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 physical positions of the flanking markers linked to Qstb2B_1 and Qstb2B_2 indicate that these two QTL are 5 Mb 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. We also provide evidence that the broad efficacy of the resistance to STB in ‘Agili 39’ is due to a natural pyramiding of these QTL. A sustainable use of this Z. tritici resistance source and a positive selection of the linked markers to the identified QTL will greatly support effective breeding for Z. tritici resistance in durum wheat.

Multi-stage resistance to Zymoseptoria tritici revealed by GWAS in an Australian bread wheat 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 colocated with QTL-2BL, 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 ).…”

Genetic approaches to exploit landraces for improvement of Triticum turgidum ssp. durum in the age of climate change

“…As pivotal examples leaf and stem rust resistance sources were mapped in the Portuguese DW landraces PI 192051 and Aus26582, by developing RIL mapping populations, beside alternative contribution from other sources (Qureshi et al, 2017;Qureshi et al, 2018;Aoun et al, 2019). Similarly, a resistance gene to Zymoseptoria tritici was mapped in the Tunisian DW landrace 'Agili 39' (Ferjaoui et al, 2022).…”

Specific virulence patterns in Tunisian Zymoseptoria tritici strains isolated from bread and durum wheat

“…tritici , and (b) mapping resistance genes requires the use of specific isolates with pathogenicity to DW as the majority of Z . tritici –BW‐derived isolates are nonpathogenic on DW, known as host species specificity (Ferjaoui et al, 2022).…”

“…Several studies conducted in Tunisia with regard to DW landraces have shown that these latter may harbour sources of resistance to Z . tritici (Ben M'Barek et al, 2022; Ferjaoui et al, 2022). Ferjaoui et al (2022) demonstrated that the observed STB resistance in the Tunisian landrace Agili39 is due to two minor and two major quantitative trait loci (QTLs) acting in an additive mode and provided evidence that the broad efficacy of this resistance was due to a natural pyramiding of these QTLs.…”