Within-season changes in Alternaria solani populations in potato in response to fungicide application strategies

Firuz Odilbekov,Eva Edin,Laura J Grenville-Briggs,Hilde Coolman,Erland Liljeroth,Hadis Mostafanezhad

doi:10.1007/s10658-019-01826-8

Firuz Odilbekov, Eva Edin + Show 4 more

Open Access

https://doi.org/10.1007/s10658-019-01826-8

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Abstract

Early blight, caused by the fungus Alternaria solani, is a common foliar disease in potato. Quinone outside inhibitor (QoIs) fungicides have commonly been used against A. solani. To avoid or delay development of fungicide resistance it is recommended to alternate or combine fungicides with different modes of action. Therefore, we compared two different fungicide programs against early blight in field trials and studied within season changes in the pathogen population. An untreated control was compared with treatments using azoxystrobin alone and with a program involving difenoconazole followed by boscalid and pyraclostrobin combined. Isolates of A. solani were collected during the growing season and changes in the population structure was investigated. We also screened for the amino acid substitution in the cytochrome b gene and investigated changes in sensitivity to azoxystrobin. Treatment with azoxystrobin alone did not improve disease control in 2014 when the disease pressure was high. However, lower severity of the disease was observed after combined use of difenoconazole, boscalid and pyraclostrobin. The efficacy of both fungicide treatments were similar during the field trial in 2017. Two mitochondrial genotypes (GI and GII) were found among isolates, where all isolates, except two, were GII. All GII isolates had the F129 L substitution while the two GI isolates were wild type. Population structure analysis and principal component analysis (PCA) of amplified fragment length polymorphisms (AFLP) data revealed within season changes in the A. solani populations in response to fungicide application. Isolates with the F129 L substitution had reduced sensitivity to azoxystrobin in vitro and their sensitivity tended to decrease with time.

Highlights

The genus Alternaria is found in a wide range of environments worldwide
Treatment 0: Samples were collected randomly from the field before all treatments untreated control (UTR) Untreated control, but treated against late blight TR1 Treatment 1: Difenoconazole two times followed by four times boscalid and pyraclostrobin combined TR2 Treatment 2: Azoxystrobin two times GI genotype I wild type a genotype II with F129 L substitution - Not determined DAP days after planting when the fungicide was sprayed on methods described by Edin (2012) and for identification of the GII genotype primers developed by Pasche et al (2005) were used
The population of A. solani in the investigated fields was dominated by isolates with the F129 L substitution and only two wild-type isolates were found among the investigated isolates from both years

Summary

Introduction

One of the most economically important members of the genus is Alternaria solani Due to heavy defoliation during epidemics, the disease can cause major yield losses (Shtienberg et al 1990; Rotem 1994; Leiminger and Hausladen 2014). This fungus is commonly found in commercial potato production fields in Sweden. Personal communications with potato growers and advisors confirmed the increasing problems and Edin et al (2019) confirmed in their study that A. solani is the causal agent of early blight in southeastern Sweden

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