Prevalence of Septoria Leaf Blotch (Zymoseptoria tritici (Desm.) Quaedvlieg & Crous) in Some Provinces of the Marmara Region of Türkiye and Evaluation of Commercial Bread Wheat Cultivars for Resistance

Abstract

hemibiotrophic fungus Zymoseptoria tritici (Desm.) Quaedvlieg & Crous, is a devastating foliar disease of wheat globally. This study aimed to determine the current prevalence of SLB in some provinces of the Marmara Region of Türkiye and to evaluate the resistance levels of commercially grown bread wheat cultivars against local pathogen populations. Materials and Methods: Field surveys to determine disease prevalence were conducted during the 2014 and 2015 growing seasons in the provinces of Bursa, Bilecik, Kocaeli, and Sakarya. To assess host resistance, 18 commercial bread wheat cultivars were screened against a highly virulent local isolate (Bursa-177) obtained from targeted samplings in 2016. Resistance assays were performed under both controlled greenhouse conditions at the seedling stage in 2017 and artificially inoculated field conditions at the adult plant stage in 2018. Disease severity was statistically analyzed to classify cultivar reactions.Results: Surveys revealed a heterogeneous disease distribution. SLB was widely prevalent in Bursa, recording the highest incidence rates in the Karacabey district, whereas disease incidence and prevalence remained lower in Bilecik across both the 2014 and 2015 growing seasons. Overall, the epidemic expanded across the region in 2015, with both the total number of infected fields and mean disease incidence more than doubling. Notably, while the disease was present in Sakarya in 2014, it was undetected in both Kocaeli and Sakarya during the 2015 season due to a severe yellow rust epidemic that masked SLB symptoms. In greenhouse assays, the positive controls and the vast majority of commercial cultivars (14 out of 18) were highly susceptible, with only a single genotype, 'Tahirova-2000', exhibiting a distinct resistant reaction at the seedling stage. However, field trials revealed a marked shift in host responses. This initial seedling resistance was rendered ineffective under high disease pressure in the field. In contrast, cultivars 'Nusrat' and 'Altuğ' displayed the lowest disease severity, indicating the presence of robust Adult Plant Resistance (APR).Conclusion: The study confirms the establishment of SLB in the Marmara region with significant spatial variation. The disparity between seedling and adult plant reactions, particularly in 'Tahirova-2000', suggests stage-specific resistance or pathogen adaptation. 'Nusrat' and 'Altuğ' were identified as promising sources of partial resistance. These findings highlight the necessity of integrating field-based screening to identify durable resistance sources for effective disease management.