Alternative strategies to treat potato early blight

Abstract

Potato, Solanum tuberosum, is a staple crop grown worldwide. Like all other plants that are cultivated in the world’s vast agricultural system, potatoes are constantly under attack by plant pathogens. Early blight is a potato disease caused by a fungal pathogen called Alternaria solani. In Sweden this pathogen is particularly problematic in the starch potato industry causing premature defoliation and reduced starch yield. The most common current treatment is application of fungicides. The focus of the research presented in this thesis has been to test and evaluate alternative ways to combat this pathogen in an applied Swedish field environment. A three-year observational study was conducted, as were multiple field trials, to achieve a broader understanding of how to manage early blight. The results of the observational study led us to design further field trials to test the importance of potassium. We found interesting differences in disease severity among the farms. The field trials consisted of evaluating cultivar tolerance, biological control measures such as the use of biocontrol agents (BCAs) and plant resistance inducers (PRIs), and the role of plant nutrients. The most important finding in this thesis is that the best treatment strategy is highly farm specific, and it is crucial to customize the treatments at a field level. The soil composition is the single largest factor that impacts the rate of infection. A sandier soil is much more likely to suffer from early blight induced yield loss and the recommended treatments should be based on the sand content of the soil in the specific field. Further results conclude that the potassium content in the soil and leaf plays a role in disease rate since a depletion caused heavier infection. The BCAs and PRIs evaluated showed potential for future alternative strategies but none of the evaluated substances proved to be efficient under field conditions. Lastly, it was observed that there are differences among starch potato cultivars currently grown, that affect the disease rate of early blight.