Posts Tagged: UC Riverside

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.”

While it is possible for rice to flourish in flooded soils, the plants yield less food or even die if the water is too deep for too long. This work simulated prolonged floods of five days or longer, in which plants were completely submerged. It also simulated drought conditions.

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.

“This means that increasing suberin could help combat climate change by removing and storing carbon from the atmosphere.”

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.

With dwindling water supplies, the timing of rainfall matters

How to help plants in drought-stricken states

A new UC Riverside study shows it's not how much extra water you give your plants, but when you give it that counts.

This is especially true near Palm Springs, where the research team created artificial rainfall to examine the effects on plants over the course of two years. This region has both winter and summer growing seasons, both of which are increasingly impacted by drought and, occasionally, extreme rain events.

Normally, some desert wildflowers and grasses begin growing in December, and are dead by June. A second community of plants sprouts in July and flowers in August. These include the wildflowers that make for an extremely popular tourist attraction in “super bloom” years.

“We wanted to understand whether one season is more sensitive to climate change than another,” said Marko Spasojevic, UCR plant ecologist and lead study author. “If we see an increase or decrease in summer rains, or winter rains, how does that affect the ecosystem?”

The team observed that in summer, plants grow more when given extra water, in addition to any natural rainfall. However, the same was not true in winter.

“Essentially, adding water in summer gets us more bang for our buck,” Spasojevic said.

Their findings are described in a paper published in the University of California journal Elementa.

Over the course of the study, the team observed 24 plots of land at the Boyd Deep Canyon Desert Research Center, in the Palm Desert area. Some of the plots got whatever rain naturally fell. Others were covered and allowed to receive rain only in one season. A third group of plots received additional collected rainwater.

While adding water in summer resulted in higher plant biomass, it generally did not increase the diversity of plants that grew, the researchers noted. Decreasing rainfall, in contrast, had negative effects on plants across both summer and winter, but may lead to some increased growth in the following off-seasons.

Implications of the work extend beyond learning when additional water resources might be applied simply to help plants grow. Whole communities of animals depend on these plants. They are critical for pollinators such as bees and butterflies, and they play a big role in controlling erosion and movement of soils by wind.

“Studies like this one are critical for understanding the complex effects of climate change to dryland ecosystems,” said Darrel Jenerette, UCR landscape ecologist and study co-author.

Desert plants also play an important role in removing carbon dioxide and nitrogen from the atmosphere to use as fuel for growth. Microbes that live in the soil can use the carbon and nitrogen released by plant roots, then send it back into the atmosphere where it can affect the climate.

“Drylands cover roughly a third of the land surface, so even small changes in the way they take in and emit carbon or nitrogen could have a big impact on our atmosphere,” said Peter Homyak, UCR environmental scientist and study co-author.

As the team continues this research over the next few years, they expect to see changes in soil carbon and nitrogen cycling, given that plants are already being affected by changes in seasonal rainfall, as this study shows.

“Can changes in precipitation patterns alter the feedback between plants and microbes, destabilizing the carbon locked in soils and sending more of it into the atmosphere? We are working on figuring that out,” Homyak said.

Editor's note: Jenerette and Homyak are affiliated with University of California Agriculture and Natural Resources through UC Riverside's Agricultural Experiment Station.

Is 'palmageddon' coming to California?

Representatives from the date and ornamental palm industries, arborists and pest managers, parks and recreation officials, and home owners are uniting behind a University of California, Riverside initiative to slow the spread of the South American palm weevil, a palm tree-killing insect that has established in San Diego County.

“Everyone recognizes the threat and agrees it is significant,” said Mark Hoddle, UC Cooperative Extension specialist in biological control based at UC Riverside.

However, Hoddle said, action is hampered significantly by a lack of financial support at the state and federal level for research to answer questions about the distribution of the weevil in Southern California, how far it can fly from infestation zones, control options, and the most efficient and sensitive ways to monitor and trap it.

Hoddle recently helped organize a symposium just outside San Diego on the South American palm weevil. Recent detection in California of the weevil, which has traditionally been found in South and Central America, the Caribbean and Mexico, has scientists, farmers and nursery industry officials worried because it threatens California's $70 million ornamental palm industry and $68 million commercial date industry.

“My personal feeling is we might be on the verge of a crisis now,” Hoddle said. “The big problem is we don't know how far the weevil has spread. We really need help from the public in tracking its spread.”

The South American palm weevil (Rhynchophorus palmarum) is not to be confused with the palm weevil Rhynchophorus vulneratus, which originated from Indonesia and was incorrectly identified as the red palm weevil, Rhynchophorus ferrugineus, when it was found killing palm trees in Laguna Beach in 2010. R. vulneratus was declared eradicated from California on Jan. 20, 2015.

Feeding by larvae of the South American palm weevil damage the growing area of the crown of palm trees. The tree is then unable to produce new fronds, and within months it dies. Canary Islands date palms are particularly vulnerable and it is likely date palms will be attacked too. California also has a native palm species (Washingtonia filifera), which grows in desert oases and may be vulnerable to attack.

Detection of the South American palm weevil was officially confirmed May 9, 2011. Seven additional detections were made in July and August 2011. These initial detections by the USDA were in San Ysidro in San Diego County, about two miles from the Mexican border. It is likely that the weevils flew from Tijuana, Mexico, where infestations and dead palms had been detected in December 2010.

As a result of those detections, weevil traps were set up throughout California, Arizona and Texas with financial support from the USDA. A total of 111 South American palm weevils were captured in California; 109 in San Diego County and two in Imperial County. They were also found in Alamo, Texas, and Yuma, Ariz.

The traps were monitored from 2011 to 2013. Then, monitoring stopped when federal funding for the program expired.

Since monitoring stopped, it appears the problem has worsened, said Hoddle, who is also director of UC Riverside's Center for Invasive Species Research. In May 2016 he did a casual eight-hour driving survey in Tijuana, Mexico and found about 125 dead Canary Islands date palms that had been killed by the South American palm weevil.

In August, 2016, Hoddle placed 10 weevil traps at Sweetwater Regional County Park, about 15 miles east of San Diego. Since then, he has been catching about five to seven weevils per trap per month. In the coming months, he plans to start monitoring the heath of the palm trees in Sweetwater Regional Park using a drone.

Hoddle considers the South American palm weevil situation more dire than what he encountered with Rhynchophorus vulneratus because he fears the South American palm weevil has spread further and it spreads the red ring nematode (Bursaphelenchus cocophilus), which also kills palm trees.

Red ring nematodes, which have not yet been detected in California, can enter palm trees through the damage South American palm weevils do to the trees. The nematodes can also enter the bodies of the weevils when they are larvae. Then, the larvae turn into adult weevils which are strong flyers and they can then spread the nematode to other palms when the feed or lay eggs on them.

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