- Author: Ben Faber
UF scientists make big stride toward greening-resistant citrus trees
by Brad Buck
University of Florida scientists achieved a major milestone in their quest to develop a citrus greening-resistant tree by sequencing the genome of a fruit plant that's a close cousin to citrus trees.
You'd need to print 54,000 pages of copy paper to see the complete genome sequence. But within it, scientists believe they've found genes to lay the groundwork to make citrus more tolerant and even resistant to certain diseases, including citrus greening.
UF/IFAS researchers sequenced the genome from trifoliate orange, in collaboration with scientists from the University of California at Berkeley, the U.S. Department of Energy's Joint Genome Institute and UF's Interdisciplinary Center for Biotechnology Research. The new genome will help those who breed new citrus trees that will survive under today's challenging conditions, including invasive pests, viruses and changing climates. Their research provides a powerful new tool to control the deadly consequences of the greening disease, which has severely damaged the state's multibillion dollar-a-year citrus industry.
“Very importantly, trifoliate orange and its hybrids have genes that can confer high tolerance to citrus greening and resistance to the Asian citrus psyllid, the insect that transmits greening to citrus,” said Zhanao Deng, a professor environmental horticulture and a senior author on the new UF/IFAS-led study. “This genome can be used as a reference template to sequence widely used trifoliate orange hybrid rootstock varieties.”
“Most people – even citrus growers – rarely see trifoliate orange. This is because they usually are the rootstock part of the tree, mostly underground,” said Fred Gmitter, a UF/IFAS professor of citrus breeding genetics and a co-author on the study.
Trifoliate oranges or their hybrids are grown at nurseries, and farmers use them as rootstock to grow the citrus that's above ground. Trifoliate orange and its hybrids were used as the rootstock for more than three million citrus trees in Florida alone in 2018-2019, UF/IFAS researchers say.
Trifoliate orange and its hybrid rootstocks accounted for 82% of the top 20 rootstocks used in the 2018-2019 citrus propagation cycle in Florida.
“Our trifoliate orange genome will allow scientists to develop new tools that can more speedily transfer beneficial genes into sweet oranges, grapefruit and breeding of new scion cultivars, which grow above the ground,” Deng said.
“Releasing the first trifoliate orange genome can be valuable for our citrus gene-editing efforts,” Gmitter said. Scientists are using gene editing to produce canker-resistant and greening-tolerant citrus.
“Because of our high-quality genome, re-sequencing of trifoliate orange hybrid rootstock varieties will be much easier, much quicker and much more cost-efficient,” said Deng. “Re-sequencing will enable development of new breeding tools, such as DNA marker-based selection, genomic selection of new rootstock varieties with resistance and tolerance to citrus greening, citrus tristeza virus and citrus nematodes. The new varieties might give higher yield and fruit quality.”
Citrus breeders want to introduce desirable genes from trifoliate orange into sweet orange, grapefruit and other varieties. It took decades to produce the first citrus scion variety (‘Sun Dragon') from crossing trifoliate orange and transferring some of its genes across multiple generations into sweet orange. With this new information from genome sequencing, that timeline can be dramatically reduced.
This project was funded by two grants from the Citrus Research and Development Foundation (CRDF) and a grant from the USDA/NIFA Citrus Disease Research and Extension (CDRE) program.
To see a video about the research and its implications, click here.
FredGmitter at it. Photo credit: Brad Buck, UF/IFAS.
- Author: Ben Faber
WASHINGTON, D.C. (September 14, 2020) –Going directly to those hurt most by the devastating citrus greening disease, researchers are asking organic citrus growers and other organic stakeholders to help them develop a holistic research program in their fight against the ruinous disease.
Citrus greening disease has been decimating domestic citrus in the United States over the past decade, and organic growers have been hit especially hard with few effective tools to control the disease. A research team led by the University of Florida is collaborating with The Organic Center, University of California, Riverside, a number of organic citrus growers and industry members to conduct a national review of how citrus greening disease is adversely impacting organic growers and other industry members.
Researchers are asking organic growers to fill out a survey based on their knowledge and experience about this devastating disease on their citrus crops. Here is the survey link. Information gathered will be used to develop a large-scale holistic research project proposal targeted toward protecting organic citrus growers from citrus greening, slowing its spread, and reducing damage to currently infected groves.
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The project is funded through the USDA Organic Agriculture Research and Extension Initiative (OREI) program.
Researchers are requesting that survey responses be submitted by October 20. More information on this project is available on The Organic Center's website. |
- Author: Ben Faber
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CRB Announces its
The Citrus Research Board (CRB) in coordination with the University of California Statewide Integrated Pest Management Program (UC IPM) is rolling out a new CRB Webinar Series, geared toward citrus growers and industry professionals.
Make sure you mark your calendars for the rest of the talks in the series. |
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For more information, please contact
Petr Kosina, with UC IPM, at pkosina@ucanr.edu
- Author: Ben Faber
There are always new things to see in the field. Some things show up on occasion, but reliably, like citrus leafminer starts damaging new leaves in the fall. You start to see the leaf spots from Persea mite in the fall, even though they started their nesting/feeding activities in the late spring. Then some things show up irregularly. There's a fungus that hits citrus and other plant species – oleander, bottlebrush, holly, Natal plum, Brazilian pepper, eucalyptus – but mostly landscape species.
Sphaeropsis tumefaciens pops up here and there, this year and then not for several years. I've only seen it in Ojai, but Craig Kallsen in Kern Co. says that it's not uncommon in Bakersfield backyard citrus. It creates knobby growths, galls or tumors along branches. I've seen it on mandarin (‘Pixie'), lemon, Valencia and ‘Late Navel'. Whenever I see it, I immediately think of glyphosate damage.
A lot of times, you can see twisted leaf growth coming out of the galls. Classic herbicide phytotoxicity symptoms. But symptoms are just that, they don't tell you what caused that symptom to happen. In the several cases I've, seen only one out five has been an orchard that used herbicides. So it wasn't a reaction to glyphosate that caused the unusual growths.
These woody growths take several years to form. They don't show up just after an herbicide spray. It probably take a few years for them to show up. It's not until someone is pruning that they probably notice the galls.
In fact, it might be the pruning that is spreading the spores that causes the infection. Moisture helps spread the fungus. Another reason not to prune citrus during the rainy season.
While looking through the literature, I came across a reference to galls forming in avocado caused by Sphaeropsis – this in Mexico, http://www.avocadosource.com/WAC2/WAC2_p129.pdf. I have seen symptoms like that here
Also causing a whole fruit to form a gall. Truly a bizarre sight
But of course, this is my speculation, since these symptoms have not been tested foe their cause, as far as I know.
What causes the symptoms in Mexico might be different in California.
How to treat these galls in citrus? Cut them out if you can, but in many cases they are right in the middle of a structural branch. It is desirable to get it out of the orchard to prevent its spread. With the limited experience we have with this disease, it doesn't seem to impair yield at the levels of infection i have seen.
- Author: Ben Faber
A recent Ventura County ACP-HLB Task Force sponsored webinar was held, the topics and speakers listed below The PDF's from the speakers are available online
Webinar Agenda 8-13-20
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9:30 a.m. |
Welcome, and update on status of HLB in California: Leslie Leavens, chair, Ventura County ACP-HLB Task Force. |
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9:45 a.m. |
Update on area-wide participation rates and CDFA buffer treatments: Sandra Zwaal, Ventura County Grower Liaison |
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10 a.m. |
Final report on 2017-2020 ACP surveying project in Ventura County, and overview of Phase Two research: Beth Grafton-Cardwell, IPM Specialist and Research Entomologist, University of California-Riverside, and Director of Lindcove Research and Extension Center (retired); and Monique Rivera, Assistant Extension Specialist, Department of Entomology, UC Riverside. |
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10:40 a.m. |
Final report on deployment of detection canines to scout Ventura County commercial groves for evidence of early HLB infection: John Krist, CEO, Farm Bureau of Ventura County. |
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11 a.m. |
Implications of canine detection data for HLB management in Ventura County commercial citrus: Neil McRoberts, western regional director, National Plant Diagnostic Network, and professor of plant pathology, UC Davis. |
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11:30 a.m. |
Adjourn |
For more information, contact us by email at taskforce@farmbureauvc.com.
