Water and temperature relations of softrot bacteria: growth and disease development

Abstract

SummaryThe effect of water availability and the temperature of the growth substrate on growth and disease development of softrot bacteria were studied using artificial media and plant material. Water availability was measured as the osmotic potential of a solution (ψosm) and was assessed for solutions of PEG4000 and KNO3 as artificial osmotica and for plant tissue of chicory heads. Growth of softrot bacteria was found at water potentials from ψ= ‐0.12 MPa to ψ= ‐8.0 MPa but the lag phase of the growth curve increased with decreasing water potential. The relative growth rates of the three softrot pathogens showed a sigmoidal relationship with water potential, the relative growth rates decreasing rapidly at water potentials lower than ψ= ‐1.5 MPa. The water potential of harvested chicory heads decreased with storage time of the harvested crop but was still within the growth limits for softrot bacteria. In relation to temperature, the relative growth rate of Erwinia carotovora subsp. carotovora (Ecc) was highest at 10°C, of Erwinia carotovora subsp. atroseptica (Eca) at 15°C and of Pseudomonas marginalis (Pm) at 5°C. Chicory heads of two cultivars, Rumba and Salsa, inoculated with Ecc, had a significantly higher disease severity at 30°C (0.72 for Rumba and 0.47 for Salsa) than at lower or higher temperatures. In conclusion, temperature and water availability during forcing of chicory were not factors limiting populations of softrot bacteria. Possibilities for crop protection thus only avail during chicory root storage. During storage a high death rate combined with a low growth rate of the softrot bacteria may result in a decrease of bacterial populations below the minimum densities needed for infection during the forcing of chicory heads.

The epidemiology of Pectobacterium and Dickeya species and the role of calcium in postharvest soft rot infection of potato (Solanum tuberosum) caused by the pathogens: A review

“…Studies by Schober and Zadoks (1999) on chicory heads showed that the highest growth rate of Pcc occurred at 10°C while that of Pa was at 15°C and at water potential ranging from -0.12 to -0.8 MPa. The lag phase of the growth curve increased with decreasing water potential (Schober and Zadoks, 1999). Depletion of oxygen in tubers due to tissue respiration impairs host resistance.…”

“…However, Pa has a wider host range compared to Pcc and Pcb (Czajkowski et al, 2011). Pectobacterium carotovora subspecies carotovora and Pa are virulent at 28 to 32°C but Pcc is more pathogenic at higher temperatures than Pa (Schober and Zadoks, 1999;Rashid et al, 2012). Studies by showed that Dickeya dadantii is more virulent than Pa and Pcb under Zimbabwean climatic conditions.…”

Linking Plant Disease Risk and Precipitation Drivers: A Dynamical Systems Framework

“…An extensive body of research links water availability, and specifically ambient soil moisture or plant water potentials, to the dynamics of plant pathogens (Crist and Schoeneweiss 1975;Malajczuk and Theodorou 1979;Dickenson and Wheeler 1981;Madar et al 1989;Boyer 1995;Schober and Zadocks 1999;Suleman et al 2001;Desprez-Loustau et al 2006;Ferrin and Stanghellini 2006). Many pathogens have a nonlinear response to changes in the hydration of their environment, which is manifest in terms of pathogen growth rates, survival, disease intensity, and reproductive behavior.…”

Saturation excess overland flow accelerates the spread of a generalist soil-borne pathogen

“…), and there are also potential feed-forward mechanisms by which hydrology can directly impact pathogens. For example, the growth and spread rates of many soil pathogens vary with water potential (Crist et al, 1975;Ferrin et al, 2006;Colhoun, 1973;Malajczuk et al, 1979;Dickenson et al, 1981;Madar et al, 1989;Cook et al, 1972;Boyer, 1995;Schober et al, 1999;Suleman et al, 2001;Desprez-Loustau et al, 2006), meaning that pathogen infection can influence, while also being influenced by, root zone water dynamics. The potential for pathogen propagules and infectious material to be transported by surface flow adds scope for further complex hydrologicalpathogen feedback processes.…”