BY STAN BLADE, P.Ag.
FROM LAB
TO FIELD
Copingstrategies fordrought
WATER—OR, MORE ACCURATELY,
the lack of it—has been on the minds
of many producers in Western Canada
this summer. Drought, and its devastat-
ing effects, have been with us since the
beginning of agriculture. A number of
recent studies indicate drought as one of
the major reasons for the collapse of the
Maya Empire in AD 850 to 900. In the
20th century, geopolitics were shaped by
devastating droughts in China, portions
of the former Soviet Union, India and
Ethiopia. Here in North America, the
media has been focused on the California
drought, with the result that people are
wondering whether it is politically correct
to eat almonds.
What has science done to address the
issue of lack of water? One of the first
actions was simply to define drought
and measure its severity. There is a wide
range of definitions for what drought
actually means—even though we all know
it when we see it. It is difficult to define
because it results from an interaction
between a number of factors: precipita-
tion; evapotranspiration (moisture given
off during normal plant processes); the
amount of sunlight; the soil composition
and moisture status; and insects, diseases
and weeds. In 1965, the Palmer Drought
Severity Index was developed as a com-
prehensive indicator of moisture status.
It uses readily available temperature and
precipitation data to calculate water avail-
ability for agriculture.
Two main approaches are taken in ag-
ricultural research to address the impact
of drought. First, plant breeders have
sought to incorporate traits that might
limit the impact of low water availability.
These include enhanced rooting systems,
increased waxiness of leaves, changes
to the size and function of stomata (the
openings in leaves that enable movement
of carbon dioxide and oxygen into and
out of the leaf), changes to the structure
of the leaf canopy, early maturity (which
can escape some seasonal drought), and
changes to the earliness and duration
of flowering. Second, agronomists have
made major contributions to soil moisture
management through a vastly improved
understanding of irrigation management
and innovations such as reduced tillage.
Due to the complexity of drought, it has
been difficult for researchers to develop
rigorous methods for testing new ways to
enhance crop response to drought. The re-
search community has identified four ma-
jor coping strategies to reduce the impact
of drought on crops (in some cases, plants
use a combination of these strategies).
Drought escape:
Researchers have
focused on two specific mechanisms: early
flowering leading to early maturity, and
variation in the growing period depending
on the amount of water deficit. In Austral-
ia, plant breeders at the Commonwealth
Scientific and Industrial Research Organ-
isation have credited earlier flowering as
the biggest factor in increased wheat yield.
Drought avoidance:
This response
refers to the ability of plants to maintain
relatively high tissue water potential
despite low soil moisture. New work has
shown how drought can turn on specific
genes, which leads to enhanced rooting
patterns in crops, thus ensuring that
enough water will be available to maintain
plant function.
Drought tolerance:
Plants with this
trait are able to withstand low soil mois-
ture even with low tissue water poten-
tial. In this case, work in both cereals
and broad-leaved crops has shown that
drought will trigger genes to produce a
host of water regulators in plant cells to
protect the plant from death. A recent
review from China’s leading crop-improve-
ment centre describes hundreds of genes
that are involved in such a response.
Drought recovery:
So-called “resurrec-
tion plants” can come back to life in 24 to
48 hours, even after receiving no water for
months (and, in some cases, years!). This
is due to a complex biochemical process,
which holds many possible opportunities
for arid agriculture. I recently had the
pleasure of meeting with Jill Farrant, PhD,
a professor of cell biology at the Univer-
sity of Cape Town in South Africa, who
specializes in such plants.
New research tools are providing fresh
ways of looking at how crops can handle
drought conditions. These tools are also
showing us the complexity of the rela-
tionships between plants and the many
elements of drought.
Dr. Stan Blade is dean of the Faculty of
Agricultural, Life and Environmental Sciences
at the University of Alberta.
Fall
2015
Grains
West
44
REDUCING THE EFFECTSOF LOWWATER AVAILABILITYONPLANTS
