Abstract A two-step modeling approach was used for predicting the effect of temperature on the growth of Xanthomonas arboricola pv. pruni, causal agent of bacterial spot disease of stone fruit. The in vitro growth of seven strains was monitored at temperatures from 5 to 35˚C with a Bioscreen C system, and a calibrating equation was generated for converting optical den- sities to viable counts. In primary modeling, Baranyi, Buchanan, and modified Gompertz equations were fitted to viable count growth curves over the entire temperature range. The modified Gompertz model showed the best fit to the data, and it was selected to estimate the bacterial growth parameters at each temperature. Secondary modeling of maximum specific growth rate as a function of temperature was performed by using the Ratkowsky model and its variations. The modified Ratkowsky model showed the best goodness of fit to maximum specific growth rate estimates, and it was validated successfully for the seven strains at four additional temperatures. The model generated in this work will be used for predicting temperature-based Xanthomonas arboricola pv. pruni growth rate and derived potential daily doublings, and included as the inoculum potential component of a bacterial spot of stone fruit disease forecaster

This research was supported, in part, by grants from the Ministerio de Educación, Ciencia y Deporte (AGL2013-41405-R and from the University of Girona (SING12/13 and MPCUdG2016/085. Gerard Morales was the recipient of predocotoral fellowships from the University of Girona (BR 2013/31) and from MECD (FPU13/04123) from Spain