Fungicide sensitivity levels in the Lithuanian Zymoseptoria tritici population in 2021

Abstract

Zymoseptoria tritici causes the disease known as septoria leaf blotch in winter wheat and is a major factor in yield loss worldwide. Farmers are inclined to use fungicides to protect their crops; however, the efficacy of these measures is rapidly decreasing due to the natural mechanisms of mutation emergence in pathogen populations. Increasing fungicide resistance is being recorded worldwide, therefore, screening of the current situation in Lithuania is essential to determine the subsequent steps of crop protection strategies. In this study, in vitro fungicide sensitivity tests, mutation detection, and field experiments were carried out. The mean EC50 values for prothioconazole-desthio and mefentrifluconazole were 0.14 and 0.28 mg/l, respectively. Increased frequency of the mutation S524T, linked to DMIs resistance, was observed. Results revealed that the dominant point mutation in the gene CYP51 was I381V, and the most frequent CYP51 haplotype was D13 (V136C, I381V, Y461H, S524T). The mutation G143A, linked to QoI resistance, was detected in ¾ of the population. Mutations conferring resistance to SDHIs were not detected in single pycnidium isolates. Two-year field experiments likewise showed no decline in field efficacy of SDHI fungicide in Lithuania. Moreover, the baseline sensitivity of the Lithuanian Z. tritici population to QiI fungicide fenpicoxamid was established. The findings of this study provide an update on the current status of fungicide resistance in the Lithuanian Z. tritici population.

Plasticity of the MFS1 promotor is not the only driver of Multidrug resistance in Zymoseptoria tritici

“…In total, our study has identified six new inserts (type IID to F, type VI to VIII) within the MFS1 promoter region. This increases the total count of inserts found in this region to 13 when considering previous research (Omrane et al, 2017; Mäe et al, 2020; Lavrukaitė et al, 2023). The high frequency of inserts in P MFS1 suggests that the zone of 360 bp, located between -108 and – 468 relative to the start codon, is a hotspot for insertions.…”

“…Table 1 summarizes the current knowledge of MFS1 promoter inserts from previous (Lavrukaitė et al, 2023;Mäe et al, 2020;Omrane et al, 2017) and the present study. We have arbitrarily numbered all known and sequenced inserts chronologically according to the date of their discovery.…”

“…From 2008 to 2017, the landscape of MDR strains was predominantly dominated by the genotype harboring the type I allele (75%) (Garnault et al 2019). In 2018 and 2021 respectively, new inserts (furtheron named type IV and V inserts) were found but were not associated with the MDR phenotype (Lavrukaitė et al 2023; Mäe et al 2020). A population survey using PCR around the previously identified MFS1 promoter inserts revealed an unsuspected P MFS1 allele diversity (at least 8 different amplicon sizes; Huf et al, 2020).…”

“…In the field, multidrug resistance (MDR) detection is commonly achieved through genotyping using endpoint PCR (Huf et al, 2018; Lavrukaitė et al, 2023; Mäe et al, 2020; Omrane et al, 2017). However, the reliability of a single PCR method in accurately identifying MDR without the occurrence of false negatives or false positives is of critical concern.…”

Sensitivity of Lithuanian Zymoseptoria tritici to Quinone Outside Inhibitor and Succinate Dehydrogenase Inhibitor Fungicides

“…The presence of these mutations at the Qo site, and hence resistance to QoI fungicides, is widespread, leading to a decline in their use against this disease in Europe and the United States of America [9][10][11]. However, in Lithuania and other Northeastern European countries, QoI fungicides are still moderately effective and are therefore used to control STB and other diseases [12,13].…”