Fungicide resistance and soil survival of Alternaria solani

Sammanfattning

Alternaria solani is a major pathogen affecting potato (Solanum tuberosum), causing early blight and significant yield annual losses globally. Due to the pathogen’s ability to develop resistance to QoI fungicides and boscalid, a SDHI fungicide, concerns have arisen regarding future fluopyram resistance. Fluopyram is a SDHI fungicide that inhibits fungal respiration and is one of the active ingredients of a relatively new fungicide, Propulse. This study aimed to assess the level of resistance of A. solani isolates to fluopyram and whether the isolates studied showed signs of fungicide resistance 2 years after introduction of Propulse. Another objective was to study the survival of the pathogen in soil during winter as this could influence its epidemiology. The study was separated into three experiments: a germination assay testing spore viability across fungicide concentration, the prevalence of A. solani on treated or non-treated leaves and an evaluation of soil type on fungus survival. The germination assay revealed a significant reduction in spore germination at high fluopyram concentrations, although it did not completely inhibit spore viability. A. solani was detected in all leaf samples, with fungicide-treated leaves unexpectedly containing higher levels of Alternaria spp.. The presence of A. solani despite treatment, as seen on leaf samples and germination assay, might indicate the possibility of lower sensitivity to the fungicide. The results from the soil experiment aligned with current literature, showing enhanced survival of A. solani in dry clay soils. These findings, although demonstrating fluopyram’s current effectivity on the pathogen, hint towards future challenges. Increased temperatures tend to lead to drier soils which could promote A. solani infections. Although, further research is required to validate these observations.