Analysis of the resistance to Zymoseptoria tritici in a Tunisian durum wheat landraces

Septoria tritici blotch (STB) caused by the fungal pathogen Mycosphaerella graminicola (anamorph: Zymoseptoria tritici) is one of the most important foliar diseases of durum wheat (Triticum turgidum ssp. durum) in Tunisia. It attacks plants from seedling stages to maturity causing serious yield losses. Breeding for resistance to STB in durum wheat can provide an effective, economic and environmentally-safe strategy to reduce yield losses. However, this is hampered by lack of sources of resistance. In this context, a collection of 420 accessions of durum wheat from the National Bank of Gene (BNG) were evaluated for resistance to two virulent isolates of Z. tritici, namely TunBz-1 (across two environments) and TM220 (across one environment) under field conditions at three different development stages. The evaluation scale was ranged from 0% (immune plant) to 100% (100% of leave covered with symptoms). Three effects were studied on the collection: environmental effect E1-E2 (years 2016-2017), isolate effect I1-I2 (TunBz-1 and TM220) and physiological stage effect S1-S2 (seedling and adult). Results highlighted different sources of resistance between both seedling and adult stages. Moreover, 51 and 67 accessions have differential response to the two studied isolates respectively in seedling and adult stage. Furthermore, the Venn diagram has identified 23 accessions in the collection that are resistant to both isolates at both stages and that resistance was stable across environments. These accessions are located mainly in the center of Tunisia. Resistance to isolate TunBz-1 is expressed since seedling stage and there is stability of this resistance throughout the environments. The center of Tunisia seems to be a diversity center that includes different sources of resistance to STB. This collection could be the subject of a genome-wide association study (GWAS) as it presents different types of STB resistance categories that can be targeted via SNPs.