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California Avocado Growers Seminars Series 2021
Scheduled Dates and Topics
February 17, (9 - 11 AM)
The Efficacy of Gibberellic Acid on Improved Fruit Set
Avocado Flowering and Varieties
Texas A&M AgriLife researchers have made a discovery that will help combat fastidious pathogens, which cost U.S. agriculture alone billions of dollars annually.
For the past few years, Kranthi Mandadi, Ph.D., a Texas A&M AgriLife Research scientist and associate professor in Texas A&M's Department of Plant Pathology and Microbiology, along with his colleagues, has been working on developing new biological technologies to fight fastidious or “unculturable” pathogens. Mandadi and members of his team are based at the Texas A&M AgriLife Research and Extension Center in Weslaco.
The results of their work, “Plant hairy roots enable high throughput identification of new antimicrobials against Candidatus Liberibacter spp.” were recently published in Nature Communications.
Fastidious plant diseases and their costs
Fastidious plant pathogens infect citrus, tomatoes, potatoes, grapes, peppers and other crops grown throughout Texas. Often transmitted by insect vectors, these disease agents cause billions of dollars of damage each year. The U.S. citrus industry alone would save $3 billion per year through control of just one of these diseases — citrus greening. Additionally, the fastidious pathogen that causes Pierce's Disease in grapes is the No.1 threat to the $1 billion wine industry in Texas.
“Currently, invasive fastidious pathogens are causing several major outbreaks in row crops, specialty crops and citrus, with immense costs to Texas and the U.S.,” said Juan Landivar, Ph.D., director of the AgriLife center at Weslaco, which has been involved in efforts to combat fastidious plant pathogens for many years.
Landivar said an expanded effort against fastidious plant diseases would protect the health of crops, environments, economies and people across the country.
A way to grow “unculturable” bacteria
Some plant pathogens can be grown as pure cultures in the laboratory in the presence of artificial nutrient solutions. Being able to culture disease agents in the lab facilitates their study by providing researchers with a reliable supply of experimental material. However, an estimated 99% of bacteria in the world are fastidious, or unable to grow outside their native environment.
“The greatest obstacle to understanding and controlling fastidious pathogens was the inability to cultivate them in a laboratory setting and to screen for lots of potential therapies,” said Leland “Sandy” Pierson, Ph.D., professor and head of Texas A&M's Department of Plant Pathology and Microbiology. “But Dr. Mandadi and his team have developed a breakthrough method as an alternative means to propagate fastidious bacteria. These bacteria are believed to be responsible for Huanglongbing, also known as citrus greening disease, and other insect-vectored diseases such as potato zebra chip and tomato vein greening disease.”
The breakthrough came in the form of the “hairy root” system. This technology utilizes the pathogen-infected host tissues to produce so-called hairy roots that can serve as biological vessels for the propagation of these pathogens in the laboratory.
“Classical microbiological techniques developed early in the 19th century cultured animal and mammalian viruses in host cells, tissues and embryonated eggs,” Mandadi said. “In a similar manner, we hypothesized that plant hairy roots could be suitable for propagating fastidious pathogens. And indeed, hairy roots supported the accumulation and growth of fastidious plant bacteria.”
Microbial hairy roots appear similar to normal root tissues that develop from the plant and mimic a bacterium's natural environment, he said. This allows the growth of the fastidious pathogens in controlled laboratory conditions.
Expedited screening for antimicrobial treatments
While microbial hairy root cultures are not traditional “pure” test tube cultures, they allow on-demand access to the fastidious bacterium in the laboratory. This enables the expedited screening of diverse antimicrobials like chemical inhibitors, immune modulators as well as gene/CRISPR-based therapies.
Other advantages are that hairy root cultures are easy to produce in the laboratory and can be maintained for several months to a year in laboratory growth chambers. Depending on the pathogen and the efficacy of screening, it is also at least four times faster than conventional screening methods, according to Sonia Irigoyen, Ph.D., and Manikandan Ramasamy, Ph.D., both AgriLife Research scientists and co-authors of the study.
In addition, the hairy root bioassays are scalable, so they can be used to pre-screen from a few to several hundred potential therapies simultaneously in a high-throughput manner. The microbial hairy root system can also be used to obtain mechanistic insights into antimicrobial function.
“Use of this technique has already led to the discovery of six new antimicrobial peptides with proven efficacy in plant materials,” Mandadi said. “These antimicrobials, either singly or in combination, could be used as near- and long-term therapies to control citrus greening, potato zebra chip and tomato vein greening diseases.”
Collaborators in the fight
“Typically, the type of breakthrough Dr. Mandadi and his team came up with is unusual for a university system off-campus center, as such centers usually have limited personnel and resources,” Landivar said. “Fortunately, the support we have received from the Texas A&M University System and other funding agencies and collaborators has helped make it possible for the Weslaco center to perform this world-class-level research.”
Besides a team of researchers at the Weslaco center, Mandadi collaborates with scientists at Texas A&M University, Texas A&M University Kingsville-Citrus Center, University of Florida, University of California System, and industry stakeholders including Citrus Research and Development Foundation, Texas Citrus Pest and Disease Management Corporation, Bayer and other entities.
Southern Gardens Citrus, a subsidiary of U.S. Sugar in Florida, has partnered with Texas A&M to commercialize the hairy root system as well as new therapies for application in the field.
Landivar also said funding from the U.S. Department of Agriculture National Institute of Food and Agriculture's Emergency Citrus Disease Research and Extension program, NIFA ECDRE, and support from the Foundation for Food and Agricultural Research and AgriLife Research's Insect-Vectored Disease Grant are making it possible to facilitate development of innovative technologies and discovery of therapies to combat diseases caused by fastidious bacteria.
To expand on his research, Mandadi recently partnered on a new project with Citrus Research and Development Foundation, Bayer, Southern Gardens Citrus, University of Florida and University of California-Davis. That project is funded by the NIFA ECDRE program. The overall goal is to bring together academics, growers and agrochemical industry to discover, develop and commercialize therapies for citrus greening disease.
Mandadi said use of the hairy root system has already been instrumental in finding several potential new treatments for citrus greening and potato zebra chip, as described in the Nature Communications article.
“We hope this technology can be further expanded to find even more therapies against current and emerging fastidious pathogens and, ultimately, with the support of industry, deploy them as field-ready products,” he said.
Are you interested in learning more about Nitrogen Management?
Are you a Certified Crop Adviser seeking Continuing Education Units and/or
preparing for the new California Nitrogen Specialty Exam?
Has your grower clientele asked you if you are eligible to sign off on a Nitrogen Management Plan?
Registration for the brand new UC Nitrogen Management course is now open at
The UC Nitrogen Course is taught online through a video series delivered by UC Researchers and Extension Specialists. Each module is eligible for Certified Crop Advisor (CCA) continuing education units (CEUs).
The course is open to anyone interested in learning more about N management in California. The curriculum addresses all the learning objectives set forth by the American Society of Agronomy (ASA) for the new California Nitrogen Management Specialty Exam.
The 7-part video series opens next week November 9, 2020
Register at http://ucanr.edu/NitrogenCourse
You may join the course at any time up until December 31, 2020.
Map of Nitrogen Management Areas in Ventura County. The whole state is subject to nitrogen management protocols.
Produce Exposed to Smoke
When assessing the safety of exposed produce, the difficulty is knowing what has been burning. If it is just vegetation smoke then it's probably safe to eat produce after rinsing off the ash (just the same as having a bonfire in your garden), although it might still taste/smell smoky.
If the air pollution has particulate matter from treated timber, tires, non-food grade oils, or anything plastic or chlorinated that burned it may include a mixture of Polycyclic Aromatic Hydrocarbons (PAHs), dioxins, and metals. Exposure to fire retardant may have also occurred.
An unpublished literature review on the health impacts of PAHs from traffic-related air pollution on lettuce grown in urban agriculture found that:
- Some PAHs can be absorbed into plant tissue, and so cannot be simply washed off.
- The health risk from eating these PAHs is a small proportion of the health impact from breathing them, and it is far below the EPA's level of concern for lifetime cancer risk.
- It is possible that the health benefit of eating the vitamins and nutrients in green leafy vegetables might outweigh that negligible negative impact.
- There is not enough research available on the cumulative impacts of air pollution on produce to make any solid conclusions about the health impacts.
Produce Safety after Urban Wildfire study conducted following Oct 2017 fires in Sonoma County.
Fires & Food Safety flyer by USDA FSIS, 2/2013.
Food Safety after Fire by USDA FSIS, 8/2013.
Some technical guidance tip sheets and power points that may be helpful can be found here:
- Soil Sampling, Risk Mapping & Exposure Prevention - Rob Bennaton
- Contaminants in Soils, Data Collection-Interpreting Test results and Minimizing Exposure by Cornell University
- Testing Laboratories in California
- UCCE Soils in Urban Agriculture
- Best Practices for Produce Safety After A Fire
- Produce Safety After a Fire Tool Kit