Posts Tagged: mandarins
Another Mandarin Species!!!
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
Observations on Mandarin Mulching Research
Two years ago, UCCE Placer/Nevada embarked on a study to evaluate pruning and mulching in five local mandarin orchards. In a blog posted in June 2017, I discussed the beginnings of the study, the specific treatments and what the study was hoping to accomplish in the coming years. As the study enters the third year and data analysis begins, there are some observations that we should share.
The environment in our orchards is changing. We are experiencing unpredictable temperature swings and extreme periods of rainfall. Soil moisture levels this past winter and spring reached saturation levels for a prolonged period.
Roots need both water and oxygen. In saturated soils, oxygen in the soil pore spaces is displaced by water. This year, tree stress increased as the roots struggled to breathe. When root cells can't get oxygen, they die. Without them, the rest of the tree starts to die too. Many of us suffered tree loss due to the suffocation of root systems.
As orchards and fields began to dry, temperatures began to swing from high to low in unpredictable patterns. Stress was further introduced into the system. In the past few weeks, recorded temperatures in the five orchards have gone from lows in the 40's to recorded highs of 105 in the first few weeks of June. Citrus has a tendency to drop fruit that the tree cannot support and increased tree stress can increase fruit drop.
Field observations over the past few weeks show that drop is occurring at a much higher rate and volume in treatments that haven't been mulched. The picture on the left is from underneath the canopy of a tree without mulch (Control) and to the right is a mulched tree. These two trees are in the same orchard, approximately 18 feet apart.
Soil moisture levels are being monitored under both of these trees. Moisture levels under the mulched tree are consistent with what one would expect. The soil profile is able to retain moisture with minimal depletion at a 6-12” depth. Most moisture depletion is occurring in the top 6” of soil and is minimal compared to the Control. Moisture levels in the Control deplete at a more rapid rate throughout the soil to a depth of 12”. Once again, tree stress is on the rise. The soil moisture in the Control profile becomes much harder to replenish, resulting in longer irrigation cycles.
Soil temperature at a depth of 9” is also being monitored. Data from the Control show rather significant increases and decreases in temperatures in short periods of time. Data from the mulched tree reflect more temperature stability with the highs lower than those in the Control soil. Again, it seems that the Control may be under more stress due to the rapid temperature swings that the root mass is encountering.
It would certainly seem that a cursory examination of the data with field observations shows that mulching is a beneficial production practice in an orchard. However, there are some considerations to be had before one just charges ahead with this practice.
First, as we learned, timing is everything. Mulch should only be applied when the moisture in the soil profile is at capacity. Experience has taught us that applying the mulch when soil moisture is low results in playing catch up. I have observed orchards that were never able to replenish the full soil moisture content during the irrigation season.
Second, monitoring soil moisture is important. Mulching will change your irrigation timing and frequency. In our study, the period between irrigation cycles in mulched orchards has increased. Maturation appeared to be slowed in orchards that chose to stay with their old programs and not effectively monitor the soil moisture. Mulch reduces moisture loss from the soil, so if irrigation was not adjusted, the soil under the mulch stayed too wet. While less dramatic than the saturated soil situation this spring, stress was induced by the tree roots struggling to obtain oxygen and maturation slowed.
Certainly, mulching requires a little more effort on the grower's part. But is the not the reduction or control of the stress induced in the growing system beneficial to the entire orchard system? As a grower, I know that adding a little bit of stress into my trees at the right time and conditions is good for the fruit. Adding that stress at a time when it will not damage the tree or cause crop loss is key. Mulching certainly seems to mitigate stress in the growing system when stress is detrimental to the crop and system. Further data analysis will also provide us with more insight into the benefits that the mulch provides to the soil biology and composition. We will share those insights as they become available.
Did You Miss the Farmer-to-Farmer Breakfast?
A room full of farmers came out on a rainy Wednesday morning to enjoy breakfast together. Our guest speaker, Domenic Fino of Golden Pacific Crop Insurance Services, came all the way from Dinuba, California. He is a farmer, with a family legacy of farming and has been in the crop insurance business for 17 years.
Revenue - While farm acreage and the number of zeros after the dollar sign may be smaller for local farms, revenue earned is revenue that can be lost and can be insured. Fino explained a type of insurance called Whole Farm Revenue Protection (WFRP) that was designed specifically for small to medium producers with diversified operations and unique specialty crops. WFRP has been around for the last five years but has only been available in Placer and Nevada Counties in the last two years. WFRP is currently available in all counties in all 50 states.
Records - Fino brought a wealth of experience and information to local producers. He helped explain that WFRP works only if the producer is able to keep proper records and has been reporting revenue on their taxes. “Garbage in, garbage out” Fino said, speaking of how important diligence in record-keeping and setting up the policy makes processing easier when there are claims.
Reporting - Whereas most types of insurance require claims to be made right after a loss, WFRP is unique in that a producer may only complete a claim after filing taxes for the year.
Restrictions – At the farmer-to-farmer breakfast, producers also learned of a few crops that are excluded from WFRP, mushrooms and timber. However, there is a program that can provide assistance for those products called Non-Insured Assistance Program (NAP) which is accessed through the Farm Service Agency. Several mandarin growers learned that while you must have at least two crops for WFRP with the second making at least 17% of your revenue, if you only sell mandarins, there is another option.
Single Crop Insurance - Mandarin only crop insurance is already available in six Southern California counties. Any mandarin farmer may request that type of crop insurance in their county. Once enough farmers request a single crop insurance in a county, it can create a bank of information that will eventually make that type of insurance written specifically for that county.
For more information about WFRP, visit the USDA Risk Management Agency website. https://www.rma.usda.gov/Fact-Sheets/National-Fact-Sheets/Whole-Farm-Revenue-Protection-2018
Did you miss this event? If you are interested in learning more about crop or whole farm revenue protection insurance, UCCE can provide information. Call 530.889.7385 or e-mail us, cefake@ucanr.edu or dmacon@ucanr.edu
Interested in attending a farmer-to-farmer breakfast? There is another one right around the corner. Wednesday, February 13, at Happy Apple Kitchen in Chicago Park. Look for a sign-up link coming soon.
Hot Mandarins. What to Look forward to After a Fire
Mandarins, also known as “zipper skins” and “easy peelers” can have very fragile peels/skins/rinds/exocarp that make them easily subject to more damage than most oranges and lemons. Some are a bit tougher skinned than others, but some are so fragile that any rough handling often prevents them from going through conventional packing operations.
These skins were recently put to the test in the recent fires in Ojai. There was a mix of different varieties - ‘Pixie', ‘Gold Nugget', ‘W. Murcott', ‘Yosemite Gold', ‘Tahoe Gold' and others. Some of them were more sensitive than others, some were closer to the fire, all were affected by smoke to some degree. In Matilija Canyon where smoke was present for many more days than in the east of the Ojai Valley and possibly more ash, the trees have started flowering sooner. That might be temperature difference, either cooler or warmer, so it is hard to say how much effect the smoke has had versus, the ash and/or heat. Smoke has many different gasses in it, one of which is ethylene which is a naturally occurring ripening agent. Smoke not only has gasses, but it occludes the sun so less or more or altered light might have an effect on these fruit. It's not a controlled experiment, so some little scientist is going to have to come along and wriggle out these different effects. Whatever. Fire and smoke have an effect on mandarins as we have seen in other crops, such as cherimoya, avocados and other citrus.
Heat damage. Fruit facing the fire.
Ash effects on fruit coloring. Fruit was covered with ash for several days until rain washed it off. Might be a pH effect (ash is alkaline), temperature effect, uneven light radiation, or other…….
Same sort of uneven coloring, that actually looks like an ashy color, but the ash has washed off the cluster by rain
And here's something interesting where fruit facing the fire is much lighter colored than fruit facing away from the fire. Here are two pieces of fruit, one from the side directly facing the fire, and the other from the other side of the tree. The side of that fruit facing the fire was also lighter colored. So, it had an effect through the canopy (small tree). The canopy was otherwise intact, unaffected heat or flames.
Oh yeah, and there is the characteristic fruit drop from either the heat, smoke gases, water stress or ….
And then there's the fruit that looks like it had actual embers on the skin.
If the tree survives and keeps its green leaves, sometimes the fruit is affected in ways that don't appear for a while. The peel may be affected, but in many cases the fruit is just as sweet as it could be. It just looks terrible. That might even be a selling point. "Here have a wonderous piece of history that braved the horror of the Ojai fires."
Satsumas and Navels - Too Late?
There have been some complaints about satsuma mandarin fruit having problems. These are prone to a rind/skin/peel breakdown when the fruit is not picked promptly. It's not clear what the cause is - wet winter, warm winter - but it is less of a problem if the fruit is picked when it is mature. A lot of the time in southern California, satsumas will develop good flavor and sweetness, but for lack of cool weather, they don't turn bright orange, a hallmark of the fruit. So growers will leave the fruit on longer, hoping for color, but the fruit becomes over mature, and more susceptible to breakdown. This weakening of the peel then opens it up to infection by fungi, such as Alternaria. In warm winters, the peel matures more rapidly and is more susceptible. Early maturing varieties like ‘Okitsuwase' are especially prone to breakdown later in the season, since their rind matures earlier. They end up being a mess, as can be seen in the photo below.
Navels can have a similar problem in these winters with erratic rainfall. Common wisdom is you don't irrigate in the winter, right? Wrong. With no, low and widely spaced rain events, the tree roots dry out, and rewet with rain. Navels are building their sugar in the winter and they become suction balls for water as the sugar increases. The fruit will continue to grow as the tree takes up water. When the roots run out of water, and then are suddenly rewetted during this period, the fruit can suck up water so rapidly that the skin cant expand fast enough and will split. So this is what happens with uneven irrigation or rainfall this time of year. One of those abiotic problems in citrus.
satsuma rind breakdown
split navels