Discolored leaves. Decaying roots. Dead wood. Mother Nature offers a fascinating and colorful backdrop of clues to track microscopic killers. Much like any medical mystery, experts are called in to diagnose or identify a disease from its symptoms and recommend management strategies to prevent further damage or loss of healthy plants.
In the world of crop science mysteries, plant pathology solves the crime. The usual suspects include bacteria, fungi and viruses.
Humans and animals depend on plants for their food supply and ultimately for their survival. When diseases threaten crops, a high-quality, affordable food supply is placed at risk. For growers, plant diseases can reduce crop yields. For consumers, reduced crop yields can drive higher food prices. Plant pathology research holds enormous implications for a sustainable food supply.
Florent Trouillas, who was named UC Cooperative Extension specialist in the Department of Plant Pathology at UC Davis and the Kearney Agricultural Research and Extension Center last year, explains the bottom line of most concern to growers.
"Once we identify a disease causal agent, a main question remains from growers. What growers really want to know is how to control the disease and prevent its spread to new healthy plants; they look to the University of California for solutions," Trouillas said.
A crisis in the food production system can impact other areas of society as well. In fact, history is filled with examples of how plant diseases influenced economies, environments and human societies.
Another historical illustration of plant pathology research occurred in the 1920s. The most common trees in the forests of the United States at the turn of the century were the majestic American chestnuts. The trees generated income for humans and the timber industry, served as a food source for people and animals, and provided habitat for wildlife. Then the trees started dying, until by the late 1920s, they had become the first tree in modern times on the brink of extinction. Plant pathologists were particularly adept at identifying plant diseases by this time and diagnosed the Cryphonectria parasitica fungus as the cause of the chestnut blight. By preventing the extinction of the pivotal species, plant pathology had a direct impact on the economy and the environment.
More recent major plant disease outbreaks in the United States involving plant pathology research have included Sudden Oak Death with devastating effects in California and Oregon forests, pitch canker killing California native pine species, and citrus canker in Florida, which has had a huge economic impact on the industry.
Veterinarians treat diseases in animals, physicians in humans. Trouillas describes the role of plant pathologists in similar terms. “We study the pathology of plant systems. Plant pathologists treat plants," he said.
Healthy plants ensure a sustainable food source and habitat for so many other organisms, including the human species.
“Simply offering healthy options is not enough to motivate children to make healthy choices,” said Sheri Zidenberg-Cherr, UC Cooperative Extension specialist in the Department of Nutrition at UC Davis.
“Moreover, imposing restrictions rather than providing children with options to make healthy choices can have long-term negative effects,” said Rachel Scherr, assistant project scientist, also in the UC Davis Department of Nutrition.
In 2012, more than one-third of children in the U.S. were overweight or obese, according to the Centers for Disease Control and Prevention. Studies have shown that obese children are more likely to be obese as adults, increasing their risk for health problems including heart disease, type 2 diabetes, stroke, cancer and osteoarthritis. To target the complex issue of eating habits, Zidenberg-Cherr and her UC Cooperative Extension and UC Davis colleagues designed a school-based program and tested it in Sacramento and Stanislaus counties through the leadership of UCCE nutrition, family and consumer science advisors Terri Spezzano and Yvonne Nicholson.
“Parents shared with me that their children are voicing input on meals and asking if they can add fruit to their salads,” a participating teacher told the researchers.
During the first year that the Shaping Healthy Choices Program was implemented in Sacramento County schools, the number of children classified as overweight or obese dropped from 56 percent to 38 percent. The participating students also improved their nutrition knowledge, ability to identify different kinds of vegetables and amounts of vegetables that they reported eating.
“I tried zucchini and yellow squash when I was little and didn't like it, but now I tried it and I love it!” said a 9-year-old student.
The Shaping Healthy Choices Program takes a multifaceted approach, combining nutrition education with family and community partnerships, regional agriculture, foods available on school campus and school wellness policies.
The garden-enhanced, inquiry-based nutrition curriculum was developed by Jessica Linnell, a doctoral candidate in the Graduate Group in Nutritional Biology; Carol Hillhouse, the School Garden Program director at the Agricultural Sustainability Institute; and Martin Smith, a UCCE specialist in the Departments of Human Ecology and Population Health and Reproduction. The family and community partnerships featuring family newsletters were developed by Carolyn Sutter, a graduate student in the Graduate Group of Human Development, and Lenna Ontai, a UCCE specialist in the Department of Human Ecology. Lori Nguyen, a doctoral candidate in the Graduate Group in Nutritional Biology, Sheridan Miyamoto, postdoctoral scholar in the Betty Irene Moore School of Nursing, and Heather Young, dean of the Betty Irene Moore School of Nursing, organized community-sponsored health fairs.
Gail Feenstra, deputy director and food systems analyst for the UC Agricultural Sustainability Institute, helped the schools set up systems to add fresh, locally grown produce to their menus. Jacqueline Bergman, a postdoctoral scholar in the Department of Nutrition, coordinated school-site specific wellness committees.
The UC Cooperative Extension and UC Davis team worked with classrooms to use Discovering Healthy Choices, a standards-based curriculum that incorporates interactive classroom nutrition, garden and physical activity education for upper elementary school students. Teachers partnered with UCCE to incorporate cooking demonstrations to show the connections between agriculture, food preparation and nutrition. To reinforce the lessons at home, Team Up for Families – monthly newsletters containing nutrition tips for the parents – were sent home with the students. School Nutrition Services purchased fruits and vegetables from regional growers and distributors to set up salad bars and prepare dishes made with fresh produce. The Shaping Healthy Choices Program activities were integrated into the school wellness initiatives.
“My students shared things they learned about safe food handling and safety in cooking,” said a teacher who participated in the study. “Parents said their children want to help in preparing meals at home.”
“My daughter is more interested in trying new foods and eating more fruits and vegetables,” reported one parent. “She often surprises the family by making a surprise salad snack for everyone.”
Preliminary analysis shows that nine months after the classroom education ended, the decrease in the students' body mass index percentiles, or BMI percentiles, was sustained. “This is a big deal,” said Zidenberg-Cherr, while cautiously encouraged by the program's success. “We are in the process of analyzing several aspects of the program — the data set is so complex and I have to feel 100 percent confident in our statements.”
Through a partnership with UC CalFresh, the researchers have expanded the comprehensive program to schools in Placer, Butte and San Luis Obispo counties. Determining feasibility for expansion of the program for broader dissemination is planned for the 2015-2016 school year.
This project was funded by grants from the UC Division of Agriculture and Natural Resources and the U.S. Department of Agriculture.
The University of California Global Food Initiative aims to put the world on a path to sustainably and nutritiously feed itself. By building on existing efforts and creating new collaborations among UC's 10 campuses, affiliated national laboratories and the Division of Agriculture and Natural Resources, the initiative will develop and export solutions for food security, health and sustainability throughout California, the United States and the world.
Holtz has been pioneer in ag burn alternatives throughout his 26-year-career with UCCE, and going back still further on his family almond farm near Modesto. Beginning in the early 1990s, Holtz and his father experimented with chipping almond prunings instead of burning them, long before air quality regulations required wide implementation of the practice.
When Holtz heard a four-acre stone fruit orchard was slated for removal at the UC Kearney Agricultural Research and Extension Center in Parlier seven years ago, he took the opportunity to study the impact of grinding up and incorporating the whole trees before planting a new orchard.
“When an orchard is pushed out, there is about 100 tons per acre of organic matter that is taken out of the system,” Holtz said. “My previous research showed positive results from organic matter. Our San Joaquin Valley soils are typically critically low in organic matter. Why remove it if it is good for the soil?”
A local company was contracted to grind up and incorporate the trees using an Iron Wolf, essentially a 50-ton rototiller, in selected research plots. (See video below.) At first, Holtz was concerned that the Iron Wolf left “firewood-sized” chucks of wood in the plots, pieces much larger than he had studied before in his wood chipping research. But the worry turned out to be unfounded.
In comparison plots, trees were pushed together and burned. The ashes later were spread out on the soil. All the plots were fertilized at the normal rate.
Over the years, Holtz has compared laboratory analyses of the nutrients available to the trees in the soil and nutrients in the leaves. Initially, the burn treatments had more nutrients available. The second year, nutrient availability was about equal. Leaf analyses in the third year began to show a higher level of nutrients in the leaves of trees growing in the area where old trees had been ground up and incorporated. In the fifth and sixth years, Holtz didn't see any differences in growth, but data suggests slightly higher yields where the trees were ground up.
“A lot of growers feared if we added that much carbon to the soil, the microbes breaking down the organic matter would tie up nitrogen and the trees would be stunted,” Holtz said. “But the research results suggest that the trees will do just as well or better in the presence of the additional organic matter.”
One potential barrier to grinding up old trees is the cost. Holtz said the Iron Wolf treatment cost $800 per acre and it is not readily available in the San Joaquin Valley. Burning is nearly cost-free for the farmer, but contributes to air pollution and is highly regulated.
Another option for almond farmers preparing to remove an orchard and replant is employing a large tub grinder, which leaves much finer particles of wood than the Iron Wolf, is more readily available but more expensive. Holtz said he hopes that growers in the future will receive incentives to grind up their orchards and incorporate the wood chips into their soils before they plant a second- or third-generation orchard.
“I'm trying to find growers who would be interested in trying this approach to conduct on-farm research,” Holtz said.
In the video below, the Iron Wolf grinds up whole trees and incorporates the organic matter into the soil:
An initiative to enhance competitive and sustainable food systems is part of the UC Division of Agriculture and Natural Resources Strategic Vision 2025.
California's continuing water crisis is leading to decreased and more variable water supplies for San Joaquin Valley farmers, and the region's forage production sector is being hit particularly hard.
“Corn silage and alfalfa have traditionally used lots of water and current and future water restrictions are forcing many farmers to rethink their forage production strategies,” said Jeff Dahlberg, UC Cooperative Extension specialist. “I know of one dairy that had to cut-off their summer irrigations of alfalfa to get their corn silage done.”
To help the agriculture industry make do with less water, a team of UC researchers began a long-term research project last year by growing alfalfa, sorghum and corn under a state-of-the-art center pivot irrigation system. The system, donated by industry partners, is installed at the UC West Side Research and Extension Center near Five Points. Reinke Inc. donated the center pivot, Senninger Irrigation donated nozzles, and Rain for Rent created the infrastructure that gets water and power to the 16-acre research plot.
“We see tremendous possibilities for overhead irrigation in cotton, alfalfa, corn, onions and wheat production,” said Jeff Mitchell, UC Cooperative Extension specialist and the project lead. “There is also great potential for overhead irrigation in California's $5 billion dairy industry for more efficiently producing feed crops like alfalfa, corn and sorghum.”
All aspects of production – including irrigation system performance, crop growth and development, weed control, water application, and economic viability – are being monitored by researchers from UC Cooperative Extension, Fresno State University and UC Davis, plus farmer cooperators and industry partners.
The primary focus of the study is comparing regular irrigation levels with regulated deficit irrigation, a system in which water is withheld at certain times in crop development in order to minimize crop losses even when water is short.
The researchers will apply small, precise amounts of water during the vegetative growth stage for sorghum and both immediately before and after monthly harvests and during the mid- to late-summer period for alfalfa when San Joaquin Valley productivity typically is reduced under flood irrigation.
“We expect to produce marketable and economic yields for sorghum using 25 percent less water as has been achieved under pivots in Texas and similar increases in crop water productivity for alfalfa,” Mitchell said. “This work will inform and improve future water management strategies in California.”
Overhead irrigation systems, such as center pivot systems, are the most prevalent form of irrigation nationwide; however, they have not been widely adopted in California to date. Recent technological advances in overhead irrigation – which allows integration of irrigation with global positioning systems (GPS) and management of vast acreage from a computer or smart phone – have boosted farmers' interest in converting from gravity-fed surface irrigation systems, which are still used on 5 million acres of California farmland.
The research is funded in part with a grant from the UC California Institute for Water Resources. In addition to Dahlberg and Mitchell, UC Cooperative Extension alfalfa specialist Dan Putnam and UCCE advisor in Fresno County Dan Munk are collaborators on the project.
An initiative to improve California water quality, quantity and security is part of the UC Division of Agriculture and Natural Resources Strategic Vision 2025.
Because of its gentle topography and proximity to coastal cities, however, two-thirds of the coastal sage scrubland has already been converted to housing or farming, said Edith Allen, UC Cooperative Extension specialist in the Department of Botany and Plant Sciences at UC Riverside. The remaining coastal sage scrub is threatened by an invasion of exotic species and nitrogen deposition.
“Nitrogen deposition is caused by nitrogen oxide emissions from cars and industry. In addition, another plant fertilizer, ammonia, is emitted from agriculture and livestock operations,” Allen said. “The airborne emissions eventually settle on the soil surface, throwing the fragile coastal sage ecosystem out of balance, even 100 miles or more away from the emission sources.”
The combined deposition of nitrate and ammonia is up to 30 kilograms per hectare per year in the Los Angeles air basin. In contrast, in areas without the basin's air quality problems, about 2 kilograms are deposited per hectare each year.
“Growers fertilize small grain fields with 30 kilograms per hectare, so this represents a substantial nitrogen input,” Allen said.
Further compromising the coastal sage scrubland, grass species from the Mediterranean have been accidentally introduced into the ecosystem by activities associated with a booming agriculture industry, population growth, grazing and road building. The high nitrogen favors these exotic annual grasses.
“We've made a bad problem worse,” Allen said. “The exotic grasses are able to take up nitrogen at a faster rate, grow faster than native plants and displace them.”
In recent years, Allen worked with graduate students Robert Cox and Kristine Preston to understand vegetation-type conversion rate and recovery in coastal sage scrublands in western Riverside County. They compared information gathered by the Forest Service 85 years ago with 2002 California Department of Fish and Wildlife maps updated to 2009 using Google Earth. The analysis included measures of climate, topography, vegetation, land use, nitrogen deposition and fire in 151 study sites.
The analysis showed that 24 percent of the sites that were mapped as annual grassland in 1930 had recovered to coastal sage scrubland.
“In those parts of the county that did not receive much nitrogen, the native vegetation was able to recover,” Allen said. “Overall, the study shows that coastal sage scrubland conservation and restoration efforts are most likely to be successful on sites with low nitrogen deposition and low invasion of exotic grasses.”
For that reason, it only makes sense to try to restore coast sage scrub in areas where nitrogen deposition is low. For broader conservation, the best option is improving air quality.
This research determined that regions where nitrogen deposition is above the level of 11 kilograms per hectare per year will spontaneously convert to grassland.
“We have a value that can be used by regulatory agencies,” Allen said. “Right now, air pollution regulations aren't strong enough to protect the environment.”
Today, most passenger cars emit very low amounts of nitrogen oxides. The bigger problems in the Los Angeles Basin are diesel trucks and pollution generated in the ports of Los Angeles and Long Beach.
“Our population is growing. The volume in the ports is growing. As we come up with better, cleaner technologies, we're staying at the same pollution levels,” Allen said. “People need to realize that we will need lower nitrogen emission levels to protect our natural plant communities.”
The research was published last fall in the journal of Global Ecology and Conservation.
An initiative to maintain and enhance sustainable natural ecosystems security is part of the UC Division of Agriculture and Natural Resources Strategic Vision 2025.