Fungicide Sensitivity Monitoring of Alternaria spp. Causing Leaf Spot of Sugarbeet (Beta vulgaris) in the Upper Great Lakes

Abstract

Alternaria leaf spot (ALS), caused by Alternaria spp., can occur wherever sugarbeet is grown. Infection by Alternaria spp. and disease management has historically been considered a minor issue in sugarbeet production in the United States. An increase of both incidence and severity in 2016 of ALS high enough to cause yield loss has been observed in Michigan. With a renewed need to consider potential management of this disease, the sensitivity was determined for populations of Alternaria spp. to three classes of fungicides currently labeled for management of leaf spot on sugarbeet, including demethylase inhibitor (DMI), quinone outside inhibitor (QoI), and organo-tin fungicides. Leaves with symptoms of ALS were sampled from sugarbeet fields in east-central Michigan and southwestern Ontario, Canada. Monoconidial isolates were obtained to determine sensitivity to each fungicide class above. A spiral gradient dilution method was used to estimate the fungicide effective concentration (in milligrams per liter) that caused a 50% inhibition of fungal growth in vitro for all isolates. Significant temporal shifts were detected in the frequencies of sensitivity phenotypes to DMI and QoI but not organo-tin fungicides from 2016 through 2017. Individual isolates of Alternaria spp. were recovered with cross-resistance to DMI and multiple resistance to DMI, QoI, and triphenyltin hydroxide fungicides. To our knowledge, this is the first report of a fungus other than Cercospora beticola with resistance to organo-tin fungicides. Fungicide sensitivity monitoring indicates that an effective integrated disease management approach combining fungicide efficacy trials and monitoring pathogen biology is essential for developing effective resistance management recommendations.

Antifungal Activity of Thirty Essential Oils to Control Pathogenic Fungi of Postharvest Decay

“…Because of the tolerance observed in Alternaria spp. populations to different fungicides (QoIs, benzimidazole, fludioxonil, cyprodinil, boscalid, and pyraclostrobin) [39][40][41], it was suggested the need to study Alternaria isolates not previously exposed to fungicides to have a better estimate of the shifts in sensitivity [42]. Here, we have used different sources of EOs not previously applied as fungicides on A. alternata, and yet this tolerance was well observed.…”

First Record of Alternaria pogostemonis: A Novel Species Causing Leaf Spots in Pogostemon cablin

“…Alternaria , consisting of hundreds of species, is considered one of the most critical phytopathogens affecting plant tissues, including leaves, cereal grains, fruits, and vegetables [ 32 , 33 , 34 , 35 ]. It has been recorded as a critical fungal pathogen because of its worldwide occurrence on various hosts [ 32 , 33 , 34 , 35 ].…”

Characterization of the Molecular Mechanisms of Resistance against DMI Fungicides in Cercospora beticola Populations from the Czech Republic

“…Research and better understanding of the fungicide resistance mechanisms, mediating this sensitivity reduction will be helpful for a sustainable and appropriate disease and fungicide-resistance management. However, despite of the effectiveness of these fungicides, lack of effective pest management strategies along with overreliance on DMIs have led to the evolution of fungicide resistance in plant pathogenic fungi including C. beticola populations, globally [8,20,29,38,39].…”