Breakthrough on citrus disease unlikely

An organisation that advises the United States federal government on science and technical matters has dire news for the citrus industry.

In a report released Tuesday morning, the National Academies of Sciences, Engineering, and Medicine says a single breakthrough discovery for managing citrus greening in the future is unlikely. Greening has progressed from "an acute to a chronic disease throughout the state" and has caused Florida's industry a cumulative loss of US$2.9 billion in grower revenues from 2007 to 2014.

According to the report, significant barriers to finding a solution still exist.

"Among them, the inability to culture the bacteria in the laboratory, the lack of advanced diagnostics for early disease detection, and the absence of standardised research metho-dology that would improve the comparability of results across studies," the report says.

Greening is spread by a tiny invasive bug called the Asian citrus psyllid, which carries bacteria that are left behind when the psyllid feeds on a citrus tree's leaves.

Andrew Meadows is spokes-man for Florida Citrus Mutual, the marketing and lobbying arm for the state's citrus growers. He called the report frustrating, but he wasn't particularly surprised by the findings.

"We would love to have a silver bullet," he said. "But you have to adapt to what you have."

Meadows said that before Hurricane Irma in 2017, citrus growers had found ways to work around the disease, at least temporarily, and were expecting a rebound year. But the hurricane devastated the crop. Initial estimates pegged the year's crop yield at the lowest since 1942.

Florida typically grows the most oranges in the US, and most are used for juice. In the 2016-2017 growing year, the value of the crop was US$800 million.

Growers have been using a variety of stopgap measures to work around the disease, Meadows said. Nutritional supplements for the trees, psyllid control, and water quality are among the temporary solutions, as is planting with greening-tolerant rootstocks.

The psyllid isn't native to Florida but is believed to have arrived from someone who, perhaps unknowingly, brought a slip of a tree from Asia. The bug was first spotted in the state in 1998, and some think it then spread during hurricanes and storms. Greening was first spotted in 2005. There isn't a cure, and no country has ever successfully eradicated it.

Greening slowly kills a citrus tree. The infection reveals itself first with mottling of leaves, then stunting of shoots, gradual death of branches and eventually, small, deformed fruits with bitter juice.

The Citrus Research and Development Foundation, a US$124-million state citrus-industry initiative, asked the Academies to review its research, and that's how the report came about.

The National Academies are private non-profit institutions that were chartered to provide analysis and advice to the nation on science, technology and health.

- AP