Germination Differences Between Clodinafop-Propargyl-Resistant and -Susceptible Alopecurus japonicus Steud. Populations Under Multiple Abiotic Stresses

Clodinafop-propargyl-resistant Alopecurus japonicus Steud. has severely threatened wheat production, while its fitness and stress adaptability have not been systematically clarified. This study compared seed germination and seedling emergence of resistant AHHN-6 and susceptible HNLH-1 under multiple abiotic stress treatments including temperature, pH, water potential, soil moisture, salt and burial depth. Both biotypes exhibited >95% germination under optimal temperature and moisture conditions, indicating the highly resistant biotype AHHN-6 bears no germination-related fitness cost; however, fitness costs were detected in several other resistant populations across the sampling regions. The resistant population displayed markedly higher tolerance to adverse conditions: its 50% inhibitory water potential and salt concentration were −0.43 MPa and 124.22 mmol·L−1 versus −0.35 MPa and 56.25 mmol·L−1 for the susceptible population, and it could emerge normally from deeper soil layers. Collectively, resistance to clodinafop-propargyl does not reduce performance under benign environments but confers enhanced abiotic stress resistance, promoting the long-term survival and spread of resistant A. japonicus in farmlands.