plant surface microbiology.pdf

5 Diversity and Functions of Soil Microflora in Development of Plants 79
deserticola. The greatest plant growth and AM colonization responses in sterilized
and nonsterilized soils was observed with pea, G. deserticola and
sodium alginate pellets as carrier for F. oxysporum inoculum.Application of F.
oxysporum increased shoot dry matter, N and P concentrations of pea and
sorghum plants and the level of AM fungi colonization.
Piriformospora indica, a newly described axenically cultivable phytopromotional
endosymbiont, which mimics the capabilities of AM fungi, was
recently described by Varma et al. (1999) and Singh et al. (2000). The fungus
has a broad host spectrum and inoculation with the fungus and application
of culture filtrate promotes plant growth and biomass production. It mobilizes
the insoluble phosphate and translocates the phosphorus to the host in
an energy-dependent process. As a biological hardening agent of micropropagated
plants, it renders more than 90 % survival rate for laboratory to
field transferred plantlets. Regenerative protoplasts of P. indica have been
successfully isolated, which opens up the possibility of improving symbiosis
by transgenic manipulation of the fungal component in a symbiosis-specific
manner.
In the ectomycorrhizal (EM) symbiosis between fungi and trees, the fungus
completely ensheaths the tree roots and takes over water and mineral nutrient
supply, while the plant supplies photosynthate (Wiemken and Boller 2002). N
and P are the main elements limiting plant growth in terrestrial ecosystems.
One of the great assets of the ectomycorrhizal symbiosis is its capability to
short-circuit nutrient uptake from organic material to the symbiotic partner.
In addition to mobilizing mineral nutrients from organic sources, EM fungi
may also link plants to rock directly though secretion of organic acids and
solubilizing nutrients from the mineral part of soil. Many EM fungi also retain
considerable saprotrophic potential, for example, production of lignindegrading
enzymes, a quality that benefits the symbionts in the acquisition of
nutrients from lignin-rich organic material.
Sulfur nutrition of plants is largely determined by sulfate uptake of the
roots, the allocation of sulfate to the sites of sulfate reduction and assimilation,
the reduction of sulfate to sulfide and its assimilation into reduced sulfur-containing
amino acids and peptides and the allocation of reduced sulfur
to growing tissues (Rennenberg 1999). EM colonization of oak and beech tree
roots can alter the response of sulfate uptake to sulfate availability in the soil
and enhance xylem transport of sulfate to the leaves. Simultaneously, sulfate
reduction in the roots seems to be stimulated by EM association. These interactions
between EM association and the processes involved in sulfur nutrition
are required to provide sufficient amounts of reduced sulfur for
increased protein synthesis that is used to enhance tree growth.
Information on the diversity of ericoid mycorrhizal endophytes in the Ericaeae
and Epacridaceae has been compiled over the years by several authors
(Varma and Bonfante 1994; Read 1996; Bergero et al. 2000; Berch 2001; Perotto
et al. 2002). Hymenoscyphus ericae and Oidiodendron sp. appear to be the