, class 2=1–25%, class 3=26–50%, class 4=51–75%, class 5=76–100% of shoot tips infected; CBB, incidence class 1=no symptom, class 2=plants with water-soaked spots only, class 3=plants with water-soaked spots and 1–50% of plants with systemic infection (corresponding to symptom classes 4 and 5), class 4=51–89% of plants with systemic infection, class 5=over 90% of plants with systemic infection. This classification allowed to calculate the means over the incidence classes per site. Prevalence was defined as field incidence: percentage of infected fields per ecozone.