IDENTIFICATION OF QTL AND CANDIDATE GENES FOR FUSARIUM HEAD BLIGHT RESISTENCE IN DURUM WHEAT

Fusarium head blight (FHB) is one of the most widespread and damaging wheat diseases worldwide, with significant economic and health impacts. The causal agent is the fungus Fusarium graminearum, which attacks the cereal inflorescence during anthesis and in later stages of kernel development, causing severe losses in yield and quality due to the production of mycotoxins, like deoxynivalenol (DON), which are harmful to human and livestock. The genetic basis of FHB resistance has been extensively studied in bread wheat, but less information is available on durum wheat. The aim of this work was to study FHB resistance in a newly-developed durum wheat segregant RIL (Recombined Inbred Lines) population obtained by crossing the parental lines 025B-318 and Saragolla, respectively FHB resistant and susceptible. The RILs were evaluated for FHB resistance and bio-agronomic traits in two replicated field trials carried out in Valenzano (BA) and Bologna (SIS) for two years. FHB incidence and disease severity were recorded in the RIL population and in the parental lines after the infection. Severity was averaged as the percentage of infected spikelets per plant, while incidence was averaged as the number of infected spikes for plant. In the susceptible cv Saragolla, high FBH incidence and severity were observed when plants were grown in the field and in greenhouse, and no significant differences were detected between the two growth conditions. On the contrary, line 02-5B-318 was completely resistant to FHB in greenhouse condition, while showing an incidence and severity of about 94% and 80%, respectively, which were significantly lower (P>0.001) than Saragolla, in field conditions. Histogram for FHB rating of RI Lines followed a normal distribution, confirming the quantitative nature of the trait. A genetic linkage map consisting in about 5,000 SNP markers from a 90K Illumina Infinium assay, was developed in order to perform a QTL analysis that identified several QTL regions. All the SNPs were searched for putative functions and the pectin methylesterase gene (wheat-pme1) was found involved in FHB resistance. The role of wheat-pme1 as a candidate gene for Fusarium resistance was validated in RT-qPCR expression studies on 02-5B-318 and Saragolla. Expression of wheat-pme1 was induced by Fusarium infection only in the susceptible plants, whereas a down-regulation of gene expression was observed in the resistant plants. These results suggest that the more pronounced de-methylesterification of cell wall pectin observed during Fusarium infection in the susceptible Saragolla plants could be associated to the activity of this enzyme, and indicate wheat-pme1 as a possible susceptibility factor involved in wheat-Fusarium pathosystem.