University of California Cost and Returns Study. Change them to fit your operation. Then select ...
- The Citrus Family Treeon June 1, 2023 at 11:29 am
A bacterial disease called huanglongbing (a.k.a. citrus greening) that causes plants to defoliate, decay, and eventually die, is threatening commercial production on every arable continent ...
- How Huanglongbing Affects Oranges' Detachment Force, Fruit Properties (IMAGE)on August 1, 2021 at 2:41 pm
Photo shows an HLB symptomatic sweet orange tree. A study found that HLB symptomatic orange trees are more likely to have problems with preharvest fruit drop than asymptomatic trees. Disclaimer ...
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