Dispatches from the fight against citrus greening

APHIS expands quarantine areas: In August, USDA’s APHIS announced the expansion of the Asian citrus psyllid (ACP) quarantines in California, Texas, and Louisiana. On Sep. 18, APHIS announced a psyllid quarantine area in Nevada’s Clark County.

The map below shows Asian citrus psyllid and citrus greening quarantine areas in the continental U.S. It does not show quarantines in American Samoa, the Northern Marianas, Hawaii, Puerto Rico, and the U.S. Virgin Islands. The map also does not show smaller citrus greening quarantines in the LA and Orange Counties.

Obstacles to greening research: Until recently, no laboratory had successfully grown the citrus greening bacterium, Candidatus Liberibacter asiaticus (CLas). Studying CLas has been extremely difficult: Samples must be obtained directly from infected trees or from the psyllids and could not be kept alive in a lab. To work around that problem, researchers often resorted to studying related species of bacteria that fare better in a laboratory setting.

Another alternative tested was introducing citrus greening genes to bacteria that found labs a more congenial environment. According to research published earlier this year, this approach allowed Stanford researchers to identify 130 compounds that could potentially inhibit the growth of CLas.

This month, Washington State University researchers announced the first successful efforts to culture CLas in a lab. After three years of work, the USDA-funded scientists have been able to keep CLas alive for two years in a lab with the use of highly specialized growing environments. Using these techniques, others will soon be able to more easily and reliably conduct research directly on CLas, avoiding workarounds.

Antibiotic spray may be a bust: A recent University of Florida study has found that spraying with oxytetracycline, an FDA-approved antibiotic, may be almost completely ineffective in combating the citrus greening bacterium, Candidatus Liberibacter asiaticus (CLas).

No finding has been made regarding the effectiveness of another approved antibiotic, streptomycin, though there is some skepticism of its long-term, larger-scale effectiveness. Field trials had suggested that antibiotics could help keep trees healthier but were perhaps less effective in protecting yields or preventing early drop and damage to fruit.

Injection of this antibiotic does seem to reduce CLas levels in trees. Such treatment, however, may not be cost-effective and has not yet been approved.

Dogs helping battle greening: Researchers in Florida report some early successes in training dogs to detect citrus greening infection in trees. According to UPI, at least on major citrus company is employing the dogs.

Pea powder to the rescue? A Georgia lab, Jones Laffin Co., has suggested that a designer food additive made from peas could be used to remediate the bitter flavor in juice extracted from fruit affected by citrus greening.