It’s holiday time and while most folks have visions of sugar-plums dancing in their heads, my mind takes a detour to the dark side as I think of how plant pathogens can influence the holidays. Interestingly, the examples that first come to my mind are positive influences on the holiday season.
Poinsettias anyone? If you are lover of brightly-colored poinsettias and enjoy them sitting on tables in your home, you have a plant pathogen to thank for the look of most modern poinsettia varieties. In their native, tropical habitat, poinsettias have an upright tree-like form, and grow up to 10 ft. in height. Modern, ornamental varieties of poinsettias are infected with phytoplasmas, bacteria-like organisms that colonize the phloem (i.e, the food-conducting “piping”) inside the plant. The presence of phytoplasmas leads to a stunted, compact growth form with lots of extra branching. And guess what you get with all of that branching? You got it: lots and lots of flowers.
Hitting the slopes. If you are a skier and hate the thought of dry, snowless winter, don’t despair. There is a plant pathogen that can come to your rescue. When Mother Nature doesn’t cooperate and you’re speeding down the slopes on artificial snow, take a minute at the end of your run to talk to the owner of your favorite ski slope about how the artificial snow is made. Chances are he/she is using a product called Snomax®. The active ingredient in Snomax® is a protein derived from Pseudmonas syringae pv. syringae, a bacterial pathogen involved diseases such as bacterial blight of lilac, bacterial canker of stone fruits and bacterial brown spot of snap beans (a personal favorite given that this disease was the subject of my PhD thesis). So while Pseudmonas syringae pv. syringae can wreak havoc in the summer, it can atone for its sins in the winter by helping provide a snowy wonderland for skiers to enjoy.
Pathogenic kiss? As you stand under the mistletoe canoodling with your sweetie this holiday season, consider exactly what it is that you are standing under. Mistletoes (there are lots of different kinds) are parasitic seed plants that infect their hosts (usually some type of tree or shrub) and siphon off water, minerals and sugars (as well as other organic compounds) that they use to grow and reproduce. The typical “holiday” mistletoe is leafy and green and can photosynthesize, so it is not totally reliant on its host for all of its nutritional needs. Other mistletoes are devoid of chlorophyll (the green pigment involved in photosynthesis) and are totally reliant on their parasitized host for water and nutritients. Whichever mistletoe you choose to hang from the rafters, remember the sacrifice of its parasitized host each time you enjoy a clandestine kiss from a loved one.
With that, enjoy the holiday season and I’ll see you with my next article in the new year.
To learn more about common diseases and disease management, explore the Plant Disease Diagnostics Clinic (PDDC) website (https://pddc.wisc.edu/) and in particular, check out the University of Wisconsin Garden Facts fact sheets that can be found there. Also, follow the PDDC on Facebook and Twitter @UWPDDC to receive updates on emerging diseases and their management.