Happy Thanksgiving! For Americans, Thanksgiving usually means one thing above all else: turkey. But when I think of turkey, I don’t think of food, or even of the bird … instead, I think of a common fungus that’s all around us.
It’s amazing how first impressions can stick. In my introductory plant pathology course in college, the TA told us that Alternaria conidia (asexual spores) reminded him of drumsticks. Ever since then, that’s all I can see when I’m looking at these spores. Alternaria spores are produced in chains; if you click on the top picture, you should be able to see 7 Alternaria spores, with the middle one outlined to show its drumstick shape.
Alternaria is an interesting fungus, as there are both pathogenic and saprophytic species. Pathogens can infect healthy plants and cause disease. Saprophytes break down dead or dying material. We’re lucky such organisms exist; without them, nothing would ever degrade and every dead tree, fallen leaf, and grass clipping through history would still be with us, cluttering up our space. Distinguishing between the different species of Alternaria and determining if what you’ve found on a sample is a pathogen causing a problem, or just a saprophyte happy to consume dying cells, can be difficult. One characteristic of diseases caused by Alternaria fungi is that the lesions tend to have a bulls-eye pattern. The fungus spreads outwards from the initial infection and, as it spreads, it kills cells and begins to produce spores. This repeating pattern of dead cells and sporulation causes concentric bands to form, giving the lesion an overall bulls-eye pattern.
Early Blight on tomato, caused by Alternaria solani. Note the concentric rings in the brown lesion on the stem.
I’m thankful that every day I get to work with plant diseases, both helping clients manage plant pathogens and keep their plants healthy, but also getting the opportunity to enjoy the minute beauty of nature, in all its forms.