Lactobacillus plantarum strains PM411 and TC92 can efficiently control bacterial plant diseases, but their fitness on the plant surface is limited under unfavourable low relative humidity (RH) conditions. To increase tolerance of these strains to water stress, an adaptive strategy was used consisting of hyperosmotic and acidic conditions during growth. Adapted cells had higher survival rates under desiccation than non-adapted cells. Transcript levels and patterns of general stress-related genes increased immediately after the combined- stress adaptation treatment, and remained unaltered or repressed during the desiccation challenge. However, there were differences between strains in the transcription patterns that were in agreement with a better performance of adapted cells of PM411 than TC92 in plant surfaces under low RH environmental conditions. The combined-stress adaptation treatment increased the survival of PM411 cells consistently in different plant hosts in the greenhouse and under field conditions. Stress-adapted cells of PM411 had similar biocon- trol potential against bacterial plant pathogens than non-adapted cells, but with less variability within experiments

Funding was provided by Spain MINECO (Ministerio de Economía y Competitividad) (AGL2012-39880-C02-01 and AGL2015-69876-C2-1-R) and FEDER of the European Union and in part by project FP7-KBBE.2013.1.2-04 613678 DROPSA of the European Union. N. Daranas was recipient of a research grant 2015 FI_B00515 (Secretaria d’Universitats i Recerca, Departament d’Economia i Coneixement, Generalitat de Catalunya; ESF, EU). The research group is accredited by SGR 2014-697 and TECNIO net from Catalonia