A
survey of the levels of free phosphorus (phytate) in
the kernels of 39 barley cultivars grown in western
M.C. Therrien
AAFC Brandon Research Centre
Phytic acid is a form of bound
phosphorus (P) in barley grain that is not available when fed to livestock.
This reduces the nutritional value of the grain, as well as being a problematic
source of excess P where manure is applied to agricultural land (Lott et al.,
2000). Since most of the barley grain production in western Canada is fed to
livestock (CAPI, 2007), estimating the level and range of phytic
acid in barley cultivars would be useful in determining the feasibility of
reducing phytic acid content in barley through
breeding using the natural variation found in this crop. A number of mutant forms
of low phytate barley exist, including the cultivar
CDC Lophy-1 (CFIA, 2007), developed by Dr. B.G. Rossnagel, and colleagues, at
the
Materials and Methods
Thirty-nine
barley cultivars were grown in small (5 m2) plots in a three-replicate
Completely Randomized Design (CRD) at two locations (Brandon and Hamiota, MB) over two years. Grain was harvested and dried
to approx. 12% moisture and a 50 g subsample was obtained from each plot.
Samples were ground and assayed for levels of free phosphorus (FP), using the
colorimetric reaction method of Dorsch et al. (2003),
a rapid assay method suitable for breeding programs. The amount of FP was
determined for each sample, as mg FP per gram of ground barley. A set of
standards was also included. CDC Lophy-1 served as a check for optimal FP
levels.
Data
were analyzed using the PROC MIXED procedure in SAS (SAS Institute, 1988).
Genotype by Environment Interaction (GEI) analysis was also performed on the
data using the method of Kang and Gauch (1996).
Results and Discussion
The
cultivars used in this study, along with their average concentration of FP, are
shown in Table 1.
Table 1. Average
levels of Free Phosphorus (FP; expressed as mg FP per g sample) for 39 barley
cultivars averaged over four site-year combinations.
|
Two-row Feed |
FP |
Two-row Malt |
FP |
Six-row Feed |
FP |
Six-row Malt |
FP |
Hulless |
FP |
|
Champion |
0.407 |
Select |
0.439 |
|
0.386 |
Robust |
0.398 |
Freedom |
0.569 |
|
Cowboy |
0.430 |
Harrington |
0.480 |
Lacombe |
0.435 |
|
0.509 |
McGwire |
0.619 |
|
Dolly |
0.463 |
Metcalfe |
0.513 |
Vivar |
0.466 |
Legacy |
0.565 |
Rattan |
0.595 |
|
Trey |
0.483 |
Newdale |
0.552 |
Virden |
0.477 |
Tradition |
0.626 |
Enduro |
0.699 |
|
Coalition |
0.507 |
Merit |
0.594 |
Alston |
0.491 |
Excel |
0.635 |
Fibar |
0.755 |
|
Helgason |
0.520 |
Stratus |
0.602 |
Desperado |
0.497 |
Mean |
0.537 |
Merlin |
0.869 |
|
Conlon |
0.524 |
Copeland |
0.628 |
Ranger |
0.528 |
Std. Error |
0.053 |
Mean |
0.701 |
|
Mean |
0.476 |
|
0.663 |
Binscarth |
0.545 |
CV |
9.9 |
Std. Error |
0.043 |
|
Std. Error |
0.017 |
TR05915 |
0.676 |
Rosser |
0.551 |
|
|
CV |
6.1 |
|
CV |
3.6 |
Calder |
0.685 |
Dillon |
0.992 |
|
|
|
|
|
|
|
Mean |
0.583 |
Mean |
0.537 |
|
|
|
|
|
Check |
|
Std. Error |
0.027 |
Std. Error |
0.053 |
|
|
|
|
|
Lophy-1 |
4.887 |
CV |
4.6 |
CV |
9.9 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
The
level of FP ranged from 0.386 mg g-1 to
0.992 mg g-1 for the conventional cultivars, whereas CDC Lophy-1
(low phytic acid check) had an average 4.887 mg g-1 of FP. Differences in FP
levels were highly significant amongst cultivars (Table 2). There were
significant differences amongst classes of barley, as well, with the two-row
feed cultivars having a lower FP level (hence, a higher phytic
acid level), and the hulless cultvars
having a higher FP level than the two and six row malt, and six-row feed
cultivars, which were similar to one another. In all cases, FP levels were well
below that of CDC Lophy-1.
Table 2. Analysis of Variance of Free
Phosphorus (FP) levels for 39 barley cultivars grown over 4 environments.
|
Source |
df |
Sums
Sq |
Mean
Sq |
F
Value |
Prob.
> F |
|
Model |
42 |
2.64 |
0.06 |
7.24 |
0.0001 |
|
Error |
413 |
3.58 |
0.01 |
|
|
|
Corr.
Total |
455 |
6.22 |
|
|
|
|
Cultivar |
37 |
0.73 |
0.02 |
2.28 |
0.0001 |
|
Replicate |
2 |
0.02 |
0.009 |
1.11 |
0.3298 |
|
Environment |
3 |
1.89 |
0.63 |
72.47 |
0.0001 |
While
there appeared to be enough variation in FP content across conventional
cultivars, a Genotype x Environment (GxE) Analysis
was conducted to calculate a broad-sense heritability estimate (H2)
for the FP character. This would give an indication of how easily this trait
could be enhanced through conventional breeding. GxE
analysis indicated a large environmental influence on FP, as well as a large GxE interaction. This contributed to a low heritability
estimate (H2=0.3862) for the FP character (Table 3.)
Table 3. Genotype by Environment
Analysis and Broad-sense Heritability Estimate (H2) for the Free
Phosphorus (FP) trait in barley grain.
|
Source |
Sums
of Squares |
Contrib.
Ratios |
H2 |
|
Genotype(G) |
0.73 |
0.12 |
0.3862 |
|
Environment(E) |
1.89 |
0.30 |
|
|
G
x E |
1.28 |
0.21 |
|
|
Total |
6.22 |
|
|
Our
results suggest that breeding for improved FP, using only conventional barley
germplasm, would not be practical as the desired levels approaching that of CDC
Lophy-1 could not be attained in a reasonable time frame, if at all. Use of low
phytate mutants is the only practical alternative.
Literature Cited
Canadian
Food Inspection Agency (CFIA). 2007. Notification of registration: CDC Lophy-1.
Electronic access:
http://www.inspection.gc.ca/english/plaveg/variet/07-03e.shtml
Canadian
Agri-Food Policy Institute (CAPI). 2007. General
Information – Barley. Electronic Access: http://www.capi-icpa.ca
Dorsch, J.A., Cook, A., Young,
K.A., Bauman, A.T., Volkmann, C.J., Murthy, P.P.N., and Raboy,
V. 2003. Seed phosphorus and inositol phosphate
phenotype of barley low phytic acid genotypes. Phytochemistry 62:691-706.
Kang,
M.J. and Gauch, H.G. 1996. Genotype-by-Environment
Interaction. CRC Press,
Lott,
J.N.A., Ockenden,
SAS
Institute. 1988. SAS user’s guide: Statistics. Version 6.04 ed., SAS Inst.,