Agriculture Reference
In-Depth Information
CO
2
, particularly to oxygen, which leads to photorespiration and/or Mehler
reaction (Flexas et al., 2002) nonradiative energy dissipation mechanisms
(Souza et al., 2004) and chlorophyll concentration changes (Pastenes et
al., 2005). However, these processes ultimately lead to the lower quantum
yield of PSII (Govindjee et al., 1999). Measurements of F
V
/F
M
may provide
rapid indication of change in current plant productivity in response to wa-
ter change, andmay be a good tool in genetic improvement or programs
enabling genotypes with particular characteristics to be selected at an early
stage, but further work is required to examine its potential. Chlorophyll
fluorescence measurements allow the discrimination among the tolerant
and sensitive genotypes. Under water deficit condition, the tolerant geno-
types maintain a higher photosynthetic activity than the sensitive. Studies
conducted in tomato by Srinivasa Rao et al. (1999) and Bahadur et al.
(2010) indicated that PSII activity (F
V
/F
M
) of drought tolerant genotypes
was less decreased with imposing water stress than susceptible genotypes.
9.3.4 WATER USE EFFICIENCY (WUE)
WUE is traditionally defined either as the ratio of dry matter accumula-
tion to water consumption over a season or as the ratio of photosynthesis
(A) to transpiration (E) over a period of time (IWUE). It is among one of
traits that has been studied a lot because it can give an idea of the variation
among genotypes in ability to use water efficiently under limited water
supply. The large assemblage of literature on crop WUE as derived from
research on carbon isotope discrimination allows some conclusions on the
relations between WUE on the one hand, and drought tolerance and yield
potential (YP) on the other. Briefly, apparent genotypic variations in WUE
are expressed mainly due to variations in water use. Higher WUE is gener-
ally achieved by specific plant traits and environmental responses that re-
duce YP. Under most dry land situations where crops rely on unpredictable
seasonal rainfall, the maximization of soil moisture use is a crucial com-
ponent of drought resistance (avoidance), which is generally expressed in
lower WUE (Blum, 2005). It is now well documented that high YP and
high yield under water-limited conditions are generally associated with re-
duced WUE mainly because of high water use. Features linked to low YP,
such as smaller plants (Martin and Ruiz-Torres, 1999) or short growth du-
ration (Lopezcastaneda and Richards, 1994), ascribe high WUE because
