University Distinguished Professor Michigan State University East Lansing, MI, USA
Abstract Text: Plant pathogens infecting potted culinary herbs have gone largely understudied in the U.S. despite an increase in herb demand by consumers over the last decade. Our objective was to identify the plant pathogens frequently associated with greenhouse-grown potted herbs. In 2024, forty-four symptomatic plants were collected from two Michigan greenhouses. Samples consisted of twelve herb species including basil, lavender, rosemary, oregano, marjoram, mint, fennel, dill, sage, lemon verbena, chervil and lemongrass. Foliar symptoms observed on plant samples included chlorosis, leaf spots, necrotic lesions, foliar discoloration, and necrotic leaf tips. Root rot symptoms observed included root discoloration and root stunting and dieback. Plant samples including basil, rosemary, oregano, marjoram, chervil and sage exhibited foliar and root rot symptoms. Mint, dill, parsley and lemon verbena exhibited only foliar disease symptoms. Fennel samples displayed root rot symptoms, but the foliage appeared healthy. Fifty isolates were obtained and hyphal tipped (3X) to obtain pure cultures. Morphological characteristics were used to identify isolates to genus and Sanger sequencing conducted. Phytophthora spp., Pythium spp., Xanthomonas spp. and Botrytiscinerea were most commonly obtained. Koch’s postulates were conducted. All herbs sampled yielded pathogenic isolates, but basil, marjoram and lavender yielded the most. Identifying plant pathogens commonly associated with herbs will facilitate future development of effective disease control strategies.
