16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11917
Preliminary Findings on the Arbuscular Mycorrhizal
Colonization of Organic Wheat
Kirk, A.1,2, Fox, S.1, Entz, M.2 & Tenuta, M.3
Key words: Spring wheat, arbuscular mycorrhiza, heritage wheat, phosphorus
Abstract
Arbuscular mycorrhizal fungi aid many crop plants in the uptake of phosphorus, which
is one of the most limiting nutrients in organic crop production. Genotypic variation for
mycorrhizal colonization exists in wheat cultivars. Mycorrhizal colonization and yield
were studied in 5 modern wheat cultivars and 5 older wheat cultivars to investigate if
differences in colonization exist between the cultivars. Cultivars that may be better
suited for organic production are identified.
Introduction
Modern wheat varieties that have been bred under conventional management
systems may not be the best suited varieties for organic production. Although modern
crop varieties are high yielding under optimal conditions, some researchers have
reported that modern varieties suffer greater yield losses than ancestral varieties when
grown under stressful conditions (Mason and Spanner 2006).
In many regions of the world phosphorus (P) is one of the most important nutrients
limiting crop production (Zhu et al. 2001). Due to increased nutrient deficiencies in
organic systems, arbuscular mycorrhizal fungi (AMF) are important for the uptake of
nutrients, especially P.
It has been reported that genotypic variation for mycorrhizal colonization exists
between cereal cultivars (Baon et al. 1993; Zhu et al. 2001; Kaeppler et al. 2000).
Dependency upon mycorrhizal colonization also varies between crop cultivars.
Hetrick et al. (1992) found landraces have a greater benefit from mycorrhizal
symbiosis then modern cultivars, suggesting mycorrhizal dependence is stronger in
older populations of wheat. It has been hypothesized that selection of germ plasm
under fertilized conditions may have reduced that frequency of genes that promote
mycorrhizal associations (Hetrick et al. 1992).
The objective of this study was to determine if selecting wheat varieties under
conventional management has reduced their ability to colonize with AMF. A second
objective of this study is to identify cultivars that may be better adapted to organic
conditions due to higher levels of mycorrhizal colonization.
1
Cereal Research Centre, Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, MB,
Canada R3T 2M9, E-Mail sfox@agr.gc.ca.
2
Department of Plant Science, University of Manitoba, Winnipeg, MB, Canada R3T 2N2, E-mail
M_Entz@umanitoba.ca
3
Department of Soil Science, University of Manitoba, Winnipeg, MB, Canada R3T 2N2, E-mail
tenutam@cc.umanitoba.ca.
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11917
Materials and methods
This experiment was conducted at two long term organic locations, Glenlea and
Carman, Manitoba, Canada. The experiment was established in the spring of 2007.
The experimental design is a randomized complete block, with four replicate blocks at
each site. Soil samples were collected in early spring and showed 9 ppm or 77 kg/ha
of available P at Glenlea, and 14 ppm or 155 kg/ha of available P at Carman. The
seeds of five older and five modern bread wheat varieties (Triticum aestivum L.) were
obtained (Table1). Plot size was 3 x 0.6 m at Glenlea and 4.5 x 0.6 m at Carman.
Both locations were seeded in early May and were harvested in late August using a
plot combine. To estimate root colonization by AMF 3 soil cores plot-1 were obtained
at the 4 leaf stage. The soil cores were bulked to give one sample per plot. Roots
were washed by hand, root mass was measured, then the roots were stored in 70%
ethanol. A random subsample of roots was cleared with 10% KOH, then stained using
chlorazol black E. The magnified intersections method (McGonigle et al. 1990) was
used to score 100 root intersections for colonization by hyphae, arbuscules, vesicles,
and spores. All data were statistically analyzed using the mixed model (P<0.05) with
the SAS statistical package.
Results
Percent colonization by arbuscules varied from 5.75% (Neepawa) to 11.25% (Mida) at
Glenlea and from 12% (Neepawa) to 21% (McKenzie) at Carman (Table 1). Although
colonization did not appear to follow a trend at Glenlea, percent colonization generally
decreased from the most recently released cultivars to the oldest cultivars at Carman.
At Glenlea there was no statistically significant (P>0.5) difference between the modern
and older cultivars. As shown in Figure 1, at Carman the modern cultivars had a
significantly higher (P<0.5) level of colonization then the older cultivars.
Table 1: Year of release, percent colonization by arbuscules, and yield (kg/ha) for the
10 wheat cultivars at Glenlea and Carman, Canada, in 2007.
Cultivar
Year of Release
Arbuscular Colonization
Yield (kg/ha)
Glenlea
Carman
Glenlea
Carman
9.75z
19z
1381.60cdy
2306.54ay
2004
8
13.25
1859.06a
2053.67a
1997
8.5
14
1793.30ab
1729.13b
AC Barrie
1994
6
14.5
1137.05d
1112.86e
CDC Teal
1991
8
19.5
1477.90bc
1424.46cd
Neepawa
1969
5.75
12
1350.52cd
1317.63cde
Selkirk
1955
7.75
13.25
1313.64cd
1210.09de
Mida
1944
11.25
11.25
1283.27cd
1588.88bc
Marquis
1918
8.25
10.25
1442.80cd
1218.29de
FBC Dylan
2006
5602 HR
McKenzie
Red Fife
1886
9
13
1892.00a
1515.68bc
Means within the same site year followed by the same letter within a column are not significantly different
(P>0.05) according to Fischer’s protected LSD.
z
Means are not significantly different (P>0.05) according to Fischer’s protected LSD.
y
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11917
Average % Colonization
30
25
20
15
10
5
0
Modern
Heritage
Figure 1: Average % colonization by arbuscules (white) and by hyphae and
arbuscules (dark) for modern varieties (1991-2006) and for heritage varieties (18861969) at Carman, Manitoba, Canada.
There was no general yield trend at Glenlea, while yields generally decreased with
year of release at Carman. Yields ranged from 1137.05 kg/ha (AC Barrie) to 1892
kg/ha (Red Fife) at Glenlea and from 1112.86 kg/ha (AC Barrie) to 2306.54 kg/ha
(FBC Dylan) at Carman (Table 1).
Discussion
Variation in mycorrhizal colonization was observed at both locations. The results at
Carman are in agreement with the findings of Zhu et al. (2001), where the modern
cultivars had higher colonization than the older cultivars in the study. All cultivars
were found to be mycorrhizal in this study. In general, mycorrhizal colonization is
known to increase the uptake of P per unit weight of root (Baon et al. 1993).
Colonization was shown as arbuscular colonization because it is thought that most
nutrient exchange occurs at the arbuscules (Peterson et al. 2004). Although it may
seem that cultivars with higher colonization by arbuscules should have the ability to
take up more nutrients this may not be the case.
Hetrick et al. (1993) found no relationship between the degree of root colonization and
the degree of benefit from AMF symbiosis. Some researchers have found that
efficiency or response to mycorrhiza is greater in older cultivars than modern cultivars
(Hetrick et al. 1993; Zhu et al. 2001). Therefore, although modern cultivars were
found to have higher levels of colonization than older cultivars at Carman, more
research is needed to assess the benefit the cultivars are receiving from symbiosis
with AMF.
It was hypothesized that heritage cultivars may be better suited for organic production.
At Glenlea, a site which had high weed and disease pressure, Red Fife (1886), a
heritage variety, had the highest yield. At Carman the highest yielding cultivar was
FBC Dylan (2006), an organically bred variety. The high yields may be associated
with mycorrhizal colonization since FBC Dylan had high colonization at Carman and
Red Fife had moderately high colonization at Glenlea. AC Barrie, a variety commonly
grown by conventional farmers in Canada had the lowest yield at both sites under
organic management.
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11917
Conclusions
The objective was to identify cultivars that may be better suited to organic conditions
due to higher levels of mycorrhizal colonization. No significant differences in
arbuscular mycorrhizal colonization were found between cultivars, although there were
significant yield differences at both locations. The yields of the individual cultivars
provide an opportunity to identify cultivars that were better suited to organic conditions
in this year, although yields were different between sites. More research needs to be
done to determine the benefit the cultivars are receiving from mycorrhizal colonization.
Acknowledgments
We gratefully acknowledge financial support from Agriculture and Agri-Food Canada;
The Canadian Wheat Board; and Manitoba’s ARDI program.
References
Baon J. B., Smith S. E., Alston A. M. (1993): Mycorrhizal responses of barley cultivars differing in P
efficiency. Plant Soil 157:97-105.
Hetrick B. A. D., Wilson G. W. T., Cox T. S. (1992): Mycorrhizal dependence of modern wheat
varieties, landraces, and ancestors. Can. J. Bot. 70:2032-2040.
Hetrick B. A. D., Wilson G. W. T., Cox T. S. (1993): Mycorrhizal dependence of modern wheat
cultivars and ancestors: a synthesis. Can. J. Bot. 71:512-518.
Kaeppler, S.M., Parke, J.L., Mueller, S.M., Senior, L., Stuber, C., and Tracy, W.F. 2000. Variation
among maize inbred lines and detection of quantitative trait loci for growth at low phosphorus
and responsiveness to arbuscular mycorrhizal fungi. Crop Sci. 40: 358-364.
Mason H. E., Spanner D. (2006): Competitive ability of wheat in conventional and organic
management systems: a review of the literature. Can. J. Plant Sci. 86:333-343.
McGonigle T. P., Miller M. H., Evans D. G., Fairchild G. L., Swan J.A. (1990): A new method which
gives an objective measure of colonization of roots by vesicular-arbuscular mycorrhizal fungi.
New Phytoligist 115:495-501.
Peterson R. L., Massicotte H. B., Melville L. H. (2004): Mycorrhizas: anatomy and cell biology.
NRC Research Press. Ottawa, Canada. 173 pp.
Zhu Y. -G., Smith S. E. (2001): Seed phosphorus (P) content affects growth, and P uptake of
wheat plants and their association with arbuscular mycorrhizal (AM) fungi. Plant Soil
231:105-112.