Tomomi Okubo
tomomi.okubo@oist.jp
Office: 81-989-823-447
- Citrus fruits from the mandarin family have important commercial value but how their diversity arose has been something of a mystery
- Researchers analyzed the genomes of the East Asian varieties and found a second center of diversity in the Ryukyu Islands along with the previously known center in the mountains of southern China
- They discovered a new citrus species native to Okinawa that arose about two million years ago when the Ryukyu archipelago became disconnected from mainland Asia
- Other citrus from Okinawa and mainland Japan, including shiikuwasha and tachibana, are hybrids of this newly discovered wild species with different mainland Asian varieties
- This research may have commercial implications and opens the potential to create additional hybrids with favorable traits
Citrus fruits from the mandarin family are popular throughout the world for their tasty and healthy characteristics. Within Japan, the tiny shiikuwasha and the ornamental tachibana are of special cultural and historical importance. However, the origin of these two varieties, and other East Asian citrus, was always something of a mystery, until now.
In a new study, published in Nature Communications, scientists from the Okinawa Institute of Science and Technology Graduate University (OIST), and collaborators from other institutes, analyzed 69 genomes from the East Asian mandarin family, alongside their mainland Asian relatives, to reveal a far-ranging story of isolation, long-distance travel, and hybridization.
The story starts in the Hunan Province of southern China, which is the center of wild mandarin diversity and the genetic source of most well-known mandarins. When the scientists re-analyzed previously published genomic data, they unexpectedly found that wild mandarins of this mountainous region are split into two subspecies.
"We found that one of these mandarin subspecies can produce offspring that are genetically identical to the mother," said Dr. Guohong Albert Wu, a research collaborator at the Lawrence Berkeley National Laboratory in California. "Like many other plants, wild citrus typically reproduces when the pollen of the father combines with the egg of the mother, mixing the genes from both parents in the seed. But we found a subspecies of wild mandarins from Mangshan, in southern China, where the seed contains an identical copy of the mother's DNA without any input from a father. So, the seed grows to be a clone of the mother tree."
Back in Okinawa, the researchers looked more carefully at a strange shiikuwasha-like citrus that produces small, acidic fruit and had been ignored by local farmers since it has little commercial value. To their surprise, they found that this strange citrus represented a previously undescribed species, which they named the Ryukyu mandarin or, more formally, Citrus ryukyuensis. And in contrast to the well-known shiikuwasha, which reproduces clonally (like the subspecies in Mangshan), the new species always reproduces sexually.
Remarkably, the researchers found that all shiikuwasha are hybrids of a very specific type--one parent is from the local Ryukyuan species and the other, from mainland Asia. Surprisingly, all shiikuwasha have the same mainland mandarin parent, meaning that all shiikuwasha are half-siblings.
They concluded that tens of thousands of years ago a mainland Asian mandarin was transported, either by people or by natural methods, to the land that would become the Ryukyu Islands. There it mated with the native Ryukyu citrus. The researchers traced the ancestry of this mainland Asian mandarin back to Mangshan, where it acquired its ability to reproduce asexually. This ability was passed on to its children.
Thus, all the shiikuwasha varieties found in Okinawa's markets today are descended from this mating, and reproduce asexually, allowing stable varieties like golden shiikuwasha to be propagated from generation to generation.
And what of tachibana and the other East Asian mandarin variations?
"They're all hybrids!" explained Dr. Chikatoshi Sugimoto, Postdoctoral Scholar in OIST's Molecular Genetics Unit. "The tachibana lineage also seems to have descended from the newly described Ryukyu species and another mandarin from China, but its birthplace was probably what is now mainland Japan."
Once they saw the genetic pattern in shiikuwasha and tachibana, the researchers also recognized another half-sibling family comprising various traditional Ryukyuan types--oto, kabuchii, tarogayo, and other unnamed citrus. This family, which the researchers called 'yukunibu' (sour citrus in the native Okinawan language), is much younger than shiikuwasha and tachibana. It arose when the famous kunenbo--also the father of satsuma mandarins--hybridized with the native Ryukyu mandarin. Kunenbo was brought to Okinawa from Indochina around 4-500 years ago by maritime trade. Like the mainland parents of shiikuwasha and tachibana, it was also able to clone itself by seeds, due to its distant Mangshan ancestry, and it passed this trait on to its children.
"It's fascinating to puzzle out the story of mandarin diversification and its relationship to the biogeography of the region," concluded Prof. Dan Rokhsar, Principal Investigator of OIST's Molecular Genetics Unit. "But it also could have commercial value. What other possibly hybrid types are there? Could we create new hybrids that are more resilient to disease or drought, or have other desirable characteristics? By looking into the past, we can create all sorts of possibilities for the future."
And the whole article: https://www.nature.com/articles/s41467-021-24653-0
Population divergence times of C. ryukyuensis (2.2–2.8 Mya) and two subspecies of mainland Asian mandarins (C. reticulata): common mandarin and mangshanyeju (1.4–1.7 Mya). Extant common mandarins are recent admixtures with both mangshanyeju and pummelos
source: https://www.nature.com/articles/s41467-021-24653-0#MOESM8
- Author: Ben Faber
The Vertebrate Pest Council hosted a series of seminars this spring that provided updates and information on managing vertebrate pests. The series was popular, and several individuals who were not able to attend requested that we provide this content a second time. As such, we have again partnered with Target Specialty Products to provide a second offering of these three 2-hour sessions. The new dates and sessions include:
Day 1 (Sept 28): Field rodents
Day 2 (Sept 29): Updates and information on the use of rodenticides
Day 3 (Sept 30): Managing commensal rodents
To be clear, if someone received credit for participating in a session back in the spring, they won't be able to receive credit a second time. However, perhaps there will be a new session of interest that they have yet to attend. Likewise, with the end of the year fast approaching, individuals may be seeking additional CE units to fulfill their DPR obligations. Perhaps these seminars will be of interest. These are unique seminars in that there generally is not any other place where you can get continuing education credits exclusively for vertebrate species.
CHECK OUT THE AGENDA ATTACHED
rodent webinar
- Author: Ben Faber
Manipulating the Avocado & its Environment
for Optimum Temperature & Light
California Avocado Society, California Avocado Commission & UC Cooperative Extension
AVOCADO GROWER WEBINAR
Tuesday, Aug. 17
9-11 a.m.
Register Here: https://us02web.zoom.us/webinar/register/WN_kByWCEvfTC-TwZgjmSWptw
And if you want to hear about irrigation from another viewpoint - greenhouses and berries - which is still good information for avocado growers, check out
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- Author: Ben Faber
** HLB Update **
for San Diego County Citrus Growers and Affiliates
The California Department of Food and Agriculture (CDFA) and the United States Department of Agriculture (USDA) have confirmed the first detection of Huanglongbing (HLB) in San Diego County. The disease was detected in a lemon and orange tree in a residential Oceanside neighborhood. This detection triggers a 5-mile HLB quarantine to restrict the movement of citrus, a mandatory survey, and treatment of all citrus trees within 250-meters of the site. Owners of commercial properties (25 or more citrus) in the HLB quarantine can expect to be contacted by state officials and your grower liaison, Sandra Zwaal szwaal2@gmail.com for next steps. The full CDFA press release can be found in the CDFA website.
Now more than ever, citrus growers need to inspect their trees for signs of HLB, the Asian citrus psyllid (ACP), and keep up with ACP area wide treatments! To determine if your location is in the HLB quarantine, visit the interactive HLB quarantine map. To see if you require mitigation to move your citrus, please review this Information for Citrus Growers/Grove Managers in an HLB Quarantine document. A detailed CDFA response to an HLB detection can be found in the CDFA Action Plan for ACP and HLB. A summary can also be found in this flyer.
A hybrid San Diego ACP Grower Workshop will be held in-person and on Zoom on August 26, 2021 (9-11am) at the Fallbrook Public Utilities District. The workshop will cover the impact of the HLB quarantine and to provide ACP and HLB information. The workshop is free to attend. Register here for this workshop.
ACP TREATMENTS
The San Diego County ACP Fall area wide treatments begin August 30 through September 13. If you have not already done so, please schedule your fall ACP treatment with your pest control company. To reduce risk of HLB, keep ACP populations low. Research has shown that ACP area wide treatments are designed to keep ACP populations low. Additional best practices per the University of California include monitoring your citrus for ACP populations. They are an excellent resources on how to monitor ACP and provides a list of ACP-effective materials specifically recommended for ACP area wide or coordinated treatments.
NEGLECTED/ABANDONED & REMOVED CITRUS
Unattended or abandoned trees can harbor breeding populations of the ACP and infect neighboring citrus with HLB. If you are unable or unwilling to care for your citrus, please consider removing them to help protect neighboring citrus. Removed, neglected, and abandoned citrus should be reported to the San Diego County Dept. of Agriculture, Weights & Measures CQP.AWM@sdcounty.ca.gov or by calling them at either (858) 614-7770 or (858) 694-2739. For tree/orchard removal or pest control referrals, please contact Sandra Zwaal szwaal2@gmail.com or (949) 636-7089.
UPCOMING EVENTS San Diego Citrus Grower Workshop
The workshop will cover the impact of the HLB quarantine and to provide ACP and HLB information. Held in-person and on Zoom at the Fallbrook Public Utilities District. The workshop is free to attend.
Aug 26 (9-11am) - In-person & Zoom registration
Citrus Pest & Disease Prevention Program (CPDPP) Meetings
The Citrus Pest and Disease Prevention Program (CPDPP) meetings are free and open to the public. The virtual meeting agendas and minutes are posted in www.cdfa.ca.gov/citruscommittee/. Click on the links below to register for meetings:
Aug 11 (9am) – CPDPC Full Committee Meeting
USEFUL RESOURCES
Citrus Pest and Disease Prevention Program (CPDPP) Committee Members
Information for Citrus Growers/Grove Managers in an HLB Quarantine
HLB Voluntary Best Practices
San Diego Ag Commissioner's Office
UC Scientific Research Summaries for ACP/HLB
UC Science-based analyses to guide policy decisions, logistics, and operations:
UC recommendations for ACP management and treatment options
Citrus Insider
Please feel free to contact me with questions.
Sandra Zwaal
ACP/HLB Grower Liaison for San Diego County
Szwaal2@gmail.com
(949) 636-7089
- Author: Ben Faber
Thinking about the weather and what others are thinking about it. Here's some websites that have caught my eye. Check them out, starting with the Alerts.
Alerts
https://www.readyventuracounty.org/vc-alert/
https://twitter.com/NWSLosAngeles
https://www.readyventuracounty.org/
Weather Climate Discussions
National Weather Service
https://www.weather.gov/losangeles
Daniel Swain – Weather West
SCRIPPS Center for Weather Forecasting
University of Washington weather forecasting
https://cliffmass.blogspot.com/
CA Avocado Commission weather – click on GreenSheet download
https://www.californiaavocadogrowers.com/publications/greensheet
Climate Change Assessment for Southern California
Good Weather and Water Podcast- UCANR
https://www.watertalkpodcast.com/
Atmospheric Rivers
https://water-talk.squarespace.com/episodes/episode-11
Collaborative Weather Monitoring
Air Quality
Climate Change Assessment for Southern California
And What Do You Need to Do About Heat, if a Grower
Why and How to Cool Avocado Trees
Mitigating Heat in the Orchard
Connecting to the Changes Around Us
With Climate Change Will We Grow Cactus?
Heat, Wind, Freeze, Wind, Repeat