RT Dissertation/Thesis
T1 Characterisation of the sensitivity of Zymoseptoria tritici to demethylation inhibitors in Europe 
A1 Huf,Anna
WP 2021/06/07
AB The fungal pathogen Zymoseptoria tritici (formerly Septoria tritici) causes Septoria tritici blotch (STB), one of the most yield reducing diseases of wheat worldwide. In addition to cultural control measures and the cultivation of wheat varieties with a level of disease resistance, STB control relies heavily on the application of foliar fungicides with different modes of action. The demethylation inhibitors (DMIs) have been one of the most widely applied fungicides for many decades and belong to one of the most important fungicide modes of action in STB management. DMIs inhibit the sterol 14α-demethylase, an essential enzyme in the ergosterol biosynthesis pathway, encoded by the CYP51 gene of fungi. Widespread and intensive use of the DMIs over time has led to a continuous negative shift in the sensitivity of Z. tritici towards DMIs that have been used for a long time. This shift in sensitivity is mainly driven by the accumulation of mutations in the CYP51 gene resulting in the selection of various CYP51 haplotypes. More recently, CYP51 overexpression and an increased efflux activity, based on the overexpression of the MFS1 transporter, have been shown to be additional mechanisms affecting DMI sensitivity of Z. tritici. Inserts in the CYP51 promotor (CYP51p) and MFS1 promotor (MFS1p) were observed to be responsible for CYP51 and MFS1 overexpression. The prevalence and contribution of different DMI resistance mechanisms to a reduced DMI sensitivity of Z. tritici were investigated in isolates from across Europe in 2016 and 2017. The CYP51 gene of all isolates was sequenced and the CYP51p and MFS1p was investigated for inserts in order to determine the character of the CYP51 haplotypes as well as to identify CYP51 overexpression or if an increased efflux activity was occurring in these isolates.  
Overall, it was shown that the occurrence of CYP51 haplotypes was still the most frequent and important mechanism conferring a reduction in sensitivity to DMIs by Z. tritici in Europe. Nevertheless, an increase in the frequency of isolates exerting CYP51 overexpression and those exhibiting increased efflux activity was observed compared to earlier studies. Glasshouse data demonstrated that DMIs can still contribute to disease control, and in some cases give full control, of STB even if isolates expressed CYP51 overexpression and/or an increased efflux in addition to also carrying moderately or highly adapted CYP51 haplotypes. However, in order to prevent the further increase and spread of further adapted CYP51 haplotypes plus additional resistance mechanisms in the Z. tritici population across Europe, anti-resistance-management strategies should be a high priority in the use of DMIs. In addition, especially integrated disease management strategies, such as the appropriate choice of cultivars, should be applied in order to keep STB disease pressure low and consequently reduce the number of fungicide applications. Moreover, resistance-management strategies may exploit the limited cross-resistance between different DMIs, for example, by the use of mixtures or alternation of different DMI fungicides. However, control strategies should also incorporate the use of fungicides with different MOAs. The aim of all these strategies is to reduce selection of adapted Z. tritici isolates and consequently to prolong the efficacy of DMIs in STB management. 

K1 Pflanzenschutz
K1 Fungizid
K1 Septoria tritici
K1 Resistenz
PP Hohenheim
PB Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
UL http://opus.uni-hohenheim.de/volltexte/2021/1891