Examining Spatial Distribution and Spread of Fire Blight in Apple Orchards: Two Case Studies

Fire blight, caused by the bacteria Erwinia amylovora, is an incredibly destructive disease of apples, capable of spreading rapidly through an orchard block. The pathogen is endemic to many apple production regions worldwide, but it is often introduced into newly planted sites on infested host material, while locally it is typically vectored by wind-driven rain, hail, and insects. Here we presented two case studies of orchard blocks infected with fire blight at the Cornell AgriTech Research orchards in which CRISPR pattern characterization was used to identify strains present in the blocks and spatial analyses were used to describe the distribution and spread of the disease over the course of 2 years. Results indicated two very different sources of introduction (a nearby block or planting material) and patterns of spread (from a corner of the field or from focal points within the block). Describing the distribution and spread of fire blight within and between orchard blocks has the potential to improve our understanding of the disease movement, inform appropriate management recommendations, and facilitate trace-back efforts.