Control of seed-borne pathogens on vegetables by microbial and other alternative seed treatments

In the EU-project "Seed Treatments for Organic Vegetable Production" (STOVE) physical and biologfoal methods aimed at the control of seed-borne vegetable pathogens are being investigated. These include formulated, commercialised microbial preparations, resistance inducers, non-commercialised antagonistic micro-organisms and plant extracts/ compounds of natural origin. Trials are being carried out against seed borne pathogens, e.g Alternaria dauci, Septoria petroselini, Xanthomonas campestris, Phoma valerianellae, Fusarium spp., Colletotrichum sp. in different hosts, such as carrot, parsley, brassicas, lamb's lettuce, basil and bean. Treatments ofbrassica seeds with MSMX (based on Streptomyces sp.) and BA2552 (based on Pseudomonas chlororaphis) reduced the infection with Alternaria spp. in emerged plants from 25 % (control) to below 6 %, the same level achieved after chemical treatment. From bean seeds infected with Colletotrichum sp. 10 % of the emerged plants showed disease symptoms, while treatments of seeds with the resistance inducers salicylic acid, ChitoPlant, Bion and Milsana resulted in 100 % healthy plants. Effects on germinability were differing among the treatments. Two non-commercialised micro-organisms gave good protection against Phoma valerianellae on lambs lettuce and Alternaria dauci and A. radicina on carrot seeds. In an in vitro assay with plant extracts, the Minimum Inhibitory Concentration (MIC)-values for Xanthomonas campestris pv. campestris and Clavibacter michiganensis subsp. michiganensis were lowest for oreganoand thyme- oil and C2000 (Citrex). For Alternaria dauci and Botrytis aclada MIC-values were lowest for oregano-oil, clove-oil, thyme-oil, cinnamon-oil and for C2000. Field trials with those seed treatments that gave highest efficacy are currently under way.