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Basal resistance (BR, a local resistance against pathogens induced by general elicitors) is a multi-faceted defence mechanism appearing in many shapes and with many given names, such as induced (acquired) resistance (protection, defence), as well as a part of innate immunity. Here, we give a historical overview of concepts, present results and an outlook associated with bacteriological studies in the Plant Protection Institute (PPI). The topics on BR briefly covered are its elicitors, light and temperature dependence, changes in plant physiology, transcription and protein expression during it and its effect on bacteria. We emphasize the importance and relevance of its quick form, early BR, which might be a plant defence mechanism in nature against all kinds of pathogenic and saprophytic bacteria.
The development of local early basal resistance (EBR), is a form of non-specific general defence response of plants to bacteria, greatly depending on temperature. This symptomless defence mechanism is easily detected by its inhibitory action on the hypersensitive response (HR) caused by a subsequent incompatible pathogenic bacterium. Both EBR and HR were investigated at different temperatures ranging from 30 °C to 5 °C. At normal temperatures (30-20 °C) both heat-killed Pseudomonas syringae pv. syringae 61 (polyvirulent to many plants) and Pseudomonas savastanoi pv. phaseolicola S21 (pathogenic to bean) induced EBR in tobacco leaves within a few hours, but below 10 °C it was greatly delayed and at 5 °C usually no EBR response could be detected within 2-3 days. The time required for development of EBR did not depend on the bacterial pathovars or strains. However, the induction time of HR was not as sensitive to low temperatures as that of EBR, instead, it depended on the bacterial pathovars used.
Pseudomonas viridiflava is an opportunistic, post-harvest pathogenic bacterium that causes soft rot of fruits and vegetables. In vivo expression technology was used to identify genes that participate in the pathogenicity of P. viridiflava. Genetic loci that are induced in planta were identified. Ten such loci were partially sequenced and annotated. Here we describe five of them, which influence the pathogen's stress tolerance in planta. Three of the identified ORFs that show sequence identity to known genes encode membrane proteins, the remaining two encode enzymes in catabolic pathways.
Compared to the known method of conjugation the frequency of transposon mutagenesis following conjugation was enhanced 11-fold by two hours of pre-incubation of recipient Pseudomonas viridiflava 1 on conjugation media. The increased frequency was ƒ = 1.3 × 10 −4 . In other species of Pseudomonas, Pectobacteira and Xanthomonas high rates of transposon mutants were similarly obtained; however, in these strains the increased frequency was less than 5-fold.