This chapter focuses on crop breeding strategies needed to solve some of the problems and exploit some of the opportunities that may result from global climate change. We will emphasize the choice of traits and methods for selecting these traits. A unique feature of global climate change is the projected increase in atmospheric carbon dioxide concentration ([CO2D. This should result in increases in productivity for many crop species. Grain yields of some cereal crops may have increased by 7-25% over the last 100 years solely as a result of the increase in [CO2] during this period (Goudriaan and Unsworth, 1990; Mayeaux et al, 1997). But, the major increases in crop yield that have occurred during the last 50-100 years were mainly due to factors other than increased [CO2] including various technological advances (Amthor, 1998). However, as will be shown in this review, potential crop productivity may be increased by breeding or selecting cultivars that are more responsive to elevated [CO2]. Climatic changes, such as increases in temperature, also may occur in the 21st century (Houghton et al., 1996) and in some cases decrease crop productivity. Plant breeding has the potential to overcome some of the problems caused by heat stress. Plant breeding programmes operate within time frames of decades and it is likely that this will continue into the near future, with genetic engineering complementing rather than replacing traditional breeding methods, especially for annual crop species. The changes in atmospheric [CO2] and climate are likely to be rapid; consequently, it is appropriate to begin designing new breeding strategies and cultivars for the 21st century. This can be facilitated by considering past, present and possible future climates. Our analysis will emphasize the separate and interactive effects of increases in atmospheric [CO2] and global warming on the productivity, grain quality and water relations of crops, and potential effects on

┬ęCAB International 2000. Climate Change and Global Crop Productivity (eds K.R. Reddy and H.F. Hodges)

problems caused by pests. Earlier reviews of part of this topic were provided by Badger (1992) and Hall and Allen (1993).

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