Differential sensitivity among Puccinia striiformis f. sp. tritici isolates to propiconazole and pyraclostrobin fungicides

Authors: KANG, ZHANHAI - Hebei Academy Of Agriculture; LI, XING - Hebei Academy Of Agriculture; WAN, ANMIN - Washington State University; WANG, MEINAN - Washington State University; Chen, Xianming

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2019
Publication Date: 2/26/2019
Citation: Kang, Z. H., Li, X., Wan, A. M., Wang, M. N., and Chen, X. M. 2019. Differential sensitivity among Puccinia striiformis f. sp. tritici isolates to propiconazole and pyraclostrobin fungicides Canadian Journal of Plant Pathology 41(3):415-434
DOI: https://doi.org/10.1080/07060661.2019.1577301

Interpretive Summary: Stripe rust is a destructive disease of wheat worldwide. In the United States, fungicides have been widely used to control the disease, but it is not clear whether any tolerance has developed in the pathogen population. In this study, historical and recent isolates of the stripe rust pathogen were tested for sensitivity to Tilt (propiconazole) in the triazole group and Headline (pyraclostrobin) in the strobilurin group by testing urediniospores for germination and infecting wheat seedlings and adult-plants at various concentrations under controlled conditions. No germination was observed for any isolate when urediniospores were treated with either Tilt or Headline at the concentration of the full rate (1.00) in the label (1.56 ml/l for Tilt and 3.52 ml/l for Headline). However, significant differences in germination were observed among the isolates in the treatments of reduced fungicide concentration rates, equal or less than 0.20 of the full rate Tilt and = 0.006 of the full rate Headline. No sporulation was observed at the rates of 1.00 and 2.00 of Tilt or 0.50 and 1.00 of Headline applied one day before; 0.25 and higher rates of Tilt or 0.50 and 1.00 of Headline applied at the same day; and at the rate of 1.00 of Headline applied three days after inoculation, but significant differences were observed at the lower rates in the seedling tests. Similar results were also obtained in the adult-plant tests. Thus, the fungicides are still effective for control stripe rust at the labeled full rates, but different sensitivities exist among the pathogen isolates. This study provides the baseline for continual monitoring the stripe rust pathogen populations for fungicide sensitivity.

Technical Abstract: Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive disease of wheat worldwide. In the United States, fungicides have been widely used to control the disease, but it is not clear whether any tolerance has developed in the pathogen population. In this study, historical and recent Pst isolates were tested for sensitivity to Tilt (propiconazole) in the triazole group and Headline (pyraclostrobin) in the strobilurin group by testing urediniospores for germination and infecting wheat seedlings and adult-plants at various concentrations under controlled conditions. No germination was observed for any isolate when urediniospores were treated with either Tilt or Headline at the concentration of the full rate (1.00) in the label (1.56 ml/l for Tilt and 3.52 ml/l for Headline). However, significant differences in germination were observed among the isolates in the treatments of reduced fungicide concentration rates, = 0.20 of the full rate Tilt and = 0.006 of the full rate Headline. No sporulation was observed at the rates of 1.00 and 2.00 of Tilt or 0.50 and 1.00 of Headline applied one day before; 0.25 and higher rates of Tilt or 0.50 and 1.00 of Headline applied at the same day; and at the rate of 1.00 of Headline applied three days after inoculation, but significant differences were observed at the lower rates in the seedling tests. Similar results were also obtained in the adult-plant tests. Thus, the fungicides are still effective for control stripe rust at the labeled full rates, but different sensitivities exist among Pst isolates. This study provides the baseline for continual monitoring the Pst populations for fungicide sensitivity.