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New avocado proves tasty, safer to harvest at UC ANR Research and Extension Centers
A new avocado, one that complements the widely known ‘Hass,' will hit the world market soon. The ‘Luna UCR' variety (trademarked and patent pending) has several characteristics that should be of interest to both growers and consumers, said Mary Lu Arpaia, University of California Cooperative Extension subtropical horticulture specialist based at UC Riverside.
From the grower perspective, the tree is about half the size of the leading variety while producing approximately the same yield per tree as ‘Hass,' meaning that growers could plant more trees per acre, therefore increasing yield. It also makes harvesting easier and safer.
Another advantage is the flowering behavior of the tree. Avocado trees are categorized into either Type A or Type B flower types. It is generally accepted that you need both flower types in a planting to maximize productivity. The ‘Hass' is an “A” flower type and ‘Luna UCR' is a Type “B.”
This is a potential boost for growers since the current varieties that are “B” flower types ripen green and generally receive lower prices for the grower. Similar to ‘Hass,' however, the ‘Luna UCR' colors as it ripens.
“Hopefully, it will receive similar returns to the ‘Hass' once it is an established variety,” Arpaia added.
Fruit breeding is a long-term process that she has navigated by building upon the work of her predecessors. Of course, Arpaia has had strong support from colleagues as well, including Eric Focht, a UC Riverside staff researcher and co-inventor of ‘Luna UCR.'
“We had been looking at ‘Luna UCR' for some time and it was always a very good eating fruit,” Focht said. “After the 2003 release of ‘GEM' (registered and patented as ‘3-29-5', 2003) and ‘Harvest' (patented as ‘N4(-)5', 2003) varieties, ‘Luna UCR' was always the top contender for a next release due to the small, narrow growth habit, “B” flower type and the fruit quality.”
“It's a very nice-looking fruit as well and seemed to be a pretty consistent bearer from year to year.”
A glimpse at how it all started
In spring 1996, Arpaia took over the UC Avocado Breeding Program following Guy Witney who led the program from 1992 to 1995, and Bob Bergh whose initial efforts in the 1950s were foundational in the inception of ‘Luna UCR.'
Arpaia recalls the first trials in the early 2000s of ‘Luna UCR,' which were tested alongside other promising selections from the Bergh program. “There were a lot of varieties that didn't perform well, some of which had poor storage life, an important trait that we need if we are going to get the fruit to consumers across the country,” said Arpaia.
The original seed and selection were planted at the Bob Lamb Ranch in Camarillo, and originally advanced trials of the ‘Luna UCR' variety were planted in four locations: UC Lindcove Research and Extension Center in Tulare County, UC South Coast Research and Extension Center in Orange County, a privately owned farm in San Diego County and another one in Ventura County.
The RECs are among the nine hubs operated by UC Agriculture and Natural Resources to support research and educate the public on regional agricultural and natural resource challenges.
ANR Research and Extension Centers become vital
Unfortunately, the 2017 Thomas Fire burned the avocado trees in Ventura, said Arpaia. After a change in management, the trial located in San Diego County was also terminated, leaving the two trials at Lindcove and South Coast REC.
“South Coast REC has a long history of supporting research and extension activities of high value crops important to California, including avocados,” said Darren Haver, director of the South Coast REC, which was often used to show growers the new varieties that were being developed.
“Many of the REC staff have worked with the avocado-breeding program researchers for more than two decades and continue to work closely with them to ensure the success of new avocado varieties, including ‘Luna UCR',” he added.
In addition to the support provided by South Coast and Lindcove RECs, Arpaia said that UC Kearney Agricultural Research and Extension Center in Fresno County – another UC ANR facility – made it possible for her team to conduct critical postharvest and sensory research, and consumer testing of the fruit, which included up to six-week trials of fruit ratings for storage life and taste.
“UC ANR has played an important role in our ability to not only identify ‘Luna UCR', but in preparing it for the world market, too,” she said.
Preparing to share with the world
Since 2015, Focht had been collecting data for the patent application. Now that he and Arpaia have successfully patented and trademarked ‘Luna UCR,' they are preparing to expand production by engaging interested growers with the commercial partner, Green Motion who is based in Spain.
“Green Motion contracted for 1,000 trees to be generated by Brokaw Nursery and those trees are currently being distributed, with earliest field plantings likely taking place in fall,” explained Focht.
Focht also said that Mission Produce, based in Oxnard, CA has contracted to graft over a small number of “B” flower type pollinizer trees to the new ‘Luna UCR' variety, possibly making way for a small number of avocados to be available the following year.
Once planted, the avocado trees will come into “full” production in about five years.
To read this story in Spanish, visit: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=58991
The scent that could save California’s avocados
Scientists search for pheromone to disrupt insect mating
UC Riverside scientists are on the hunt for a chemical that disrupts “evil” weevils' mating and could prevent them from destroying California's supply of avocados.
Avocado weevils, small beetles with long snouts, drill through fruit to lay eggs. The weevil grubs or larvae bore into avocado seeds to feed, rendering everyone's favorite toast topping inedible.
“They're extremely hard to control because they spend most of their time deep inside the fruit, where they're very well protected from insecticides and natural enemies,” said UCR researcher Mark Hoddle, a UC Cooperative Extension entomology specialist.
Not only are the insects reclusive, they are also understudied, making information about them hard to come by. “All books on avocado pest management will tell you these weevils are bad. They're well recognized, serious pests of avocados, but we know practically nothing about them,” Hoddle said.
One strategy for controlling pests is to introduce other insects that feed on them. However, that is unlikely to work in this case. “Natural enemies of these weevils seem to be extremely rare in areas where this pest is native,” Hoddle said.
To combat avocado weevils in Mexico, an area where they are native, and to prevent them from being accidentally introduced into California, Hoddle is working with Jocelyn Millar, a UCR insect pheromone expert. They are leading an effort to find the weevil's pheromone, with the goal of using it to monitor these pests and prevent them from mating in avocado orchards.
Pheromones are chemicals produced and released into the environment by an insect that can be “smelled” by others of its species, and affect their behavior.
“We could flood avocado orchards with so much pheromone that males and females can't find each other, and therefore can't reproduce,” Hoddle said. “This would reduce damage to fruit and enable growers to use less insecticides.”
Alternative control strategies could include mass trapping, using the pheromone as a lure, or an “attract-and-kill” approach, where the pheromone attracts the weevils to small sources of insecticide.
The work to identify, synthesize and test this pheromone in the field is supported by grants from the California Department of Food and Agriculture, as well as the California Avocado Commission.
An initial phase of the project sent Hoddle to a base of operations three hours south of Mexico City, an area with large weevil populations. Using a special permit issued by the USDA, Hoddle brought weevils back to UCR's Insectary and Quarantine facility.
Hoddle and Sean Halloran, a UCR entomology researcher, captured the chemicals that avocado weevils release into the air. Possible pheromone compound formulas were identified from these crude extracts and are now being synthesized in Millar's laboratory.
“Weevil pheromones have complicated structures. When they're made in a lab, they can have left- or right-handed forms,” said Hoddle. Initially, Millar's group made a mixture of both forms to see if the blend would work as an attractant, as it is far cheaper to make the blend than the individual left- or right-handed forms.
Field work in Mexico with the pheromone cocktail by Hoddle, his wife Christina Hoddle, an associate specialist in entomology, and Mexican collaborators did not get a big response from the weevils, suggesting that one of the forms in the blend could be antagonizing the response to the other.
As the next step, the researchers plan to synthesize the individual forms of the chemicals and test the insects' response to each in Mexican avocado orchards.
Because the levels of avocado imports from Mexico are increasing, the risk of an accidental weevil invasion is rising as well. Hoddle is hopeful that the pheromone will be successfully identified and used to lower the risk this pest presents to California's avocado growers.
“We've been fortunate enough to be awarded these grants, so our work can be implemented in Mexico and benefit California at the same time,” Hoddle said. “The tools we develop now can be used to make sure crops from any exporting country are much safer to import into California.”
You, too, can grow California’s oldest living orange variety
Sweet Mother Orange Tree released from quarantine
The 1000th tree okayed for growing by California's Citrus Clonal Protection Program happens to be the oldest living orange variety in the state.
The program, housed at UC Riverside, is the first of its kind in the world. It began in the 1950s, and its scientists spend up to three years testing and clearing citrus trees of disease so they can be released to commercial and private growers.
By law, every citrus tree newly propagated in California can be traced back to one mother tree created at UCR through the protection program. Program Director Georgios Vidalakis and his group begin their process by testing incoming trees for more than 30 citrus diseases, whether the diseases are known to have emerged in the state or not.
The treatment for any disease identified in that first round of testing is to make a new mini tree from a few cells of the original budwood — short, leafless twigs with buds meant for propagation. “We use special plant cells for this process that diseases cannot penetrate,” Vidalakis said.
After the mini tree grows large enough, program scientists go back and do a second round of testing for disease, making sure they picked the right cells for propagation and eliminating any prior trace of illness.
If it passes the arduous second set of tests, the new tree gets a variety index or VI number that accompanies it for the rest of its life, and it is released to the public.
Dubbed the Mother Orange Tree, Bidwell's Bar is a sweet Mediterranean orange brought to California from Mazatlán, Mexico, and planted in 1856. It was first planted near the Bidwell Bar Bridge near Oroville, then dug up and replanted twice.
Its survival skills are some of the reasons Tom Delfino, former California Citrus Nursery Society director, recommended the old orange tree for the protection program.
“Apparently this variety is very rugged,” Delfino said. “Not only has it survived a lot of cold Northern California winters, but the tree has been dug up and replanted twice — once to protect it from impending flood, and again to make way for the Oroville Dam.”
Much of the state's orange industry is based in areas with warm weather. Delfino, who lives in the San Francisco Bay Area, finds citrus an exciting challenge to grow. By suggesting Bidwell's Bar for approval, he was hoping the protection program would clear it so he could buy its budwood.
On the occasions he has visited the original tree, Delfino said the fruit in reaching distance was always gone. “I think it must be tasty because locals grab it for themselves,” he said. “Makes me even more eager to grow and eat my own. I'm extremely pleased the VI testing is completed so I can acquire it.”
Delfino also hopes that this variety will catch on with commercial growers.
“My thought is our citrus industry is concentrated in the southeastern San Joaquin Valley and is subject to a number of pests that like the warm climate there,” Delfino said. “Though this has seeds, which may be a deterrent, it can be grown in colder areas that discourage some of those insects.”
The tree arrived in California nearly two decades before the better-known Washington Navel orange grown by Eliza Tibbets in Riverside. The navel is named for a structure at the bottom end of the fruit, which resembles a belly button. This structure is actually a separate fruit inside the larger fruit. The Washington Navel is also seedless, contributing to its popularity.
“Bidwell's Bar is an example of what was grown in California before the Washington Navel came to dominate, and now that it has a VI number, others can grow it too,” said Tracy Kahn, curator of the Givaudan Citrus Variety Collection at UCR.
Kahn says it's important to preserve the genetic material from a tree with such significance to California. “Some people were worried it was going to die, but now we have an officially cleared source of this historic tree, and it is protected for future generations,” Kahn said.
New strategies to save the world’s most indispensable grain
Genetic insights help rice survive drought and flood
Plants — they're just like us, with unique techniques for handling stress. To save one of the most important crops on Earth from extreme climate swings, scientists are mapping out plants' own stress-busting strategies.
A UC Riverside-led team has learned what happens to the roots of rice plants when they're confronted with two types of stressful scenarios: too much water, or too little. These observations form the basis of new protective strategies.
“This one crop is the major source of calories for upwards of 45 percent of humanity, but its harvests are in danger,” said Julia Bailey-Serres, UCR geneticist and study lead. “In the U.S., floods rival droughts in terms of damage to farmers' crops each year.”
In particular, the researchers examined the roots' response to both types of conditions, because roots are the unseen first responders to flood and drought-related stress.
Their work is described in a new paper published in the journal Developmental Cell.
One key finding is about a cork-like substance, suberin, that's produced by rice roots in response to stress. It helps protect from floods as well as from drought.
“Suberin is a lipid molecule that helps any water drawn up by the roots make it to the shoots, and helps oxygen from shoots to reach roots,” Bailey-Serres said. “If we reinforce the plant's ability to create suberin, rice has better chances for survival in all kinds of weather.”
The researchers were able to identify a network of genes that control suberin production and can use this information for gene editing or selective breeding.
“Understanding suberin is particularly exciting because it is not susceptible to breakdown by soil microbes, so carbon that the plant puts into suberin molecules in the roots is trapped in the ground,” said Alex Borowsky, UCR computational biologist and study co-author.
The researchers also identified the genes controlling some of rice's other stress behaviors.
“One of our interesting findings is that when rice plants are submerged in water, the root cell growth cycle goes on pause, then switches back on shortly after the shoots have access to air,” Bailey-Serres said.
In the future, the research team plans to test how modifying these stress responses can make the plant more resilient to both wet and dry conditions.
“Now that we understand these responses, we have a roadmap to make targeted changes to the rice genome that will result in a more stress-tolerant plant,” Bailey-Serres said.
Though heavy rains and droughts are both increasing as threats, Bailey-Serres has hope that new genetic technology can increase its resilience before it's too late.
“With genome editing, the fact that we can make a tiny but targeted change and protect a plant from disease is amazing. Though our crops are threatened, new technologies give us reasons to hope,” Bailey-Serres said.
Avocado growers to get irrigation tools, strategies from UC ANR’s Montazar
CDFA grant supports research to optimize water use for iconic California crop
California growers, who account for more than 90% of avocado production in the U.S., will soon be getting some help in weathering the extreme fluctuations of climate change.
Ali Montazar, a University of California Cooperative Extension irrigation and water management advisor, recently received a grant to develop tools and strategies that optimize growers' irrigation practices across Southern California – the state's avocado belt. California avocados are valued at more than $411 million, according to the National Agricultural Statistics Service.
“This region faces uncertain water supplies, mandatory reductions of water use, and the rising cost of water – while efficient use of irrigation water is one of the highest conservation priorities,” Montazar said. “Water is the most critically important input to avocado production.”
At the California Avocado Commission's suggestion, Orange County was added to the study to better capture the range of climates and cropping systems across the region, Montazar said.
He hopes to develop “crop coefficients” that avocado growers can use to determine the optimal irrigation for their crop based on a host of factors: soil type and salinity, canopy features, row orientation, slopes, soil and water management practices, and more.
“Growers are unclear on how much water the crop actually needs under those conditions,” Montazar said.
He will incorporate data from the actual water use in the experimental orchards – including information from the newest soil moisture and canopy temperature sensors – to help ensure growers do not under- or overwater their crops. Overirrigating contributes to a devastating disease, avocado root rot, caused by the plant pathogen Phytophthora cinnamomi.
Another component of the grant supports outreach in disseminating these resources and best practices to the broader agricultural community.
“Developing and adopting these tools and information may have a significant impact on water quality and quantity issues and bolster the economic sustainability of avocado production not only in the well-established production region of Southern California, but also in Kern and Tulare counties where new avocado plantings are growing,” Montazar said.
Preliminary findings and recommendations are expected at the end of 2022.
