Pathogenesis by Pectolytic Erwinias

Abstract

Although E. carotovora pv. carotovora (Ecc), E. carotovora pv. atroseptica (Eca) and E. chrysanthemi (Echr) can be considered as true plant pathogens able to cause systemic infection and vascular disorders, as well as showing host specificity when they cause decay of the harvested crops, they tend to behave as opportunistic pathogens. In many crops, such as potatoes, latent infection is common and transition to an active state depends on how host resistance and pathogenicity of the bacteria interact with each other and with environmental factors. Although ill defined, pathogenicity is the result of several determinants interacting with each other. However, temperature is the overriding factor which affects pathogenicity. In tubers, virulence of the three erwinias increased with increasing temperature from Eca to Ecc to Echr reflecting their growth temperature characteristics. In the field, stem disease or blackleg is caused by Eca at temperatures <25C and by Echr at higher temperatures. However, although Ecc can cause a rot when potato stems are inoculated and can move up the stem from a rotting mother tuber, it is apparently unable to cause disease under field conditions when inoculated erwinia-free seed tubers are planted even under warm conditions.