Triazole Fungicide Sensitivity Among South African Puccinia Graminis F. Sp. Tritici Isolates

Abstract

Fungicide application plays an important role in the successful production of winter cereals in South Africa. While fungicide treatments are critical for crop protection, the appearance of insensitivity in fungal populations is likely to limit their efficacy. This study aimed to confirm a possible correlation between CYP51 sequence variants and fungicide insensitivity among 45 South African Puccinia graminis f. sp. tritici isolates collected between 1981 and 2020. Urediniospore germination percentages were measured for each isolate in replicated experiments against triazole-based fungicides, propiconazole and tebuconazole, to determine EC50 estimates. The isolates showed significant differences in their sensitivity among the fungicide dilutions and the untreated control. The propiconazole dilutions differed significantly from each other, except for the x0.20 and x0.40 dilutions, which were highly efficient in suppressing germination. Significant differences in sensitivity were detected among all the tested tebuconazole dilutions. Sequencing results identified two allelic variants of the CYP51 gene among the isolates. While alleles 1 and 2 differed from each other, both were identical across the isolates, even regarding the mutations and deletions present within the introns. The genetic variation in the CYP51 gene and the differences in sensitivity detected among the isolates, confirm the underlying genetic potential for P. graminis f. sp. tritici to develop fungicide insensitivity in South Africa.

Keywords: Wheat, Puccinia graminis f. sp. tritici, stem rust, fungicide sensitivity, CYP51 analysis