Predictive modelling of the combined effect of temperature and water activity on the in vitro growth of Erwinia spp. infecting potato tubers in Belgium/Modélisation prédictive de l'effet combiné de la température et de l'activité de l'eau sur la croissance in vitro d'Erwinia spp. infectant les tubercules de pomme de terre en Belgique

Erwinia carotovora ssp. atroseptica (Eca), Erwinia carotovora ssp. carotovora (Ecc) and Erwinia chrysanthemi (Ech), are the main cause of potato tuber decay (soft rot) in storage and stem rot in the field (blackleg). The bacteria are characterized by the production of several extracellular pectic enzymes among them Pectate Lyase (PEL) activity is the most important key of pathogenesis. It has been reported that ecological parameters such as humidity and temperature, greatly influence the disease development. The objective of this work was to determine the in vitro effect of water activity (0.960, 0.980, 0.997) and temperature (10, 15 and 20°C) and their interactions on the growth parameters of Eca, Ecc and Ech using optical density (OD) measurement. The maximum specific growth rate (µ^sub max^) was calculated under each a^sub w^-temperature combinations for the three Erwinia species. Statistical analysis showed a significant effect of a^sub w^ and temperature on µ^sub max^. We noticed that Eca and Ecc grow faster than Ech in our condition. A second aim of this work was to monitor the PEL specific activity under the combined effect of these two factors (a^sub w^-temperature). Our results showed an increase of PEL specific activity with the temperature whatever are the bacterial strains. But contrary to growth, this research did not show an increase of PEL specific activity with a^sub w^ except the treatment at 15 and 20°C for all bacteria strains. According to our obtained results on growth and PEL production we concluded that Eca 03034/1 and Ecc 030033 had the same ecological behavior comparatively to Ech 03/016/1 in the range of the values of the two factors (a^sub w^ and temperature) investigated here. To our knowledge, this research is the first publication which pointed out the combined in vitro effect of a^sub w^ and temperature on the growth of Erwinia genius according to literature data. [PUBLICATION ABSTRACT]