Agriculture Reference
In-Depth Information
tolerance [78]. Although demonstrated for some species [79,80], and key
genes of symbiosis establishment revealed [81], the genetic inheritance of
this association in crop species is still elusive and deserves more attention
of biologists, geneticists and breeders. However by improving any of the
molecular or physiological features that improve the ability of crops to
access soil nitrogen, crop growth and yield under stress conditions could
increase with concomitant reduction of the energy required to meet the
growing food demand.
11.4.4 ENERGY AND PESTICIDES
The production, transportation, and application of pesticides are all energy
expensive, consuming 15% of the energy resources used by agriculture
[82]. Many pesticides are manufactured using ethylene and propylene,
both of which are made from catalytic reactions with crude petroleum or
methane produced from natural gas. The production of modern pesticides
consumes between 2,000-6,000 BTUs per kilogram of material, depend-
ing on the final chemical make-up [82]. In the U.S. 42,000 metric tons of
oil are consumed annually as the active ingredient for insecticides alone
[83]. Since the use of pesticides are limited in low-input systems, breeding
for increased crop tolerance and resistance to economically devastating
insect pests and pathogens could lead to improved yields, profit, and sus-
tainability of these systems. Breeding for insect and disease tolerance can
be more challenging than other limiting factors for several reasons. Many
traits that improve tolerance to agricultural pests have been inadvertently
breed away from in conventional breeding programs disregarding poten-
tial threats, however landraces in several crop species have been found
to possess genotypes with improved resistance to pest and pathogen at-
tack. Pest size, feeding strategy, reproduction, or infection behaviors can
elicit different defense responses from the host plant, which can also differ
among crop species. More importantly, insect and pathogenic pests are
capable of adapting new behavioral and morphological responses to over-
come the defenses of the targeted host [84]. However, several traits have
been shown to promote crop tolerance and improve resistance to insect
and pathogens for several economically valuable crop species.
