Phenotypic and molecular characterization of the response to two soil-borne viruses in durum wheat landraces for the identification of new sources of resistance

Durum wheat cultivation is increasingly threatened by viral diseases worldwide. Soil-borne cereal mosaic virus (SBCMV) and wheat spindle streak mosaic virus (WSSMV) cause significant crop losses in Europe. These viruses are transmitted through a soil-inhabiting vector, the plasmodiophoromycota Polymyxa graminis Led. There are very few methods available to eradicate P. graminis, whose resting spores survive in infested soil for decades, but they are either too expensive or not environmentally friendly. Therefore, it is crucial to develop resistant wheat varieties to mitigate the damage. For this purpose, more than 200 durum wheat genotypes, mostly landraces, were selected from the Global Durum Wheat Panel germplasm collection. Then, an experiment was conducted in a semi-controlled environment: the genotypes were sown in pots containing soil infested by P. graminis carrying SBCMV and WSSMV and maintained through the winter period. In early spring, visual assessment of viral symptomatology was performed. Subsequently, the viral loads of the two viruses in leaf tissues were determined through qRT-PCR analysis. The tested genotypes exhibited different responses to the two viruses: SBCMV showed very diversified viral loads among genotypes, whereas WSSMV infected all genotypes. We identified 23 genotypes, with low viral loads of both viruses and reduced symptoms, that could be of particular interest for breeders aiming at new resistant durum wheat varieties. A pilot GWAS allowed to identify genomic regions putatively associated to resistance to SBCMV or WSSMV, as well as possible candidate genes involved in these traits.