Fungicide sensitivity and resistance in the blackleg fungus,

Abstract

Fungicide use has become a fundamental part of many crop protection systems around the world, including to control blackleg disease on canola (Brassica napus L.). In Australia, most canola growers routinely apply at least one fungicide, and potentially multiple fungicides with different modes of action, in a single growing season. There is evidence for the emergence of fungicide resistance in Leptosphaeria maculans, the causal agent of blackleg disease, to the demethylation inhibitor (DMI) class of fungicides in Australia. However, it is not known whether resistance exists towards other chemical classes such as the succinate dehydrogenase inhibitors (SDHI). In this work, 397 samples were screened for resistance towards seven fungicide treatments in stubble-borne L. maculans populations collected from eight canola-growing agro-ecological regions of Australia from 2018 to 2020, a time frame that bridges the introduction of new chemicals for blackleg control. We confirmed that DMI resistance in L. maculans is pervasive across all of the sampled canola-growing regions, with 15% of fungal populations displaying high levels (resistance scores >0.5) of resistance towards the DMI fungicides. Although resistance to newly introduced SDHI fungicides was low, we found evidence of positive cross-resistance between established DMIonly fungicides and a newly introduced combined DMI and quinone outside inhibitor fungicide, suggesting that the efficacy of the latter may be limited by widespread DMI resistance. Proactive surveillance, as performed here, may provide a means to avoid the rapid loss of fungicide efficacy in the field.

Identification of candidate genes for LepR1 resistance against Leptosphaeria maculans in Brassica napus

“…LepR1 can also be an significant source of blackleg resistance for the cultivars in Australia, which has virulent L. maculans population causing the breakdown of the cultivars containing R gene like LepR3 and ineffectiveness of R genes like Rlm1 and Rlm3 ( Li et al., 2005 ; Van de Wouw et al., 2014 ; Van de Wouw et al., 2021 ). Other studies have also shown that cultivars with LepR1 are more effective than those with R genes Rlm1, Rlm3, Rlm4 , and LepR3 ( Alnajar et al., 2022 ; Rashid et al., 2022 ).…”

Emergence of Fungicide Sensitivity in Leptosphaeria maculans Isolates Collected from the Czech Republic to DMI Fungicides

“…Nevertheless, DMIs are categorized as medium-risk fungicides by FRAC. There have only been a few studies on resistance to fungicides, which have been mostly focused on L. maculans sensitivity to strobilurins (quinone outside inhibitor; QoI) [32,33] and other DMI fungicides [20][21][22]24,34]. However, similar to other phytopathogenic fungi [35][36][37][38][39][40][41], resistance to DMI fungicides in L. maculans has also been documented [21,22].…”

“…This made it difficult to determine the sensitivity of the isolates to these fungicides based on mean EC 50 alone. However, this is not surprising because none of the other studies were based on the sensitivity of L. maculans isolates to tetraconazole, metconazole, and prochloraz, but rather to flusilazole, fluquinconazole, prothioconazole, and tebuconazole [20][21][22]24,34]. Resistance to DMI fungicides is quantitative, meaning it develops in a stepwise gradual progression [18].…”

BioClay™ prolongs RNA interference‐mediated crop protection against Botrytis cinerea

“…Current fungal disease management strategies are largely reliant on the use of chemical fungicides, host resistance and cultural practices such as crop rotation. However, fungicide usage can lead to the target species developing resistance and synthetic fungicides can be harmful to humans, beneficial organisms and the broader environment (Van de Wouw et al, 2021). Alarmingly, fungicide‐resistant fungal strains have been reported for every major class of antifungals used in agriculture (Fisher et al, 2018).…”