Chemistry Reference
In-Depth Information
management practices that affect the abundance of indigenous mycorrhizae, or
through the use of mycorrhizal inoculants.
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While it has become widely
accepted that mycorrhizal symbiosis, in combination with legumes, can be
harnessed to improve crop productivity, maximise root functions, and also
reduce fertiliser use, there is still need to establish the distribution and
functions of AMF species in different habitats and different land-use systems
in order to facilitate inoculation programs. With improved methods and
technologies in utilisation, approaches to studying AMF should be streamlined
in order to derive maximum benefits from the association.
Although ectomycorrhizae have not been given much attention in
agroecosystems, they are equally crucial in afforestation programmes.
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Through hyphae, nutrients and water can be absorbed by trees.
Ectomycorrhizae are mostly found in woody plants, ranging from shrubs to
forest, and many belong to the families Pinaceae, Fagaceae, Butulaceae,
Casuarinaceae and Myrtaceae. Most of the above host plants are specific, such
that if mycorrhizae are absent growth is highly reduced.
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Over 4000 species of
Basidiomycotina and a few Ascomycotina form ectomycorrhizae. Many of
these fungi produce mushrooms and puffballs on forest floor.
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5.4.3
Plant Growth Promoting Rhizobacteria (PGPR)
Beneficial free-living soil bacteria are referred to as plant growth promoting
rhizobacteria or PGPR and they stimulate plant growth either directly or
indirectly through secretion of phytohormones that enhance plant growth or
uptake of solubilised iron from the soil.
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Solubilisation of nutrients such as
phosphorous through production of organic acids releases insoluble phos-
phorus into more soluble forms.
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Paterno
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concluded from his study that
Azotobacter vinelandii and Bacillus cereus produced high amounts of indole
acetic acid (IAA). Karawal
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reported that the 30 isolates of Pseudomonas
fluorescens he tested were indole-positive, indicating production of IAA.
However, the Pseudomonas fluorescens showed higher IAA production when
tryptophan concentrations were increased. Gachie (unpublished,University of
Nairobi, 2012), in her screening experiment of rhizobacteria (40 isolates of
Bacillus spp, 36 isolates of Azotobacter spp and 53 isolates of Pseudomonas
spp), all from soils collected from potato-producing districts in Kenya,
identified rhizobacteria isolates with plant growth promoting, phosphorus
solubilisation potential, while other isolates controlled the Ralstonia solana-
cearum potato pathogen which is widespread in Kenyan soils and is a major
constraint to growth of the potato industry.
5.4.4 Trichoderma
Trichoderma species are cosmopolitan fungi found in decaying wood and
vegetable matter. Their dominance in soil may be attributed to their diverse
metabolic capability and aggressive competitive nature.
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They colonise roots,
