Phenotyping of barley (Hordeum vulgare) responses to spot blotch caused by different isolates of the fungus Cochliobolus sativus : Searching for resistance sources in barley germplasm

Abstract: Barley is one of the major crops in the world, and spot blotch, caused by the fungus Cochliobolus sativus, is an important disease that affects it. Spot blotch can cause major yield losses and reduce the quality of the seeds, especially in wet, warm climates. The pathogen can also infect the roots of barley plants, causing common root rot. Due to climate change and the spread of the pathogen through modern transportation, the risk of yield losses due to spot blotch has been increasing. Cochliobolus sativus is a hemibiotrophic fungus that is usually found in nature in its asexual form (Bipolaris sorokiniana). I used the tape method, a so far little used technique for testing resistance, to try to find good sources of resistance to C. sativus in barley. The tested lines were provided by Nordic breeders, who previously tested them under standard field and greenhouse conditions. Different fungal isolates that had been isolated from different locations in Sweden were used in this experiment. The lesions were later scored with a 1-9 scale, and the plants were classified as resistant, moderately resistant, moderately susceptible, or susceptible to a certain fungal isolate. It was found that there is a significant barley genotype-fungal isolate interaction, which means that barley lines may respond differently to each fungal isolate. The barley lines suggested as resistance sources were resistant or moderately resistant to all three fungal isolates. The barley lines coded as PPP112, PPP201, PPP206, PPP207, PPP250, PPP252, PPP260, PPP265, PPP269, PPP272 and PPP274 are the genotypes thus identified as potential resistance sources for breeding. I found that there is a positive correlation between lesions in the leaves with diffuse necrotic reactions and gray spots and fungal aggressiveness, suggesting possible mechanisms of infection that could be studied further. In the end, I could not compare the results from the tape method with the results provided by breeders, since the fungal isolates used in these experiments were too different. SLU, Swedish