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

Table 5.3 (Continued )
Mechanisms Organisms Effect on plant growth References
Augmented
nutrient
uptake
Azospirillum
spp.
5.5
Interaction of Diazotrophic PGPR with Other Microorganisms
The colonization of roots by inoculated bacteria is an important step in the interaction
between beneficial bacteria and the host plant. However, it is a complex phenomenon
influenced by many biotic and abiotic parameters, some of which are now
apparent. In order to successfully utilize PGPR in agriculture, it is important to
understand the mechanisms that enable them to colonize the rhizosphere and the
factors that lead to the stimulation of their beneficial effects. It is reasonable to
assume that PGPR must colonize the rhizosphere of the host plant to be most
beneficial [152,153]. Root colonization is a complex phenomenon under the influence
of many parameters (Figure 5.2). Various techniques that may be classified as
classical, immunological and molecular are applied for monitoring the inoculant
strains in the rhizosphere in relation to survival and colonization in the rhizosphere.
5.5.1
Interaction of Diazotrophic PGPR with Rhizobia
Pectinolytic activity may increase mineral
uptake by the hydrolysis of middle
lamellae of roots, also caused enhanced
uptake of IAA by roots of wheat and maize
Bacterial nitrate reductase increased
reduced nitrogen in roots and total
and dry weight in wheat
Biocontrol
Siderophore Azospirillum Reduces iron availability, thus
Azotobacter making it unavailable to
Rhizobium phytopathogens. They may act
Cell wall Paenibacillus as an important source of iron for higher
lysing enzyme
plants in alkaline and calcareous soil
Chitinase and antifungal activity
Cellulase and mannanase
Antibiotics Azotobacter Antifungal compound – inhibits
the production of conidia of
fungus (Botrytis cinerea)
Azospirillum
Paenibacillus
Bacillus
5.5 Interaction of Diazotrophic PGPR with Other Microorganismsj93
Bacteriocins Polymyxin – active
against bacteria and fungus
Coproduction of antifungal
(surfactrin and iturin like) compounds
[45,140–143]
[112,144–147]
[77,148]
[117,149–151]
Symbiotic nitrogen fixation in legumes is accomplished by rhizobia occurring within
root nodules. This process is dependent on the efficiency of the Rhizobium strain