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Dose and number of applications that maximize fungicide effective life exemplified by Zymoseptoria tritici on wheat - a model analysis.

ABSTRACT: Two key decisions that need to be taken about a fungicide treatment programme are (i) the number of applications that should be used per crop growing season, and (ii) the dosage that should be used in each application. There are two opposing considerations, with control efficacy improved by a higher number of applications and higher dose, and resistance management improved by a lower number of applications and lower dose. Resistance management aims to prolong the effective life of the fungicide, defined as the time between its introduction onto the market for use on the target pathogen, and the moment when effective control is lost due to a build-up of fungicide resistance. Thus, the question is whether there are optimal combinations of dose rate and number of applications that both provide effective control and lead to a longer effective life. In this paper, it is shown how a range of spray programmes can be compared and optimal programmes selected. This is explored with Zymoseptoria tritici on wheat and a quinone outside inhibitor (QoI) fungicide. For this pathogen-fungicide combination, a single treatment provided effective control under the simulated disease pressure, but only if the application timing was optimal and the dose was close to the maximum permitted. Programmes with three applications were generally not optimal as they exerted too much selection for resistance. Two-application fungicide programmes balanced effective control with reasonable flexibility of dose and application timing, and low resistance selection, leading to long effective lives of the fungicide.

SUBMITTER: van den Berg F

PROVIDER: S-EPMC5027893 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Dose and number of applications that maximize fungicide effective life exemplified by <i>Zymoseptoria tritici</i> on wheat - a model analysis.

van den Berg F F Paveley N D ND van den Bosch F F

Plant pathology. 20160610 8

Two key decisions that need to be taken about a fungicide treatment programme are (i) the number of applications that should be used per crop growing season, and (ii) the dosage that should be used in each application. There are two opposing considerations, with control efficacy improved by a higher number of applications and higher dose, and resistance management improved by a lower number of applications and lower dose. Resistance management aims to prolong the effective life of the fungicide, ...[more]

PMID: 27708459

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Project description:Zymoseptoria tritici is a globally distributed fungal pathogen which causes Septoria tritici blotch on wheat. Management of the disease is attempted through the deployment of resistant wheat cultivars and the application of fungicides. However, fungicide resistance is commonly observed in Z. tritici populations, and continuous monitoring is required to detect breakdowns in fungicide efficacy. We recently reported azole-resistant isolates in Australia; however, it remained unknown whether resistance was brought into the continent through gene flow or whether resistance emerged independently. To address this question, we screened 43 isolates across five Australian locations for azole sensitivity and performed whole-genome sequencing on 58 isolates from seven locations to determine the genetic basis of resistance. Population genomic analyses showed extremely strong differentiation between the Australian population recovered after azoles began to be used and both Australian populations recovered before azoles began to be used and populations on different continents. The apparent absence of recent gene flow between Australia and other continents suggests that azole fungicide resistance has evolved de novo and subsequently spread within Tasmania. Despite the isolates being distinct at the whole-genome level, we observed combinations of nonsynonymous substitutions at the CYP51 locus identical to those observed elsewhere in the world. We observed nine previously reported nonsynonymous mutations as well as isolates that carried a combination of the previously reported L50S, S188N, A379G, I381V, Y459DEL, G460DEL, and N513K substitutions. Assays for the 50% effective concentration against a subset of isolates exposed to the tebuconazole and epoxiconazole fungicides showed high levels of azole resistance. The rapid, parallel evolution of a complex CYP51 haplotype that matches a dominant European haplotype demonstrates the enormous potential for de novo resistance emergence in pathogenic fungi.IMPORTANCE Fungicides are essential to control diseases in agriculture because many crops are highly susceptible to pathogens. However, many pathogens rapidly evolve resistance to fungicides. A large body of studies have described specific mutations conferring resistance and have often made inferences about the origins of resistance based on sequencing data from the target gene alone. Here, we show the de novo acquisition of resistance to the ubiquitously used azole fungicides in genetically isolated populations of the wheat pathogen Zymoseptoria tritici in Tasmania, Australia. We confirm evidence for parallel evolution through genome-scale analyses of representative worldwide populations. The emergence of complex resistance haplotypes following a well-documented recent introduction of azoles into Australian farming practices demonstrates how rapidly chemical resistance evolves in agricultural ecosystems.

Dataset Information

Dose and number of applications that maximize fungicide effective life exemplified by Zymoseptoria tritici on wheat - a model analysis.

Publications

Dose and number of applications that maximize fungicide effective life exemplified by <i>Zymoseptoria tritici</i> on wheat - a model analysis.

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