Focus Group SOIL-BORNE DISEASES Mini-paper – The use of microbial biocontrol agents against soil-borne diseases Ilaria Pertot; Claude Alabouvette; Estefanía Hinarejos Esteve; Soraya Franca INTRODUCTION The value of the global biopesticide market is expected to reach $4,556.37 Million by 2019, at a compound annual growth rate of 15.30% from 2014 to 2019 (source: Marketsandmarkets.com, 2014; last access 31/03/2015). The reasons for such growth can be found in: the increasing concerns on the impact of residues and overuse of synthetic chemical pesticides and the increasing relevance of pests and pathogens due to growth in food demand, the withdrawal of several chemical pesticides including soil fumigants, the appearance of new invasive species and pesticide resistant strains of pests, the effect of climate change and the specialised monoculture. The decrease of the cost of several biopesticides, the introduction of technologically advanced products, the increase knowledge of farmers and the strict thresholds in pesticides residues set by many food retailers are also promoting the switch form chemical to biopesticides. In addition in EU the Directive on the Sustainable Use of Pesticides (2009/128/EC) is also expected to stimulate the biopesticide market positively. Some active ingredients have been included in Annex 1 according Regulation EC 1107/2009 and several new others are most probably under development by multinational agrochemical companies following recent acquisitions. According the present regulation if a microorganism has fungicide activity should be registered in order to be applied for such use. The high cost of registration prevents a large number of potential biocontrol agents to reach the market. Since each registered use should be supported by specific efficacy trials, the companies tend to register the products against those pathogens with the largest potential market. This results in products potentially active against a large number of soilborne pathogens, but authorised only on the specific one on which the registration trails have been carried out. Several microorganisms (estimated in few hundred of strains) have shown efficacy against soil- borne pathogens and nematodes in literature in the last 50 years. Some of them are the active substances of some existing biopesticides. The full list of approved active substances based on a microbial strain is presented in table 1. Some of these strains are successfully used from several years against soil-borne diseases and pathogens as Coniothyrium minitans used to reduce the inoculum of Sclerotinia sclerotiorum and S. minor on high value vegetable crops, Pseudomonas chlororaphis used against soil-borne disease of cereals in northern EU countries or several Trichoderma strains applied against a wide spectrum of soil-borne pathogens. Although several of these strains have been developed a few years ago, they never achieved a large market, mainly because the competiveness with synthetic chemical fumigants, which are commonly cheaper, easy to apply, with a wide spectrum of activity and high efficacy. The banning of methyl bromide and several other compounds has now revived the interest in 1 EIP-AGRI FOCUS GROUP SOIL-BORNE DISEASES, MINI PAPER - MICROBIAL BIOCONTROL AGENTS microbial biocontrol agents against soil-borne diseases in particular in integration with other agronomic practices or resistant/tolerant varieties. The mechanisms of action of microbial biocontrol agents against plant pathogens include direct antibiosis, hyperparasitism, induction of resistance and competition for space and nutrients. Some microbial agents also act as biofertilizer and/or plant growth promoters by fixing N, solubilizing P, chelating Fe, producing hormone-like substances, degrading 1-aminocyclopropane- 1-carboxylate (ACC) deaminase, degrading organic matter and releasing nutrients in soil. Table 1. List of the active substances active against plant pathogens based on a microbial strain and their status; in bold the microorganisms with claimed or possible activity against soil-borne pathogens and nematodes (http://ec.europa.eu/sanco_pesticides/public/index.cfm?event=homepage&languag e=EN, last accessed on 15/03/2015) Substance Category List (*) Status under Date of Expiration of Reg. (EC) No approval approval 1107/2009 Ampelomyces quisqualis strain FU C Approved 01/04/2005 31/07/2017 AQ10 Aureobasidium pullulans (strains FU, BA C Approved 01/02/2014 31/01/2024 DSM 14940 and DSM 14941) Bacillus amyloliquefaciens MBI FU C Pending 600 Bacillus amyloliquefaciens FU C Pending strain FZB24 Bacillus amyloliquefaciens FU C Approved 01/04/2015 31/03/2025 subsp. plantarum D747 Bacillus firmus I-1582 NE C Approved 01/10/2013 30/09/2023 Bacillus pumilus QST 2808 FU C Approved 01/09/2014 31/08/2024 Bacillus subtilis str. QST 713 BA, FU C Approved 01/02/2007 30/04/2018 Candida oleophila strain O FU C Approved 01/10/2013 30/09/2023 Coniothyrium minitans FU C Approved 01/01/2004 31/10/2016 Gliocladium catenulatum strain FU C Approved 01/04/2005 31/07/2017 J1446 Purpureocilium lilacinum strain NE C Approved 01/08/2008 31/07/2018 251 Phlebiopsis gigantea (several FU A 4 Approved 01/05/2009 30/04/2019 strains) Pseudomonas chlororaphis FU C Approved 01/10/2004 30/04/2017 strain MA342 Pseudomonas sp. Strain DSMZ C Approved 01/02/2014 31/01/2024 13134 Pseudozyma flocculosa FU C Pending Pythium oligandrum M1 FU A 4 Approved 01/05/2009 30/04/2019 Saccharomyces cerevisiae strain FU C Pending LAS02 Streptomyces K61 (formerly S. FU A 4 Approved 01/05/2009 30/04/2019 griseoviridis) Streptomyces lydicus WYEC 108 FU, BA C Approved 01/01/2015 31/12/2024 Trichoderma asperellum FU A 4 Approved 01/05/2009 30/04/2019 (formerly T. harzianum) strains ICC012, T25 and TV1 2 EIP-AGRI FOCUS GROUP SOIL-BORNE DISEASES, MINI PAPER - MICROBIAL BIOCONTROL AGENTS Trichoderma asperellum (strain FU C Approved 01/06/2013 31/05/2023 T34) Trichoderma atroviride FU A 4 Approved 01/05/2009 30/04/2019 (formerly T. harzianum) strains IMI 206040 and T11 Trichoderma atroviride strain I- FU C Approved 01/06/2013 31/05/2023 1237 Trichoderma atroviride strain FU C Pending SC1 Trichoderma gamsii (formerly T. FU A 4 Approved 01/05/2009 30/04/2019 viride) strain ICC080 Trichoderma harzianum strains T-22 and ITEM FU A4 Approved 01/05/2009 30/04/2019 908 Trichoderma polysporum strain FU A 4 Approved 01/05/2009 30/04/2019 IMI 206039 Verticillium albo-atrum (formerly FU A 4 Approved 01/05/2009 30/04/2019 Verticillium dahliae) strain WCS850 Zucchini yellow mosaic virus FU C Not Approved (ZYMV mild strain) Zucchini Yellow Mosaik Virus, FU C Approved 01/06/2013 31/05/2023 weak strain FU= fungi; BA= bacteria; NE=nematodes, * A: Existing active substances divided into four lists for phased evaluations, B: Substances not considered in scope of the directive, either because already banned or never notified under directive 91/414/EEC or because not considered as plant protection products, C: New active substances Main groups of biocontrol agents: characteristics, mechanism of action, use, advantages and limitations Bacillus spp. Characteristics Members of the Bacillus genus are among the beneficial bacteria mostly exploited as biopesticides to control plant diseases but also nematodes. The most known species hosting biocontrol agents are B. subtilis and B. amyloliquefasciens, but also B. firmus and B. pumilus. They are Gram positive rod-shaped bacteria that can form a protective endospore that can tolerate extreme environmental conditions. Mechanism of action Bacillus spp. can control fungal pathogens by competition, direct antibiosis and induced resistance. In the rhizosphere, competition takes place for space at the root surface and for nutrients, noticeably those released as seed or root exudates. Competitive colonisation of the rhizosphere and successful establishment in the root zone is a prerequisite for effective biocontrol, regardless of the mechanism(s) involved. Direct antagonism involves the production of several microbial metabolites among which lipopeptides play the major role. Surfactin in particular is involved in the mechanism of resistance induction. The bio-nematicide Bacillus firmus also colonizes the rhizosphere of the plant where it parasitizes the eggs and larvae of nematodes especially of the rootknotnematodes Use Bacillus strains are effective against a broad spectrum of plant pathogens and they can be used either as foliar application or root application before trasplanting. In case of soil or root 3 EIP-AGRI FOCUS GROUP SOIL-BORNE DISEASES, MINI PAPER - MICROBIAL BIOCONTROL AGENTS application the ability of the specific strain to colonise and permanently establish on the roots of the specific crop is crucial. Sometime the colonization is not simply crop-specific, but cultivar- specific. Root application of Bacillus spp. should be preferably targeted to improve resistance of the plant or to protect the early stage of seed germination, rather to directly control soil-borne inoculum of pathogens. Advantages, limitations and ways to improve efficacy The advantage of Bacillus spp.-based products is their long shelf-life at room temperature, given by the fact that they produce endospores. There is also a lot of knowledge gained in the fermentation process and the ways of production are commonly optimised. It is a relatively easy microorganism to ferment with relatively low cost of production compared for example to fungal biocontrol agents. Main limitation is due to the fact that the Bacillus strains should colonise the roots in order