Citrus greening, also named Huanglongbing (HLB), is probably the most devastating citrus disease threatening the global citrus industry. To prevent its further spread, early diagnosis before the appearance of the dreaded symptoms is particularly important. But the unculturable nature of the bacteria, their low concentration and uneven distribution in their hosts make it extremely difficult to detect HLB infection.

Hailing Jin, an associate professor of plant pathology and microbiology at the University of California, Riverside, recently published a paper in the journal Molecular Plant in which she reports having profiled small ribonucleic acid (sRNA) from citrus plants, some of which were affected by HLB.

Her research showed that several sRNAs were found to have been induced specifically by HLB, meaning they could potentially be developed into early diagnosis markers for the disease.

The study also showed that in a three-year field trial in southwest Florida diseased trees suffered from severe phosphorus deficiency and that application of phosphorus solutions to the diseased trees significantly alleviated HLB symptoms, improving fruit yield.

In the trial, 19 healthy sweet orange trees were grafted with HLB-positive bark or leaf pieces. As controls, five trees were mock-inoculated with pathogen-free healthy tissue. Phosphorus solutions were applied to the 19 HLB-positive trees three times a year. After two years of treatment, the diseased trees displayed significantly reduced HLB symptoms.

“Compared with the mock-treated plants, the phosphorus-treated trees had a greener appearance and more vigorous growth,” Jin said. “Fruit yield increased approximately two-fold compared with the mock-treated plants.”

She cautioned that the application of phosphorus solutions did not cure the trees.  Her research suggests, however, that additional phosphorus application may help diseased trees look healthier and improve fruit yield.

Jin was joined in the research by Hongwei Zhao, Ruobai Sun, Chellappan Padmanabhan, Airong Wang, Michael D. Coffey, Thomas Girke, Timothy J. Close, Mikeal Roose and Georgios Vidalakis at UC Riverside; and researchers at Nanjing Agricultural University, China; the U.S. Department of Agriculture; Fujian Agriculture and Forestry University, China; and the University of Florida.

The research was supported by a grant to Jin from California Citrus Research Board.

In California’s coastal winegrape-growing regions, a spring freeze can be devastating. Tender shoots and leaves burn back, causing damage that reduces the crop yield when it is harvested many months later.

“We’ve had some very severe frosts in San Luis Obispo County and on the Central Coast over the years,” said Mark Battany, UC Cooperative Extension advisor in San Luis Obispo and Santa Barbara counties. “In 2011 we had the most severe frost in 30 years and many millions of dollars of crop and wine value were lost because of that freeze.”

Farmers take various measures to protect their crops when temperatures dip below freezing, such as mowing or tilling the vineyard row middles, or running sprinklers with water pumped from underground aquifers or diverted from streams.

“Sprinkler frost protection is very effective in many areas,” Battany said. “The concern we have in California is that water is becoming more limited. We don’t have the ability to easily import water from other areas to our coastal regions, and our local supplies are being stretched quite thin.”

Some farmers are considering wind machines, which mix warmer air high above the ground with air closer to the ground to raise the temperature. But wind machines are expensive, and the potential effectiveness depends on the strength of the temperature inversion. UC scientists are now gathering data to help inform farmers before making the costly investment.

Battany and his colleagues - Rhonda Smith, UCCE advisor in Sonoma County, Richard Snyder, UCCE specialist in the Department of Land, Air and Water Resources at UC Davis, and Gwen Tindula, UCCE staff research associate - are collecting temperature inversion data at different locations in 60 coastal vineyards throughout three counties to document inversions during frost events.

The scientists installed 35-foot-high meteorological towers with data loggers at the top and at the five-foot height to measure the difference in temperature. In the first year of the study, there were useful inversion conditions on nearly three-fourths of the nights when there was frost.

“That’s a fairly good success rate,” Battany said. “The wind machine will provide quite a bit of protection under those conditions.”

The study will continue this year and in 2014. Farmers who wish to install their own meteorological towers with data loggers can do so at a cost of about $250 each. Installation instructions and specifications are available on the UCCE website.

The UCCE research is funded with a grant from the American Vineyard Foundation and a CDFA Specialty Crops Block Grant.

For more details, see the video below:

A team of researchers, led by a University of California, Davis, plant scientist, has identified a lettuce gene and related enzyme that put the brakes on germination during hot weather -- a discovery that could lead to lettuces that can sprout year-round, even at high temperatures.

The study also included researchers from Arcadia Biosciences and Acharya N.G. Ranga Agricultural University, India.

The finding is particularly important to the nearly $2 billion lettuce industries of California and Arizona, which together produce more than 90 percent of the nation's lettuce. The study results appear online in the journal The Plant Cell.

"Discovery of the genes will enable plant breeders to develop lettuce varieties that can better germinate and grow to maturity under high temperatures," said the study's lead author Kent Bradford, a professor of plant sciences and director of the UC Davis Seed Biotechnology Center.

"And because this mechanism that inhibits hot-weather germination in lettuce seeds appears to be quite common in many plant species, we suspect that other crops also could be modified to improve their germination," he said. "This could be increasingly important as global temperatures are predicted to rise."

Most lettuce varieties flower in spring or early summer and then drop their seeds -- a trait that is likely linked to their origin in the Mediterranean region, which, like California, characteristically has dry summers. Scientists have observed for years that a built-in dormancy mechanism seems to prevent lettuce seeds from germinating under conditions that would be too hot and dry to sustain growth.

While this naturally occurring inhibition works well in the wild, it is an obstacle to commercial lettuce production.

In the California and Arizona lettuce industries, lettuce seeds are planted somewhere every day of the year -- even in September in the Imperial Valley of California and near Yuma, Ariz., where fall temperatures frequently reach 110 degrees.

In order to jump-start seed germination for a winter crop in these hot climates, lettuce growers have turned to cooling the soil with sprinkler irrigation or priming the seeds to germinate by pre-soaking them at cool temperatures and re-drying them before planting -- methods that are expensive and not always successful.

In the new study, researchers turned to lettuce genetics to better understand the temperature-related mechanisms governing seed germination. They identified a region of chromosome six in a wild ancestor of commercial lettuce varieties that enables seeds to germinate in warm temperatures. When that chromosome region was crossed into cultivated lettuce varieties, those varieties gained the ability to germinate in warm temperatures.

Further genetic mapping studies zeroed in on a specific gene that governs production of a plant hormone called abscisic acid -- known to inhibit seed germination. The newly identified gene "turns on" in most lettuce seeds when the seed is exposed to moisture at warm temperatures, increasing production of abscisic acid. In the wild ancestor that the researchers were studying, however, this gene does not turn on at high temperatures. As a result, abscisic acid is not produced and the seeds can still germinate.

The researchers then demonstrated that they could either "silence" or mutate the germination-inhibiting gene in cultivated lettuce varieties, thus enabling those varieties to germinate and grow even in high temperatures.

Other researchers on the study were: Post-doctoral researcher Heqiang Huo and staff researcher Peetambar Dahal, both of the UC Davis Department of Plant Sciences; Keshavulu Kunusoth of Acharya N.G.

Ranga Agricultural University, India; and Claire McCallum of Arcadia Biosciences, which provided the lettuce lines with variants of the target gene to help confirm the study's findings.

Funding for the study was provided the U.S. Department of Agriculture National Institute of Food and Agriculture and the National Science Foundation.

 

The University of California, through its Division of Agriculture and Natural Resources, will convene some of the world’s leading experts April 9 at the Global Food Systems Forum to address how to sustainably feed 8 billion people by 2025. The discussion will bring together people from a dynamic range of disciplines, including farmers, researchers, policymakers, economists, environmentalists and geopolitical experts. The general public can view the event live by webcast.

The daylong forum, part of ANR’s Statewide Conference in Ontario, Calif., will feature two moderated panels and keynote addresses by Mary Robinson, former president of Ireland and president of the Mary Robinson Foundation – Climate Justice, and Wes Jackson, founder and president of The Land Institute.

Michael Specter, global issues writer for The New Yorker magazine, will moderate the first panel, which will focus on the geopolitical, ethical, economic, environmental and technical challenges facing food systems from a global perspective. Award-winning author and journalist Mark Arax will moderate the second panel, which will address the implications, responsibilities and innovative opportunities from a California perspective.

The panelists will include a mix of UC and non-UC experts and thought leaders. View a list of speakers at http://food2025.ucanr.edu/Speakers.

“As a public research university, we’re a recognized leader in tackling the world’s toughest challenges,” said Barbara Allen-Diaz, UC vice president for agriculture and natural resources. “Building on our expertise in agriculture and finding practical, science-based solutions, it falls to us to convene these sorts of conversations and look far beyond the borders of our campuses. Only through discussions of this nature will people find the common ground to move the world forward on what is a compelling, complex and crucial issue.”
 
The general public is encouraged to view the live webcast and join the conversation on Twitter by following (hashtag)Food2025. To learn more about the UC Global Food Systems Forum and to sign up to view the webcast, visit http://food2025.ucanr.edu.

Food forum at a glance

• WHAT: Live webcast of UC Global Food Systems Forum at http://food2025.ucanr.edu
• WHO: World-renowned leaders in food systems dialogue. See a list at http://food2025.ucanr.edu/Speakers
• WHEN: April 9, 2013 (9 a.m.-5 p.m. PDT)
• WHERE: Register for the webcast at http://food2025.ucanr.edu/Webinar