Molecular Breeding for Phosphorus-efficient Rice - Translational Genomics for Crop Breeding: Abiotic Stress, Yield and Quality - page 77

(a) (b)

+P

Situ Bagendit- Pup1 Batur- Pup1 Dodokan- Pup1

K N

K20-2

Bsp

K29-3

low P

K46-2

grain weight plant -1

(c) (d)

- Pup1 IR74- Pup1

Fig. 5.5. Pup1 breeding lines. The recipient parents selected for Pup1 introgression were genotyped with three Pup1
markers ( a ). IR64, IR74, and Situ Bagendit have intolerant Nipponbare-type (N) alleles for all three markers. In contrast,
Dodokan and Batur have some Kasalath-type (K) alleles, including marker K46-2, which targets OsPSTOL1. The Indonesian
Pup1 breeding lines (BC 2 F 4 ) were evaluated in an upland field experiment in West Java (Indonesia) under high- and low-P
conditions ( b ). The IR64- Pup1 and IR74- Pup1 breeding lines were tested under irrigated field conditions in P-deficient soils
showing vigorous growth ( c ) and yield advantage ( d )ofIR74- Pup1 lines. For a color version of this figure, please refer to
the color plate.

accompanying stresses may be equally “patchy,”
a common problem of field screenings is the
high variability and low reproducibility of data.
An additional concern is that accompanying
stresses, such as Al toxicity, directly affect root
growth with subsequent indirect effects on P
uptake. In such cases, observed genotypic dif-
ferences in response to low P may be incorrectly
attributed to differences in tolerance, when the
driving factor in fact was differences in toler-
ance of Al toxicity (or other abiotic stresses).
It is therefore important to carefully select and
analyze soils intended for P screenings.
To avoid complications associated with
screening in soil, most studies on P deficiency
have been conducted in hydroponic culture solu-
tion at P concentrations ranging from 3 μM
(Wissuwa et al. 2005) to 15 μM (Ni et al. 1998).
This rather wide range of P concentrations high-
lights the fact that P concentrations alone may be
slightly misleading; the total amount of P avail-

able per plant over a period of time should be
the most important criterion, and that in turn will
depend on plant age, duration of the experiment,
interval of renewing nutrient solutions, total vol-
ume, and number of co-cultivated plants sharing
the same solution. Thus, P treatments in nutrient
solution experiments should ideally be defined
by total nutrient per plant and unit time (e.g., μg
P plant − 1 day − 1 ).
Whether the ease of screening and the high
repeatability of nutrient solution experiments
outweigh the main drawback, namely, the uncer-
tainty about whether results obtained can be
transferred to field situations, is a matter of
debate. In the field, tolerance of P deficiency
will depend on multiple tolerance mechanisms
that can be classified into three broad categories
(Ismail et al. 2007): (1) root interception of P
as affected by root growth, anatomy, and archi-
tecture; (2) P-acquisition efficiency due to rhi-
zosphere modifications by the plant root that