Location: Sugarbeet and Bean ResearchTitle: Studies on a major Alternaria sp. causing Alternaria leaf spot of sugar beet
|JAYAWARDANA, MALINI - Michigan State University|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2022
Publication Date: 11/1/2022
Citation: Hanson, L.E., Jayawardana, M.A. 2022. Studies on a major Alternaria sp. causing Alternaria leaf spot of sugar beet [abstract]. Plant Health 2022. 112(11s):S3.46. https://doi.org/10.1094/PHYTO-112-11-S3.1.
Technical Abstract: Alternaria leaf spot of sugar beet has been a minor issue in the United States for decades, although it has been a serious issue in some other parts of the world. In 2015-2019 it became a more serious issue in Michigan, with estimates of up to 30% of foliar losses on beet being due to this disease. This raises questions about the genetics of the pathogen and potential sources for disease in beet. The major reported pathogens include Alternaria alternata, Alternaria brassicae, and A. tenuissima (now A. alternata). To investigate the situation in Michigan, samples were collected from fields where the disease was a problem and compared to a small number of isolates collected before it was a serious issue. In addition, isolates were compared to strains from other crops grown in the region such as dry bean, potato, blueberry, and apple. All strains collected during this study fit the morphological description of A. tenuissima but fell into multiple genetic groups. These included three genetic clades previous reported as A. alternata subspecies arborescens and A. alternata subspecies alternata, but none of the isolates were in the genetic clade A. alternata subspecies tenuissima. Additional genetic clades were found but there was not clear separation between the host from which isolates were collected and specific genetic clades for sugar beet or potato, and all isolates were able to cause disease on potato, tomato, and sugar beet in laboratory assays. No significant differences were found between isolates collected before the disease became a serious issue in the region and those collected in recent years. This supports the wide host range of this pathogen and provides. Further testing for susceptibility genes, as has been proposed by breeders, is ongoing.