Agriculture Reference
In-Depth Information
is relatively a new endeavor and has been considered only during the past
2-3 decades. Traditionally, the majority of the plant breeding programs
has focused on development of cultivars with high yield potential in favor-
able (i.e., stress-free) environments. Such efforts have been very success-
ful in improving the efficiency of crop production per unit area and have
resulted in significant increases in total agricultural production (Warren,
1998). However, genetic improvement of plants for stress tolerance can
be an economically viable solution for crop production under stressful en-
vironments (Blum, 1988). The progress in breeding for stress tolerance
depends upon an understanding of the physiological mechanisms and ge-
netic bases of stress tolerance at the whole plant level, cellular level and
molecular level. Considerable information regarding the physiological and
metabolic aspects of plant heat-stress tolerance is available. However, in-
formation regarding the genetic basis of heat tolerance is generally scarce,
though the use of traditional plant breeding protocols and contemporary
molecular biological techniques, including molecular marker technology
and genetic transformation, have resulted in genetic characterization and/
or development of plants with improved heat tolerance. In particular, the
application of quantitative trait locus (QTL) mapping has contributed to a
better understanding of the genetic relationship among tolerances to dif-
ferent stresses.
10.6
TRADITIONAL BREEDING STRATEGIES
Development of new vegetable cultivars tolerant to heat stress is a ma-
jor challenge for vegetable breeders. The responses of crops to high tem-
perature stress are dynamic depending upon the extremity and duration
of the high temperature condition as well as the plant type and other en-
vironmental factors in the surroundings. However, the identification and
confirmation of the traits that confer tolerance to heat stress still remain
elusive (RodrÃguez et al., 2005; Wahid et al., 2007). The aim of the scien-
tists involved in research on high temperature stress is to discover the plant
responses that lead to heat tolerance as well as management of the plants
in high temperature stress environments.
Traditional breeding of heat resistant crops basically based on screen-
ing and selection. The common technique of selecting crops for heat stress
resistance has been to grow breeding materials in a hot target production
