Fludioxonil sensitivity of Fusarium sambucinum causing potato dry rot and seed piece decay in Idaho and its relationship to disease control in the field
Wednesday, July 28, 2021
12:15 PM - 12:30 PM
Fusarium sambucinum causes seed piece decay in potato before and after planting and Fusarium dry rot in storage. Fludioxonil is a commonly used fungicidal seed piece treatment for Fusarium disease management in potato. Fludioxonil sensitivity of F. sambucinum isolates recovered from symptomatic tubers in Idaho was determined in vitro using the spiral gradient endpoint dilution method. Fludioxonil resistance was observed in 77% of isolates tested. The objective of this study was to determine if lab-detected fludioxonil resistance for selected Idaho F. sambucinum isolates relates to decreased disease control in the field. In a randomized complete block design field trial with five replications, Russet Burbank seed pieces were inoculated with both fludioxonil-sensitive (3) and fludioxonil-resistant (20) F. sambucinum isolates and then treated with a commercially formulated fungicide containing only fludioxonil. Our test hypothesis was that isolates identified as fludioxonil-resistant would cause more dry rot than fludioxonil-sensitive isolates in the field. In most cases, fludioxonil-sensitive isolates caused lower seed piece incidence (8-18%) and severity (2-8%) compared to sixteen fludioxonil-resistant isolates (incidence and severity, 34-98% and 5-81%, respectively; (P≤0.0248). However, among the twenty fludioxonil-resistant isolates, two isolates appeared to be effectively managed by the fludioxonil seed piece treatment in that seed piece decay severity was similar to fludioxonil-sensitive isolates (5-18%, P=0.9970-1.000). Overall, our data from one field season indicate that most but not all isolates identified as resistant to fludioxonil in the lab led to increased disease incidence and severity in the field when used with a fludioxonil seed piece treatment.