Greening is killing citrus trees, but have we found a cure?

Citrus Huanglongbing (HLB), also known as greening, is a serious plant disease, leading to the production of bitter fruits that are green, misshapen and unsuitable to sell. Once infected, there is no cure, with the plant typically dying within a few years.

Greening is a global concern, affecting Florida, California and Texas, as well as Australia and the Mediterranean region. To prevent the spread of HLB, the causal agent (Candidatus Liberibacter asiaticus) must be stopped using quarantine measures, controlling the insect that spreads the disease (Asian citrus psyllid) and removing the diseased trees. The development of greening and its effect on citrus plant leaves is illustrated below.

The appearance of HLB symptoms in 5-month-old cultivar Valencia seedlings fed by Asian citrus psyllid for 2 to 20 days. The HLB symptoms were monitored at 30, 60, and 90 days postinoculation (dpi). Credit: Sheo Shankar Pandey and Nian Wang

Early diagnosis of HLB-diseased trees is crucial. HLB can be diagnosed by observing blotchy mottle symptoms using molecular tools. However, the symptoms do not show until months after the disease has been transmitted, by which time it has likely spread throughout the grove.

Professor Nian Wang and postdoctoral research associate Dr Sheo Shanker Pandey from the University of Florida developed a strategy for early diagnosis of HLB before the appearance of blotchy mottle symptoms. Using a low-cost straining method to identify insect feeding sites, the researchers tested the identified sites for the causal agent using quantitative real-time PCR (polymerase chain reaction).

Through this method, the researchers detected the HLB causal agent two days after transmission. Early detection will enable citrus growers to prevent the spread of HLB in their fields, a crucial finding for regions affected by greening.

Further information about Professor Wang and Dr Shanker Pandey’s study can be found here.

Image credit: ©stock.adobe.com/au/Leonid Tit