Evaluation of sugar beet genes involved in Rhizoctonia solani resistance

Sugar beet (Beta vulgaris ssp. vulgaris) is one of the most cultivated crops in Sweden and contributes to approximately 14 % of the sugar crops grown in the world, the remaining 86 % being sugar cane (OECD-FAO 2019). As with any commercially produced crop, sugar beets can be exposed to pests and pathogens, which can cause yield losses. One common pathogen in sugar beet production is Rhizoctonia solani, which is a soil-borne pathogenic fungus, estimated to affect approximately 25 % of the cultivated sugar beet area in the United States and approximately 10 % of the cultivated sugar beet area in Europe (Harveson et al. 2009). It causes three diseases in sugar beets: crown-rot, root-rot and damping-off, which result in root damage but differ at point of infection. As sugar beet is an economically important crop efforts are being made by breeding companies to develop sugar beet varieties with increased tolerance to pathogens like R. solani. In this thesis, genes that are believed to be involved in R. solani resistance are evaluated in sugar beet material provided by MariboHilleshög. The expression patterns of five genes, previously discovered through RNA sequencing, were tested through RT-qPCR in two tolerant and two susceptible sugar beet genotypes to determine if the RNA sequencing results could be replicated. The RT-qPCR showed that the RNA sequencing results could not be fully replicated as only some genes followed the expected expression pattern between tolerant and susceptible genotypes. This was possibly a result of genetic differences between genotypes, or because of uneven R. solani infection in the analysed material. The correlation between allele distribution and R. solani tolerance was also examined for one gene in a larger sugar beet population consisting of 95 lines of varying R. solani resistance, and showed that there possibly could be a correlation between allele distribution and R. solani tolerance for the gene tested. However, as the population consisted mainly of tolerant and medium tolerant individuals, further research is needed on susceptible individuals before it is determined whether or not a pattern exists