Screening criteria for microbial bioprotectants for seed coating to protect seeds and seedlings from diseases

Biological control of seedborne pathogens and soilborne seedling pathogens is an alternative to chemical seed treatments. Limited survival and shelf life is one of the major bottlenecks for a broader implementation of seed treatments with microbial biological control agents (MBCA). Microbial inocula are typically coated on seed lots that have been dried and cleaned before. After coating, seeds are dried, stored, handled for packaging, distributed and used by the grower. During these processes, conditions challenge survival of the coated MBCA. Systematic analysis of seed technologies including various seed processing steps and seed handling, identified various detrimental conditions for microorganisms during seed coating and thereafter when MBCA-coated seeds are dried, stored and distributed. Screening systems for new antagonists for seed applications should consist of various bioassays simulating very different stress components on the applied microorganisms. Proposed bioassays have in common that viability of the tested microorganisms has to be assessed after exposure to differential conditions. Improved methodology for high throughput viability testing will allow larger screening programs and will support the development of new MBCAs for seed applications.