MORPHOLOGICAL AND PHYSIOLOGICAL TRAITS ASSOCIATED WITH WHEAT YIELD INCREASES IN MEDITERRANEAN ENVIRONMENTS

This chapter reviews the wheat physiology/breeding work relative to the constraints of dryland cropping in Mediterranean environments and explores opportunities for additional yield improvement associated with morphological and physiological traits. The chapter discusses the environmental constraints to crop growth in the parts of the world that experience Mediterranean-type climates. Water stress is a major limitation to wheat growth and yield in Mediterranean and other environments. Grain yield (GY) is defined as the product of the biomass produced and the harvest index. Biomass can be increased by agronomic manipulation or by genetic means. Germination, ear initiation, terminal spikelet, and anthesis act as physiological switch for the allocation of assimilates to different organs of the plant, hence phenology and assimilate partitioning are closely related. Breeders have changed the structure of cereals considerably, both indirectly through changes in phenology and directly through the introduction of dwarfing genes. The chapter explains the effect of plant morphology and physiology on water usage. In water-limited environments, biomass production is a function of the water used by the crop (WU) and the efficiency with which it is converted into biomass (WUE). Biomass production can be defined by the amount of radiation intercepted (RI) and the radiation-use efficiency (RUE)—that is, the efficiency of the conversion of this radiation to dry matter. © 1994 Academic Press Inc.