2.1 Pathogen sampling and identification in potato fields with
blackleg disease symptoms
Pectinolytic bacteria were isolated from symptomatic plant tissues on
crystal violet pectate medium (Hélias, Hamon, Huchet, Wolf, & Andrivon,
2012). Isolates were purified on agar plates and characterized at the
genus (Dickeya and Pectobacterium ) and species (D.
solani and D. dianthicola ) levels using the PCR primers listed
in Table S1 . Two sampling strategies were used. From 2004 to
2015, a national inventory was conducted in French potato producing
areas. Each year (with the exception of the year 2006), fields
exhibiting blackleg symptoms were randomly sampled by collecting
diseased plants from which isolates were recovered and characterized.
From 541 fields, around 1600 isolates were collected and taxonomically
characterized. In parallel, from 2013 to 2016, 19 of the potato fields
exhibiting more than 1% of blackleg incidence were deeply sampled.
Around 30 plants with blackleg symptoms were collected along a transect
in each field, and a single isolate was retained from each of the 548
plants. The resulting 548 isolates were characterized taxonomically.