full detail

2. TOPIC : WATER USE
EFFICIENCY -
TERMINOLOGY INTRINSIC
WUE – IMPORTANCE AS A
DROUGHT RESISTANT
TRAIT
PRESENTED BY
ZUBY GOHAR ANSARI
TAM/2014/26

3. INTRODUCTION
 Water is highly essential to plant growth &
development. Water constitute more than 80% of the
most of plant cells and tissues in which there is
active metabolism. It forms continuous liquid phase
through the plant from the root epidermis and liquid
phase continum generally extend into the soil or
substrate in which the plant is rooted .
 Various plant factors are affected by water contents
in cells and tissues. Various physiological factors
which are influenced by water are cell division, cell
expansion, photosynthesis, transpiration, membrane
permeability and N metabolism.

4.  Different morphological factors includes plant height,
root growth, No. of primary branches, leaf area, No.
of flowers and final yield are also influenced by cell
water status.
 Available water for irrigation to agricultural purposes
is depleting year by year due to increased
industrialization and urbanization. Rainfed
agriculture is still affected due to erratic monsoon
year by year. Under these conditions, water needs to
be conserved and utilized efficiently . Specially under
water limited situations , crop productivity is
determined by how efficiently water is utilized.
Among the several physiological traits, WUE is one
of the important trait, which can be explored to
develop new genotypes, tolerant to situation.

5. WHAT IS WUE
 It is defined as in different context by
 1. Hydrologist: It is the ratio of the volume of
water used for productivity to the volume of water
potentially available for irrigation & amount of
water available from soil.
 2. Agronomists: Amt of economic yield produced
by unit of water applied where both evaporation
and transpiration are considered.
 3. Physiologist: It is the amount of water used in
transpiration to produce unit amount of dry
matter during a particular growth period.
 WUE=Dry matter produced (g) / Water lost in
transpiration(Kg)

6. SIGNIFICANCE
 The widely accepted yield model of Passioura (1986)
adequately emphasis the importance of both
transpiration and WUE. Accordingly, it can be
visualized that increasing either total transpiration or
WUE, at a given transpiration, would enhance total
biomass production. Most yield improvements have
been achieved by increasing the transpirational
components through management and breeding.
Similarly in certain grain crops yield was improved
by increasing H.I.
 C4 species typically having a WUE of 4-5.5 g/Kg
compared to the C3 species (1.5-3 g/Kg).

7.  Perhaps because of this trait, the C4 species
have significantly higher productivity compared
to C3 species under arid and semi-arid tropics.
 Genetic variability of WUE in field crops:
 1. Cereals: 2.25 to 5.86 g/Kg
 2. Pulses: 2.26 to 3.87 g/Kg
 3. Oilseeds: 1.81 to 3.71 g/Kg

8. FACTORS AFFECTING WUE
Environmental factors :
 1. Vapour pressure deficit ( VPD) : It depends
on atmospheric humidity. Under high RH, VPD will
be low and vice versa. VPD is the driving force for
transpiration, hence an increase in leaf to air vapor
pressure difference substantially increases the
transpiration, there by decrease in WUE. This
situation occur under water limited situation or high
leaf temp. hence the prevailing RH & leaf temp.
influences the VPD and it has major effect on WUE.
Therefore high WUE can be achieved through
minimizing the VPD, by planting the crops early in
the season, where VPD is generally lower.

9.  2. Light: The solar radiation has a vital role to
play in determining WUE. Optimum irradiance
will cause maximum efficiency of water use. High
irradiance will increasing the leaf temp. and
reducing the stomatal resistance there by
decrease WUE.
 3.Temperature: Leaf temp. have profound effect
on WUE. Leaf temp. depend on atmospheric
temperature & leaf water content. High
atmospheric temp. coupled with lower water
uptake ( moisture limited conditions) increases
high VPD , there by increases transpiration and
finally WUE is affected. The genotypes maintain
low leaf temp. are always good at efficient
utilization of water.

10.  4. CO2 concentration: Enhanced Co2
concentration in atmosphere will increase WUE , by
higher photosynthesis, & higher dry matter
accumulation. Such increased Co2 concentration is
one of the component in global warming & increase
in productivity of crops was estimated initially due to
global warming or green house effect.
 5. Moisture stress: Drought stress is a complex
combination of stress because of both water deficit
and high temp. moderate drought increases WUE up
to 100% while extreme drought could substantially
decrease WUE. A common response to water stress
is simultaneous decrease in photosynthesis &
transpiration & increase in leaf temp..

11. If transpiration decrease faster than the
photosynthesis, causes increase in WUE.
Under severe moisture stress condition,
leaves become less efficient with respect
to water and Co2 exchange. Water lost is
prevented due to stomatal closure, nut
water still be lost through the cuticle, but
Co2 entry through stomata is severely
restricted, causing low WUE. Mid- season
stress drastically affects WUE .

12.  6. Agronomic practices & crop
management: Early sown crops will escape the
moisture stress while delayed sowing favors heavy
weed growth which creates severe competition.
Depth of sowing also influences water availability
and there by seedling emergence, vigor, & final
yield.
 7. Antitranspirants: WUE can be improved by
using antitranspirant which reduces transpiration. It
may influence stomatal closure ( PMA, ABA, CCC,
Salicylic acid etc.) or film forming (hexadecanol,
cetyl alcohol etc.) on leaf surface or increase plant
reflectivity (kaolinite) & reduce leaf temp.

13.  8. Use of mulches: Used to conserve water up
to 10 – 50 %. It depend on the crop in which it is
used, rainfall, wind velocity, and temp. of soil and
water. Organic mulches ( straw, rice dust, saw dust
etc.) light colored & light reflecting mulches reduce
soil temp. But black colored mulches such as
polythene sheets, petroleum prdts increase temp.
up to 5-8 degree Celsius. Plastic mulches are costly
& suitable to areas where soil temp. are low &
unfavorable to crop growth.
 9. Use of shelter belts: Decrease the
damaging effect of wind on crops and modify micro
climate. Examples are cotton, onion, sweet potato,
tomato & wheat.

14.  10. Methods and quantities of water
application : Frequent irrigation keep soil wet for
longer time but loss of evaporation more. Heavy
application of water causes deep percolation
losses. Selection of proper method of irrigation is
important based on soil and crop. WUE is higher
with sprinkler irrigation than surface method. Drip is
also increase production & decrease water use by
crop. WUE of a crop increases in order of wild
flooding, border strip, check basin, basin & furrow
irrigation.
 11. Fertilizer application: WUE of a crop
invariably increases with application of fertilizers on
deficit soils under adequate soil moisture
conditions. This is particularly with yielding varieties
and hybrids.

15.  12. Weed control: weeds due to early
establishment & a better root system are able to
exhaust soil moisture effectively than crop plants.
Therefore, both yield & WUE are reduced.
Controlling weeds is essential for high WUE of
crops.

16. PLANT FACTORS INFLUENCING WUE
 1. Leaf movements: Leaf is the substrate where both
assimilation and transpiration takes place to the
maximum. Transpiration normally shows a positive
relationship with increasing irradiance. Hence leaf
movement & surface reflectance pattern provide
energy load on the leaf. Leaf pubescence helps in
controlling the leaf temperature & water balance.
The orientation of leaves directly towards incident
irradiation results in relatively higher loss of water &
hence decreasing the WUE. Nictinastic movement
observed in leaves at mid day or high temp. is to
conserve moisture through low transpiration.

17.  2. Root system: The distribution of roots, its density
can influence water use by crops. Thus the rate of
root growth & their spread can affect WUE,
particularly during early stages of crop growth. Root
growth has direct relation with transpiration and it
was established in several crops. Plants with deeper
root growth are able to extract more soil moisture
from deeper soil profiles & cause higher
transpiration. Under less water stress conditions
these types display lower WUE & no effect on yield.
 3. Influence of nutrients: N, Mg, Fe are constituents of
chlorophyll & availability of these nutrients influence
leaf chlorophyll content and dry matter
accumulation. Hence these nutrients influence WUE
in terms of dry matter accumulation.

18.  P being plays important role in root growth & its
activity, availability of this nutrients influence
transpiration, there by WUE. K plays critical role in
stomatal movements & indirectly influence stomatal
conductance & WUE.
Transpiration Efficiency (TE)
. Physiological methods of estimating WUE is TE,
where on dry matter is calculated based on
transpiration loss.
. Transpiration efficiency is synonym of WUE.
. PASSIOURA, 1986 has given an excellent model,
where crop yields under field condition can be
explained by following

19.  GRAIN YIELD= T* TE*HI
 Where T= Total transpiration,
 TE=Transpiration efficiency or WUE,
 HI= Harvest index
 This relationship assumes greater importance when
the water availability is limited. Under such situations
genetic variations in dry matter accumulation depend
on TE & T. The total transpiration (T) from crop
canopy is cumulative effects of the avg. rate of water
uptake, duration of transpiration and canopy cover.
TE or WUE is the amount of biomass produced per
unit amount of water transpired.
 It can be visualized that increasing either T & TE, at
a given transpiration would enhance the biomass
production.

20.  Increase in T cannot be done under water limited and dry
land conditions. However T can be increased with
introgression of better root traits, which tap higher water
uptake.
 T.E. or WUE is the prime physiological traits, which can
be exploited to improve high dry matter accumulation. It
can be computed that at a rainfall of 800mm and 40% of
which is available for transpiration, 0.1g/kg increase in
TE or WUE would results in 0.3t/ha increase in total
biomass. Hence, TE is important physiological trait that
would determine total dry matter production.

21. INTRINSIC WUE
 WUE can be measured at whole plant level using
“gravimetric method” & at a single leaf level
using ‘gas exchange studies’. The physiological
methods of measuring WUE at single leaf level
by measuring Co2 fixation & stomatal
conductance is called intrinsic WUE.
 Biomass produced is a function of photosynthetic
rate. Hence IWUE is the ratio of carbon
assimilation rate (A) to transpiration (T).
Transpiration rate is determined by the intrinsic
stomatal conductance & the existing leaf to air
vapor pressure difference.

22.  If the plants being studied in a similar
environment, it can be expected the leaf to
air vapor pressure will be similar and hence,
the major factors that determines
transpiration that the intrinsic stomatal
conductance factor (gs), therefore,
IWUE=A/gs= carbon assimilation
rate/stomatal conductance factor
 IWUE can be used as useful trait to detect
genotypic variability. However it has
limitations, as the plants has to be grown in
glass house condition only to get reliable
data.

23.  In the field conditions variability in the data
observed due to dynamic vapor pressure. It
can be measured with the equipment “infra
red gas analyzer”.
Scope for plant improvement and
crop yields:
 For the improvement of crop yields under
water limited situations, improving WUE is
the potential option. However for any
successful breeding programme, existence
of genetic variability for WUE in a crop is
essential. As several report says, in most of
the crops, genetic variability exists for WUE.

24.  Some of the variabilities are
 Rice – 2.49 – 5.41 g/Kg
 Wheat – 4.60 – 5.27 g/Kg
 Cowpea – 2.74 – 3.00 g/Kg
 Soybean – 1.66 – 2.44 g/Kg
 Chickpea – 1.61 – 2.23 g/Kg
 Groundnut – 1.41 – 3.30 g/Kg
Breeding for high WUE is it
possible?
 Though WUE is an important component of
yield in the model proposed by Passioura
(1986)

25.  The existing genetic variability in WUE could
not be exploited through breeding. Many such
attempts were not successful since any
improvement in WUE was often associated with
reduction in dry matter accumulation and yield.
Because most often plants have evolved to
maximize the WUE through a reduction of
transpiration and there by CGR & dry matter
accumulation is reduced. Since stomatal
conductance (gs) is associated with
transpiration & internal Co2 partial pressure
(Pi), WUE & transpiration are strongly
interdependent. This interdependency is the
major reason for the lack of success in
breeding for increased WUE

26.  Success in breeding for high WUE
depend on
gm = Mesophyll efficiency
gs = stomatal diffusion factor
Pi = internal Co2 partial pressure
1. The intrinsic mesophyll efficiency & the
Co2 diffusion process are associated with
stomata that regulate carbon assimilation.
2. Transpiration rate on the other hand is
controlled by the differences in gs at a
given vapor pressure deficit(VPD).

27.  3. These two physiological traits (gm and
gs) determines Pi i.e. internal Co2 partial
pressure, which directly influences the
change in WUE.
 4. Depending on contribution of gm or gs to
Pi, genotypes and species are classified as
gs dependent ( conductance type) or gm (
capacity type) dependent.
 In capacity types, mesophyll factors will
determine carbon assimilation. So in these
types, WUE is interdependent of gs & hence
transpiration will not be associated with
WUE.

28.  Selection for high WUE from these capacity types
will result in high CGR, high dry matter and final
yields. Hence screening the germplasm for
capacity types and using as donor parents in a
breeding programme, will lead to enhanced crop
yields. G’nut, beans, wheat, grasses have
capacity type genotypes. The capacity types can
be determined by measuring WUE through IRGA
or carbon isotope discrimination (CID).the
success in developing g’nut genotype with high
WUE and high yields occurred in our university at
RARS, Tirupati, where dept. of plant physiology
evolved and release 2 g’nut genotypes Abhaya
and Greeshana become popular in farming
community.