The plasmid pME6863, carrying the aiiA gene from the soil bacterium Bacillus sp. A24 that encodes a lactonase enzyme able to degrade N-acyl-homoserine lactones (AHLs), was introduced into the rhizosphere isolate Pseudomonas fluorescens P3. This strain is not an effective biological control agent against plant pathogens. The transformant P. fluorescens P3/pME6863 acquired the ability to degrade AHLs. In planta, P. fluorescens P3/pME6863 significantly reduced potato soft rot caused by Erwinia carotovora and crown gall of tomato caused by Agrobacterium tumefaciens to a similar level as Bacillus sp. A24. Little or no disease reduction was observed for the wild-type strain P3 carrying the vector plasmid without aiiA. Suppression of potato soft rot was observed even when the AHL-degrading P. fluorescens P3/pME6863 was applied to tubers 2 days after the pathogen, indicating that biocontrol was not only preventive but also curative. When antagonists were applied individually with the bacterial plant pathogens, biocontrol activity of the AHL degraders was greater than that observed with several Pseudomonas 2,4-diacetylphloroglucinol-producing strains and with Pseudomonas chlororaphis PCL1391, which relies on production of phenazine antibiotic for disease suppression. Phenazine production by this well characterized biological control strain P. chlororaphis PCL1391 is regulated by AHL-mediated quorum sensing. When P. chlororaphis PCL1391 was co-inoculated with P. fluorescens P3/pME6863 in a strain mixture, the AHL degrader interfered with the normally excellent ability of the antibiotic producer to suppress tomato vascular wilt caused by Fusarium oxysporum f. sp. lycopersici. Our results demonstrate AHL degradation as a novel biocontrol mechanism, but also demonstrate the potential for non-target interactions that can interfere with the biocontrol efficacy of other strains.

This review outlines the responsive polymer methods currently in use with their potential application to plant protection and puts forward plant-specific mechanisms as stimuli in newly devised methods for smart release of crop protection agents (CPAs). CPAs include chemicals (fungicides, insecticides, herbicides), biochemicals (antibiotics, RNAbased vaccines for plant viruses), semiochemicals (pheromones, repellents, allomones), microbial pesticides, growth regulators (insect and plant) or micronutrients, all with crop protection effects. This appraisal focuses on emerging uses of polymer nano-encapsulated CPAs. Firstly, the most interesting advances in controlled release methods are critically discussed with their advantages and drawbacks. Secondly, several plant-specific stimulibased smart methods are anticipated for use alongside the polymer nano-or microcapsules. These new CPA release methods are designed to (i) protect plants against infection produced by fungi or bacteria, and (ii) apply micro-nutrients when the plants need it the most. Thus, we foresee (i) the responsive release of nano-encapsulated bioinsecticides regulated by plant stress enzymes, and (ii) the delivery of micro-nutrients synchronized by the nature or intensity of plant root exudates. Such continued advances of nano-scale smart polymer-based CPAs for the protection of crops herald a "small revolution" for the benefit of sustainable agriculture.Keywords: responsive polymers; crop protection agent (CPA); CPA nanocapsule; nanoscience; nanotechnology; plant-specific stimuli; intelligent self-regulated release OPEN ACCESSPolymers 2010, 2 230 Glossary of TermsAllomone: a pheromone that induces a behavioral or physiological change in a member of another species that is of benefit to the producer. Bio-insecticide: the natural substance made and used for eliminating plant-eating insects. Cuticle: the layer of cutin (waxy waterproof substance, consisting of derivatives of fatty acids) covering the epidermis of the aerial parts of plants. Elicitor: a substance that induces the defense mechanisms in higher plants. Epidermis: the outer protective layer of plant cells. Parasitic plant: a plant that derives some or all of its sustenance from another plant. Perennial plant: a plant that lives for more than two years. Phloem: a plant tissue that conducts organic nutrients substances to all parts of the plant. Phytopathogen: an organism that causes a disease in a plant. RNA-based vaccines for plant viruses: Double-stranded RNA (dsRNA) is a RNA with two complementary strands, which is converted to small interfering (siRNA), involved in the RNA interference (RNAi) pathway, including plant viruses RNA silencing. Root exudate: any substance released through the pores of a diseased or injured plant root.

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Plant health is one of the issues that have to be maintained and closely monitored during cultivation and harvest. In this regard, prevention is the key factor in organic production. Biological control of plant pathogens and plant growth stimulation can be done through beneficial microorganisms. Different bacterial bio-preparates are available on the market, many of them based on selected strains of Bacillus species. In our previous studies, we isolated autochthones strains of Bacillus spp. with beneficial traits for plant protection and growth promotion. Considering the interest for biological production, and public concern for healthy products without significantly reduced yield, different biological control strains of Bacillus spp. that could be used as bio-inoculants for plant protection were analyzed.Thirteen biocontrol strains of Bacillus spp. were analyzed in comparison with three referent strains of B.subtilis and B.licheniformis. Qualitative and semi-quantitative analysis of these biocontrol Bacillus spp. strains was studied in order to characterize their enzymatic activity with implications either in cell wall degradation of plant pathogenic microorganisms, or in metabolism of various substrates. Genetic variability was studied by rep-PCR analysis compared with reference strains of B.subtilis and B.licheniformis. Microbiological studies performed in order to characterize the selected beneficial bacteria for their ability to produce lytic enzyme involved in plant pathogenic inhibition and plant growth stimulation revealed chitinase, cellulose, protease, lipase, amylase, decarboxylase, ACC-deaminase and phosphatease activity. The molecular techniques revealed significant genetic differences among the bacterial strains analyzed. The study allowed the detection of several enzymatic mechanisms involved in plant growth and protection, and revealed the potential of autochthon microbiota to be used for biotechnological purposes.