Characterization of DMI, QoI and SDHI fungicides sensitivity of Ramularia collo‑cygni isolates in Argentina

NEIL DAVID HAVIS; QUIROZ, FACUNDO; ERREGUERENA, IGNACIO; KALINA GORNIAK; THIES MARTEN HEICK; CARMONA, MARCELO

JOURNAL OF PLANT DISEASES AND PROTECTION

EUGEN ULMER GMBH CO

Año: 2022 vol. 129 p. 1343 - 1353

1861-3829

Ramularia leaf spot (RLS) caused by the fungus Ramularia collo-cygni (Rcc) has become a threat to barley production inArgentina. All barley varieties are susceptible to RLS; thus, disease management relies on fungicides like quinone-outsideinhibitors (QoIs), demethylation inhibitors (DMIs) and succinate dehydrogenase inhibitors (SDHIs). Europe reported Rccresistance to fungicides associated with mutations in the fungicide´s target genes. The aim of this work was to assess theimpact of mutations on sensitivity levels in isolates of Rcc to QoIs, DMIs, SDHIs and a multi-site fungicide used for RLScontrol in Argentina and others countries. Twenty-one Rcc isolates were collected in the Buenos Aires province in the years2012, 2015 and 2017 and tested against azoxystrobin (QoI), epoxiconazole and prothioconazole-desthio (DMIs), isopyrazamand fuxapyroxad (SDHIs) and chlorothalonil. For EC50 determination, a sensitivity assay was performed and cytb, cyp51and sdh genes were sequenced for mutation analyses. All isolates showed G143A mutation that confers total resistance toQoIs (EC50>1 mg L−1). Three mutations in the target genes of DMIs (Y403C/S, G404D) were observed. Isolates with bothamino-exchanges showed an increase in the EC50 towards DMIs. Mutations B-H266L and C-N87S in the target genes ofSDHIs were detected, and both were related to a sensitivity reduction. Mutations occurrence tended to increase from 2012to 2017 along with higher EC50 values. We found six haplotypes showing that Rcc is potentially adapting to fungicides inArgentina. Eforts must focus on new active ingredients and resistant varieties for a less fungicide-dependent agriculturebased on IPM strategies.