Abiotic Stress Factors and Crop Yield

Agricultural production and productivity are highly sensitive to changes in climate and weather conditions. Therefore, changes in regional and global climate, particularly climatic variability, affect local as well as global food, fiber, and forest production (Easterling et al., 2007). Atmospheric carbon dioxide, temperature, rainfall patterns, ozone, and UV-B radiation have changed since the dawn of industrial revolution, and the scientific community expects current trends to continue into the future (Houghton et al., 2001; IPCC, 2007). Although crop productivity may benefit from rising CO2 levels, the increased potential for abiotic stresses, such as increased incidence of drought, flooding, heat waves, and higher UV-B radiation, may challenge community dependence on local agricultural production. Hence, the overall impact of climate change on agriculture will depend on the balance among these climatic factors. These climate change factors have reduced productivity of many crops at both regional and global scales (Teramura, 1983; Lobell and Asner, 2003; Ciais et al., 2005; Lobell et al., 2008). A recent study suggests that, due to climate change, southern Africa could lose production of approximately 30% of its main crop maize (Zea mays L.) by 2030, and in southern Asia, production loss of many regional staples, such as rice

(Orzya sativa L.), millets (Pennisetum sp.), and maize could be up to 10% (Lobell et al., 2008). Similarly, Lobell and Asner (2003) estimated that each degree centigrade of increased temperature during an average growing season may reduce U.S. soybean (Glycine max L. Merril) and maize production by 17%. Studies indicate that climate change scenarios that include a combination of factors, such as heat stress, drought, and flooding, reduce crop yields more than a change in a single factor alone (Easterling et al., 2007). Therefore, it is expected that the interaction of abiotic stress factors will influence crop productivity in future climates.

The genotype (thus the genetic background) of a plant defines its range of performance and is determined by a set of heritable traits (Hall, 2001). Consequently, the phenotype produced by a particular genotype results from the interaction of these genotypic traits within the environment where the plant is grown. Therefore, crop yield is determined by genotypic effect, environmental effect, and the effect attributed to the genotype by environmental interaction. In the natural habitat, crop plants are subject to a combination of abiotic conditions that may include one or more stresses, such as heat, drought, and UV-B radiation. Interactions among these factors elicit a variety of responses in plants depending upon the intensity, duration, and timing (developmental stages in a plant species) of the stress. In most cases, abiotic stress conditions reduce crop performance and yield. One important strategy for coping with abiotic stresses is to develop new cultivars with tolerance to the abiotic stress conditions that have minimum yield loss or stable yield under multiple stress conditions. Selection of tolerant cultivars and genetic traits in a population is crucial for developing new cultivars that can adapt to a wide range of environments. This can only be accomplished by subjecting the species of interest to different abiotic stress conditions and determining responses of various growth- and yield-related traits to these stressors. Studies utilizing vegetative and reproductive parameters simultaneously under realistic growth conditions are limited. Therefore, plant processes to a combination of stress factors are not well understood (Rizhsky et al., 2004; Koti et al., 2007; Tegelberg et al., 2008).

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