Sunday, April 20, 2014
YOLO COUNTY NEWS
99 CENTS

Nutritionist finds clues to saving citrus from dreaded disease

UC Davis nutrition expert Carolyn Slupsky shows off a lemon tree as she explains research done by her team to find effective ways to treat and prevent the spread of citrus greening disease, also known as huanglongbing or HLB. Some Florida producers are masking the bitter taste of HLB-infected fruit in orange juice by giving consumers what is essentially sugar water. Courtesy photo

By Diane Nelson

A nutrition expert at UC Davis has discovered important clues to the deadly attack strategy of a puzzling plant pathogen that has destroyed hundreds of thousands acres of citrus across the world.

The novel research by Carolyn Slupsky, associate professor and nutritionist with the UCD department of food science and technology and Agricultural Experiment Station, and her team may pave the way for safe, effective ways to treat and prevent the spread of citrus greening disease, also known as huanglongbing or HLB.

“HLB is not just bad for growers and for the economy,” Slupsky said. “The loss of fresh oranges and other citrus could seriously impact our health.”

HLB is a disease caused by a microbe called Candidatus Liberibacter asiaticus and spread by the Asian citrus psyllid, a tiny insect that feeds on the leaves and stems of citrus trees. There is no cure yet for HLB, so once a tree is infected, it will slowly die. The disease has decimated citrus groves in Asia, Brazil and the Dominican Republic. Florida has lost one-third of its citrus to the disease. Both HLB and the Asian citrus psyllid have recently been spotted in California.

HLB is a silent killer — an infected tree can live for years without symptoms, allowing the pathogen to spread undetected to other trees. Symptoms emerge over time, as a tree’s fruit starts to turn green and misshapen, with a bitter, metallic taste.

Is there a way to spot HLB before visual symptoms occur? The microbe that causes HLB can sometimes be found in a leaf sample, but since the pathogen isn’t evenly distributed throughout the tree, results can be misleading.

“Just because the pathogen doesn’t show up in one leaf, that doesn’t guarantee the tree isn’t infected,” said MaryLou Polek, vice president of science and technology for the California Citrus Research Board. “So when you sample a leaf, there’s a high probability of a false negative result.”

Slupsky and Andrew Breksa, a research chemist with the USDA Agricultural Research Service based in Albany, tried a different tack, searching for clues in a tree’s chemical fingerprint. They used nuclear magnetic resonance spectroscopy to study the amino acid composition of juice from three types of citrus: fruit from healthy tress, symptom-free (asymptomatic) fruit from HLB-positive trees, and fruit with symptoms from HLB-positive trees.

“We found major differences in the chemical fingerprint among healthy, asymptomatic and symptomatic fruits,” Slupsky said.

With further research, the profiles may prove to be a reliable, rapid, and early indicator of the presence of the HLB pathogen. With early detection, growers and regulators can know which trees might need to be removed before the disease spreads throughout the orchard (and beyond).

“These findings are huge for citrus growers, backyard gardeners and everyone who loves fresh citrus,” Polek said.

And there’s more. While analyzing the amino acids, Slupsky and Breksa discovered what looks like a mechanism underlying the microbe’s mode of attack.

“The pathogen responsible for HLB seems to cause havoc with a tree’s ability to defend itself from infection,” Slupsky said.

Trees need amino acids for growth, development and defense. From Slupsky and Breksa’s studies, it looks like the HLB pathogen affects the trees’ ability to create, use and recycle some of those amino acids. For example, a tree can convert the amino acid phenylalanine into cinnamic acid, a precursor to compounds important to the tree’s defense systems. But juice from oranges of HLB-positive trees had significantly higher concentrations of phenylalanine.

Also, juice from oranges grown on HLB-infected trees contained a lot less of the amino acid proline, which a tree usually synthesizes when it knows something is wrong.

“It could be that the pathogen is outsmarting the tree by undermining its defenses,” Slupsky said. “That’s a spectacular discovery, because when we understand the mechanisms behind the attack, we have a chance at blocking them. Maybe we can find ways to enhance a tree’s natural immunity.”

As tough as HLB has been on citrus in Florida, the stakes are even higher in California where so much of the world’s fresh citrus is produced.

“Florida’s citrus industry produces mostly orange juice, and they can use additives and filtration to adjust for the bitter taste of HLB-affected fruit,” Polek said. “It can be reduced to sugar water, essentially, and then built back up to taste like orange juice. We produce fresh citrus here in California, and chemistry is not an option.”

Losing fresh citrus is a real possibility if HLB spreads throughout California, and that prospect is the driving force behind Slupsky’s research.

“From a nutritional standpoint, it’s hard to beat the importance of fresh citrus,” Slupsky said. “Oranges provide energy, pectin, and a wide variety of nutrients, vitamins and minerals. They’re one of the most consumed fruits in the United States. I can’t imagine life without fresh citrus.”

Slupsky and Breksa collaborated with Thomas G. McCollum of the ARS Horticultural Research Laboratory in Fort Pierce, Florida, along with Anne Slisz and Darya Mishchuk of Slupsky’s lab. A peer-reviewed article on their findings was published in the Journal of Proteome Research in June 2012.

— UC Davis College of Agricultural and Environmental Sciences

Special to The Enterprise

LEAVE A COMMENT

Discussion | No comments

The Davis Enterprise does not necessarily condone the comments here, nor does it review every post. Read our full policy

  • Recent Posts

  • Enter your email address to subscribe to this newspaper and receive notifications of new articles by email.

  • .

    News

    A springtime ritual

    By Wayne Tilcock | From Page: A1 | Gallery

     
    Tom Adams seeks Davis school board seat

    By Jeff Hudson | From Page: A1

     
    Hub of activity: DHS newspaper keeps evolving

    By Zoe Juanitas | From Page: A1 | Gallery

    Holy fire ceremony draws thousands in Jerusalem

    By The Associated Press | From Page: A2 | Gallery

     
    Tour renovated YCCC facility Thursday

    By Enterprise staff | From Page: A3

     
    Tour Davis Waldorf School on Wednesday

    By Enterprise staff | From Page: A3

    The fifth annual Tour de Cluck is soon to be hatched

    By Special to The Enterprise | From Page: A3 | Gallery

     
    Ortiz lawn signs available

    By Enterprise staff | From Page: A3

    Sign up soon for spring cooking classes

    By Enterprise staff | From Page: A3

     
    Robb Davis team to rally on Saturday

    By Enterprise staff | From Page: A3

    Steadfast in their support

    By Lauren Keene | From Page: A4, 7 Comments | Gallery

     
    Yolo Hospice offers free grief workshops

    By Enterprise staff | From Page: A4

    Sign up for Camp Kesem caterpillar crawl

    By Enterprise staff | From Page: A4

     
    Quilters gear up for annual show

    By Sebastian Onate | From Page: A4

    KDVS launches fund drive on Monday

    By Jeff Hudson | From Page: A5

     
    Calling all Scrabble fans

    By Enterprise staff | From Page: A5, 1 Comment | Gallery

    League hosts a series of candidate forums

    By Enterprise staff | From Page: A5

     
    Hub webpage is seeing traffic increasing

    By Zoe Juanitas | From Page: A8

    Preschool open house set at Davis Waldorf

    By Enterprise staff | From Page: A16

     
    Birch Lane celebrates its 50th anniversary

    By Enterprise staff | From Page: A16

    Hotel/conference center info meeting set

    By Enterprise staff | From Page: A16

     
    Lescroart welcomes all to book-launch party

    By Special to The Enterprise | From Page: A16 | Gallery

    DEVO set to serve up 14th annual Winkler Dinner

    By Enterprise staff | From Page: A16 | Gallery

     
    Learn Chinese crafts at I-House

    By Sebastian Onate | From Page: A16

    .

    Forum

    Take ownership of your health

    By Special to The Enterprise | From Page: B5

     
    Not thrilled with lack of symmetry

    By Special to The Enterprise | From Page: A7

    Reliving the agony and ecstasy of spring

    By Marion Franck | From Page: A7

     
    Keep your baby safe

    By Special to The Enterprise | From Page: A7

     
    Core values on campus

    By Our View | From Page: A12, 1 Comment

    Road diet? No, city diet!

    By Letters to the Editor | From Page: A12, 5 Comments

     
    We’re reveling in our equality

    By Letters to the Editor | From Page: A12, 1 Comment

    Vote no; it’s fiscally responsible

    By Letters to the Editor | From Page: A12, 2 Comments

     
    Rick McKee cartoon

    By Debbie Davis | From Page: A12

     
    Bill is an affront to UC Davis ag biotech and local farmers

    By Special to The Enterprise | From Page: A13, 1 Comment

    Don’t want to sit in Fix 50 traffic? Consider alternatives

    By Special to The Enterprise | From Page: A13, 1 Comment

     
    .

    Sports

    Devils burn up the track

    By Enterprise staff | From Page: B1

     
    UCD softball shut out by Santa Barbara

    By Thomas Oide | From Page: B1 | Gallery

     
    Aggie men shoot 9-under, lead own tourney

    By Bruce Gallaudet | From Page: B1 | Gallery

    Stars shine in Woody Wilson Classic

    By Evan Ream | From Page: B1, 1 Comment | Gallery

     
    UCD roundup: Aggie baseball swept away by Highlanders

    By Enterprise staff | From Page: B2

    A’s score 3 in ninth, rally past Astros 4-3

    By The Associated Press | From Page: B6

     
    .

    Features

    .

    Arts

    .

    Business

    Yolo Federal Credit Union gets WISH funds

    By Enterprise staff | From Page: A9

     
    PG&E pays taxes, fees to county, cities

    By Enterprise staff | From Page: A9, 1 Comment

    Will Davis get an Old Soul?

    By Wendy Weitzel | From Page: A9

     
    Pediatricians, nurse practitioner hired at Woodland Healthcare

    By Enterprise staff | From Page: A9 | Gallery

    Asian stocks mostly higher after mixed U.S. earnings

    By The Associated Press | From Page: A9

     
    Davis Roots will showcase its graduating startups

    By Enterprise staff | From Page: A14

    University Honda wins another President’s Award

    By Enterprise staff | From Page: A14 | Gallery

     
    Dutch Bros. raises $19,000 for girl with leukemia

    By Enterprise staff | From Page: A14 | Gallery

    .

    Obituaries

    .

    Comics

    Comics: Sunday, April 20, 2014

    By Creator | From Page: B8