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American and Chinese researchers have found that citrus trees attacked by the Huanglongbing disease (HLB) are suffering from severe phosphorus deficiency. Application of phosphorus solutions to the diseased trees significantly alleviates HLB symptoms and thus improves fruit yield in a three-year field trial in southwest Florida. Phosphorus solutions were applied to HLB-positive sweet orange trees in a field trial three times per year for more than three years. After two years of treatment, the diseased trees displayed significantly reduced HLB symptoms. Fruit yield increased approximately two-fold compared with control plants. The researchers say that application of phosphorus solutions did not cure the trees, but this treatment may help the diseased trees to look healthier and improve fruit yield.

The citrus disease Huanglongbing, meaning "yellow shoot disease" in Chinese and also called citrus greening in English-speaking countries, is the most destructive disease threatening the citrus industry worldwide. Powerful diagnostic tools and management strategies are desired to control it. A new study, published online in the journal Molecular Plant, profiled small Ribonucleic Acids (sRNAs) from both diseased and healthy plants and found that some of these tiny molecules could potentially be developed into early diagnosis markers for HLB. More importantly, the study demonstrates that the diseased trees suffered from severe phosphorus.

In particular, miR399, which is induced by phosphorus starvation in other plant species, was discovered to be induced by HLB infection in the diseased citrus trees. It is known that miR399 is important for phosphorus translocation in plants by suppressing a phosphorus signalling pathway gene. The study found that the phosphorus level in leaves of HLB-positive plants was on about 65% of that in healthy plants, suggesting that HLB is associated with phosphorus starvation in the citrus plants, which may in turn contribute to the expression of HLB symptoms.
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Source: Oxford University Press
    20-02-2013 09:45