Insight into the Role of Arbuscular Mycorrhizal Fungi in Sustainable Agriculture - Environmental Sustainability: Role of Green Technologies - page 5

Fig. 2 Arbuscular mycorrhizal fungal structures showing Arum- and Paris -types

of carbon by the fungus. First, the AM hyphae
receive suitable signals from host roots in the
form of root exudates, and most specifi cally
strigolactones (Akiyama et al. 2005 ; López-Ráez
et al. 2008 ), which results in the branching of the
hyphae. In response, the branched hyphae secrete
a diffusible signal to the host roots, which initiates
the expression of symbiotic-related genes (Kosuta
et al. 2003 ). Based on the distribution of AM fun-
gal structures within the roots, AM colonization
patterns within host roots are divided into three
types: Arum- ,

wheat ( Triticum aestivum ), barley ( Hordeum
vulgare ), potato ( Solanum tuberosum ), sugarcane
( Saccharum offi cinarum ), tomato ( Lycopersicon
esculentum ) and sunfl ower ( Helianthus annuus )
can benefi t from mycorrhizal association, certain
crops belonging to Amaranthaceae, Brassicaceae
and Chenopodiaceae do not form AM symbiosis
(Brundrett 2009 ).
A wide range of AM fungi have been found to
be associated with crop species (Fig. 3 ). In spite of
the general assumption that the diversity of AM
fungi is low in agricultural soils, several studies
have reported high AM fungal diversity in agricul-
tural soils (Jansa et al. 2002 ; Oehl et al. 2003 , 2004 ;
Ambili et al. 2012 ). Many studies on the diversity
of AM fungi in agricultural soils have indicated the
dominance of AM fungal communities by species
belonging to the genus Glomus or the species that
were once under Glomus (Jansa et al. 2002 ;
Muthukumar and Udaiyan 2002 ; Sjoberg et al.
2004 ; Mathimaran et al. 2005 ). Nevertheless,
spores of AM fungi belonging to Acaulospora ,
Entrophospora , Gigaspora , Sclerocystis and
Scutellospora have also been reported along with
Glomus in agricultural soils (Jansa et al. 2002 ;
Muthukumar and Udaiyan 2002 ).

Paris- and intermediate-types

(Dickson 2004 ).
In the Arum -type, the hyphae grow intercellu-
larly in the root cortex and penetrate to form
'arbuscules' intracellularly, whereas in Paris - type
association, intracellular hyphal coils frequently
having intercalary arbuscules spread cell to cell
in the cortex (Fig. 2 ). Intermediate-type AM
exhibits characteristics of both Arum- and Paris-
types. Most of the cultivated crops form Arum
type, while Paris- type is common in plants of
natural ecosystem (Ahulu et al. 2005 ).
Though most agricultural crops such as fl ax
( Linum usitatissimum ), corn ( Zea mays ), rice
( Oryza sativa ), sorghum ( Sorghum bicolor ),