From: Barbara Lamar (altamiratexas@earthlink.net)
Date: Sun Aug 12 2001 - 12:29:21 MDT
Here's an example of the sort of research I'd like to see much more of. The
research of Wang et al on the genetics of domestic corn (maize) and teosinte
could lead to perennial grain crops. It turns out that domestic corn and
wild teosinte (ancestor of domestic corn) are genetically extremely close.
Certain sub-species of teosinte are perennial. Now that the genes have been
identified, the difficulty in developing perennial corn will be in
preserving the perennial nature of the wild sub-species while engineering
for the huge seed heads characteristic of domestic corn.
The article below is what you might call pure research, in that the
researchers were interested in the domestication of maize that took place
5000 - 10000 years ago. At the end of this post, I'll link to an article
that shows some of the practical appllications of this research.
Barbara
=========================================
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v398/n6724/f
ull/398236a0_fs.html
The limits of selection during maize domestication
RONG-LIN WANG*, ADRIAN STEC*, JODY HEY†, LEWIS LUKENS* & JOHN DOEBLEY*
* Department of Plant Biology, University of Minnesota, St Paul, Minnesota
55108 , USA
† Department of Genetics, Rutgers University , Piscataway, New Jersey
08854-8082, USA
Correspondence and requests for materials should be addressed to J.D.
(e-mail: doebley@tc.umn.edu).
The domestication of all major crop plants occurred during a brief period in
human history about 10,000 years ago1. During this time, ancient
agriculturalists selected seed of preferred forms and culled out seed of
undesirable types to produce each subsequent generation. Consequently,
favoured alleles at genes controlling traits of interest increased in
frequency, ultimately reaching fixation. When selection is strong,
domestication has the potential to drastically reduce genetic diversity in a
crop. To understand the impact of selection during maize domestication, we
examined nucleotide polymorphism in teosinte branched1, a gene involved in
maize evolution2. Here we show that the effects of selection were limited to
the gene's regulatory region and cannot be detected in the protein-coding
region. Although selection was apparently strong, high rates of
recombination and a prolonged domestication period probably limited its
effects. Our results help to explain why maize is such a variable crop. They
also suggest that maize domestication required hundreds of years, and
confirm previous evidence that maize was domesticated from Balsas teosinte
of southwestern Mexico.
======================================
http://www.harcourtcollege.com/lifesci/bioweb/depts/interviews/piper.html
Natural Systems Agriculture
A Conversation with Jon K. Piper
Jon K. Piper has been the ecologist at The Land Institute since 1985, where
he teaches classes and directs the program in Natural Systems Agriculture.
He holds a degree in biology from Bates College and a Ph.D. in botany from
Washington State University. Piper has received grants from the National
Science Foundation, the Eppley Foundation for Research, and the Charles A.
Lindbergh Foundation. He has published over 25 scientific articles and
co-authored Farming in Nature's Image with Judith Soule.
What is Natural Systems Agriculture? What elements does it draw from ecology
and what does it take from agriculture?
Research in Natural Systems Agriculture represents a new synthesis between
ecology and agriculture, with a goal to develop grain agricultural systems
that function like natural ecosystems. Because the practice of agriculture
has changed the face of the Earth more than any other human activity, the
time is ripe for such a synthesis. This research is attracting increasing
attention from both ecologists and agronomists, who have previously worked
in isolation, or even at cross purposes.
Since 1976, The Land Institute has been investigating the feasibility of a
grain agriculture that protects topsoil and does not rely on environmentally
hazardous fertilizers, herbicides, and insecticides. The long-term goal is
to find combinations of perennial plants that, when planted together, will
provide the restorative properties of a year-round cover as well as yielding
significant amounts of edible grain. Grain-producing mixtures of perennial
grasses, legumes, and sunflowers would mimic the vegetation structure and
ecological function of native grassland ecosystems in some fundamental ways.
In what ways are the systems created by Natural Systems Researchers like
naturally occurring ecosystems?
Natural systems, such as grasslands, have two important features that can
contribute to sustainability. First, such systems are composed primarily of
perennial plants, which protect and improve soil quality over time, maintain
soil biodiversity, promote nutrient cycling, reduce weed growth, and support
populations of beneficial insects. Second, natural systems comprise diverse
arrays of plant species. Benefits of biodiversity include nitrogen supplied
by legumes, management of insects that prey on crops, reduction of some
plant diseases, and ecosystem resilience. The research in Natural Systems
Agriculture aims to provide the ecosystem-level benefits of a diverse,
prairie-like vegetative structure using mixtures of high-yielding edible
grains.
How will Natural Systems Agriculture help to protect the environment?
During the last few decades, about one third of the world's arable land area
has been lost through soil erosion. Although modern agricultural methods are
highly productive, they are sustainable only as long as topsoil is intact
and fossil fuel supplies are affordable. With topsoil on roughly 90 percent
of U.S. cropland being lost faster than it is being formed, we need to
rethink agriculture in terms of preserving this limited "ecological
capital." Natural Systems Agriculture will help prevent soil erosion by
providing a year round cover for cropland, protecting topsoil from short
periods of heavy rain or high wind, which is when unprotected land loses
most of its topsoil.
There are two types of problems associated with soil erosion, on-site and
off-site effects. The on-site effects of erosion include reduced
productivity and increased input costs to farmers to compensate for lowered
soil fertility and water-holding capacity. It has been estimated that 10
percent of all energy used in U.S. agriculture is expended simply to offset
the losses of soil nutrients and water caused by erosion.
Soil loss from cropland has severe consequences off-site as well. The major
effect is surface water pollution due to sediment deposition, pesticide
residues, and nutrient loading from chemical fertilizers and animal manure.
Sediment load both reduces surface water quality and increases the
likelihood of flooding, while nitrates from fertilizer and pesticides in
drinking water pose a human health risk. If estimated off-site and on-site
costs of soil erosion are combined, the total cost to the U.S. may be in the
billions.
Several promising plant species have been identified as good candidates for
Natural Systems Agriculture. These species include wild perennials that may
undergo selection for improved seed yield, as well as annual grain crops
into which the perennial habit could be introduced.
How can we "introduce" the perennial habit into annual crops or screen wild
perennials for improved seed yields?
Two recent insights are particularly relevant. The first is the finding that
a relatively small number of genes accounts for a large proportion of the
observed variation between wild and domesticated plants. John Doebley has
shown that genes located in five particular stretches of DNA account for
most of the considerable differences in shape between corn (maize) and the
Central American grass teosinte. This suggests that a relatively few
mutations, with large effects, may be responsible for most of the
differences between domesticated and wild-type plants.
The second insight concerns recent discoveries of the high level of
similarity in the genetic constitutions of various grasses as well as the
fact that the genes coding for such traits as seed size, shattering, and
daylength sensitivity are positioned very closely to one another. Because
these genes are so close to each other on the chromosome, chances are good
that as plant species evolved these genes moved together from species to
evolving species. This raises the possibility that genes in different
species, such as some cereals and wild grasses, may be identical.
If some of these genes are identical, the daunting time frame for developing
perennial grains may be shortened considerably because these genes could
then be moved easily and quickly through breeding or genetic engineering.
This would allow us to bring together the most agriculturally desirable
traits from wild perennials and domesticated crops in a shorter time frame
than would otherwise be necessary.
What is the greatest challenge that faces the implementation of Natural
Systems Agriculture?
Although interest in the potential and feasibility of perennial grains has
increased substantially in recent years, on-farm use of perennial grain
systems is still several years down the road. A common objection raised
regarding the development of perennial grains is the assumption that a plant
cannot simultaneously invest in both large/numerous seeds and the vegetative
organs required for the perennial growth habit. This assumption has been
challenged by several studies that have shown that, within the ranges
investigated, there are no strict "trade-offs" between increased seed yield,
vegetative growth, and the likelihood of future reproduction.
Another objection concerns the expected long-term time frame needed to
develop high-yielding perennial grains. As mentioned above, if the
preliminary research in genetics pans out, this time frame could be
significantly shortened.
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