Agriculture Reference
In-Depth Information
Exploiting Genetic Differences
There are studies showing genotypic differences for P deficiency tolerance
suggesting that P efficiency mechanisms may differ among wheat, rye and triticale
genotypes (Ozturk et al.
2005
; Manske et al.
2001
; Osborne and Rengel
2002
;
Gunes et al.
2006
). Hammond et al. (
2009
) observed a considerable diverse species-
wide variation for shoot P concentrations and several PUE measures in
Brassica
oleracea
landraces and commercial varieties. Manske et al. (
2001
) argued that
under P deficient conditions P uptake efficiency plays the key determinant for yield,
whereas P utilisation efficiency was more relevant under well P supplied condi-
tions. There are also several investigations in other
Brassica
plants aiming to
exploit genetic diversity (Akhtar et al.
2008
; Solaiman et al.
2007
; Yang
et al.
2010
,
2011
).
Batten (
1992
) pointed out that selection of more P efficient wheat occurs
unconsciously during breeding when selecting for higher yields at sub-optimal P
levels. Chin et al. (
2010
) mentioned a similar observation of an unconscious
selection for a major P deficiency tolerant rice QTL,
Pup1
, in drought tolerant
varieties developed under unfavourable conditions. Hammond et al. (
2009
) simi-
larly implicated inadvertent selection in
B. oleracea
breeding programmes.
The selection process resulting in modern (
Brassica
) crop varieties with
increased grain yield per mg shoot P (Hammond et al.
2009
) might be just a result
of higher HI (Batten and Khan
1987
), rather than a selection of physiological traits
(Rose and Wissuwa
2012
). Chin et al. (
2010
) support that hypothesis by observing a
lower frequency of the low P-tolerant QTL
Pup1
in modern irrigated rice varieties
compared to traditional varieties. There are further studies showing that enhanced
low P tolerance in wheat was due to enhanced P uptake rather than enhanced P
utilisation (Gahoonia et al.
1996
; Gahoonia et al
1999
).
A comparison of new CIMMYT wheat varieties with an older Mexican variety
showed that PUE did not differ (Egle et al.
1999
). However, P acquisition under low
P conditions was improved mainly due to a better root length density, especially
during the period during anthesis and grain filling (Egle et al.
1999
). With P
fertilisation, root length density was not significantly different between the older
and the modern varieties, but higher P uptake rates, especially during grain filling,
of the modern varieties seemed to have contributed to higher P acquisition ability at
appropriate P supply. A higher shoot growth and a subsequently higher sink
capacity of more kernels might have contributed to that effect (Egle et al.
1999
).
In maize, several studies have identified distinguishable P uptake amongst geno-
types (Da Silva and Gabelman
1992
; Zhu and Lynch
2004
; Chen et al.
2009a
,
b
;de
Sousa et al.
2012
), without providing large amounts of potential target genes for
exploiting crop biodiversity (Calder´n-V´zquez et al.
2008
).
