Agriculture Reference
In-Depth Information
field experiments or experiments in soil might be more suitable for assessing or
identifying traits for P efficiency rather than using solution culture (Hayes
et al.
2004
; Gunes et al.
2006
; George et al.
2004
,
2005
).
For agronomic and economic reasons, P efficiency is based on the cropping area
leading to improved P fertiliser recovery and use of soil P (Sattelmacher
et al.
1994
). This concept takes into account the low P availability in e.g. tropical
soils (Wissuwa et al.
2009
), limited access to P fertilisers in some regions of the
world (Tiessen
2008
), costs for fertilisation (FAO
2011
) and environmental aspects
including impaired water quality by run-off or drainage due to agricultural inten-
sification (McDowell
2012
). This unit is based on the P efficiency properties of the
plant itself, which can be divided into PAE and PUE (Wang et al.
2010a
,
b
). It is of
strong economic interest to not only enhance P acquisition, which might result in
over-mining the soil, but also enhance PUE without increasing P export from the
field via the grain (Batten
1992
; Rose and Wissuwa
2012
). Both traits are usually
linked, negatively associated with each other and are hard to distinguish
(Su et al.
2006
; Su et al.
2009
; Rose and Wissuwa
2012
), indicating a need to
choose a selection technique achieving an appropriate distinction (Batten
1992
) and
a clear positive correlation of biomass ratios with increasing PUE (Rose and
Wissuwa
2012
). In contrast to PAE, PUE is much less well understood, lacks
clearly defined and consistent terminologies or screening methodologies across
the literature which is a bottleneck for P efficiency improvement in crops
(Hammond et al.
2009
; Wang et al.
2010a
,
b
; Rose and Wissuwa
2012
). To achieve
an increase of PUE is especially important in regions of high cropping intensity
facing plateauing yields during the last decade.
Screening Approaches
When P efficiency is to be evaluated across a range of distinct or heterogeneous
genotypes e.g. high-yielding modern varieties and low-yielding land races, a tissue-
specific approach is probably required (Rose and Wissuwa
2012
). Using this
approach presupposes knowledge about the different P pools as well as about the
changing P requirements depending on the growth stage of the crop (Veneklaas
et al.
2012
).
Phosphate is compartmentalised within plant cells and exists in two main P pools
(Veneklaas et al
2012
). The first P pool consists of free inorganic orthophosphate
(P
i
), which is either metabolically active in the cytoplasm or stored in the vacuole to
buffer P demands of the cytoplasm (Mimura et al.
1996
; Lauer et al.
1989
). The
storage P
i
can have a diagnostic value (Bollons and Barraclough
1997
,
1999
),
although shoot growth seems to be reduced before severe P
i
depletion of the
vacuolar storage pool occurs (Rouached
2011
; Mimura et al.
1996
). The second P
pool represents organic forms as P esters, comprising nucleic acids, phospholipids,
