AUTHOR=Fonseka Dimitri L. , Markell Samuel G. , Zaccaron Marcio L. , Ebert Malaika K. , Pasche Julie S. 

TITLE=Ascochyta blight in North Dakota field pea: the pathogen complex and its fungicide sensitivity

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1165269

DOI=10.3389/fpls.2023.1165269

ISSN=1664-462X

ABSTRACT=<p>Worldwide, Ascochyta blight is caused by a complex of host-specific fungal pathogens, including <italic>Ascochyta pisi</italic>, <italic>Didymella pinodes</italic>, and <italic>Didymella pinodella</italic>. The application of foliar fungicides is often necessary for disease management, but a better understanding of pathogen prevalence, aggressiveness, and fungicide sensitivity is needed to optimize control. Leaf and stem samples were obtained from 56 field pea production fields in 14 counties in North Dakota from 2017 to 2020 and isolates were collected from lesions characteristic of Ascochyta blight. Based on fungal characteristics and sequencing the ITS1-5.8S-ITS2 region, 73% of isolates were confirmed to be <italic>D. pinodes</italic> (n = 177) and 27% were <italic>A. pisi</italic> (n = 65). Across pathogens, aggressiveness was similar among some isolates in greenhouse assays. The <italic>in vitro</italic> pyraclostrobin sensitivity of all <italic>D. pinodes</italic> isolates collected from 2017 to 2020 was lower than that of the three baseline isolates. Sensitivity of 91% of <italic>A. pisi</italic> isolates collected in 2019 and 2020 was lower than the sensitivity of two known sensitive isolates. Resistance factors (Rf) from mean EC<sub>50</sub> values of pyraclostrobin baseline/known sensitive isolates to isolates collected from 2017 to 2020 ranged from 2 to 1,429 for <italic>D. pinodes</italic> and 1 to 209 for <italic>A. pisi</italic>. <italic>In vitro</italic> prothioconazole sensitivity of 91% of <italic>D. pinodes</italic> isolates collected from 2017 to 2020 was lower than the sensitivity of the baseline isolates and 98% of <italic>A. pisi</italic> isolates collected from 2019 to 2020 was lower than the sensitivity of the known sensitive isolates. Prothioconazole Rf ranged from 1 to 338 for <italic>D. pinodes</italic> and 1 to 127 for <italic>A. pisi</italic>. Based on <italic>in vitro</italic> results, 92% of <italic>D. pinodes</italic> and 98% of <italic>A. pisi</italic> isolates collected displayed reduced-sensitivity/resistance to both fungicides when compared to baseline/known sensitive isolates. Disease control under greenhouse conditions of both pathogens provided by both fungicides was significantly lower in isolates determined to be reduced-sensitive or resistant in <italic>in vitro</italic> assays when compared to sensitive. Results reported here reinforce growers desperate need of alternative fungicides and/or management tools to fight Ascochyta blight in North Dakota and neighboring regions.</p>