Page 2 Plant-Bacteria Interactions Edited by Iqbal Ahmad, John ...

fungal infectivity, efficiency and ability to survive, multiply and spread, which may
help in utilizing obligate biotrophic AMF in biotechnological exploitation and sustainable
agriculture. There is a need to understand and better exploit AM symbionts
in different global ecosystems.
Although AMF are ubiquitous, it is probable that natural AM associations are not
efficient in increasing plant growth [31]. Cropping sequences as well as fertilization
and plant-pathogen management practices also dramatically affect the AMF propagules
in the soil and their affects on plants [32]. The propagation system used for
horticultural fruit and micropropagated plants can benefit most from AM biotechnology.
Micropropagated plants can withstand transplant stress from in vitro to in
vivo systems, if they are inoculated with appropriate AMF [33,34]. To use AMF in
sustainable agriculture, knowledge of factors such as fertlizer inputs, pesticide use,
soil management practices and so on influencing AMF communities is essential
[32,35,36]. This area deserves further research because a sound scientific knowledge
is necessary for improving the AM biotechnology aimed at selecting infective and
efficient inoculants to be used as biofertilizers, bioprotectants and biostimulants to
make agriculture, horticulture and forestry sustainable.
Although the potential of AMF in enhancing plant growth is well recognized, it is
not fully exploited. AMF are rarely found in nurseries due to the use of composted
soil-less media, high levels of fertilizer and regular application of fungicide
drenches. The potential advantages of inoculation of plants with AMF in horticulture,
agriculture and forestry are not perceived as significant by these industries,
partly due to inadequate methods for large-scale inoculum production. Monoxenic
root organ in vitro culture methods for AMF inocula production have also been
attempted by various researchers under field conditions [37,38]; however, these
techniques, although useful in studying various physiological, biochemical and
genetic relationships, have limitations in producing inocula of AMF for commercial
use. Pot culture in pasteurized soil has been the most widely used method for
producing AMF inocula, but this method is time consuming and often not pathogen
free. To overcome these problems, soil-free methods such as soil-less growth media,
aeroponics, hydroponics and axenic cultures of AMF have been used successfully to
produce AMF-colonized root inocula [37,39–41]. Substrate-free colonized roots produced
by these methods can be sheared and used for large-scale inoculation purposes.
Mohammad et al. [42] compared growth responses of wheat to sheared root
and pot culture inocula of AMF at different phosphorus levels under field conditions
and concluded that phosphorus fertilization can be substituted by AMF inoculum
produced aeroponically to an extent of 5 kg ha 1 .
13.2.2
Arbuscular Mycorrhiza–Rhizobacteria Interactions
13.2 Rhizosphere and Microorganismsj247
Increased microbial activity in rhizosphere soil affects plant health and growth. A
range of stimulated rhizosphere microorganisms such as saprophytes, pathogens,
parasites, symbionts and so on carry out many activities important to plant health
and growth. Some of these microbes affect root morphology and physiology by