Agriculture Reference
In-Depth Information
annual crops. Gyaneshwar et al. (
2002
) suggested that acid producing microorgan-
isms are able to increase the solubilization of phosphatic rock. The PSB in conjunc-
tion with single super phosphate and rock phosphate reduce the P dose by 25 and
50 %, respectively (Sundara et al.
2002
).
Pseudomonas striata
and
Bacillus poly-
myxa
solubilized 156 and 116 mg P L
−1
, respectively (Rodríguez and Fraga
1999
).
Pseudomonas fluorescens
solubilized 100 mg P L
−1
containing Ca
3
(PO
4
)
2
or 92 and
51 mg P L
−1
containing AlPO
4
and FePO
4
, respectively (Henri et al.
2008
).
Mycorrhiza
Mycorrhizae are mutualistic associations between fungi and plant roots. The host
plant gets mineral nutrients from mycorrhizal fungi, while as the fungus partener is
provided with photosynthetic products from the host plant (Jakobsen et al.
2002
).
Fungi become integrated into the root structure, or fungi lives in close association
with plant roots. Fungal hyphae may live on the external surface of roots (ectomy-
corrhizal) or may invade root cells (endomycorrhizal). Mycorrhiza belong to fun-
gi kingdom Basidiomycetes, Ascomycetes and Zygomycetes. Mycorrhizal fungi,
and fungi generally, have a strong influence on soil structure (Rillig and Mummey
2006
). Their hyphal strands help to hold soil aggregates together, and they also
excrete organic substances that help cement the aggregates (Rillig and Mummey
2006
). Hyphae conduct water and immobile nutrients (like P) to roots despite dis-
ruption of capillary water flow in soil. Of the many types of mycorrhizal associa-
tion the most important association which are economically as well as ecologically
importance are: ectomycorrhizal associations, and the endomycorrhizal association
of the vesicular-arbuscular (VA) type (Rillig and Mummey
2006
). In case of ecto-
mycorrhizal associations, the fungi attack the cortical region of the host root devoid
of piercing cortical cells. Ectomychorrhizae are recognized to occur in the families
of Salicaceae, Fagaceae, Pinaceae, Betulaceae, Tiliaceae, Juglandaceae and Ceasal-
pinionideae. The ectomycorrhizal roots lack root hairs and are covered by a sheath
of fungal hypae which almost looks like host tissue. This tissue is called Pseudopa-
renchamatous sheath. Hyphae from this sheath enter into the cortex and remain in
the outer cortical region to form a network called Hartig's net (Alizadeh
2011
). The
nutrients absorbed by the hyphae are transported to the plant with the help of this
Hartig's net. Infection of host plants by ectomycorrhizal fungi frequently leads to
changes in feeder roots that are apparent to the naked eye but in case of endomycor-
rhizal associations of the VA type, the fungi penetrate the cortical cells and form
clusters of delicately divided hyphae known as
arbuscules
in the cortex (Alizadeh
2011
). They also form vesicles, which are membrane-bound organelles of varying
shapes, inside or outside the cortical cells. Arbuscules are supposed to be the sites
where resources are exchanged among the host plant and the fungi (Alizadeh
2011
).
Vesicles in general serve as storage space but when they are old they can serve as
reproductive structures. Vesicles and arbuscules, together with large spores, com-
prise the diagnostic features of the VA mycorrhizas. Most ectomycorrhizal fungi
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