IV.2. IMPROVING CROP RESISTANCE: A NEW PLANT BREEDING TECHNIQUE 
BORROWS FROM THE PAST  From
http://www.idrc.ca/books/reports/1997/17-01e.html
Copyright 1997 © International Development Research Centre, Ottawa,
Canada info@idrc.ca | May 2, 1997

Given enough time, everything that is old will become new again. This
clichÈ  holds true for population breeding, an ancient crop improvement
technique in which an entire population of plants is screened for the
small minority with the best traits. The technique dominated plant
breeding for millennia, but fell into disfavour in the early 1900's as
word of Gregor Mendel's experiments with pea plants spread. Pedigree
breeding techniques and the high yielding pure line crops that launched
the Green Revolution owe their existence and success to Mendel, a
diligent Austrian monk and the "father of modern genetics", whose work
in the mid-1800's was ignored for 35 years.  

    But crop scientist Raoul Robinson believes the single-mindedness
with which pedigree breeding has been adopted around the world is
largely responsible for modern agriculture's addiction to chemical
pesticides. "Plant breeding has four broad objectives: to
improve the yield, the quality of crop product, the agronomic
suitability, and the resistance to pests and diseases," he stated at a
recent meeting held at the International Development Research Centre
(IDRC).

       According to Dr. Robinson, modern plant breeding has been
"spectacularly succesful in the first three of these objectives. This
is demonstrated by very large increases in agricultural production, and
the fact that the world is still able to feed itself in spite of
massive increases in the size of the population." However, breeders
have generally fared much worse with the fourth goal. In some cases,
pedigree breeding has actually reduced the level of resistance to
pests. "This is why we use chemical pesticides in such large
quantities," he explains.  

     Reducing pesticide use. Dr. Robinson says the key to
reducing the amount of pesticides entering our food chain is to refine
the population breeding approach used by our ancestors. He points to
the success of recent work in Mexico as an example of what can be
accomplished. With funding from IDRC, Robinson and a team of
researchers from the Colegio de Postgraduados in Montecillos, Mexico
and the University of Guelph in Canada used mass selection techniques
to dramatically increase the yield of black beans - from 400 to 1,500
kilograms per hectare - without the help of pesticides.  

      "Our best lines are now outyielding the commercial lines. The
commercial lines have been sprayed and ours have not," says Dr.
Robinson. His technique, called "horizonal resistance breeding", relies
on the genetic variability present within the landraces of Mexican
beans. (A landrace is a genetically diverse, cultivated plant
population.) Unlike their genetically uniform pure line cousins, he
explains, individual plants within a landrace display varying degrees
of resistance to pests: some are highly susceptible to parasites and
usually die, most are moderately susceptible to parasites but can still
produce seed when attacked, and others are highly resistant and
tolerate parasitism well. Through careful selection, the plant breeding
team simply shifted the resistance displayed by the majority of plants
towards those individuals with more resistance.

    Health and economic benefits Results of this
Mexican-Canadian collaboration have important implications for small
scale farmers throughout the South. Breeding techniques that reduce the
need for pesticides offer both health and economic benefits, especially
in rural communities. For example, the improper use of pesticides is a
serious health threat to agricultural workers and a major source of
water pollution. 

      Mass selection also offers long-term benefits of broader
significance to all of humanity. Today, small farms are the repository
of much of the agricultural diversity on Earth. Any breeding technique
or program that encourages farmers to preserve and enhance this
diversity may help to safeguard the genetic pool from which future
improvements in crops will likely come.