Agriculture Reference
In-Depth Information
9.2 RESPONSES OF PHYSIOLOGICAL TRAITS UNDER
DROUGHT STRESS
The screening of more number of genotypes for drought tolerance would
be accelerated with a greater understanding of physiological traits related
to water stress. Many physiological characters responsible for continued
growth under water stress have been identified. For example, osmotic ad-
justment is considered to be an adaptation to drought stress by which an
increase in the solute content of cells can lead to maintenance of turgor
and turgor-related processes at low water potential (Kumar and Elston,
1992). Variation in water use WUE, leaf area, specific leaf area (SLA),
leaf area ratio (LAR) and leaf gas exchange (i.e., carbon assimilation (A
N
),
transpiration, stomatal conductance (gs) and internal CO
2
concentration)
in response to water deficit are important parameters to serve as an in-
dex for drought tolerance (Anyia and Herzog, 2004). Drought avoidance
by maintaining high leaf water content is negatively associated with leaf
area as well as SLA. High assimilation rate under water deficit is associ-
ated with high relative leaf water content (RWC). Decline in assimilation
rate are due mainly to stomata closure, however, evidences of nonstoma-
tal regulation were also found. Instantaneous WUE (iWUE, a molar ratio
of assimilation to transpiration) and leaf internal CO
2
(Ci) are negatively
correlated, while Ci is moderately related with SLA. Drought tolerant
genotypes had the higher leaf water retention, CMS, RWC, and the lower
Relative Water Loss in comparison to drought sensitive genotypes. The
interacting effect of all above parameters depends on growth strategy of
the species considered, and their ability to adjust during drought stress.
Some of the physiological parameters, which are noticeably affected by
water deficit conditions, are discussed below:
Physiological traits relevant for the responses to water deficits and/or
modified by water deficits span a wide range of vital processes (Table 9.3).
TABLE 9.3
Response of Physiological Traits to Drought Conditions
Plant traits
Effects relevant for yield
Modulation under stress
References
Stomatal con-
ductance/leaf
Temperature
More/less rapid water
consumption.
Leaf temperature reflects
the evaporation and hence
is a function of stomatal
conductance
Stomatal tolerance in-
creases under stress
Jones (1999),
Lawlor and
Cornic (2002)
