Agriculture Reference
In-Depth Information
Chapter 11
Grain Yield Improvement in Water-Limited
Environments
Greg J. Rebetzke, Scott C. Chapman, C. Lynne McIntyre,
Richard A. Richards, Anthony G. Condon, Michelle Watt,
and Anthony F. van Herwaarden
SUMMARY
techniques aimed at more effi cient
screening.
(4) Greatest benefi ts arising from modeling
and physiology refl ect an understanding of
the frequency and nature of drought stress,
and traits with potential to improve water-
use effi ciency.
(5) The physiological complexity of adapta-
tion to drought together with the known
polygenic control of productivity traits will
likely limit the implementation of trans-
genes in breeding programs. Transgenic
approaches largely focus on assessment of
traits affecting cell and plant survival when
these are unlikely to increase productivity
in managed cropping systems.
(6) Tremendous potential lies in the use of
molecular markers for major genes such as
resistance to disease and soil constraints,
thereby enabling breeders to enrich popu-
lations for important alleles conferring
adaptation to drought.
(1) Climate change threatens to reduce rainfall
and increase rainfall variability in many of
the world's rainfed and irrigated wheat-
growing regions.
(2) Breeding for improved productivity in
water-limited environments has been suc-
cessful but at rates of genetic gain well
below that observed in favorable environ-
ments. Breeders should not target selec-
tion for severe drought, as performance
under severe stress does not correlate well
in intermediate- to higher-yielding envi-
ronments where growers derive most of
their income.
(3)
Genetic gain under drought will rely on
multidisciplinary skills that focus on
breeding but with support from the fol-
lowing: simulation modeling; improved
physiological understanding and rapid,
cost-effi cient phenotyping; and molecular
INTRODUCTION
increase by as much as 40% by 2020, highlighting
the need for improved productivity. Despite this
growing demand, many factors have potential to
impact crop productivity globally, including
climate change, scarcity of water resources, and
land-use change and degradation. Climate change
will impact through direct and indirect effects of
increasing atmospheric CO
2
levels, and warming
The distribution of wheat production environ-
ments is broad, encompassing a range of tempera-
ture and radiation regimes, and both irrigated and
nonirrigated, rainfed environments. Rosegrant
et al. (1997) predicted that global demand for
wheat for human and animal consumption will