Factors Affecting Growth And Activity Of Rhizospheric Microorganisms And Phyllspheric

Associative and antagonistic activities of rhizosphere

Microorganisms of the rhizosphere produce an amino acid ,growth promoting ,vitamin B, auxins , gibberellins and antibiotics etc which support of other rhizospheric microbes as well as the plant . Gibberellins and Gibberellins like substances are produced by bacteria such as Azotobacter ,Pseudomonas, Arthrobacter ,and Agrobacterium . In the presence of microorganisms, the plant produce exudates in a greater amount that includes organic acids and monosaccharides .Microorganism also influences the root hair development ,mucilage secretion and lateral root development of the several plants. The fungi inhabiting the surface of the root influence the substance by the root system .

Secretion of antibiotics by microorganism and inhibition of growth of the pathogenic microorganisms is and antagonistic activity in the rhizosphere .Plant root exudates influence pathogenic fungi, bacteria ,and nematodes in a various way . The i.e effect may be the form of the attraction of fungal zoospores,or bacterial cells towards the root ; stimulation of germination of dormant spores and hatching of cysts of the nematode .In the context , the presence of antagonistic microorganisms in rhizosphere an important role in the proliferation and survival or inhibition of root infecting pathogens in soil either through soil l fungistatic , (inhibition of fungal growth .sporulation , or spore germination but not death ). inhibition or antibiosis of pathogens in the rhizosphere.

factors. affecting growth and activity of microorganisms

1. Soil type : Soil texture and pH affect the soil rhizospheric microorganism .Well, aerated and clay soil with abundant organic matter is suitable for most of the microorganisms . The actinomycetes prefer alkaline soil /root zone and fungi prefer acidic /root zone .the proximity of the root is also an important factor as there is more availability of root exudates near the root ,which in most of the cases favor microbial growth .The count of bacteria .fingi ,algae ,and other microbes declines with the depth of soil (rhizospheric).
2. Light : Light is also another important factor affecting the growth and activity of rhizospheric microbes .Eg. Trichoderma has been found in the rhizospheric soil having the light intensity and Penicillium and Rhizoctonia (fungi ) has been found predominantly in rhizospheric with low light intensity .The microbial load rhizospheric soil decrease with decrease in light intensity.izospher
3. Moisture: Water availability in the rhizospheric soil influence the growth of the microorganism and their types.
4. Temperatur: Most of the mid=croorganisms grow optimally at a mesophilic temperature range (in the rhizosphere as well) .Temperatur also affects the moisture level of the soil . A higher temperature is also interlinked wit the intensity light proportionally, and the microbial growth in the rhizosphere.
5. Vegetation/plant type; The vegetation is very critical factors for the diversity of rhizospheric microorganisms and their activity .This is because the root exudates differ by plant type and hence the microbes ,as per the different types of nutrient in exudates .The age of plant also alter the rhizospheric microorganisms .In a rhizospheric soil around the root of very young seeding decomposition( very less) .However .during later development the dead and sloughed off tissue may contribute appreciably to the composition of the community . In the end of growing season when the roots are dying ,the microbial abundance declines and gradually fades becoming indisposable from normal soil flora
6. Root exudates :The root exudates preferentially enhance the microbial population in rhizosphere in most of the cases it c contains a vast array of metabolites utilized by microbes for their growth .Root exudates have a pronounced effect on germination of the resting structure ,like spores ,of many fungi by stimulating or by exerting fungistatic.The root exudates may inhibit the germination of dormant fungal propagules (fungi stasis ). The chlamydospores of Fusarium, conidia of Verticillium , Sclerotia of Sclerotium and oospores of pythium terminates in proximity to the roots. The stimulation of the germination of the desirable fungi is important because the plant pathogenic fungi are inhibited not being the vigorous competitors (fungi stasis). Roots may also liberate antimicrobial agents like alkaloids that directly the microbial growth in the rhizosphere

Phyllosphere ( term coined by ruined)

The zone on leaves inhabited by microorganisms is termed as a philosopher and leaf surface is termed as phylloplane . The leaf surface inhabited by a specific set of microorganisms .The inoculation of the leaves occurs by:

-Deposition of airborne microbes

-Splash dispersion during rain

-Wind

Most of the microbes are saprophytes feeding upon plant material of a different kind .Bacteria are most abundant on the leaf surface and the first to get colonized are newly emerged leaflets. The highest number is encountered closed to the meristematic leaf base . The establishment of specific flora on the leaf surface is aided by the critical epidermal hair like appendages and waxes which help in the anchorage of the microorganisms .The microorganisms may die or survives and proliferate on leaves depending on the extent of influence of the material in leaf diffusates or exudates . The principal nutritive factor in the leaf exudates includes amino acids, glucose , fructose , and sucrose . If the catchment areas on leaves are significant substances such specialized habitat may provide niches for nitrogen fixation and secretion of the substance capable of promoting the growth of the plant .

The dominant and useful microorganisms on the leaf surfaces includes ;

Bacteria - Beijerinckia, Phytomonas , Erwinia, Sarcina and other

Blue-green algae; Anabaena , Calothrix .Nostoc , Tolypothrix, etc .

Fungi; Cladosporium , Alternaria, Helminthosporium , Rhodotorulla , Torula, Torulopsis, Candida, Saccharomyces, Aspergillus , Rhizopus, Penicillium . etc.

Biochemical reactions in phyllosphere (phyllo spheric effect )

leaf surface microorganism may perform an effective function in controlling the spread of airborne pathogens causing plant diseases . The spore of a pathogen on the surface of leaves and pods result in the formation of an antimicrobial substance called phytoalexins . Alternatively , the phytoalexin may be a normal presence in the plant and concerned) and fix nitrogen.Some of the microbes on leaf surface fix nitrogen .The important nitrogen fixes on leaf surface are Beijerinckia , Xanthomonas , Rhizobium ,etc . The spraying of leaves with a queues sucrose solution or bacterial suspension enhances the growth of some legumes and cereals .

Reference

Rangaswami, G and PT Bagyaraja. Agricultural Microbiology. 2nd. Prentice Hall of India, 1993.

Alexander, M. Introduction To Soil Microbiology . Academic Press, 1961.