Agriculture Reference
In-Depth Information
limiting conditions could even come to characterize some of today's prime agricul-
tural lands, depending upon how scenarios of climate change unfold in the future.
1.1 Background of Stress-Tolerant Crop Genetics
Historically, tolerance of adverse environmental conditions was not a primary char-
acteristic favored in the domestication of crop species and subsequent genetic selec-
tions in traditional agriculture. Indeed most domesticated crop species are largely
incapable of prolonged survival in the wild (Gepts
2004
). Many traits that enhance
chances of plant survival under adverse environmental conditions—like small
stature and large root systems, photosynthetic reductions, or accumulation of de-
fensive proteins—come at physical cost of lower production of harvestable output
under optimal growing conditions (Cattivelli et al.
2008
). Selection and replanting
by farmers has tended to trade-off between plants that apportioned more of their
energy to harvestable product versus survival. Recalling also that, for most of his-
tory, subsistence agriculture was quite diversified and spatially diffused, it stands to
reason that, all other factors being equal, as long as a better-yielding variety did not
fail too often, farmers would favor its higher expected yields, in any given season,
over other varieties with lower yields but better assurance against failure in the un-
certain event of a poor season. Moreover, diversification across multiple crops and
livestock, often supplemented with other food sources like hunting and gathering,
meant that, if a harvest did fail, other sources could be depended upon. Moreover,
in most regions over most of history, if soils in one location tended to hinder growth
of favored varieties, they would be passed over or abandoned in favor of other
areas with more suitable soils (thus, effectively relegated to the category known as
'marginal' lands). Crop survival mechanisms were not, in short, the primary genetic
characteristics for which subsistence farmers were selecting historically.
With the advent of scientific breeding in the last century, this trade-off was, if
anything, further accentuated, at least initially. Evidence shows that early Green
Revolution varieties with greater yield gains, also experienced greater yield vari-
ances (Traxler et al.
1995
). While improved varieties yielded significantly better
than existing varieties under optimal growing conditions, under adverse conditions
they did not necessarily perform better—and may have performed worse—than ex-
isting (usually locally adapted) varieties. The benefits from an improved variety's
increased yield potential were realized by maintaining optimal growth conditions
with other inputs, such as irrigation and nitrogen application, thus creating incen-
tives for farmers to procure these complementary inputs. Especially where these
complementary inputs were available at economical or even subsidized rates, Green
Revolution farmers favored varieties with higher mean yields, not necessarily high-
er survival rates under stressful conditions. This trade-off, thus, lies at the root of
contentions that the Green Revolution did not equitably help all farmers, particu-
larly neglecting to benefit those farmers who are relegated to cultivating marginal
lands (Hazell et al.
2002
).
