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.
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.
“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.
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
The California Department of Food and Agriculture (CDFA) is seeking a grower representative with operations in the Fresno County area to sit as a member on the Citrus Pest and Disease Prevention Committee. The Committee advises the CDFA Secretary on activities associated with the statewide citrus specific pest and disease work plan that includes – but is not limited to – outreach and education programs and programs for surveying, detecting, analyzing, and treating pests and diseases specific to citrus.
Committee members receive no compensation but are entitled to payment of necessary travel expenses in accordance with the rules of the Department of Personnel Administration. The term for one grower representative from Fresno County expires on Sept. 30, 2023. Applicants should have an interest in agriculture and citrus pest and disease prevention. Individuals interested in being considered for a committee appointment should send a resume by Feb. 15, 2021 to the California Department of Food and Agriculture, Citrus Pest and Disease Prevention Division, 1220 N Street, Sacramento, California 95814, Attention: David Gutierrez.
For additional information on the committee vacancy, contact: David Gutierrez, Branch Chief, Citrus Pest and Disease Prevention Division at (916) 274-6300, or e-mail David.Gutierrez@cdfa.ca.gov.
Please thank this video’s sponsor Trece for their industry support.
Another pest in almonds? Just what we needed, right? Only this one you can’t see. Almond growers have been dealing with nematodes for a long time; however, the peach root knot nematode is new to California almond orchards. Watch this brief interview with UC Riverside Nematologist Andreas Westphal as he explains and read more about it in Pacific Nut Producer Magazine.
Please thank this video’s sponsor Trece for their industry support.
So how much potassium does an almond or pistachio orchard need? How and when should it be applied? Watch this brief interview with UCCE Orchard Systems Advisor Phoebe Gordon as she shares some facts and considerations for growers to maintain a healthy orchard and prevent potassium deficiencies. Read more about best practices for orchard management in Pacific Nut Producer Magazine.
Please thank this video’s sponsor Trece for their industry support.
An Asian citrus psyllid (ACP) sample – confirmed positive for Candidatus Liberibacter asiaticus (CLas), the bacteria that causes Huanglongbing (HLB) – was collected from a residential property in the Fallbrook area of San Diego County. Confirmed by Citrus Research Board’s Jerry Dimitman Laboratory, this adult psyllid sample is the first CLas-positive ACP found in San Diego County.
While the first confirmation of a CLas-positive ACP in San Diego County is concerning, as of today, HLB has not been detected in any San Diego County trees but surveying and sampling of area trees is ongoing. This find signals a critical time for homeowners and growers alike to continue to control ACP populations to stop the potential spread of this deadly disease, as oftentimes a CLas-positive ACP precedes the detection of an HLB-positive tree.
The HLB quarantine zone will not be expanded as a result of this CLas-positive ACP detection and CDFA staff is swiftly conducting surveys and collecting samples from HLB host plants that are located within a 250-meter radius around the find, per the ACP/HLB Action Plan.
While treatment is not mandatory for area commercial growers as a result of the detection, San Diego County commercial growers who have additional questions can contact Sandra Zwaal, San Diego County Grower Liaison, at szwaal2@gmail.com.
CLICK HERE for additional information from Citrus Pest and Disease Prevention Program (CPDPP) Citrus Insider.
Source: Citrus Pest and Disease Prevention Program (CPDPP) Citrus Insider
The U.S. Department of Agriculture (USDA) is allocating more than $70 million to support 383 projects under the Plant Protection Act’s Section 7721 program to strengthen the nation’s infrastructure for pest detection and surveillance, identification, threat mitigation, to safeguard the nursery production system and to respond to plant pest emergencies. Universities, states, federal agencies, nongovernmental organizations, nonprofits, and Tribal organizations will carry out selected projects in 49 states, the District of Columbia, Guam, and Puerto Rico.
“State governments, academic institutions, and other essential cooperators across the country use these USDA funds to protect American crops and natural resources and ensure the marketability of our agricultural products across the globe,” said Greg Ibach, Under Secretary for USDA’s Marketing and Regulatory Programs.
The fiscal year 2021 project list includes 29 projects funded through the National Clean Plant Network (NCPN). The NCPN helps our country maintain the infrastructure necessary to ensure that pathogen-free, disease-free and pest-free certified planting materials for fruit trees, grapes, berries, citrus, hops, sweet potatoes, and roses are available to U.S. specialty crop producers.
Since 2009, USDA has supported more than 4,400 projects and provided nearly $670 million in funding through the Plant Pest and Disease Management and Disaster Prevention Program. Collectively, these projects allow USDA and its partners to quickly detect and rapidly respond to invasive plant pests and diseases.
In FY 2021, funded projects include, among others:
USDA will use $14 million to rapidly respond to invasive pest emergencies should a pest of high economic consequence be found in the United States. In the past, USDA has used these funds to rapidly respond to pests such as grasshoppers, Mormon crickets, the Asian giant hornet, coconut rhinoceros beetle, exotic fruit flies, and the spotted lanternfly.
As the United States and the world recognize the International Year of Plant Health through June 2021, this funding highlights USDA’s continued commitment to safeguarding our agricultural resources for current and future generations.
Learn more about the Plant Protection Act, Section 7721 on the USDA Animal and Plant Health Inspection Service (APHIS) website: www.aphis.usda.gov/ppa-projects.
Yellow starthistle is a noxious weed common in many areas of California’s grasslands, and is often a priority for control, due to its effects on decreased livestock carrying capacity, decreased plant diversity, and interference with recreational uses (reviewed in DiTomaso et al. 2006). A number of conventional herbicides are highly effective in controlling yellow starthistle (DiTomaso et al. 2006, USFS 2014), but in many settings, there is increased pressure to decrease use of conventional herbicides and find alternative control methods.
Organic herbicides have received increased attention, including in the UC Weed Science Blog (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=5623, https://ucanr.edu/blogs/UCDWeedScience/index.cfm?tagname=organic%20herbicide), but often require repeated applications when trying to control plants during the growing season (Reiter and Windbiel-Rojas 2020).
When considering the use of organic herbicides, it is important to not just substitute them into management protocols for conventional herbicides, but to consider their mode of action, and how that may shape promising approaches for their use. For example, D-Limonene (Avenger) and Capric and Caprylic acids (Suppress) contact-kill tissues, but are not systemic. This may make their effectiveness weaker when controlling weeds during the growing season, but could be promising in killing flowers and preventing seeding, as has been found with a number of conventional herbicides on yellow starthistle (DiTomaso et al. 2006), and in the use of both conventional herbicides and the organic herbicide Suppress in decreasing flowering of Wooly Distaff Thistle (DiTomaso et al. 2017).
To assess whether these organic herbicides could provide effective control of yellow starthistle, we collaborated with Putah Creek Riparian Reserve to compare the effects of the timing and type of herbicide on yellow starthistle. Plots were mowed in December 2018 to assure good contact of the organic herbicides with growing plants. In 3 m x 3 m plots (7 replicates per treatment), we applied one of four herbicide treatments (no herbicide (control), the conventional herbicide Transline (clopyralid), the organic herbicide Avenger (D-Limonene), and the organic herbicide Suppress (caprylic and capric acids). These were applied in the spring of 2019 at 3 timings: early spring, mid-spring, and then at the initiation of yellow starthistle flowering in the late spring (see table below for details on applications).
In the year of treatment, only the early and mid-spring applications of Transline decreased yellow starthistle, essentially eliminating it (see Photo 2), and there were no effects of the organic herbicides on the cover of yellow starthistle.
However, all three herbicides applied at flowering resulted in damage to yellow starthistle (see Photo 3.)
In the following growing season, vegetation cover assessed in the late spring of 2020 showed that the most effective control of yellow starthistle was achieved from the late-season (at flowering) spray in the previous year—with equally effective control of the organic herbicides and Transline (Figure 1).
Of course, more time is needed to assess the long-term effects of late-season applications of organic herbicides, but based on two years of results, organic herbicides applied during the growing season have little effect on yellow starthistle, but applications at flowering are promising. Late-season applications are also beneficial because most desirable plants have already senesced at this time, providing the opportunity for yellow starthistle control with minimal unintended effects on other vegetation. — By Valerie Eviner, Professor of Ecosystem Management & Restoration, UC Davis Department of Plant Sciences
References:
DiTomaso, JM, GB Kyser, and MJ Pitcairn. 2006. Yellow starthistle management guide. Cal-IPC Publication 2006-03.
DiTomaso, JM, GB Kyser, DJ Lewis and JA Roncoroni. 2017. Conventional and organic options for the control of Wooly Distaff Thistle (Carthamus lanatus). Invasive Plant Science and Management 10: 72-79.
USFS. 2014. Field guide for managing yellow starthistle in the Southwest. USDA TP-R3-16-07.
Reiter, M and K Windbiel-Rojas. 2020. Organic herbicides and glyphosate for weed control: results of coordinated experiments in urban landscapes. CAPCA Advisor Magazine. February 2020. Pp 24-30.