Investigating fungicide resistance of Alternaria solani, a Solanaceae pathogen, on potato crops in south-eastern Sweden and its relationship with soil

Sammanfattning: Alternaria solani is a worldwide present fungus that can cause a lot of damage such as early blight in potato crops. Potato can suffer a lot of yield losses because of this pathogen, and the main method used today to fight against it, is the application of fungicides. Yet fungicides are chemicals that contaminate the environment and are not assimilated so they can be found in water for example, which can cause problems for human health as well. As the climate is becoming warmer and warmer, it is also expected that the A. solani severity will increase, which will induce more use of fungicides. A. solani resistance to fungicides has been reported and seems to develop quickly. Firstly, it is important to study A. solani resistance development to new fungicides as it may improve the possibility for early detection of fungicide resistance. In this study, we looked at the mycelial growth of A. solani field isolates by increasing the concentration of fluopyram, a fungicide, in two growth assays (liquid and solid). Secondly, to be able to predict the occurrence of early blight it is also important to investigate the survival and growth of A. solani in the soil. Here we did a soil assay where we incubated A. solani infected rye kernels in different soils under differents conditions (unsterilized wet, unsterilized dry or sterilized) followed by a qPCR performed on the rye kernels to assess the A. solani quantity. In our experiment, the growth of A. solani decreased with the increase of fluopyram concentration. Moreover, the growth reduction with decreased fluopyram concentration was reduced for the later collection year, which indicates that the sensitivity to flupyram decreased over the years. The growth of A. solani in the soil was affected by the said soil condition (dry, sterilized or unsterilized). Our results are pointing to A. solani surviving better in dry soils which is concerning knowing the expected temperature rise, as well as the drought experienced today but also in the future.