IDENTIFICATION OF CANDIDATE GENES INVOLVED IN RESISTANCE TO FUSARIUM GRAMINEARUM IN DURUM WHEAT

Wheat is one of the most important crop species world-wide, ad is affected by several fungal diseases. One of the key pathogens is the hemibiotrophic fungus Fusarium graminearum, the causal agent of Fusarium head blight (FHB) disease, which causes severe losses in yield and quality, due to the production of mycotoxins, like deoxynivalenol (DON), which are harmful to humans and livestock. Host resistance is the primary control measure for FHB, thus the development of resistant varieties is one of the most attracting challenges in breeding project. Despite several resistance QTLs have been identified in bread wheat, only poor information is available on tetraploid species: it was hypotized that the D-genome of hexaploid wheat encodes resistance-inducing factors that are missing in tetraploid wheat, or that this latter may carry susceptibility factors and/or suppressors. Thus, the objective of the present work was to identify and isolate some of the genes involved in FHB resistance in durum wheat through an innovate “candidate gene” approach. In wheat spikes, cell wall components including cellulose, pectin and xylan are reduced as the infection progresses, suggesting that Fusarium produces cell wall degrading enzymes to assist infection. Moreover, the mycotoxins are known to inhibit protein synthesis and may have a role in pathogenesis. For these reasons, we focused our attention on genes related to detoxification of mycotoxins, such as cytochrome P450s and ABC transporters, or plant cell wall polysaccharides enzymes, like hemicellulases (pectin methylesterases and pectin acetylesterase). At first, we carried out a bio-informatics study in phylogenetically-related species such as rice, maize, barley and Brachipodium, with the aim to identify homologous genes and their conserved regions. Starting from these, we partially reconstructed the genomic sequences of the genes in two lines, the 02-5B-318 accession of T. aestivum and the durum wheat cv. Saragolla, respectively FHB-susceptible and resistant, which are the parentals of a segregating RIL population. Since wheat is a tetraploid species (AA BB genome), each amplified fragment have been mapped on A or B genome, to distinguish the genes located on the two homologous chromosomes, by using a set of aneuploid lines. The work is going on by isolation of complete genomic sequences of the candidate resistance genes, and molecular characterization of their intron/exon structure. Moreover, for each single gene, sequences have been aligned between the two parental lines in order to search for single nucleotide polymorphisms (SNPs). These will allow to design specific primer pairs to be used for genetical map in the RIL population, in order to determine the chromosomal location of the genes and their co-localization with FHB resistance QTLs, with the final objective to transfer Fusarium resistance to durum wheat cultivated varieties and produce resistant lines.