Does seed heteromorphism affect the critical temperature thresholds for wild mustard (Sinapis arvensis) germination? A modeling approach

Wild mustard (Sinapis arvensis L.) is well-known as an important weed for cultivated land, particularly when found among cereal crops. It produces large amounts of heteromorphic (black and brown) seeds. This study aimed to estimate the critical temperature thresholds of wild mustard heteromorphic seeds. For this purpose, a novel Weibull-based thermal time model was developed, which was applied to compare the germination characteristics of the heteromorphic seeds of wild mustard. Germination was investigated by exposing the seeds to eight constant temperatures of 7.5, 10, 15, 20, 25, 30, 35, and 37.5 °C. Over both the sub- and supraoptimal ranges, the proposed model reasonably explained the germination patterns of both seed types in response to temperature. Heteromorphic seeds of wild mustard exhibited different germination behaviors in response to different temperatures. Brown seeds were more cold-tolerant and could germinate rapidly to a high percentage (68%) in a wider range of temperature environments (2.78–38.05 °C); black seeds germinated at a narrower temperature range (4.99–37.97 °C) and a large proportion of black seeds remained dormant (77%). These differences could lead to the temporal distribution of seed germination throughout the growing season.