Wheat stem rust caused by Puccinia graminis f. sp. tritici is an important wheat disease with sudden and devastating characteristics. The appearance and spread of new P. graminis f. sp. tritici races (Ug99, TKTTF, and TTTTF) have once again renewed the interest in the prevention and control of wheat stem rust. Fungicides can effectively control the epidemics of this disease in a short period of time. However, the fungal pathogen is prone to developing resistance. Therefore, we collected 89 isolates of P. graminis f. sp. tritici from four provinces in China and used the spore germination method to test the sensitivity of the isolates to fungicide triadimefon. Seven relatively triadimefon-sensitive isolates and six relatively triadimefon-resistant isolates were further tested for sensitivity to fungicides carbendazim, mancozeb, thiophanate-methyl, and kresoxim-methyl. The results showed that the mean concentration for 50% of maximal effect of the isolates to triadimefon was 16.14 mg·liter-1, and the mean resistance factor was 4.48. Only 29 isolates were resistant to triadimefon in which 27 isolates had low levels of resistance and 2 isolates had moderate levels of resistance. However, most of the 89 isolates had no resistance to triadimefon. There was a positive correlation between resistance to triadimefon and carbendazim, but there was no cross-resistance between triadimefon resistance with thiophanate-methyl or kresoxim-methyl resistance. This study provides valuable information for managing fungicide resistant isolates of P. graminis f. sp. tritici.
Keywords: fungicide resistance; stem rust; wheat.