Deciphering resistance to Zymoseptoria tritici in the Tunisian durum wheat landrace accession ‘Agili39’

Abstract

Background Septoria tritici blotch (STB), caused by Zymoseptoria tritici (Z. tritici), is an important biotic threat to durum wheat in the entire Mediterranean Basin. Although most durum wheat cultivars are susceptible to Z. tritici, research in STB resistance in durum wheat has been limited. Results In our study, we have identified resistance to a wide array of Z. tritici isolates in the Tunisian durum wheat landrace accession ‘Agili39’. Subsequently, a recombinant inbred population was developed and tested under greenhouse conditions at the seedling stage with eight Z. tritici isolates and for five years under field conditions with three Z. tritici isolates. Mapping of quantitative trait loci (QTL) resulted in the identification of two major QTL on chromosome 2B designated as Qstb2B_1 and Qstb2B_2. The Qstb2B_1 QTL was mapped at the seedling and the adult plant stage (highest LOD 33.9, explained variance 61.6 %), conferring an effective resistance against five Z. tritici isolates. The Qstb2B_2 conferred adult plant resistance (highest LOD 32.9, explained variance 42 %) and has been effective at the field trials against two Z. tritici isolates. The Qstb2B_1 QTL was mapped at the seedling and the adult plant stage (highest LOD 33.9, explained variance 61.6 %), conferring an effective resistance against five Z. tritici isolates. The Qstb2B_2 conferred adult plant resistance (highest LOD 32.9, explained variance 42 %) and has been effective at the field trials against two Z. tritici. The physical positions of the flanking markers linked to Qstb2B_1 and Qstb2B_2 indicate that these two QTL are 5Mb apart. In addition, we identified two minor QTL on chromosomes 1A (Qstb1A) and chromosome 7A (Qstb7A) (highest LODs 4.6 and 4.0, and explained variances of 16 % and 9%, respectively) that were specific to three and one Z. tritici isolates, respectively. All identified QTL were derived from the landrace accession Agili39 that represents a valuable source for STB resistance in durum wheat. Conclusion This study demonstrates that Z. tritici resistance in the ‘Agili39’ landrace accession is controlled by two minor and two major QTL acting in an additive mode.

Multi-stage resistance to Zymoseptoria tritici revealed by GWAS in an Australian bread wheat (Triticum aestivum L.) diversity panel

“…In this study, the four identified MSR-QTLs are likely to provide resources for the development of Z. tritici resistant cultivars both in Australia and globally. In comparison to previously published studies, our detected MSR-QTL QStb.wai.1B.1 was co-located with QStb.cim-1BS (Dreisigacker et al 2015), and the locus of QStb.wai.2B.1 co-located with QTL-2BL and Qstb2B_1 (Aouini 2018; Ferjaoui et al 2021) and the major gene Stb9 (Chartrain et al 2009). While the locus of QStb.wai.5A.1 co-located with QStb.cim-5AL-2 (Dreisigacker et al 2015) and QStb.B22-5A.a (Naz et al 2015).…”

“…Further, the QTLs, QTL-2BL and Qstb2B_1 were also mapped from the durum wheat ‘Agili 39’and are reported to be responsible for Z. tritici resistance at both seedling stage and adult-plant stage using multiple isolates. It has also been suggested that this locus could be the major gene Stb9 (Aouini 2018; Ferjaoui et al 2021).…”