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Spinach proteins may hold the key for managing the citrus industry's most damaging disease organism.
ERIK MIRKOV, Texas A&M plant pathologist, Weslaco, Texas, holds a transgenic citrus plant he developed using spinach genes called definsins. In Mirkov’s greenhouse and field trials, the plants are either immune or highly resistant to the citrus disease Huanglongbing, the number one threat to the global citrus industry.
Florida HLB update
Ron Brlansky, University of Florida plant pathologist, discussed the worsening ACP-HLB situation in Florida. Brlansky has 34 years with the Citrus Research and Education Center in Lake Alfred, working extensively on a wide array of citrus pests and diseases.
The first major mistake in Florida, Brlansky says, was failing to gain good psyllid control early on.
“We did not do a good job of keeping the psyllid contained in Florida, mainly due to the movement of plant materials,” Brlansky told the group.
He says the most important grower effort against the psyllid is insecticide sprays. Some growers spray once a month – 12 times a year – which is expensive and not financially sustainable over the long haul.
A major concern, Brlansky says, is the fear of insecticide resistance to the psyllid.
On young non-bearing citrus trees, growers can put on three soil-applied systemic insecticides including imidacloprid, thiamethoxam, and clothianidin. Aldicarb (Temik) is no longer allowed for use on bearing trees since the registration in citrus was cancelled.
“We’re trying to get growers to alternate insecticides to prevent resistance from occurring,” Brlansky said.
HLB shuts down the tree’s phloem, living tissue which carries photosynthetic products to roots and developing shoots and fruit. As a result, the tree basically starves to death.
Brlansky discussed a new procedure—a nutrient treatment—tried by one Florida citrus grower over the last several years in a 90-percent to 100-percent HLB-infected grove. The grower gives the trees a nutrient cocktail of sorts, including about 20 ingredients.
The nutrient kick-start allegedly has helped build new phloem in diseased trees, ahead of the plugging and collapse of the tree’s original phloem tied to HLB. The grower also practices good psyllid control in the grove.
Remarkably, the HLB-infected trees are producing good fruit despite the HLB infection. The fruit is marketable.
A doubtful Brlansky inspected the grove and after close examination confirmed the trees were generating new phloem.
Based on the lessons learned by the Florida-HLB experience, Brlansky offered suggestions below for citrus growers in California, Texas, and Arizona (when the disease is not widespread).
- Keep the pathogen out. Regulate propagating materials to prevent introduction.
- Eradication if found early. Use good available detection systems.
- Reduce the psyllid populations; this is a big challenge.
- Manage the grove as if HLB is already present.
- Always use disease-free nursery stock.
- If HLB is found, remove the infected tree and treat the stump to prevent sprouts.
- If HLB is present, remove alternative host plants, including orange jasmine (Murraya paniculata) and box orange (Severinia buxifolia).