Environmental Engineering Reference
In-Depth Information
Table 3
Arbuscular mycorrhizal fungal inoculum types
with their advantages and disadvantages
Inoculum type
entrapment of AM fungal propagules in natural
polysaccharide gels (Vassilev et al.
2005
;
Siddiqui and Kataoka
2011
) are under study.
Such technological breakthroughs would greatly
facilitate both fundamental and applied researches
on mycorrhizae as well as improve quality con-
trol of commercial inocula.
Advantages
Disadvantages
Soil based
Long shelf life
Bulk and heavy
Useful at
transplanting
Needs soil
sterilization
Soilless substrate
Weightless than
soil
Needs careful
control of
watering and
fertilizer
application
Uniform
composition
Can be dried and
stored
5
Methods of Inoculum
Production
Surface-
sterilized AM
propagules
Aeroponically
developed
colonized roots
can be sheared
Needs highly
skilled
technique
The production of inoculum is more essential for
AM fungi due to its obligate symbiotic nature.
Traditionally, AM fungi are propagated through
open pot cultures. Starter cultures are usually ini-
tiated from spores or colonized root fragments,
which are later incorporated into the growing
medium for seedling production (Brundrett et al.
1996
). The fungi spread in the substrate and colo-
nize the roots of the seedlings. Both colonized
substrates and roots can then serve as mycorrhi-
zal inoculum. Soilless culture systems such as
aeroponic cultures enable the production of
cleaner spores and facilitate uniform nutrition of
colonized plants (Singh et al.
2012
). The success-
ful propagation of some AM fungal strains on
root-organ cultures has facilitated the develop-
ment of monoxenic strains that can be used
directly as inoculum for in vitro plant production
systems or for large-scale inoculum production
(Fortin et al.
2002
).
Entrapment in
polymer gel,
alginate,
hydrogel,
hydroponic,
aeroponic and
root-organ
culture
Can be kept free
of extraneous
organisms
Relatively
expensive
Can be dried and
stored
Modifi ed from Azcon-Aguilar and Barea (
1997
) with
permission
Idczak
1992
). The aggregates can later be surface
sterilized and applied to fi eld-grown crops in
small quantities (Baltruschat
1987
). Vermiculite
is an inorganic carrier for AM inoculum produc-
tion, as it is an ideal substrate for AM fungal
sporulation (Barea et al.
1993
). Sheared-root
inocula (Sylvia and Jarstfer
1992
), prepared from
aeroponic cultures (Hung and Sylvia
1988
;
Jarstfer and Sylvia
1999
), are also routinely used
in inoculation programmes. Surface-disinfected
AM fungal propagules can also be used espe-
cially under in vitro conditions. Two methods of
off-farm inoculum production (open pot culture
and root-organ culture) are detailed below.
5.1
Off-Farm Methods
The various advantages and disadvantages of dif-
ferent off-farm inoculum production methods are
shown in Table
3
. Highly infective soil-based
inocula are quite easy to produce and handle.
However, the time span required to produce
appreciable quantities of soil-based inocula can
range between 6 and 12 months. An inoculum
form produced using light expanded clay aggre-
gates as substrate is of interest (Dehne and
Backhaus
1986
), as the porous material containing
infective mycelium and spores can be easily
separated from the plant roots (Feldmann and
5.1.1 Open Pot-Culture Production
Arbuscular mycorrhizal fungi are obligate sym-
bionts, which require a suitable host plant for its
establishment and proliferation. Conditions for
large-scale inoculum production need to be opti-
mized. Care should be taken to identify and avoid
contamination from undesired species during
monoculture. The process to attain huge amount
of targeted inoculum is rather lengthy. The
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