California Fruit and Vegetable

Tag: UC Riverside

  • Healthy Roots, Healthy Trees: HLB & Soil Microbes

    The rhizosphere, defined as the soil environment that surrounds the plant roots, is a rich and diverse habitat for microbes. Some members of the rhizosphere microbiome (or collection of microbes), are good, others bad while many are just there and don’t provide any benefits or harm to the host. One function of the good microbes in the rhizosphere is to help facilitate the availability and assimilation of nutrients and water from the rhizosphere. Just like the human gut, the plant rhizosphere conveys key nutritional functions and the analogy was made that “plants wear their gut on the outside”. One example is the symbiotic relationship between legumes (peas, beans) and rhizobia. Those bacteria help the plant fix atmospheric nitrogen in exchange for carbon supply. Another example is the symbiotic relationship between the plant and mycorrhizal fungi, whereby the mycorrhizae receive carbon from the plant in exchange for increased nutrient uptake (principally phosphorus and nitrogen). There is undeniable evidence that plants have developed a mechanism for recruiting good microbes to cope with environmental stress such as protection against opportunistic pathogens or drought. The rise of ‘omics’ technologies have helped profile entire microbial communities associated with plants and shed light in their biological functions. This research has fueled the development of novel commercial bioproducts to address the increasing consumer’s demand of environmentally-friendly products. As a result, there has been several commercial ‘probiotics’ and ‘prebiotics’ that have been marketed for agricultural use including many biocontrol agents such as fungal- (e.g., Trichoderma) and bacterial- based (e.g., Bacillus, Streptomyces, or Pseudomonas) bioproducts.

    One goal of my research program is to identify beneficial microbes for tree and vines crops, promote practices that support the presence and abundance of beneficial microbes and figure out how good microbes help combat pathogens and support plant health. As part of a collaborative project (UC Riverside, University of Florida, USDA-ARS) funded by the California Citrus Research Board and the USDA-NIFA, we profiled the microbiome of citrus trees in the context of Huanglongbing disease (or HLB). HLB is a highly destructive and lethal disease to all commercial citrus cultivars making it a threat to citrus production globally. Finding strategies that do not only rely exclusively on management of the insect vector of the bacterium (the Asian Citrus Psyllid), is a priority to the citrus industry. In our research, we found that there were significant tissue-specific microbial shifts occurring within the citrus microbiome as trees get sicker, especially in the root compartment. As HLB progressed, there were depletions of beneficial species in roots, such as mycorrhizal fungi, and enrichments of parasitic microorganisms, such as Fusarium and Phytophthora (see Figure). HLB-affected trees decline because of the clogging the phloem sieve tubes, which limit movement of sap and translocation of sugar to the roots, hence leading to feeder root collapse. Once tree is weakened, it becomes more susceptible to pathogens such as Phytophthora which further weakens the trees and exacerbate above ground HLB symptoms. In addition, several studies from Florida suggested that cultural practices that supported root health and rhizosphere microbiome richness and diversity limited root collapse.

    Figure: Citrus decline caused by HLB (https://apsjournals.apsnet.org/doi/10.1094/PBIOMES-04-20-0027- R – Ginnan et al. 2020. Phytobiomes); canopy thinning, wood dieback, feeder roots decline, collapse of beneficial microbes and enrichment of pathogens in roots.

    Our group was recently awarded another research funding by the USDA-NIFA Emergency Citrus Disease Research and Extension program (project director, M.C. Roper, Microbiology and Plant Pathology, UC Riverside). This research effort in collaboration with UC Agricultural and Natural Resources, UC Davis, University of Florida, and the USDA-ARS aims at investigating the root collapse associated with HLB- impacted trees and finding ways to mitigate it by promoting root health. In the proposed work, we will test how different sectors of the root microbiome contribute to or lessen fibrous root loss and if soil amendments (e.g., humic acid treatment, mulching) and planting of HLB tolerant rootstocks (Poncirus trifoliata and P. trifoliata hybrids) can be used to mitigate root loss associated with HLB in Florida, and how tree respond to those practices under a HLB free environment in California. While these approaches will not cure trees from HLB, it will provide a science-based information for strategies that support root and tree health and sustain orchard longevity until remedies are discovered. — By Philippe Rolsausen, Professor in Cooperative Extension, UC Riverside

  • Protein Discovery Could Help Enable Eco-Friendly Fungicides

    New research reveals an essential step in scientists’ quest to create targeted, more eco-friendly fungicides that protect food crops.

    Scientists have known for decades that biological cells manufacture tiny, round structures called extracellular vesicles. However, their pivotal roles in communication between invading microorganisms and their hosts were recognized only recently.

    UC Riverside geneticist Hailing Jin and her team found plants use these vesicles to launch RNA molecules at fungal invaders, suppressing the genes that make the fungi dangerous.  

    ​Infection of an Arabidopsis plant by the fungus that causes white mold disease. (Anna Schroll/Max Planck Institute for Chemical Ecology)

    “These vesicles shuttle small RNAs between cells, like tiny Trojan horses with weapons hidden inside,” said Jin, a professor of genetics and the Cy Mouradick Chair in the Department of Plant Pathology and Microbiology. “They can silence pathogenic fungal gene expression.”

    Using extracellular vesicles and small RNAs has several advantages over conventional fungicides. They’re more eco-friendly because they are similar to naturally occurring products. Eventually, they degrade and do not leave toxic residues in the soil. Also, Jin explained, this method of fighting fungi is less likely to breed drug-resistant pathogens.

    A sticking point for scientists in creating these fungicides has been figuring out how to load their desired small RNAs into the vesicles.

    “We’ve wondered how these weaponized small RNAs get into the bubbles,” Jin said. “Now, we think we have an answer.”

    Her laboratory has identified several proteins that serve as binding agents, helping to select and load small RNAs into the vesicles. The lab’s research is detailed in a new Nature Plants journal article.

    The Jin laboratory has been working for several years on the development of gene-silencing RNA fungicides. Work toward this goal led to the team’s landmark discovery in 2013 that gene-silencing RNA messages can be sent from the fungal pathogen to the plant host to suppress host immunity. Later, the team learned small RNAs can move both ways — from plants into pathogenic invader cells as well. In 2018, the team worked out that extracellular vesicles were the major delivery system for these small RNAs. They observed that Arabidopsis plants secrete extracellular vesicles into Botrytis cinerea, a fungus that causes grey mold disease and destroys millions of crops every year.

    “This was the first example of a host using these vesicles to deliver small RNAs to another organism,” Jin said. “Previously we saw movement of RNA, but didn’t know how the small RNA are selected and transported.”

    Now, she and her colleagues have identified several RNA-binding proteins in Arabidopsis that bind to specific small RNA molecules and load them into extracellular vesicles. This suggests the proteins play an important role in loading and stabilizing small RNAs in the vesicles. The finding can help increase the payload of gene-silencing RNAs that make it into vesicles and enhance the efficiency of disease control.

    Some scientists have taken inspiration from the RNA communication in plant vesicles to design human therapies. For example, some are attempting to load anti-cancer RNAs and drugs into extracellular vesicles in fruits or vegetables, so people can eat or drink them. Jin is hopeful that her lab’s discovery can aid these efforts. — By Jules Bernstein, UC Riverside

  • Novel Treatment Causes Killer Citrus Disease to Leak & Die

    New research affirms a unique peptide found in an Australian plant can destroy the No. 1 killer of citrus trees worldwide and help prevent infection. Huanglongbing, HLB, or citrus greening has multiple names, but one ultimate result: bitter and worthless citrus fruits. It has wiped out citrus orchards across the globe, causing billions in annual production losses.

    Untreated citrus plants on the left, as compared to treated ones on the right. (Hailing Jin/UCR)

    All commercially important citrus varieties are susceptible to it, and there is no effective tool to treat HLB-positive trees, or to prevent new infections. However, new UC Riverside research shows that a naturally occurring peptide found in HLB-tolerant citrus relatives, such as Australian finger lime, can not only kill the bacteria that causes the disease, it can also activate the plant’s own immune system to inhibit new HLB infection. Few treatments can do both.

    Research demonstrating the effectiveness of the peptide in greenhouse experiments has just been published in the Proceedings of the National Academy of Sciences.

    The disease is caused by a bacterium called CLas that is transmitted to trees by a flying insect. One of the most effective ways to treat it may be through the use of this antimicrobial peptide found in Australian finger lime, a fruit that is a close relative of citrus plants.

    “The peptide’s corkscrew-like helix structure can quickly puncture the bacterium, causing it to leak fluid and die within half an hour, much faster than antibiotics,” explained Hailing Jin, the UCR geneticist who led the research.

    When the research team injected the peptide into plants already sick with HLB, the plants survived and grew healthy new shoots. Infected plants that went untreated became sicker and some eventually died.

    Arrows point to areas of fluid leakage from the bacterial cell after treatment with the antimicrobial peptide. (Hailing Jin/UCR)

    “The treated trees had very low bacteria counts, and one had no detectable bacteria anymore,” Jin said. “This shows the peptide can rescue infected plants, which is important as so many trees are already positive.”

    The team also tested applying the peptide by spraying it. For this experiment, researchers took healthy sweet orange trees and infected them with HLB-positive citrus psyllids — the insect that transmits CLas.

    After spraying at regular intervals, only three of 10 treated trees tested positive for the disease, and none of them died. By comparison, nine of 10 untreated trees became positive, and four of them died.

    In addition to its efficacy against the bacterium, the stable anti-microbial peptide, or SAMP, offers a number of benefits over current control methods. For one, as the name implies, it remains stable and active even when used in 130-degree heat, unlike most antibiotic sprays that are heat sensitive — an important attribute for citrus orchards in hot climates like Florida and parts of California.

    In addition, the peptide is much safer for the environment than other synthetic treatments. “Because it’s in the finger lime fruit, people have eaten this peptide for hundreds of years,” Jin said.

    Hailing Jin, research leading UC Riverside geneticist

    Researchers also identified that one half of the peptide’s helix structure is responsible for most of its antimicrobial activity. Since it is only necessary to synthesize half the peptide, this is likely to reduce the cost of large-scale manufacturing.

    The SAMP technology has already been licensed by Invaio Sciences, whose proprietary injection technology will further enhance the treatment.

    Following the successful greenhouse experiments, the researchers have started field tests of the peptides in Florida. They are also studying whether the peptide can inhibit diseases caused by the same family of bacteria that affect other crops, such as potato and tomato.

    “The potential for this discovery to solve such devastating problems with our food supply is extremely exciting,” Jin said. — By Jules Bernstein, UC Riverside

  • $6.3 Million to Help UC Riverside Save Avocado Orchards

    New grants totaling $6.3 million will help UC Riverside solve problems facing American avocado orchards, including a lethal fungal disease called Laurel Wilt.

    Laurel Wilt can destroy an entire avocado orchard in a couple of weeks once symptoms develop. It is already present in Florida. Without effective treatments, it will inevitably spread to California, which is the nation’s leading producer of avocados.

    Laurel Wilt is caused by a fungus, Raffaelea lauricola, that the non-native redbay ambrosia beetle introduces in trees of the Laurel family, which includes avocado.

    The non-native redbay ambrosia beetle, which carries the fungus causing deadly Laurel Wilt. (UCR)

    “When the beetle attacks, the fungus enters and colonizes the tree’s vascular system, and within weeks, the tree wilts and dies if not managed properly,” said Patricia Manosalva, director of this project as well as UCR’s Avocado Rootstock Breeding Program.

    In addition to Laurel Wilt, avocado growers face numerous production challenges including devastating diseases such as Phytophthora root rot, or, PRR, and soil salinity, which in combination cause severe reduction in fruit yield and quality. This combination can also completely destroy avocado orchards.

    Avocado roots darkened and killed by Phytophthora root rot. (David Rosen/UCR)

    Avocado is also highly sensitive to salinity. Increasing levels of salinity in water and soil due to drought and the use of reclaimed water for crop irrigation purposes threatens avocado production worldwide.

    To combat the threats, the USDA’s National Institute of Food and Agriculture Specialty Crop Research Initiative has awarded UC Riverside $4.4 million. The grant will enable the development of next-generation technological solutions to these problems over the next four years in partnership with scientists at the universities of Hawaii, Florida, Texas, and Milan.

    The same grant will enable research on both short- and long-term solutions for managing avocado PRR, the major hindrance for avocado production worldwide, Manosalva said.

    “Under this grant we will select rootstocks harboring resistance to the current pathogen population and we will register new fungicides with different modes of actions to reduce avocado losses to this destructive oomycete pathogen,” Manosalva said.

    The UCR rootstock breeding program has already identified advanced rootstock lines that are tolerant to salinity and P. cinnamomi, the pathogen that causes PRR. These rootstocks may also confer resistance or tolerance to Laurel Wilt when grafted with different varieties. Field trials of these rootstocks will be conducted in California, Florida, Texas, Hawaii and Puerto Rico and will be screened for resistance at University of Florida.

    Another approach to mitigating avocado threats will be the further development of remote field sensors that can detect and differentiate drought from high salinity and Phytophthora root rot. UCR initially developed prototypes of these sensors and tested them in greenhouses. This grant will enable researchers to improve the sensors and test them in fields.

    Manosalva notes that UC Riverside is unique in having a highly recognized avocado breeding program first developed 70 years ago.

    “We’ve been developing agricultural science for a long time,” she said. “This grant will allow us to keep moving the UCR rootstock breeding program forward and continue developing hearty avocado rootstocks.”

    Through the Office of Technology Partnerships, UCR currently has three rootstocks available for licensing in the U.S. and may have up to five new rootstocks available in the next few years. The new rootstocks could provide increased tolerance to diseases, drought, heat, and soil salinity.

    In a related grant, the USDA’s National Institute of Food and Agriculture, Organic Agriculture Research and Extension Initiative awarded $1.9 million to a team of 15 scientists from five universities and the USDA Agricultural Research Service, or USDA-ARS. The grant will allow the researchers to study whether essential oils can help suppress certain pathogens and pests.

    Researchers from the University of Florida, Clemson University, the University of Georgia, the University of Hawaii at Manoa and the USDA-ARS as well as UC Riverside will collaborate on the project.

    Producers of essential oils claim their products may be able to treat plant pathogens such as gray mold, powdery mildew, algal stem blotch and brown rot as well as insects including mites, thrips and scales. This grant will enable the team to evaluate those claims.

    Manosalva said both grants underscore the importance of funding basic research in agricultural science. “California’s produce feeds the nation, and the world,” she said. “Our science will help feed people and empower growers everywhere.” — By Jules Bernstein, UC Riverside

    About UC Riverside

    The University of California, Riverside (www.ucr.edu) is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California’s diverse culture, UCR’s enrollment is more than 24,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of almost $2 billion. To learn more, email news@ucr.edu.

  • Autonomous Robot to Sample Leaves and Measure Water Potential

    Every backyard gardener knows how hard it can be to tell when to water the plants. Multiply that by tens or hundreds of acres and it’s easy to see the challenges growers face keeping their crops healthy while managing water resources wisely.

    To determine water needs accurately, growers hand-pluck individual leaves from plants, put them in pressure chambers, and apply air pressure to see when water begins to leak from the leaf stems. That kind of testing is time consuming and means growers can only reach so many areas of a field each day and cannot test as frequently as needed to accurately determine optimal irrigation scheduling patterns.

    A group of researchers from UC Riverside and UC Merced have received a grant for more than $1 million from the U.S. Department of Agriculture through the National Science Foundation’s National Robotics Initiative to address these challenges. From UC Riverside are Assistant Professor Konstantinos Karydis and Professor Amit K. Roy-Chowdhury, both from the Department of Electrical and Computer Engineering. UC Merced, which leads the effort, is represented by Stefano Carpin, professor of computer science; and Joshua Viers, professor of environmental engineering.

    UC Riverside Assistant Professor Konstantinos Karydis

    As part of the project, the group is developing a robotic pressure chamber that can autonomously sample leaves and immediately test them on site to provide the freshest data. The system will work to gather data even in large fields, and over a period of time, rather than just providing a snapshot.

    Frequently updated data can help growers better plan irrigation schedules to conserve water, optimize the time and effort spent by crop specialists tasked with determining and analyzing lead water potential, and help decrease some of the costs in the food-production chain.

    UC Riverside Professor Amit K. Roy-Chowdhury

    Current measuring techniques involve collecting leaf samples and transporting them to an off-site location, where testers can use very accurate, expensive pressure chambers; or sampling and analyzing leaf samples in the field using hand-held pressure chambers.

    “In the first category, leaf samples can get mixed up, making it impossible to track them back to the specific areas of the field they came from, Karydis said. “In addition, the properties of the leaf might vary given the time elapsed between being sampled and being analyzed, which in turn may yield misleading results.”

    Hand-held instruments in the field can be less accurate, but testing can be done multiple times with different leaves from the same plants. This method is time- and labor-intensive, and must be undertaken by specially trained personnel.

    Carpin has already worked with colleagues at UC Davis and UC Berkeley to create the Robot-Assisted Precision Irrigation Delivery, or RAPID, system, which travels along rows of crops adjusting irrigation flows according to sensor data that tells the robot precisely what’s needed for each plant.

    The project will use the same mobile base robot as in RAPID but equip it with a custom-made robotic leaf sampler and pressure chamber being designed by the researchers at UC Riverside, and pair it with drones that can survey the fields and direct the robot to areas of interest.

    “Using this process, growers could survey plants all day long, even in large fields,” Carpin said.

    The four-year project will support graduate students as well as summer research opportunities for undergraduates. The project has four phases: development of the chamber; developing machine vision so the robot can “see” the water coming from the leaf stems; coordinating multiple robots — in the air and on the ground; and evaluation.

    The researchers plan to have the first set of automated pressure chamber prototypes fabricated by spring 2021, and to evaluate their performance and refine designs in controlled settings over spring and summer 2021. They expect to have a completed setup by winter 2022, so they can begin controlled field testing.

    “We have to be quick about it because if we miss a peak growing season, we have to wait another nine months for the next one,” Carpin said. “We’d like to be able to start testing next summer and test every summer, and we need to be able to maximize the tests.”

    When all of the components have been designed, the designs and code will be made open source, and all the data collected during the project will be made available to the scientific community, the researchers wrote in their proposal.

    The project came about after Carpin and Viers, director of the Center for Information Technology Research in the Interest of Society, or CITRIS, at UC Merced, had been talking with area farmers about the challenges of growing almonds and grapes. Karydis and Roy-Chowdhury had been hearing the same challenges from citrus and avocado growers in the Riverside area, so the four partnered up.

    “California agriculture presents a challenge in terms of scalability,” Carpin said. “But this an exciting collaboration because we’ll get to develop a system that will work on different kinds of crops.” — By Holly Ober, UC Riverside

  • New Targets for Huanglongbing Treatments

    Scientists are closer to gaining the upper hand on a disease that has wiped out citrus orchards across the globe. New models of the bacterium linked to the disease reveal control methods that were previously unavailable.

    Metabolic models of organisms are like road maps of cities. “They show you all the biological processes, and how they work together,” said UC Riverside microbiology professor James Borneman. “They also show you which molecular pathways, if blocked, will kill the organism.” 

    Simplified metabolic model and its striking similarity to a road map. (Metallo&Vander Heiden)

    In this case, researchers created the first models of the bacterium associated with Huanglongbing or HLB, also known as citrus greening disease. The team’s work is described in a new paper published in Nature’s npj Systems Biology and Applications.

    The research team made models for six different strains of the bacterium known as CLas and doing so enabled them to identify as many as 94 enzymes essential for the bacterium’s survival. These enzymes can now be considered targets for the creation of new antibacterial treatments.

    In addition, the team identified metabolites required for the bacteria to grow.

    “Just like when humans break down the food they eat into small components called metabolites, which feed our cells, bacterial cells also require metabolites for their growth,” Borneman said.

    Knowing the metabolites needed for CLas’ growth could enable scientists to cultivate it in a laboratory setting. It is not currently possible to grow CLas on its own, hindering scientists’ ability to study it and ultimately to manage it.

    This research project involved a collaboration between UC Riverside, UC San Diego, Texas A&M University, and the U.S. Department of Agriculture. In addition to Borneman, members of the modeling team included UCR plant pathologist Georgios Vidalakis and UCSD systems biologist Karsten Zengler.

    UC Riverside is at the forefront of efforts to combat Huanglongbing. Other important areas of research include antibacterial development and delivery, immune system fortification in citrus, engineering resistant citrus via a detailed understanding of host-microbe interactions, breeding resistant citrus, and insect management, among others.

    Because microbes tend to mutate and acquire resistance mechanisms in response to drugs and other efforts to thwart them, Borneman cautions that any one solution to the problem may be short-lived.

    Transmission electron microscope image of CLas bacterium. (J.M. Bové/INRA)

    “Microbes almost always adapt to control measures, perpetuating the ‘arms race’ between pathogens and hosts,” Borneman said. “There won’t be one thing that will fix this disease. We likely will need to address all three components associated with the disease — the bacterium, the insect that transmits it, and the citrus plants — to find a long-lasting solution.”

    To that end, the research team is constructing metabolic models of citrus and the insect, the Asian citrus psyllid.

    “We expect that this multiorganism modeling endeavor will provide new insights into the mechanisms underlying this disease, which will lead to effective and sustainable Huanglongbing management strategies,” Borneman said. — By Jules Bernstein, UC Riverside

  • UC Riverside Discovers First Effective Treatment for Citrus-Destroying Disease

    UC Riverside scientists have found the first substance capable of controlling Citrus Greening Disease, which has devastated citrus farms in Florida and also threatens California.

    The new treatment effectively kills the bacterium causing the disease with a naturally occurring molecule found in wild citrus relatives. This molecule, an antimicrobial peptide, offers numerous advantages over the antibiotics currently used to treat the disease.

    Orange afflicted with Citrus Greening Disease. (UCR)

    UCR geneticist Hailing Jin, who discovered the cure after a five-year search, explained that unlike antibiotic sprays, the peptide is stable even when used outdoors in high heat, easy to manufacture, and safe for humans. 

    “This peptide is found in the fruit of greening-tolerant Australian finger limes, which has been consumed for hundreds of years,” Jin said. “It is much safer to use this natural plant product on agricultural crops than other synthetic chemicals.”

    Currently, some growers in Florida are spraying antibiotics and pesticides in an attempt to save trees from the CLas bacterium that causes citrus greening, also known as Huanglongbing or HLB. 

    “Most antibiotics are temperature sensitive, so their effects are largely reduced when applied in the hot weather,” Jin said. “By contrast, this peptide is stable even when used in 130-degree heat.”

    Jin found the peptide by examining plants such as the Australian finger lime known to possess natural tolerance for the bacteria that causes Citrus Greening Disease, and she isolated the genes that contribute to this innate immunity. One of these genes produces the peptide, which she then tested over the course of two years. Improvement was soon visible. 

    “You can see the bacteria drastically reduced, and the leaves appear healthy again only a few months after treatment,” Jin said.

    Because the peptide only needs to be reapplied a few times per year, it is highly cost effective for growers. This peptide can also be developed into a vaccine-like solution to protect young healthy plants from infection, as it is able to induce the plant’s innate immunity to the bacteria.

    Jin’s peptide can be applied by injection or foliage spray, and it moves systemically through plants and remains stable, which makes the effect of the treatment stronger.

    The treatment will be further enhanced with proprietary injection technology made by Invaio Sciences. UC Riverside has entered into an exclusive, worldwide license agreement with Invaio, ensuring this new treatment goes exactly where it’s needed in plants. 

    “Invaio is enthusiastic to partner with UC Riverside and advance this innovative technology for combating the disease known as Citrus Greening or Huanglongbing,” said Invaio Chief Science Officer Gerardo Ramos. “The prospect of addressing this previously incurable and devastating crop disease, helping agricultural communities and improving the environmental impact of production is exciting and rewarding,” he said. “This is crop protection in harmony with nature.”

    Hailing Jin, Geneticist, UC Riverside

    The need for an HLB cure is a global problem, but hits especially close to home as California produces 80 percent of all the fresh citrus in the United States, said Brian Suh, director of technology commercialization in UCR’s Office of Technology Partnerships, which helps bring university technology to market for the benefit of society through licenses, partnerships, and startup companies. 

    “This license to Invaio opens up the opportunity for a product to get to market faster,” Suh said. “Cutting edge research from UCR, like the peptide identified by Dr. Jin, has a tremendous amount of commercial potential and can transform the trajectory of real-world problems with these innovative solutions.”

    While the long-term effectiveness of this research has not yet been confirmed or published in a scientific journal and the project is still in its early stages, Dr. Jin’s promising findings have resulted in a commercial licensing agreement between UCR and Invaio Sciences. It is not uncommon for researchers to team with commercial licensing partners during the early phases of their studies. In this case, more work still needs to be done to confirm the robustness and viability of this treatment. Additional greenhouse trials are being initiated by Dr. Jin and her team at the citrus-specific Bio-Safety Level-3 Laboratory in Riverside, California. It also is expected that field trials will be conducted to show the effectiveness of the treatment under commercial grove conditions. — By Jules Bernstein, UC Riverside

    Regarding the announcement, Marcy Martin from the California Citrus Research Board shared, “While the release was understandably enthusiastic about potentially promising research and we are heartened by the commercial interest in this peptide, we are looking forward to reviewing complete studies on the effectiveness of this therapy in greenhouse and field studies.

    Importantly, this is not the time to let down our guard.  It continues to be critical for all citrus growers in the state to remain extremely vigilant in protecting their groves against the Asian citrus psyllid and HLB. The psyllid arrived from Mexico in 2008 and is now firmly established in southern California. The first HLB-positive tree was found in residential Los Angeles County in 2012. As of July 3, 2020, 1,926 HLB-affected trees have been identified and removed to slow the spread of the disease in residential areas of Los Angeles, Orange, Riverside and San Bernardino counties. Unlike Florida, where HLB has decimated commercial citrus groves, California growers invested in research early through the CRB and have been diligent in applying best-management practices; therefore, the disease has not yet been detected in any commercial groves. The CRB will continue to focus intensive efforts on a variety of promising research to find a solution to HLB.

    Moving forward, we at the CRB are proud to work on behalf of the 3,300-plus California citrus growers to invest in key studies to find a solution to HLB. Citrus growers always have been resilient and resourceful. Together, we will look toward the horizon for a solution to HLB.

    Marcy Martin, President, California Citrus Research Board

    In the meantime, we continue to monitor and review progress in potential therapies, new HLB-resistant varieties, better psyllid control strategies and more. We are enthusiastic about the commercial interest in HLB therapies and look forward to being able to share a range of potential approaches for California citrus growers as research progresses and matures. If you have any questions or would like additional information about the status of this research, please contact CRB President Marcy Martin at 559.708.3791 or marcy@citrusresearch.org.”

  • Bringing the Next Generation of Avocados to Market

    UC Riverside has entered into a $2.25 million partnership with Spain-based Eurosemillas S.A., a global leader in the commercialization of agriculture innovations, to help the university bring to market the most promising and advanced avocado scions and rootstocks in its collection.

    If successful, these varieties would meet diverse regional growing requirements, exhibit better post-harvest characteristics, increase yields, provide resistance against disease, and expand consumer market diversity.

    “Eurosemillas has successfully commercialized citrus varieties developed at UC Riverside in the past. They have the global network and expertise to do the same with the next generation of avocados,” said Brian Suh, director of technology commercialization in the Office of Technology Partnerships at UC Riverside, who worked with a team on this initiative for the past four years.

    Eurosemillas will obtain access to a small subset of the overall university avocado variety and rootstock collection for evaluation and testing on various continents to see if they perform as well as they do in California. At the same time, they will forge partnerships for commercialization that could lead to global market penetration of some of these selections.

    Niwala Abeysekara uses a leaf sensor on avocado plants in the Manosalva lab at UC Riverside. (UCR/Stan Lim)

    “After 31 years of working with UC on many other crops, we are delighted to partner with UCR again in a new product like avocado,” said Javier Cano Pecci, Chief Executive and Development Officer of Eurosemillas. “The avocado market is growing and is currently dominated by the Hass variety. This is a great opportunity for growers, marketers, retailers, and consumers to have options and diversify to include better avocado varieties and rootstocks adapted to their regions.”

    UC Riverside’s 70-year old avocado breeding programs house one of the most elite germplasm collections of scion and rootstock breeding material in the world. The University of California has partnered with California avocado growers since the inception of the industry a century ago and has had several plant breeders developing new varieties and rootstocks for the industry.

    Bob Bergh headed the variety improvement program for nearly 40 years, which released among other varieties, the ‘Lamb Hass’ and ‘GEM.’  This program is under the leadership of Mary Lu Arpaia, an extension horticulturist. The goal of the variety breeding program is to develop trees with high eating and market quality while increasing yield efficiency.

    Arpaia said for the California industry to remain viable, growers must have new varieties that yield more than Hass, are more tolerant to environmental stress, and can be produced reliably under high-density planting systems.

    “I am delighted by this partnership with Eurosemillas since it will help UC take this vision for the future toward reality,” Arpaia said.

    Mary Lu Arpaia, UC Riverside Extension Horticulturist

    The variety improvement program has four selections being readied for release that can augment the ‘Hass’ variety in terms of seasonality and have potential for expanded environmental adaptation within California.

    The rootstock breeding program was started in the 1940s by George Zentmyer and is currently directed by Patricia Manosalva, an assistant professor of plant pathology at UCR. The UCR Rootstock Breeding Program is one of the few well-recognized rootstock breeding programs worldwide and has been historically funded by the California industry through the California Avocado Commission. The main goal of the rootstock program is to develop and release the next generation of rootstocks that meet the most pressing needs of growers using traditional breeding complemented with genomic-assisted breeding approaches.

    The program is selecting rootstocks that can resist Phytophthora root rot, the most common avocado disease worldwide, as well as salinity, drought, and heat, all of which are expected to become worse as the climate warms. In collaboration with the California Avocado Commission, five UC Riverside advanced rootstocks exhibiting resistance to these major challenges are being evaluated by growers throughout California.

    “This partnership with Eurosemillas will allow us to test our five advanced rootstocks in combination with ‘Hass’ and local scions in other countries to determine their potential outside California,” Manosalva said.

    Peggy Mauk, director of agricultural operations and cooperative extension horticulture specialist, has been active in avocado research and extension for more than two decades. Over the past 25 years, avocado production in California and worldwide has been challenged by declining water quality. Avocado is the most salinity sensitive tree crop and ‘Hass’ is very susceptible to damage caused by salts. She initiated a program to find rootstocks tolerant to saline water.

    “Our UCR team in partnership with Eurosemillas is focused on finding rootstock/scion combinations that increase salinity tolerance,” Mauk said.

    Over the last 30 years, the avocado market has increased 2.5-fold and per capita consumption has quadrupled, generating interest in avocado production in many other countries, Manosalva said. But diseases, climate change, and the worldwide market’s dependence on the Hass variety threaten this burgeoning market.

    “The funding from Eurosemillas will allow UC Riverside to maintain the plant material and support and complement the current California Avocado Commission funding of the avocado scion and rootstock breeding programs, respectively, which have significant value given their uniqueness,” said Kathryn Uhrich, dean of UC Riverside’s College of Natural and Agricultural Sciences. — By Holly Ober, UC Riverside

    For more information on this avocado program contact Joyce Patrona: joyce.patrona@ucr.edu

  • $3 Million Program to Train Tomorrow’s Plant Scientists

    If you’re eating fruits, nuts, grains, or vegetables in a few years, you’ll likely owe a debt of gratitude to UC Riverside. The university has created a program to transition today’s undergraduates into professional scientists solving tomorrow’s farming challenges.

    The program, called Plants-3D, will train students to discover, design, and deploy biology and engineering solutions to the projected problem of massive-scale food insecurity due to climate change. 

    “It’s exciting that 50 students, many of whom are traditionally underrepresented in academia and the biotech sector, will now learn to use the most cutting-edge technologies in biology and engineering to help increase crop yields and nutritional value, while also helping themselves professionally,” said Julia Bailey-Serres, a UC Riverside professor of genetics who is leading the new program. 

    The program was made possible by a $3 million grant from the National Science Foundation Research Traineeship program. It will fund a total of 50 students who will receive academic and entrepreneurial training, as well as mentorship and stipends to help them travel to professional conferences.

    Plants-3D will foster a synthetic biology approach to solving agricultural problems, meaning students will learn to design biological systems that do not already exist in the natural world. This approach will enable plants to tolerate increased levels of stress due to drought, flooding, and extreme heat, as well as boost protection from pests, pathogens, and invasive plants. 

    An example project would be the discovery and design of chemical compounds to attract beneficial microbes that could reduce plant requirements for fertilizer. 

    “Not only will our trainees help improve crop resilience and yields, but many plant metabolites they discover will have applications in other fields as well, including medicine and nutrition,” said Plants-3D co-leader Ian Wheeldon, associate professor of chemical and environmental engineering.

    The program has already established relationships with companies for internships, helping ensure participants will go on to leadership positions in agricultural fields after graduate school. 

    The program will provide opportunities for UC Riverside undergraduates to participate in team research, enhancing their candidacy for graduate programs and jobs in agriculture and biotechnology. 

    Agriculture and related industries provide nearly 10% of U.S. employment opportunities, but the number of students graduating with degrees that would prepare them for these jobs is not meeting industry demand. Nearly 40% of positions are projected to go unfilled, according to the U.S. Department of Agriculture. 

    Making the problem even more dire is the rapid pace of retirement from the current agricultural workforce, which is the oldest and least diverse of all scientific workforces in the U.S., the USDA reported.

    “There is a giant, gaping need for scientists who can not only update the aging agricultural technologies of today, but who can find solutions to the challenges that climate change will pose for the farmers of tomorrow,” said Sean Cutler, UCR professor of plant cell biology. “This program will definitely help fill that need.” 

    About UC Riverside

    The University of California, Riverside (www.ucr.edu) is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California’s diverse culture, UCR’s enrollment is more than 24,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of almost $2 billion. To learn more, email news@ucr.edu.

  • When Life Gives you Sour Lemons, Use Genetics to Find Out Why!

    A team of researchers, including two from the University of California, Riverside, has identified the genes responsible for the hallmark sour taste of many citrus fruits. Published Tuesday, Feb. 25 in Nature Communications, the research could help plant breeders develop new, sweeter varieties.

    Modern citrus varieties have been bred over thousands of years to generate a broad palette of sour and sweet-tasting fruits. Analyses of their pulp reveals that a single chemical element—hydrogen—is largely responsible for the difference between sour and sweet-tasting varieties, which usually have similar sugar content. The pulp from sour fruits contains more hydrogen ions, giving it a lower pH and a tangy taste that is recognized by acid-sensitive cells in our taste buds. Conversely, pulp from sweeter varieties contains fewer hydrogen ions and tastes less acidic.

    Ronald Koes and colleagues at the University of Amsterdam in the Netherlands set out to untangle how some citrus varieties wind up with more acidic juice than others, a process that until now has remained a mystery. Their interest stemmed from a previous study showing that higher acidity in purple petunia flowers resulted in more petal pigmentation.

    Intrigued by the Faris variety of lemon tree, which produces branches bearing both sweet and sour fruits, and white and purple-tinged flowers, Koes’ team turned to UCR plant scientists Mikeal Roose and Claire Federici. Using the university’s vast Citrus Variety Collection, which preserves over 1,000 living citrus and related fruit varieties, Roose and Federici selected the Faris lemon and 20 other citrus fruits ranging from wincingly sour to sugary sweet for Koes’ team to analyze.

    By studying the expression of genes related to those controlling acidity in petunias, Koes’ team identified two citrus genes, CitPH1 and CitPH5, that are highly expressed in sour varieties and weakly expressed in sweet-tasting varieties. The CitPH1 and CitPH5 genes encode transporter proteins that pump hydrogen ions into the vacuole, a large storage compartment inside juice cells, thus increasing their overall acidity.

    Next, the team turned its attention to genes that control the levels of CitPH1 and CitPH5 in juice cells. While down-regulation of CitPH1 and CitPH5 in sweeter tasting varieties arose multiple times independently in different varieties, the researchers found that mutations in genes for a handful of transcription factors (proteins that help turn specific genes on and off) were responsible for reduced expression of CitPH1 and CitPH5, and therefore a sweeter taste.

    Roose, a professor of genetics in UCR’s College of Natural and Agricultural Sciences, said the findings could help breeders develop better-tasting citrus fruits. However, he said breeding varieties with severe mutations in the transcription factors such as those studied in the “acidless” citrus would be “overkill,” producing sugary citrus fruits with none of their popular acidic kick. Instead, plant scientists should look to target mutations that have a less dramatic effect on the production and activity of transporter proteins.

    “By understanding the mechanism acidification of fruit cells, we can now look for related genes that might reduce the expression of CitPH1 and CitPH5 just enough to engineer or select for new, sweeter varieties,” Roose said.

    The title of the paper is “Hyperacidification of Citrus fruits by a vacuolar proton-pumping P-ATPase complex.” In addition to Koes, authors at the University of Amsterdam are Pamela Strazzer, Cornelis Spelt, Shuangjiang Li, Mattijs Bliek, and Francesca Quattrocchio. Roose and Federici’s work was supported by the United States Department of Agriculture (USDA)’s National Institute of Food and Agriculture.

    About UC Riverside: The University of California, Riverside (www.ucr.edu) is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California’s diverse culture, UCR’s enrollment is now nearly 23,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion. To learn more, call (951) UCR-NEWS.