University of California, Riverside

Citrus greening, also called Huanglongbing (HLB), is probably the most devastating citrus disease threatening the global citrus industry. To prevent its further spread, early diagnosis before the appearance of the dreaded symptoms is particularly important.

Yet the nature of the bacteria, its low concentration, and uneven distribution in hosts make it extremely difficult to detect an HLB infection.

Hailing Jin, associate professor of plant pathology and microbiologyat the University of California, Riverside, recently published a paperin the journal Molecular Plant. She reports profiling small ribonucleic acid (sRNA) from citrus plants; some affected by HLB.

Jin’s research showed that several sRNAs were induced specifically by HLB, meaning they could potentially be developed into early diagnosis markers for the disease.

Want access to the very latest in agriculture news each day? Sign up for the Western Farm Press Daily e-mail newsletter.

The study also showed that in a three-year field trial in southwest Florida that diseased trees suffered from severe phosphorus deficiency. The application of phosphorus solutions to the diseased trees significantly alleviated HLB symptoms and improved fruit yield.

In the trial, 19 healthy sweet orange trees were grafted with HLB-positive bark or leaf pieces. As controls, five trees were mock inoculated with pathogen-free healthy tissue. Phosphorus solutions were applied to the 19 HLB-positive trees three times a year.

After two years of treatment, the diseased trees displayed significantly reduced HLB symptoms.

 “Compared with the mock-treated plants, the phosphorus-treated trees had a greener appearance and more vigorous growth,” Jin said. “Fruit yield increased approximately two-fold compared with the mock-treated plants.”

Jin cautioned that phosphorus solutions did not cure the trees. Her research suggests, however, that additional phosphorus application may help diseased trees look healthier and improve fruit yield.

Jin was joined in the research by Hongwei Zhao, Ruobai Sun, Chellappan Padmanabhan, Airong Wang, Michael D. Coffey, Thomas Girke, Timothy J. Close, Mikeal Roose and Georgios Vidalakis at UC Riverside; and researchers at Nanjing Agricultural University, China; USDA; Fujian Agriculture and Forestry University, China; and the University of Florida.

The research was supported by a grant from the California Citrus Research Board.

Other worthwhile reads from Western Farm Press:

What's the real story behind neonicotinoids and honey bee deaths?

California ‘killer bees’ not only in Hollywood

Dairy farmer blends Black Cow vodka from milk