Abstract

Tan spot, caused by the fungal pathogen Pyrenophora tritici-repentis (Ptr), is recognized as one of the most aggressive foliar diseases affecting wheat globally, including in Kazakhstan. Under favorable conditions for disease development, yield losses can reach 50–65%. Ptr populations demonstrate high genetic variability, with the prevalence of specific races shifting annually in response to climatic and agricultural factors. Current fungicide regimens are often insufficient to control this rapidly adapting pathogen, and an increase in resistance to commonly used compounds has been observed. In this study, the effect of strobilurin fungicides – specifically, those with external quinone inhibitors (QoIs) – on the mycelial growth of Ptr isolates was assessed. Twenty isolates were initially selected at random and evaluated for their sensitivity to azoxystrobin by determining the EC50 required to inhibit mycelial growth. Azoxystrobin was incorporated into potato dextrose agar (PDA) at serial ten-fold dilutions of 0.01, 0.1, 1, 10, and 100 µg/mL. The findings revealed resistance to QoIs among the tested isolates, as confirmed by mycelial growth inhibition assays. On average, mycelial growth was suppressed by 23.01%, 37.87%, 44.97%, 46.37%, and 48.41% at 0.01, 0.1, 1, 10, and 100 µg/mL azoxystrobin, respectively. These results indicate that QoI molecules exhibit greater fungitoxicity against spore germination compared to suppression of mycelial growth in Ptr. Notably, significant differences in pathogen sensitivity to both the active ingredients of the fungicide and among different strains were observed (p < 0.001). A significant positive correlation was also found between the area under the disease progress curve (AUDPC) and thousand grain weight of genotypes (r = 0.76; p < 0.001). Therefore, the integration of bioinformatics approaches in further research will be essential for more effective monitoring, prediction of disease outbreaks, and the development of novel chemical and biological control strategies, as well as for accelerating the breeding of wheat varieties with enhanced resistance. This research was funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP22787867).