Environmental Engineering Reference
In-Depth Information
(Kapoor et al. 2008 ). Surface sterilization of AM
fungal spores is done using various sterilizing
agents like chloramine-T or Tween 20 (Fortin
et al. 2002 ) followed by antibiotic solution wash
to remove contaminants from spore surfaces. All
the above said processes need to be carried at
reduced temperatures. The selection of culture
medium is of prime importance, because both
roots and AM fungal propagules require different
media compositions for their growth. The nega-
tive geotropic nature of transformed roots facili-
tates its contact with the AM fungal hyphae,
thereby initiating colonization. Recently, Abd-
Ellatif et al. ( 2012 ) demonstrated the successful
establishment of AM fungal association in root-
organ culture using tomato hairy roots.
growth, the soil and roots were harvested to a
depth of 20 cm and used as inoculum.
5.2.1.1 Advantage
A postharvest analysis of the inoculum showed
that fumigation of the soil was essential to
increase the AM fungus spore production per
given quantity of the soil. Further, fumigation
also increased the relative proportion of spores of
the desired AM fungal isolate relative to indige-
nous AM fungi compared to unfumigated and
inoculated plots.
5.2.2 Method 2
The second method of on-farm AM fungal inocu-
lum production involves preparing raised soil
beds (60 × 60 × 16 cm) (Gaur 1997 ; Douds et al.
2000 ). After fumigation of the beds, the AM
fungi from a starter inoculum were inoculated
into furrows in the raised beds. A succession of
hosts [(e.g. Sorghum sudanese , corn and carrot
( Daucus carota )] were grown for 1 year of
4 months each. The growth cycle was carried
over a course of 3 years. After the third cycle
started to progress, the soil in raised beds was
found to be ready to be used as inoculum.
5.2
On-Farm Methods
On-farm production of AM fungal inoculum
entails increasing the propagules of desired iso-
lates and indigenous AM fungi in fumigated and
unfumigated fi eld soils, respectively, or trans-
planting pre-colonized host plants into compost-
based substrate (Douds et al. 2005 ). This type of
AM fungal inoculum production would enable
farmers to obtain inoculum at a cheaper cost and
make their transportation easy. Furthermore,
farmers could easily produce locally adopted iso-
lates and generate a taxonomically diverse inocu-
lum in large quantities.
5.2.2.1 Advantage
An approximately tenfold increase in AM fungal
inocula was evident from year 1 to year 3, yielding
around 2.5 × 10 6 propagules per bed.
5.2.3 Method 3
Gaur et al. ( 2000 ) and Gaur and Adholeya ( 2002 )
later modifi ed the above method to yield a shorter
inoculum production cycle without the use of fumi-
gants. Raised beds were prepared as stated above
(method 2) by using 2:1 (v/v) mixture of soil to leaf
compost. The beds were either inoculated or left
uninoculated to enhance the proliferation of indig-
enous AM fungi. In this method, only one plant
growth cycle was used involving forage crops or
vegetables as host plants.
5.2.1 Method 1
The earliest method of inoculum production for
an effective strain of the AM fungus Rhizophagus
manihotis ( = Glomus manihotis ) was developed
by Sieverding ( 1987 , 1991 ) in Columbia. In this
method, fi rst, a 25 m 2 fi eld plot was tilled and
fumigated to eliminate the indigenous AM fl ora.
After the fumigant has dissipated, the inoculum
of the specifi c AM fungal strain ( R. manihotis )
was inoculated into holes drilled in the soil and
then seeded with a grass host, Brachiaria decum-
bens . Simultaneously, pre-colonized B. decum-
bens plants were also transplanted to the inoculum
preparation plots, thereby minimizing the amount
of starter inoculum needed. After 4 months of
5.2.3.1 Advantage
In this method, inoculum production was 15-
to 20-fold greater than the starter inoculum
used. This method produced only 55-69,000
Search WWH ::




Custom Search