November 2004 --
Unmasking the Genes of Food-Poisoning Campylobacter
What's your favorite way to prepare chicken? Whether you grill, fry, roast or bake it, as long as you cook it thoroughly, you'll kill any Campylobacter jejuni food-poisoning bacteria that may be on or in it.
But raw chicken juice, or raw or undercooked chicken, could harbor this microbe and lead to campylobacteriosis food poisoning. In fact, Campylobacter is thought to be the leading cause of food poisoning worldwide.
To foil Campylobacter, Agricultural Research Service scientists in Albany, Calif., and their colleagues at The Institute for Genomic Research, Rockville, Md., have decoded the sequence, or structure, of all of the genes in a specially selected C. jejuni strain.
Investigations of these C. jejuni genes may lead to the discovery of faster, more reliable ways to detect the microbe in samples from food, animals, humans and water.
What's more, the gene-based research opens the door to simpler, less-expensive tactics for distinguishing look-alike species and strains of Campylobacter and its close relatives, so that culprit microbes in food poisoning outbreaks can be fingered more quickly.
Finally, the studies may lead to innovative, environmentally friendly techniques to circumvent the genes that make C. jejuni strains so successful in causing human gastrointestinal upset and, in some cases, paralysis or even death.
The research represents the first time that a C. jejuni strain from a farm animal -- in this case, a market chicken -- has been sequenced. That farm-animal origin is important, because chicken is the leading source of this bacterium in food. Earlier C. jejuni genome sequencing, done elsewhere, was based on a specimen from a gastroenteritis patient and was lacking key features, such as the ability to colonize chickens.
New Sampling System Helps Growers Learn About Their Fields
A new cotton sampling system developed by Agricultural Research Service scientists helps growers determine the different fiber qualities produced by their cotton plants throughout a harvested field.
ARS plant physiologist Gretchen Sassenrath worked with technician Ray Adams in the ARS Application and Production Technology Research Unit at Stoneville, Miss., to design a method of spatially sampling cotton during harvesting operations. The system helps determine what underlying factors, such as soil moisture, may be affecting the fiber properties.
Soil properties will alter the moisture and temperature in a small area of a field, changing the individual microclimate for that area. For instance, if areas of a field have changes in soil quality, varying temperatures or different amounts of water collecting throughout it due to terrain features, cotton fiber properties may vary.
Adams built a cotton sampler that attaches to the picker's chute. A lever switches a paddle gate in the picker chute and, every 20 seconds, diverts some of the harvested cotton into a sampler chute for collection and later analysis. The cotton sample is harvested from a known area of the field. Fiber properties are then incorporated with the position data and entered into the database for spatial analysis.
The system works alongside the cotton yield monitor, a device that measures the quantity of cotton at any given position in the field. The yield monitor is equipped with a Global Positioning System receiver to compute position, speed and time.
The data from the yield monitor and the fiber properties are then entered into the geographic information system (GIS), a database that processes geographically-based information. A GIS map shows growers which areas of their fields need more attention and which areas are producing cotton bolls with the best fiber properties. Once the cotton fiber properties have been determined, the value of the cotton lint is calculated from the same tables that farmers use when selling their cotton.
Beneficial Fungi Could Halt Hopper Hordes
T. Jaronski, an insect pathologist with the Agricultural Research Service, is studying these fungi and other microbes in hopes of keeping soaring hopper populations in check. He works at the agency's Northern Plains Agricultural Research Laboratory in Sidney, Mont.
During outbreaks, which are often driven by droughts, grasshoppers can gobble up valuable crops, forage and ornamental plants, costing millions of dollars in damage.
One fungus, Beauveria bassiana, is already registered in the United States for the control of a variety of insects. Once grasshoppers pick up its spores on their feet and other body parts, the fungus grows quickly inside their bodies, usually killing them within a week.
Recently, Jaronski found that an effective way to deliver the B. bassiana spores and make them attractive to grasshoppers is to mix them with raw canola oil. Black and strong-smelling, the raw oil contains higher concentrations of the fatty acids that the insects find irresistible. It's also cheaper than using refined, store-bought canola oil.
Jaronski envisions the mixture of canola oil and fungal spores being sprayed on targeted strips of rangelands from the air or on the ground. Because the oil attractant lures hoppers to the strips from a wide distance, only small amounts of the fungal spores are needed.
The other fungus, Metarhizium anisopliae var. acridum, is much more host-specific than Beauveria, affecting just grasshoppers and their close relatives. Jaronski's lab has found that Metarhizium is very infectious in most American grasshoppers and the Mormon cricket, which also causes destructive outbreaks. Coupled with the raw canola oil carrier, it could also become a valuable tool for controlling grasshoppers.
Read more about this research in the October 2004 issue of Agricultural Research magazine, available online at:http://www.ars.usda.gov/is/AR/archive/oct04/hopper1004.htm
A One-Time Plowing May Not Hurt Carbon Credits
A one-time tillage will not cause great soil carbon loss, even though major damage is caused to soil structure.
That's the finding of Lloyd Owens, a soil scientist with the Agricultural Research Service in Coshocton, Ohio, after a study comparing soil carbon in the top foot of soil under a meadow with the carbon level in soil under cornfields with various levels of tillage. He found that it takes a few years of continual annual plowing before carbon losses become noticeable in fields previously unplowed for years.
Sometimes farmers plow land that is removed from a federal conservation reserve program. Such programs pay farmers to protect land with a ?permanent? vegetative cover such as grass, usually for 10 years at a time. Another reason why farmers in the northern Midwest might plow is to help control a heavy infestation of slugs.
It was just such a slug infestation that inspired Owens to study the effects of plowing on soil carbon. He found that for the first year of plowing land, the upper eight inches -- the plow layer -- held about 19 tons of carbon per acre, the same as was retained in the meadow and untilled cornfields. But after a few years of annual plowing, the loss became noticeable, and, by the fifth year, the soil carbon level fell to 15 tons an acre.
Although there was no noticeable loss of stored soil carbon in the first year of plowing, there were other trade-offs. That's because just one pass with a plow greatly damages soil structure, which increases erosion and reduces water infiltration and soil health. Also, a single plowing moves more than half the organic matter in a field a little deeper underground, away from the surface where it is needed to hold water and nutrients.
Scientists "Smear" Pests With Mustard
Got crop pest problems? Spread some mustard on them--the plant, that is, not the condiment.
Agricultural Research Service scientists are growing stands of cultivated mustard and other Brassica species as a possible alternative to using chemical fumigants to rid crop fields of nematodes, weed seeds and other soilborne pests.
The mustards? ?biofumigant? effect is attributed to isothiocyanates, chemical byproducts of the plants' decomposition that make the soil toxic to nearby pests. Indeed, farmers in parts of the United States and Europe have sought to exploit this phenomenon by preceding their crops with stands of mustard, rapeseed and other Brassica species.
But there?s still much to learn about how these biofumigant plants control pests, the conditions Brassicas prefer and their cumulative effects on the soil environment, according to Rick Boydston, an agronomist in ARS? Vegetable and Forage Research Unit at Prosser, Wash.
Since 2000, Boydston has led a team of ARS and Washington State University scientists in monitoring the mustards' biofumigant effects in greenhouse and field studies. Eventually, the resulting information could lead to new cropping systems that use mustards better, or pinpoint their limitations.
For example, scientists are checking the sprouting ability of redroot pigweed seed that has been dug out from beneath stands of white mustard, sorghum-sudangrass, winter wheat or an oat-hairy vetch mixture. Results thus far indicate delayed germination only. In contrast, 99 percent of the redroot pigweed seeds from fumigated plots didn't germinate at all.
In greenhouse studies, scientists monitored the effects of crushed seedmeal from brown mustard and field pennycress on potted irises and three pests: chickweed, prickly lettuce and root-knot nematodes. The irises suffered no ill effects, but more than half of the weeds failed to sprout, and nematode numbers fell by 70 to 80 percent.
Slowing the Loss of Ag Chemicals
Farmers might be well advised to apply chemicals between crop rows rather than in the rows, according to a study of plowed and no-till cornfields by Agricultural Research Service scientists in Beltsville, Md.
The findings from the two-and-a-half-year study at the agency's Henry A. Wallace Beltsville Agricultural Research Center show that applying chemicals between rows could be safer in terms of reducing the leaching of chemicals to groundwater, especially in areas of the country where rainfall is frequent and no-tillage management is used, such as the mid-Atlantic region.
That's one suggestion to emerge from this first year-round, multiyear study of soil and water dynamics that included charting differences in soil moisture within and between crop rows.
ARS soil scientists James Starr and Dennis Timlin monitored the water content of soil with 16 special probes that recorded soil water every 10 minutes around the clock, at depths of from two to 22 inches. Field weather stations collected data every five minutes. Starr and Timlin studied interactions between the effects of tillage, row position and season of the year on water infiltration, storage, drainage and crop water uptake.
The nearly continuous measurements allowed the researchers to envision how chemicals might move through fields. They compared in-row with between-row water movement during rainstorms, aware that wherever water goes, agrochemicals are likely to go, too.
Starr and Timlin found that the greatest water infiltration occurred within corn rows, especially during summer rainfalls of an inch or more. This was true for no-till, but results were less consistent with plow-till. Aided by the funneling of water to the plants by corn leaves, the soil in corn rows managed to capture a good share of the rain. This large amount of rainwater funneled into the corn rows can then drain through the soil toward groundwater.