Epidemiology and management of blackleg of canola in response to changing farming practices in Australia

Wouw, Angela P. Van de; Marcroft, S. J.; Sprague, S. J.; Scanlan, Jack L.; Vesk, Peter A.; Idnurm, Alexander

doi:10.1007/s13313-020-00767-9

Cited by 18 publications

(26 citation statements)

References 76 publications

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“…Late sowing of winter wheat decreases the risk of a severe Z. tritici epidemic, but can increase the risk of powdery mildew and yellow rust (Jørgensen et al, 2014). Removal of crop debris can reduce the inoculum of pathogens including Z. tritici in wheat (McDonald & Mundt, 2016) and Leptosphaeria maculans in oilseed rape (Van de Wouw et al, 2021), whereas minimum tillage may be better for suppression of the wheat diseases spot blotch Bipolaris sorokiniana and take-all Gaeumannomyces tritici (Montanari et al, 2006). Biosecurity measures to prevent the spread of invasive diseases may also contradict resistance management guidelines if the aim is elimination rather than minimal treatment, for example requiring treatment of all imported seed (Van de Wouw et al, 2021).…”

Section: Prin Ciple Ver Sus Pr Ac Ti Cementioning

confidence: 99%

“…For example, fungicide seed treatments can contribute to selection for resistance (Brent et al, 1989; Porter et al, 2009) and therefore count as an additional fungicide application for resistance management purposes (Kitchen et al, 2016), and so like any other fungicide treatment they should be applied only where the disease pressure necessitates their use (Lamichhane et al, 2019). However, farmers may not have the choice to use untreated seeds, for example in Australia where some imported seeds must be fungicide‐treated as a biosecurity measure (Van de Wouw et al, 2021). Regulations also restrict the range of fungicides available, such that the recommended degree of mixture and alternation may not be possible.…”

Section: Principle Versus Practicementioning

confidence: 99%

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Fungicide resistance management: Maximizing the effective life of plant protection products

2021

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Over a third of potential crop production worldwide is lost preharvest to pests and diseases (Oerke & Dehne, 2004), with pathogenrelated spoilage also contributing to postharvest food waste.Without effective crop protection, it has been estimated that preharvest losses would double (Popp et al., 2013).Crop protection against plant pathogens relies heavily on fungicide use in addition to varietal resistance. However, repeated use of single-site fungicides with the same mode of action (MoA) can lead to the evolution of resistance. The total economic cost of resistance against all pesticides in the United States was calculated at $1.5 billion in 2005, primarily due to additional pesticide use in order to control pests resistant to previously effective treatments (Pimentel, 2005).The first site-specific fungicides were the methyl benzimidazole carbamates (MBCs), and in their 50 years of use, resistance has been reported in almost 100 plant pathogen species (FRAC, 2020b;Hawkins & Fraaije, 2016). In some pathogens, resistance emerged after just 2 years of fungicide use (Grimmer et al., 2015). Azole resistance has been reported in 30 plant pathogens (FRAC, 2020b),

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Section: Prin Ciple Ver Sus Pr Ac Ti Cementioning

confidence: 99%

Section: Principle Versus Practicementioning

confidence: 99%

Fungicide resistance management: Maximizing the effective life of plant protection products

2021

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“…The impact of blackleg disease can be minimized through the use of cultural, chemical, and genetic approaches. Cultural practices such as rotation of crops and isolation from the previous year's stubble can significantly reduce disease (Marcroft et al, 2003 , 2004 ); however, in regions such as Australia, these approaches are becoming difficult to achieve due to increases in canola production (Van de Wouw et al, 2021 ). Fungicides can minimize blackleg disease with applications possible at seeding, four‐ to six‐leaf, and 30% bloom growth stages (Peng et al, 2020 ; Van de Wouw et al, 2016 , 2021 ).…”

Section: Introductionmentioning

confidence: 99%

“…Fungicides are available worldwide for control of blackleg disease, with growers in Australia using at least one fungicide on approximately 90% of crops (Van de Wouw et al, 2021).…”

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confidence: 99%

Independent breakdown events of the Brassica napus Rlm7 resistance gene including via the off‐target impact of a dual‐specificity avirulence interaction

Wouw

Sheedy

Ware³

et al. 2022

Molecular Plant Pathology

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Protection of many crops is achieved through the use of genetic resistance. Leptosphaeria maculans, the causal agent of blackleg disease of Brassica napus, has emerged as a model for understanding gene‐for‐gene interactions that occur between plants and pathogens. Whilst many of the characterized avirulence effector genes interact with a single resistance gene in the host, the AvrLm4‐7 avirulence gene is recognized by two resistance genes, Rlm4 and Rlm7. Here, we report the “breakdown” of the Rlm7 resistance gene in Australia, under two different field conditions. The first, and more typical, breakdown probably resulted from widescale use of Rlm7‐containing cultivars whereby selection has led to an increase of individuals in the L. maculans population that have undergone repeat‐induced point (RIP) mutations at the AvrLm4‐7 locus. This has rendered the AvrLm4‐7 gene ineffective and therefore these isolates have become virulent towards both Rlm4 and Rlm7. The second, more atypical, situation was the widescale use of Rlm4 cultivars. Whilst a single‐nucleotide polymorphism is the more common mechanism of virulence towards Rlm4, in this field situation, RIP mutations have been selected leading to the breakdown of resistance for both Rlm4 and Rlm7. This is an example of a resistance gene being rendered ineffective without having grown cultivars with the corresponding resistance gene due to the dual specificity of the avirulence gene. These findings highlight the value of pathogen surveillance in the context of expanded knowledge about potential complexities for Avr–R interactions for the deployment of appropriate resistance gene strategies.

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“…Fungicide use in canola crops has increased in Australia over the past 20 years; a survey by Van de Wouw et al (2021) found that 95% of canola growers currently use fungicides, versus only 52% in the 2000. This shift towards almost universal use of fungicides has been driven by changes such as increased area sown to canola and tighter rotations, which limit the ability for growers to employ cultural practices that can minimise blackleg disease, such as sowing into paddocks that are isolated from previous years' stubble (Van de Wouw et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Fungicide sensitivity and resistance in the blackleg fungus,

Wouw

Scanlan

Marcroft

et al. 2021

Crop & Pasture Science

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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.

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Epidemiology and management of blackleg of canola in response to changing farming practices in Australia

Cited by 18 publications

References 76 publications

Fungicide resistance management: Maximizing the effective life of plant protection products

Fungicide resistance management: Maximizing the effective life of plant protection products

Independent breakdown events of the Brassica napus Rlm7 resistance gene including via the off‐target impact of a dual‐specificity avirulence interaction

Fungicide sensitivity and resistance in the blackleg fungus,

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