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Role of Physiology in Improving Crop Adaptation to
Abiotic Stresses in the Tropics: The Case of
Common Bean and Tropical Forages
Idupulapati Madhusudana Rao
Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia
583I. INTRODUCTION
In the course of evolution, plants have developed so that their life cycle, growth habit, and other expres-
sions of survival are adapted to specific environmental conditions. The term “adaptation” can be used to
define processes conferred by genetic attributes that serve to “fit” the plant to the ambient conditions of
temperature, light, and mineral and water availability. Understanding the genetic and physiological mech-
anisms by which plants cope with changes in environmental conditions is critical for creating efficient
strategies to develop stress-resistant cultivars for sustainable production systems.
Improved crop yields achieved by plant breeders are mainly attributable to changes that fall into two
categories [1,2]: (1) agronomic change through improved genetic adaptation to overcome major biotic
(e.g., pests and diseases) and abiotic (e.g., temperature, drought, mineral deficiency and toxicity, and
salinity) constraints to crop production and (2) raising the genetic yield potential per se above that of stan-
dard cultivars in the same environment. Most advances have occurred for the first category, and these in
the 20th century. They include resistance to various pests and diseases, selective resistance to herbicides
and pesticides, elimination of seed dormancy and susceptibility to lodging and shattering, and modifica-
tion of timing of crop life cycles so that cultivars are better adapted to their environments. Although rais-
ing the genetic yield potential is equally important, research progress has been less than dramatic for most
crops.
Plant physiological research contributes to both agronomic change and cultivar improvement [3], as
illustrated by the following examples: advances in plant nutrition have led to more effective fertilizer
practices, understanding of plant-water relations to better irrigation management, and the discovery of
plant growth substances to selective herbicides and regulators. However, with cultivar improvement, em-
pirical selection for improved crop adaptation and yield potential has continued effectively without heavy
reliance on selection criteria or screening techniques from plant physiology. Crop yield is the result of a
series of genetically controlled physiological and biochemical processes. Plant and crop physiologists
face the challenge of understanding the mechanisms underlying these processes and of discovering how
they interrelate and interact with diverse edaphic and climatic (abiotic) environments.
Complex plant processes such as photosynthesis, respiration, water transport, nutrient uptake, as-
similate partitioning, or morphogenesis can be broken down into a number of elementary processes [4].
However, these processes are highly interrelated and each has complex and versatile regulatory sys-