Primary inoculum of Erwinia amylovora: alternative sources and viable but non-culturable state: A review

Fire blight is a complex and devastating plant disease caused by the necrotrophic bacterium Erwinia amylovora. One of the main factors that determine the occurrence of the disease is the infective inoculum from the primary sources in the orchard. The most accepted theory asserts that overwintering cankers are the most likely source of the primary inoculum. However, the origin remains controversial. Several studies have documented the infectious potential of alternative sources such as shoots and fruits infected in previous seasons, the soil, and even non-host plants. These alternative sources are underestimated because they harbor non-significant epiphytic populations of E. amylovora. However, the low populations of the pathogen could be related to the ability of the bacterium to induce a viable but non-culturable state (VBNC) in response to starvation or cytotoxic stress. The natural environment would favor these conditions, making it difficult to detect them through methods based on the cultivability of the bacteria. This review summarizes the main and alternate sources of primary inoculum of E. amylovora, its infectious potential, and the VBNC state as a survival mechanism during periods of stress under natural conditions.

Automated summary

Fire blight is a plant disease caused by the bacterium Erwinia amylovora. The primary sources of infection include overwintering cankers, as well as shoots, fruits, and non-host plants. The bacterium can enter a viable but non-culturable state, making it difficult to detect. This review discusses the sources of infection and the survival mechanism of E. amylovora.