BIOCOMES: First steps toward a novel seed treatment against Verticillium wilt for oilseed rape and Brassica vegetables

Abstract: The main objective of this project is to develop and optimize a seed treatment strategy against Verticillium wilt for oilseed rape (Brassica napus L.) and Brassica vegetables. Currently, no fungicides are available for the control of Verticillium. The novel biological control will be based on the selected strains of Serratia and Paenibacillus. These biological control agents have been already evaluated under field conditions. The five strains of Serratia (Serratia plymuthica HRO-C48; S. plymuthica 3Re4-18; S. plymuthica 3RP8; S. plymuthica S13 and Serratia proteamaculans SP1-3-1) and five strains of Paenibacillus (Paenibacillus brasilensis Mc2-9, Paenibacillus kribbensis Sb3-1, Paenibacillus polymyxa 302P5BS and P. polymyxa GnDWu39 and PB71) from the institute’s strain collection were chosen for their antagonistic properties against Verticillium dahliae, Rhizoctonia solani and Fusarium culmorum shown in preliminary tests. Our strategy for determining the most effective biocontrol agent involved biopriming of the surface-sterilized seeds of the oilseed rape and the cauliflower with log10 6.0-7.0 CFUs/ml (Paenibacillus) or log10 8.4-9.5 CFUs/ml (Serratia) of each selected strain. The preliminary comparison of the growth promoting activity and colonization capacity of Paenibacillus strains showed that inoculation of the seeds with the selected strains resulted in attachment of 2.8-4.1 CFUs per seed for Paenibacillus spp. and of log105.8 – log106.5 for Serratia spp. The abundances of BCA on the roots of the seedlings did not show significant alteration within the same genus. The Serratia cells labelled with fluorescent markers were mostly observed on the upper parts of the roots using confocal scanning laser microscopy and were present either as clouds around the whole root system or they formed large micro-colonies in the root tissue. While Serratia treatment resulted in different levels of plant growth promotion, the opposite effect was found after Paenibacillus evaluation. With respect to the results, two bacteria were selected for further tests: S. plymuthica 3RP8 and Paenibacillus kribbensis Sb3-1. The project being presented is a part of the overall BIOCOMES project (http://www.biocomes.eu/).