www.checkbiotech.org ; www.raupp.info ; www.czu.cz

Research in molecular biology has put highly desirable and widely adopted
traits for herbicide and pest resistance into crop plants. It is expected
that the science will soon impact the rate of progress in yield improvement,
and that genetically modified plants may show increased stress tolerance and
nutrient use efficiency. What is the likelihood of being able to replace N
fertilizer altogether? April 2007 by Dr. Tom Bruulsema.

Plants of the legume family have always been able to make their own N. A
complex symbiosis with rhizobial bacteria lets them make the ammonium they
need for protein synthesis directly from the N gas abundant in the air. They
fix N using the nitrogenase enzyme of the bacteria. It costs the plant
something for energy, but perennial species like alfalfa are efficient
enough at it that they rarely respond to N fertilizer. Transferring the
trait to non-legume crops would be a major challenge. The most important
grain crops of the world - the cereals ... corn, wheat, and rice - are all
non-legumes. They take most, if not all, of their N from the soil. They
generally do not produce high yields without N fertilizer.

Research on the genetic control of the legume symbiosis has led to
identification of the plant genes that trigger the formation of nodules.A
breakthrough was reported in the summer of 2006. Dr. Giles Oldroyd, a
scientist working at the John Innes Centre (JIC) in Britain, said: ?The fact
that we can induce the formation of nodules in the plant in the absence of
the bacteria is an important first step in transferring this process to
non-legumes. ... However, we still have a lot of work before we can generate
nodulation in non-legumes.?

Considering that both the plant and the bacteria need to take many more
steps after nodulation in order to begin the process of effectively taking N
from the air, it is clear that the science behind the transfer of the
process to non-legumes is in its infancy. The genome (DNA sequence) of the
rhizobial bacteria that fix N in alfalfa was published in 2001. At least 100
scientific studies since then have cited the article - which shows that
research is active. However, owing to the complexity of the processes
involved, much remains to be discovered.

The Brazilian Agricultural Research Corporation announced in December 2006
that it has finished mapping and sequencing the genome of another bacterium
that works as a natural fertilizer. Gluconacetobacter diazotrophicus is
found in sugarcane, sweet potatoes, and pineapples. As an endophyte - living
between the cells of the roots of its host - its association is not as
intimate as that of the rhizobia that invade the root cells of a legume to
form nodules. However, this organism is responsible for the low N
requirements of sugarcane and contributes to the high energy efficiency of
the Brazilian ethanol industry.

Genetic improvement has contributed to steady yield gains in North American
corn production. Since 1940, yields have been on an increasing trend,
growing by about 1.8 bushels per acre each year. Some anticipate that
genetic engineering will almost double the rate of yield improvement. The
past increase in yields has been accompanied by improved N use efficiency.
Biotechnology is reducing the amount of N fertilizer used to grow a bushel
of corn, because yields are increasing faster than rates applied.

Sunlight, water, and nutrients remain the major factors limiting crop
yields. Biotechnology has potential to improve the efficiency by which
plants utilize all three. But growing global demand for food, fuel,fiber,
and feed ensures that plant nutrient inputs will continue to play an
important role for the foreseeable future.

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