PGPR's disease suppression

Discussion in 'Pesticide & Herbicide Application' started by ICT Bill, Jul 13, 2008.

  1. ICT Bill

    ICT Bill LawnSite Platinum Member
    Messages: 4,115

    L.C. Van Loon
    Institute of Environmental Biology, Section Phytopathology, Utrecht University, Utrecht, The Netherlands
    Non-pathogenic soilborne microorganisms can promote plant growth, as well as suppress diseases. Plant growth promotion is taken to result from improved nutrient acquisition or hormonal stimulation. Disease suppression can occur through microbial antagonism or induction of resistance in the plant. Several rhizobacterial strains have been shown to act as plant growth-promoting bacteria through both stimulation of growth and induction of systemic resistance (ISR), but it is not clear in how far both mechanisms are connected. Induced resistance is manifested as a reduction of the number of diseased plants or in disease severity upon subsequent infection by a pathogen.

    Such reduced disease susceptibility can be local or systemic, result from developmental or environmental factors and depend on multiple mechanisms. The spectrum of diseases to which PGPR-elicited ISR confers enhanced resistance overlaps partly with that of pathogen-induced systemic acquired resistance (SAR). Both ISR and SAR represent a state of enhanced basal resistance of the plant that depends on the signaling compounds jasmonic acid and salicylic acid, respectively, and pathogens are differentially sensitive to the resistances activated by each of these signaling pathways.

    Root-colonizing Pseudomonas bacteria have been shown to alter plant gene expression in roots and leaves to different extents, indicative of recognition of one or more bacterial determinants by specific plant receptors. Conversely, plants can alter root exudation and secrete compounds that interfere with quorum sensing regulation in the bacteria. Such two-way signaling resembles the interaction between root-nodulating Rhizobia and mycorrhizal fungi within legume species.

    Although ISR-eliciting rhizobacteria induce typical early defense-related responses in cell suspensions, in plants they do not necessarily activate defense-related gene expression. Instead, they appear to act through priming of effective resistance mechanisms, as reflected by earlier and stronger defense reactions once infection occurs.

    I wish I knew what they were saying, hocus pocus I am told
  2. ICT Bill

    ICT Bill LawnSite Platinum Member
    Messages: 4,115

    More hocus pocus

    K. Krome, K. Rosenberg, J. Bertaux, S. Scheu, M. Bonkowski

    The rhizosphere is a microbially highly active interface in the plant-soil system. Soil bacteria, which are the major food source for soil protozoa, use rhizodeposits allocated by roots as energy source. Protozoan grazing on rhizobacteria repeatedly has been shown to increase plant growth. The suggested mechanism, termed ‘microbial loop’ in soil is based on the fact that protozoa release nitrogen from consumed bacterial biomass, thereby increasing the available nitrogen pool for plants, hence the growth improvement. We investigated the interactions between protozoa, rhizobacteria and different plants by comparing three treatments: a sterile treatment, a rhizobacterial treatment and a treatment with rhizobacteria plus protozoa (Acanthamoeba castellanii). The diameter of the leaf rosette of Arabidopsis thaliana increased significantly in bacterial treatment compared to the sterile treatment, but increased even more in the protozoa treatment. Watercress responded to the presence of protozoa with an increase of lateral roots, indicating non-nutrient based effects. Subsequent analyses of the auxin contents in the plants revealed a significantly higher concentration of free auxin and a lower amount of conjugated auxin in the protozoa treatments compared to the sterile and bacterial treatments. Since protozoa are known to change bacterial community composition in soil and many rhizosphere bacteria affect root growth by the release of signal compounds such as auxins, we suggest that the growth stimulating effects of protozoa were due to grazing induced shifts in the bacterial community.
  3. ICT Bill

    ICT Bill LawnSite Platinum Member
    Messages: 4,115

    Gunnar Henkes, Stefan Scheu and Michael Bonkowski
    Darmstadt University of Technology, Institute of Zoology, Rhizosphere Ecology Group, Darmstadt,
    Plant roots continuously interact with a multitude of microorganisms in their rhizosphere. For example, plants allocate a great portion of their photosynthetically fixed carbon to root-infecting symbionts, such as mycorrhizal fungi; another part is released as exudates fuelling mainly free-living rhizobacteria. Rhizobacteria are strongly topdown regulated by microfaunal grazers, particularly protozoa. Consequently, beneficial effects of protozoa on plant growth have been assigned to nutrients released from consumed bacterial biomass, i.e. the ‘microbial loop’. In recent years however, the recognition of bacterial communication networks, the common exchange of microbial signals with roots and the fact that these signals are used to enhance the efflux of carbon from roots have revolutionized our view of rhizosphere processes. Most importantly, effects of rhizobacteria on root architecture seem to be driven in large by protozoan grazers. Protozoan effects on plant root systems stand in sharp contrast to effects of mycorrhizal fungi. Because the regulation of root architecture is a key determinant of nutrient- and wateruse efficiency in plants, protozoa provide a model system that may considerably advance our understanding of the mechanisms underlying plant growth and community composition
  4. ICT Bill

    ICT Bill LawnSite Platinum Member
    Messages: 4,115

    D. Egamberdiyeva, K. Davranov
    Centre of Agroecology, University of Agriculture, Ministry of Agriculture and Water Resources, University str.1,
    Tashkent 700140, Uzbekistan,
    Uzbekistan is an agro-industrial country, in which the desert occupy more than 60% of all republic’s territory, and only 10% (4,5 million ha) of total territory is taken up for agricultural lands. After independence big changes occurred in the cropping systems of Uzbekistan. They are associated with both development of food security policy of the independent state and transition to market economy. Increase of crop yield is the most important objective of Uzbekistan on the way of achieving self-reliance in food production. Inappropriate application of mineral fertilizers in cotton production for more 70 years has resulted in pollution and salinization of agricultural lands and water resources also led to ecological catastrophe – drying of Aral Sea. These large-scale environmental problems such, salt dusts and salt movement affect agricultural fields give a vital importance to use biofertilizers and reduce chemicals in such regions. In this regards the biofertilizer “Er malhami” has developed and applied in many regions of Uzbekistan. This product includes two mixtures of strains Azotobacter chrococcum A2 and Bacillus sp. Those strains are salt tolerant that can survive in high temperature regions and salinated soils. The inoculation with those mixture bacterial fertilizers had a positive effect on yield and fibre of cotton, wheat, rice and potato in field experiments. The yield of cotton increased up to 35 dt/ha treated with bacterial inoculant, where control was 29.5 dt/ha. The fibre increased up to 32 kg/100 kg yield, where control was 35 kg/100 kg yield. Wheat yield increased to 35.0 dt/ha, where in control variant 28.0 dt/ha. Rice yield also increased up to 46.0 dt/ha, where control variant was 40 dt/ha. Potato yield increased up to 200 dt/ha, after application of bacterial fertilizers where control variant was 160 dt/ha. The bacterial fertilizers “Er malhami” also increased N, P, K uptake of shoot and root of crops under nitrogen poor, salinated soils conditions of Uzbekistan.

    That, I believe is enough for now
  5. ICT Bill

    ICT Bill LawnSite Platinum Member
    Messages: 4,115

    I don't know if you notice a thread in those.

    By surpressing disease on a site the overall health of the plant is improved, makes sense.
    The way they are going about surpressing disease is the interesting part. They are using fungi to kill off fungal pathogens and disease and are using bacterial enzyme production to nuke others. It a war down there in the soil, they are basically arming the good guys and nuking the bad guys whenwhile promoting the rhizobium that mine nutrients and make them plant available

    Okay what does that mean to an L&L company? Inoculums work and will allow you to have much less inputs (fertilizer) on the site for a great stand of turf. How much less you ask, 40 to 60 % less is a good general figure.

    The site needs to have organic matter though, it is the gas in the car that makes it run. Plants do provide a lot of nutrients through root exudates but not enough to get nutrient cycling going you need an SOM above 2% (5 to7% is better) to get it going

    How long do these things last you ask, when established they will stay with the plant its entire life. If you can introduce them at the seed stage you have basically coated the seed with good guys and the other will have to try to outcompete the existing microbes.

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