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

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.

Intact salicylic acid signalling is required for potato defence against the necrotrophic fungus Alternaria solani

“…A recent study showed that early blight is one of only four pests and pathogens affecting potato production that causes global crop losses higher than one percent (2.6%; Savary et al 2019 ). Currently, early blight is controlled by the application of fungicides, even though fungicidal resistance in A. solani populations has been reported in several countries (Rosenzweig et al 2008 ; Leiminger et al 2014 ; Odilbekov et al 2016 , 2019 ). Additionally, a lack of identified resistance genes combined with a corresponding lack of resistant varieties, together with limited knowledge of the mechanisms of defence against A. solani , contribute to a severe disease problem.…”

Genome-wide identification of Argonautes in Solanaceae with emphasis on potato

“…Desirée) were inoculated with Phytophthora infestans strain NL11388 as earlier described 44 . Leaf inoculations using 10 µl of a 20 × 10 4 spores/ml water of the fungus Alternaria solani, strain 142.2 collected from a field in Nymö, located in southern Sweden 56 were also performed. Sterile water was used as control.…”

Elevation of Systemic Defense in Potato Against Alternaria Solani by a Consortium of Compatible Trichoderma Spp.

“…During the years the disease has been managed by a regular application of synthetic chemicals on the seed treatment as well as foliar spray, but these are not long-term solutions since the pathogen population has developed resistance against these chemicals (Edin et al, 2019;Odilbekov et al, 2019). Therefore, a green and environmentally safe solution is needed to increase defense response in potato plants The use of bene cial microorganisms as biological control agents (BCAs) including T. viride, T. harzianum, Bacillus subtilis, Pseudomonas uorescens, Streptomyces graseoviridis, and Paenibacillusm acerans for inducing defense response in potato plants against A. solani has been applied for some years ago (Murmuet al, 2015;Zhang et al, 2020).…”