The Rural Voice, 2006-07, Page 38Higher yields linked to
lower nutrient levels
Has there been a nutritional price to pay for the
miraculous boost in yields plant breeders
have wrought?
By Jeffrey Carter
plant breeders have dramatically
increased the yield of food
crops but it's come with a cost.
While tonnes per acre are up, the
concentration of many nutrients is
down, according to a University of
Texas nutritionist.
Dr. Donald Davis says there's a
growing body of scientific evidence
that links this tradeoff to breeding
efforts that have resulted in higher
yields. Crop cultivars that are high -
yielding often pack less of a
nutritional punch, he says.
"This is an emerging discovery.
Not many scientists know about it ...
I describe it as the genetic dilution
effect."
Davis, together with associates
Melvin Epp and Hugh Riordan,
examined 13 nutrients in 43 garden
crops — vegetables and also
strawberries and three types of
melons — for the period 1950 to
1999. Adjustments were made for
differences in moisture content.
The data showed declines in the
median concentration of six
nutrients. The concentration of
34 THE RURAL VOICE
protein, phosphorus, iron, calcium,
iron, vitamin C and riboflavin fell by
six, nine, 15, 16, 20 and 38 per cent,
respectively, over the 50 -year period
while, at the same time, yields
increased.
There were no statistically -
significant median changes for the
other seven nutrients, ash vitamin A,
Dr. Donald Davis, University of
Texas, Austin
Photo courte
4 �y
thiamin, niacin, energy, carbohydrate
and fat.
"Cultivars commonly are selected
for yield, growth rate, pest resistance
and other attributes, but seldom have
they been selected for nutrient
content," write Davis and his
associates in the paper they published
in the Journal of the American
College of Nutrition.
The researchers argue that when
yield is the primary focus for
breeding programs, the cultivars
developed may be less able to extract
soil nutrients, transport nutrients
within the plant, or to synthesize
proteins, vitamins and other
nutrients.
Davis points to examples of other
research that suggests nutrient
concentration may be linked to
genetics. This includes recent USDA
trials comparing 14 different hard red
winter wheat and 27 different
broccoli cultivars.
In side-by-side trials, the low and
high yielding cultivars were assessed.
Direct evidence of the genetic
dilution effect was found in both
cases, with higher -yielding cultivars
having lower concentrations of
certain nutrients.
There are other explanations for the
reduction of nutrients in food crops,
Davis says. For example, cultural
practices, such as the use of chemical
fertilizers and irrigation are known to
have an impact, he says.
There have also been studies, such
as one published by Washington,
D.C. nutritionist Virginia
Worthington, that suggest organic