Possibilities of avoidance and control of bacterial plant diseases when using pathogen‐tested (certified) or ‐treated planting material

Abstract

Testing of planting material for freedom from phytopathogenic bacteria is an important, although not exclusive, method for control of bacterial diseases of plants. Ideally, pathogen‐free or pathogen‐/disease‐resistant planting material is desirable, but this situation is not always possible on a practical basis. For most bacterial pathogens, resistance is not available in cultivated hosts, and production of pathogen‐free planting material requires strict certification schemes via several routes. These include (i) indexing, with subsequent removal of infected/contaminated material from the production chain; (ii) meristem and other tissue culture production systems; (iii) thermo‐ or chemotherapy; (iv) plant or seed surface disinfection for epiphytic bacterial pathogens; (v) avoidance or decontamination of contaminated production factors such as substrate, soil or irrigation water. These methods cannot guarantee 100% freedom from the pathogen or disease during crop multiplication from certified planting material, because of factors such as sampling error, experimental error, test sensitivities, limitations of therapies (e.g. phytotoxicity or insufficient penetration), re‐introduction of the pathogen, insufficient hygiene or decontamination during planting and multiplication of clean propagating material, and manipulations during trade and production. These factors are discussed with reference to several bacterial plant diseases, in particular control of bacterial brown rot and ring rot of potato in Europe and North America. The most efficient control of bacterial diseases can be expected through a combination of the use of healthy/tested planting material and good cultivation practice, including strict crop and storage hygiene.