Study links citrus greening symptoms to phosphorus deficiency

Vicky Boyd, 02/27/2013

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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