Plant-Microorganism Interactions: Effects on the Tolerance of Plants to Biotic and Abiotic Stresses - Crop Improvement: New Approaches and Modern Techniques - page 227

through reductions in their development (Elsen et al. 2003 ; de La Peña et al. 2006 ;
Jaiti et al. 2008 ; Meira-Haddad 2008 ).
Populations of Pratylenchus coffeae, Radophulus similis, Meloidogyne javanica ,
among others, were reduced by G. mosseae and G. intraradices when associated
with banana roots (Pinochet et al. 1996 ; Elsen et al. 2003 ). The mycorrhizal fun-
gi might affect nematode reproduction by reducing galls and eggs and inhibiting
penetration (Siddiqui and Mahmood 1995 ; Meira-Haddad 2008 ; Vos et al. 2012 ).
These diverse effects indicate that this interaction is specific, and the plant geno-
type, nematode species, fungal isolates, and changes in the environment could ex-
plain these different responses (Siddiqui and Mahmood 1995 ; Hol and Cook 2005 ;
Borges et al. 2007 ; Jaiti et al. 2008 ).
Using the root compartmentalisation system of two banana cultivars, it was pos-
sible to demonstrate the direct effect of AMF on M. incognita (Meira-Haddad 2008 ).
When AMF and nematodes were inoculated in the same compartment, a reduction
in the number of eggs in the cv. Prata-anã and both the number of eggs and galls
in the cv. FHIA 01 was observed (Meira-Haddad 2008 ). Studies have shown that
plants colonised by AMF have few galls containing few females, and the nematodes
are smaller in size. Because of this characteristic, they need more time to develop to
adulthood (Diedhiou et al. 2003 ; Freire et al. 2007 ; de La Peña et al. 2006 ).
Cells of the root system with arbuscules were not infected with the pathogens,
and its proliferation was reduced in the mycorrhizal roots and also in parts of the
root system, demonstrating that bioprotection is directly linked to AMF root colo-
nisation. Cytomolecular studies have shown that the systemic and localised pro-
tective effect induced of AMF colonisation involves the accumulation of defence
molecules in combination with the elicitation reaction of the host cell wall. Modi-
fications of the cell wall associated with localised resistance and the formation of
papillae characterises systemic resistance to P. parasitica in mycorrhizal tomato
plants (Cordier et al. 1998 ).
The changes in the root system caused by the AMF promote the vigorous growth
of the plant, thus reducing the negative effect of the pathogen (Siddiqui and Mah-
mood 1995 ). The reduction of plant growth due to the establishment of nematodes
in roots is lower when colonised by mycorrhizal fungi (Cofcewicz et al. 2001 ).
The success of the plant defence system against pathogens depends primarily on
the recognition of invasion by the pathogen in the initial stages for the activation
of defence response cascades. Plants in mycorrhizal symbiosis undergo biochemi-
cal, physiological and molecular alterations related to the plant defence system for
the establishment of symbiosis (Garcia-Garrido and Ocampo 2002 ). However, the
plant defence responses are limited, transient, and restricted to specific cells; how-
ever, the reactions share similarities with the physiological reactions observed dur-
ing colonisation by pathogens (Garcia-Garrido and Ocampo 2002 ; Lambais et al.
2003 ). The mycorrhizal colonisation acts as the primary system of plant defence to
pathogen attack (Elsen et al. 2008 ).
The physiological changes in the plant caused by the symbionts prevent pathogen
attack and activate defence mechanisms because proteins related to pathogenesis,
phytoalexin production, and cell wall lignification have been reported in mycor-