Study links citrus greening symptoms to phosphorus deficiency

02/27/2013 10:47:00 AM
Vicky Boyd

citrus greening symptomsCourtesy University of California, RiversideCitrus greening symptoms include yellow, blotchy leaves.A collaborative research project has found phosphorus deficiency to be a contributor to citrus greening disease symptoms, according to a recently published study.

Hailing Jin, a University of California, Riverside, plant pathologist, led the study that looked at small bits of genetic material known as ribonucleaic acids, or sRNAs, from both diseased plants and healthy plants, according to the article abstract.

Also involved were scientists from UC Riverside, the U.S. Department of Agriculture, the University of Florida and China.

The researchers found the tiny molecules, which regulate plant responses to microbial infections, could potentially be developed into molecular markers to diagnosis infected tree.

The laboratory trial involved grafting citrus trees with either plant material infected with citrus greening bacterium or healthy material.

Samples were collected 10 and 14 weeks afterward and examined for sRNAs.

After using genetic fingerprinting, the researchers identified several new RNAs associated only with huanglongbing or HLB.

The markers potentially could identify disease trees before symptoms appeared, allowing growers to start early nutritional treatments.

More importantly, they found that diseased trees suffered from severe phosphorus deficiency.

The study found that phosphorus levels in leaves of greening-infected plants were about 65 percent of that of healthy trees.

By applying phosphorus, growers could potentially eliminate greening symptoms and improve fruit yield, based on a three-year field trial led by UF citrus horticulturist Bob Rouse in southwest Florida.

After two years of treatment, the diseased trees displayed significantly fewer greening symptoms.

The study was quick to point out that phosphorus applications did not cure the trees but did improve the symptoms and fruit yield.

Symptoms of greening, also called huanglongbing or HLB, include blotchy mottled leaves, yellow or stunted vegetative growth, premature fruit drop, and in some cases, off-flavored fruit.

The bacterial disease, which is harmless to humans, is spread by the Asian citrus psyllid.

The research was published Feb. 19 in the journal Molecular Plant.



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Dr. Richard Lasker    
Seattle  |  February, 28, 2013 at 12:41 PM

Our research shows the bacteria is actively transmitted to healthy trees regardless of any nutrient level. Excessive Nitrogen made the bacteria spread faster but overall symptoms were the same. The lowered P level in infected trees is a secondary affect of the disease, like a rash in humans. I am not sure the point of the title whereas the information in the article was entirely a different story, about the markers.

Dr Lawrence J Marais    
Visalia, CA 93292  |  March, 08, 2013 at 02:44 PM

I agree with Dr Lasker. Several other deficiency symptoms related to citrus greening disease are zinc and manganese. These symptoms are secondary effects of the disease. The detection and identification of PRP (pathogenisis related proteins) such as in citrus blight affected trees, may serve as a a pre-diagnsotic tool.

Paul    
Central Florida  |  March, 20, 2013 at 09:13 AM

I have been consulting with citrus growers for several years. We found that by adding Potassium silicate to our spray program with good foliar calcium, magnesium and Boron were able to help revitalize trees that were infected and helped younger trees stay clean. Insecticides were not being used due to organic crop. I am not saying we have cured any tree but we are managing the damage and protecting younger trees. This has been an on going test for over three years with promising results. This disease can make you think you have control and some other stress hit the tree and the damage can be back before you can blink. I personally think it is a result of to much fertilizer applications and soil microbial life destroyed leading to stressed trees that were left unprotected. This is now an issue of revitalizing soil and rejuvenating trees with intense management of fertilizers. Until we get trees, and soil healthy and continue to maintain health we will continue to see repeated episodes of new diseases outbreaks.

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