California citrus growers are being assured of safeguards to protect new plant materials as one of the locations where disease-free germplasm is housed is located within a quarantine for the disease Huanglongbing (HLB).

Officials with the California Department of Food and Agriculture (CDFA) confirmed the discovery of HLB in a residential grapefruit tree in Riverside in late July, just two miles from the University of California, Riverside (UCR) campus, and about the same distance from other important research and development facilities.

UCR’s inextricable connection with the California citrus industry as the site of the state’s first citrus experiment station won’t change with the discovery of the lethal citrus disease next to campus, even as the new quarantine is established that encompasses screenhouses and greenhouses that hold the critical Citrus Clonal Protection Program (CCPP) collection and approximately 200 acres of citrus trees grown on the university farm.

Though the finding of HLB near the university and its subsequent quarantine will impact the school citrus farm, Peggy Mauk, director of agricultural operations at UCR, says efforts have been under way for some time to prepare for a declaration.

Because university officials – namely those connected with the citrus industry – have worked to prepare the campus for an HLB quarantine since shortly after HLB was discovered in southern California, she says little will change at UCR under the new quarantine.

Citrus plant materials shipped to UCR do not leave the facility, according to Mauk, though the fruit grown on the farm does. Mauk says the university will work with CDFA and the Riverside County Agricultural Department on a compliance agreement to ship citrus fruit from the farm for processing.

This could include shipping fruit to one of the two citrus packing houses located within the Riverside HLB quarantine zone.

With the inclusion of Riverside County, nearly 450 square miles of urban landscape in three counties is now under HLB quarantine. Much of the area is in Los Angeles County.

Budwood backups

California’s CCPP was established over 50 years ago as the Citrus Variety Improvement Program and stands as a cooperative program between the UCR Department of Plant Pathology, citrus growers, the California Nursery Board, and CDFA. It is how disease-free citrus materials are provided to commercial nurseries and made available to growers and the public.

Disease-free budwood tested at UCR is stored in three locations:

According to CCPP Director Georgios Vidalakis, who also serves as a plant pathologist and Extension specialist at UCR, the “Foundation Block” – the block of pathogens-tested budwood used to provide the industry and citrus enthusiasts with disease-free materials – is located at Lindcove.

This includes about 1,000 trees representing over 350 different citrus varieties.

Lindcove

Though the University of California’s Lindcove Research and Extension Center in Tulare County is far-removed from the Riverside quarantine, it is nonetheless vital to the citrus industry because of its inclusion in the CCPP.

“Those greenhouses are basically the ‘Noah’s Ark’ of germplasm for all the varieties important to the industry,” said Beth Grafton-Cardwell, Lindcove center director and the citrus industry’s “go-to” entomologist for all things related to the Asian citrus psyllid, the tiny insect responsible for spreading HLB.

Lindcove currently sits in an ACP quarantine established in Tulare County after the first discoveries of the pest were made there in 2012. A countywide quarantine was established in 2014 after a hop-scotch of quarantine zones were created as the insect was found throughout the county’s citrus-growing zone.

Even so, Grafton-Cardwell says the UC Agriculture and Natural Resources (UCANR) facility she oversees has been fortunate not to have an ACP discovery confirmed on site, though bugs have been found in traps in nearby Lemon Cove.

She suspects consistent insecticide treatments on the facility, and treatments in nearby citrus groves have kept ACP populations relatively low in the area. This is critical because Lindcove has about 400 different citrus varieties scattered among 12,000 trees planted across the research station.

Aside from the CCPP collections at Lindcove, which are housed in positive-pressure greenhouses that help keep ACP from getting into the enclosures, Lindcove has also upgraded its own research greenhouses to USDA-approved structures.

“That was a big step and cost us a lot of money,” she said.

Though Lindcove is not under an HLB quarantine, this process has been ongoing now for about five years, according to Grafton-Cardwell, and is part of an overall philosophy by the university to protect its citrus collections and research in the case of an HLB quarantine.

The center also purchased a portable piece of citrus cleaning equipment that can strip citrus fruit of leaves and stems, and allow fruit in off-site orchards to be brought to the center for research purposes.

The center also has its own small citrus packingline that can process fruit.

Grafton-Cardwell says she is also training research station staff to recognize all life stages of the psyllid. She recently hired additional staff to monitor citrus in San Diego, Imperial, Riverside and San Bernardino counties to scour citrus groves to document how ACP treatments are working. New scouts will be added next year for Tulare and Kern counties.

The inclusion of psyllid scouts in Tulare County will help Lindcove as Grafton-Cardwell says the USDA will soon require sampling efforts to increase on site because of the quarantine greenhouses that are located there.

New Research

Grafton-Cardwell says new research programs at Lindcove will include planting citrus varieties from Florida that appear to be somewhat tolerant to HLB.

An inedible variety of citrus at Lindcove that has until recently been largely ignored because it does not produce marketable fruit may also enter the battle against HLB as it appears to be tolerant to HLB as well, she said.

Pending the acquisition of grant funds, a third project will seek to grow citrus under screen in what is known as “Citrus Under Protective Structure (CUPS).”

“The million-dollar question is ‘can it be productive’ because we know that a Navel orange under screen doesn’t produce as well,” she said. “But maybe if you do high-density plantings of mandarins it could be cost-effective.”

If built, the CUPS facility will be housed on a 10-acre section of the Lindcove center. Half of that will include the CUPS facility with a replicated grove to be planted in the open.

CUPS is also being done in Florida to see if can be cost-effective there, she said.

This would be the first such structure in California.