In a comprehensive study published in the January-March 2012 issue of the University of California’s California Agriculture journal, researchers evaluated the myriad factors that contribute to crop damage from Fusarium wilt, and conclude that an integrated management approach is most effective.

“Management of Fusarium wilt requires an integrated approach that includes crop rotation to reduce soil inoculum levels and the use of resistant cultivars during the warmest planting windows,” wrote UC Davis plant pathology professor Thomas Gordon and co-authors.

Lettuce is the fifth most valuable agricultural commodity in California, with a farm-gate value of over $1.7 billion in 2009.

Fusarium wilt affects all major lettuce production areas in California and Arizona. Caused by a soilborne fungus, it was discovered in California in 1990, when plants with symptoms that ranged from mild stunting to complete collapse were observed in fields near Huron, in the San Joaquin Valley. Diseased plants have severely rotted taproots.

Crop rotation. While soil fumigation can eradicate the Fusarium fungus, the authors note that reintroduction remains a significant risk and routine preplant fumigation is generally not an option for lettuce because of costs and regulatory restrictions. “Consequently, growers must rely on the attrition of inoculum that occurs naturally when nonsusceptible crops are grown instead of lettuce.”

To estimate the longevity of pathogen propagules, the researchers transported soil from a naturally infested commercial lettuce field in Arizona to establish microplots at the University of Arizona's Yuma Agricultural Center. After 6 and 12 months, the density of the Fusarium fungus had declined by 71 percent and 86 percent, respectively. After 34 months, the fungus was detectable at 0.5 percent of the starting population.

“These results imply that keeping a field free of a susceptible crop for a year should dramatically reduce the density of pathogen inoculum — provided there is no significant reproduction on weeds or a rotation crop — but that the pathogen will likely persist at a low level for at least several years,” Gordon and co-authors wrote in California Agriculture journal.

Field susceptibility. To assess the progression of Fusarium wilt under field conditions, the researchers established an infested plot on the Department of Plant Pathology’s research farm at UC Davis.

The field trials revealed significant differences between cultivars in susceptibility to Fusarium wilt. At three weeks after planting, two leaf lettuce cultivars (Lolla Rossa and Red Rossa) and three romaine cultivars (Caesar, Green Forest and King Henry) had low disease-severity ratings and appeared resistant. Two crisphead lettuce cultivars (Beacon and Early Queen) were highly susceptible, and three other crisphead cultivars (Grand Max, Kahuna and Salinas) were intermediate between these extremes.

By six weeks after planting, differences among the crisphead lettuce cultivars had largely disappeared. Although Salinas and Grand Max were more resistant to Fusarium wilt than other crisphead lettuce cultivars, their level of resistance appeared insufficient to prevent severe damage. On the other hand, leaf and romaine cultivars retained low severity ratings until the end of the season.

Air temperature. Air temperatures also played an important role in disease development. In the field trials at UC Davis, Fusarium wilt developed more rapidly in the first (June) trial than in the second (July) and third (August) trials. Air temperatures were highest during the June planting, with a mean daily high/low of 99°F/59°F. They were progressively lower during trials in July, 95°F/55°F, and August, 90°F/52°F. Additional temperature tests in controlled environment chamber confirmed a significant effect of temperature on the development of Fusarium wilt, with disease being most severe at the highest temperatures.

Genetic research. The research team has identified additional resistant romaine and red leaf cultivars and begun developing populations to determine the genetic basis of their resistance. Likewise, breeding is under way to transfer the resistance genes from highly resistant crisphead cultivars to less resistant types.

“The process is time consuming, so it will be several years before highly resistant crisphead cultivars are available,” the authors note. “In the future, highly resistant cultivars of multiple types will be available for vulnerable production areas and warm periods of the season.”

Gary Acton

UC Davis geophysicist Gary Acton is one of 34 international scientists that set sail from the Azores Islands on Nov. 17 aboard the drilling vessel JOIDES Resolution. They finished their Mediterranean voyage on Jan. 17, docking in Lisbon, Portugal.

“The climate change recovered at one of the drill sites will be dedicated to providing the most complete marine record of climate change over the past 2 million years of Earth’s history,” said Acton.

The vessel is run by the Integrated Ocean Drilling Program and has the unique ability to core into the deepest reaches of the ocean. The IODP Expedition 339 targeted thick sediment drifts that accumulated from warm, salty water—called Mediterranean Outflow Water—flowing from the Mediterranean through the Strait of Gibraltar. The researchers drilled, sampled and analyzed the sediment to understand the influence that the MOW water mass has on climate, sea level change and the environment.

“A fascinating aspect of these sediments is their ability to record subtle changes in environmental conditions through measurable changes,” said Acton.

Made heavy by its high salt content, the MOW’s warm waters plunge over 3,000 feet—a drop greater than that of Angel Falls, the world’s highest waterfall—into the Atlantic Ocean. It scours the rocky seafloor, coursing along the margins of Spain and Portugal. Passing Scotland and heading toward Norway, the MOW becomes part of the global conveyor belt that overturns the oceans and circulates water and heat around the globe. Along its journey, sand, silt, clay and microorganisms are deposited along the continental margin as thousands of layers of mud, eventually building into sediment drifts. Each layer contains information about Earth’s history.

“My goal is to reconstruct centennial-scale changes in climate and in Earth’s magnetic field for a time period spanning the past 400,000 years,” said Acton. “Only thick, rapidly deposited sedimentary units like those we are coring provide that ability. They are virtual prehistoric observatories.”

During the expedition, the scientists sailed more than 1,200 nautical miles, drilled 19 holes in 7 different locations, and collected 681 sediment cores—equal to about three miles of mud and sand.  Now that the researchers have returned to their homes, they will continue to collaborate as they sift through the data.

“Part of the true value of participating on an expedition like this is the incredible amount of science that can be completed, particularly when scientists with a variety of expertise are confined to a 471-foot-long ship and asked to work 12-hour shifts for two months,” said Acton. “That may seem an odd thing to do over the holidays, but we were all thrilled to be a part of this expedition and to have the chance to continue to work together following the cruise.”

The closer homes are to open spaces – parks, stream and river corridors, forests and other natural lands – the higher the value of the homes in Riverside and San Bernardino counties. However, if homes are far from such open land, homebuyers tend to place an especially high value on lot size.

These were some of the findings of research, which graduate student Monobina Mukherjee at UC Riverside conducted in collaboration with Linda Fernandez, a former associate professor in the UC Riverside Department of Environmental Sciences. A summary of this research is in the September-October 2011 issue of UPDATE, a newsletter published by the Giannini Foundation of Agricultural Economics.

Open space provides a broad range of benefits to communities – such as rural vistas, wildlife habitat and relief from urban congestion – which go beyond the benefits of the land to its owners. In conducting this research, Mukherjee and Fernandez sought to analyze how a policy of land conservation and wildlife habitat preservation influences the housing market.

Mukherjee and Fernandez's study was focused on San Bernardino and Riverside counties. Riverside implemented the Riverside County Integrated Project in 1999 to support conservation of open space and wildlife habitat. San Bernardino County has abundant open space, including wildland in national and state forests. The researchers designated study zones and used statistical analysis to determine the impact of open space and other variables on residential sale value.

“Larger yards sometimes seem to act as a substitute for public open space,” Mukherjee said. "I can see why this happens because these two counties experienced less dense, bigger parcel sales for period of time we have been analyzing."

In Riverside County, a 10 percent increase in the distance from the nearest park is associated with a small but statistically significant decrease in the sale price of the property, the study found. The same was true in San Bernardino County with respect to both wildland and city parks. The results showed that scarcity of open space in areas with big cities could lead homeowners to place even higher value on proximity to open space.

Mukherjee and Fernandez found the amenity values generated in this study could help public policymakers estimate the monetary benefits of open space and habitat conservation. The results can also be used for land-use planning and conservation decisions in Riverside and San Bernardino counties plus other regions with similar geographical characteristics and residential markets.

Bait sock collection bin.

The team first got bags of socks from the local high school, and then grocery bags of socks started appearing in a local drop off bin. Soon boxes of socks started arriving by mail. They came from all over California and as far away as Oregon, Nevada, Minnesota, Arkansas and Maryland. The boxes just keep coming: 12 one day, 16 the next, 185 at last count!

During one visit to the post office at Christmas time, we had to roll the bin to the car. Other customers standing in line were trying to hide their envy of our good Christmas fortune!

Postal bin full of socks in boxes.

The wildlife piece of this SNAMP forest study continues, along with our other scientific teams, to look at the effects of the U.S. Forest Service’s thinning projects in the Sierra. These projects are done in our national forests for fire protection and forest health. Our scientific research teams from the University of California are here to look at changes these thinning projects bring to the forest, its water cycle and its wildlife. This collaborative effort is part of state and federal efforts to refine management practices for our beautiful and complex forested ecosystems.

We have collected years of baseline data and welcome the forest thinning work that has begun this summer in both the southern site near Oakhurst and the northern site near Forest Hill. We will continue to follow the movements of the fisher over the next few years to learn more about their responses to the forest management efforts.

But in the meantime, six newspaper stories and four radio interviews later, we stand in awe of the power of the media and social networks. So, for the many cards, letters and emails we got sharing the stories behind the socks, from the drawers of loved ones who passed away to Earth Day projects for school kids, our wildlife crew is buoyed by your thoughts and support! Our faith in people’s attention to kind details in life is renewed! Thank you!

The author, Anne Lombardo, left, and UC Berkeley wildlife biologist Rick Sweitzer, pose with the pile of socks. A stuffed Pacific fisher is in the foreground.