Background and Objectives
Septoria leaf blotch (STB), caused by Zymoseptoria tritici, is one of the most significant constraints to wheat production, particularly in humid and temperate regions, where temperatures between 22–25°C and relative humidity exceeding 85% favor disease development. The disease leads to substantial reductions in grain yield and quality. The high genetic variability of Z. tritici populations and their rapid evolution of novel virulence factors indicate the need to identify virulence determinants and discover sources of durable resistance. The virulence of Z. tritici isolates against wheat STB resistance genes (Stb1 to Stb18) could critically guide the breeding programs to develop resistant cultivars. Pyramiding multiple effective Stb resistance genes into elite wheat lines offers a sustainable strategy to reduce reliance on fungicides and develop climate-resilient STB-resistant cultivars.
Materials and Methods
To evaluate STB resistance in 113 Iranian elite wheat lines (designated ERWYT-N98, ERWYT-N99, ERWYT-S98, and ERWYT-S99, including 20, 23, 30, and 40 lines, respectively), field experiments were conducted in adult plant stage over two consecutive growing seasons of 2019–2021 under artificial inoculation conditions in a randomized complete block design with three replications at two agricultural research stations of Golestan (Gorgan) and Safiabad (Dezful). Wheat lines were inoculated with virulent local isolates of Z. tritici, followed by resistance evaluation based on two key parameters: relative vertical disease progress and percentage of disease severity on infected leaves. Host response to STB was scored using the 00–99 double-digit scale.
Results and Discussion
Zymoseptoria tritici isolates from Gorgan and Dezful showed different virulence patterns, both geographically and temporally, while Gorgan isolates displayed higher virulence on known Stb resistance genes than Dezful isolates in both years of the study. No virulence was identified among the resistance genes Stb1, Stb5, Stb10, Stb12, Stb13, Stb14, Stb15, Stb16, and Stb18 at either location or year of study, indicating their effectiveness against prevalent pathogen populations. In contrast, Stb7, Stb8, and Stb9, as well as Stb11 and Stb17, were ineffective against all or some of the tested isolates, suggesting their unsuitability for current breeding programs. Polymorphism regarding significant virulence variation was observed against Stb2, Stb3, Stb4, and Stb6, suggesting their possible contribution to durable resistance, especially in combination with other effective resistance genes, particularly in north agro-climatic zone. Phenotypic evaluation of elite wheat lines revealed variable levels of resistance across the four germplasm sets. Among ERWYT-N98 lines, 24%, 43% and 33% displayed moderately resistance (including lines ER-N98-14, 18, 19 and the cultivars Tirgan and Kalateh), susceptibility and high susceptibility responses, while in ERWYT-N99 set, 29%, 29% and 42% of lines were moderately resistant (ER-N99-6, 14, 16, 18, 21, 22, 23), susceptible and highly susceptible, respectively. Regarding the south agro-climatic zone lines of ERWYT-S98, 39% demonstrated moderately resistance (ER-S98-7, 10, 11, 14, 15, 16, 17, 23, 28, 29, and cultivars Chamran2 and Mehregan), while 29% and 32% were susceptible and highly susceptible, respectively. In ERWYT-S99 set, 24%, 22%, 30% and 24% of lines displayed moderately resistance (ER-S99-3, 18, 19, 22, 25, 28, 30, 31, 36, and Chamran2), moderately susceptibility (ER-S99-4, 7, 8, 10, 24, 32, 34, 35, and Mehregan), susceptibility and high susceptibility, respectively.
Conclusion
Utilization of genetic resistance is considered the most effective, economical, and environmentally sustainable strategy for managing septoria leaf blotch in wheat breeding programs. Host resistance could significantly reduce yield loss when integrated with other disease management methods, such as cultural practices and chemical control. Results of this study indicate that the resistance genes Stb1, Stb5, Stb10, Stb12, Stb13, Stb14, Stb15, Stb16, and Stb18 are effective against current Z. tritici populations in both Iranian north and south agro-climatic zones, and their incorporation (preferably as pyramiding) into high-yielding genetic backgrounds is strongly recommended. Additionally, identification of moderately resistant and resistant wheat lines in this study highlights their potential as sources of resistance and valuable breeding parents. Utilizing these lines could help reduce reliance on chemical control, minimize disease impact, and enhance wheat productivity, particularly in disease hotspots.