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ARS Home » Midwest Area » East Lansing, Michigan » Sugarbeet and Bean Research » Research » Publications at this Location » Publication #399434

Research Project: Genetic Characterization for Sugar Beet Improvement

Location: Sugarbeet and Bean Research

Title: Diversity of Alternaria alternata, causal agent of Alternaria leaf spot of sugar beet

item Hanson, Linda
item JAYAWARDANA, MALINI - Michigan State University
item MINIER, DOUGLAS - Michigan State University

Submitted to: Journal of Sugar Beet Research
Publication Type: Abstract Only
Publication Acceptance Date: 1/30/2023
Publication Date: 2/26/2023
Citation: Hanson, L.E., Jayawardana, M.A., Minier, D.H. 2023. Diversity of Alternaria alternata, causal agent of Alternaria leaf spot of sugar beet [abstract]. Journal of Sugar Beet Research. 60(2):24-25.

Interpretive Summary:

Technical Abstract: Alternaria leaf spot of sugar beet has long been a minor issue in the United States. Recently in Michigan, the disease incidence increased, with up to 30% of leaf spot damage in 2016-2019 associated with Alternaria leaf spot. To better understand the pathogen, isolates were collected in the field and compared to isolates collected before 2012. Isolates from sugar beet also were compared to strains collected on rotation crops, such as potato and dry bean, and other plants with Alternaria symptoms in the region. All Alternaria isolates were morphologically similar to Alternaria tenuissima, producing small conidia in largely unbranched chains. However, as recently reported, isolates could not be genetically separated from A. alternata (small conidia in branched chains) using a multi-gene sequencing approach. Using this phylogeny, isolate formed at least three clades within A. alternata, and did not cluster with isolates previously suggested as a subspecies tenuissima. The results agree with previous reports that morphological differences do not reliably relate to genetic variability within this species. Isolates originally from sugar beet, dry bean, potato, and blueberry all caused lesions on sugar beet leaves, with no significant differences between severity related to original host. Isolates were found in the same genetic groups from 2005-2011 and 2016-2019. Thus, no evidence was observed for a change in the fungal population associated with the increased disease in the region. These isolates also grouped with isolates from dry bean, potato, blueberry, and previously published strains from apple and pear. The results support potential for A. alternata to infect sugar beet from a diverse range of crops.