Potential allelopathic interactions from canola and pennycress postharvest roots and stubble

Winter oilseed Brassica plants have several documented allelochemicals; however, most literature revolves around the application of seed meal to fields, or the use of aerial parts of the plant. It is not clear if these chemicals interact with the surrounding environment to the same extent if the winter oilseeds are harvested as a cash crop in the spring. To determine this, we conducted a preliminary study bioassay using water extractable compounds from canola (Brassica napus L.) and pennycress (Thlaspi arvense L.) roots diluted to 25 and 50% (v/v). These four extracts, as well as deionized water for control, were used to irrigate plates with the seeds of soybean (Glycine max L.), Palmer amaranth [Amaranthus palmeri (S.) Watson], and mare's tail (Erigeron canadensis). We measured germination percent per plate and seedling radicle and hypocotyl lengths after 8 days of treatment. Mare's tail germination was lowered by 40% on day 4 by 50% pennycress extracts, and root length was stunted by both canola and pennycress extracts by 3-5 mm. Palmer amaranth root length was stunted by 10-15 mm by both species' extracts, as well as shoots lengthened by 5-10 mm. Extract treatments did not affect soybean germination or growth. These interactions indicate potential for allelopathic interactions in the field following harvest of dual cropped winter oilseed and herbicide-resistant weeds and warrant further study into the topic. Water extractable allelochemicals in winter oilseed roots impact herbicide resistant weed germination and growth.Canola and pennycress root extract lowered the germination and root length of herbicide-resistant mare's tail.Canola and pennycress root extract shortened roots and lengthened shoots of Palmer amaranth.Canola and pennycress root extract did not affect soybean germination and growth.