Differential response of Palmer amaranth ( <i>Amaranthus palmeri</i> ) seed germination and seedling emergence under variable environmental conditions

Abstract Palmer amaranth ( Amaranthus palmeri S. Watson) is a eudicot weed that is considered as one of the most problematic weed species. It is reported to overcome several environmental and management stresses under field conditions. Research was conducted in a growth chamber and greenhouse to evaluate the effects of different stress parameters such as temperature, pH, light availability, salinity, osmotic stress, cover crop residue, and soil moisture on seed germination in Palmer amaranth. Seed germination was higher at alternating temperatures of 35°C/25°C and 25°C/15°C (83% and 56%, respectively) compared to 45°C/35°C and 15°C/5°C (˂1%). A pH change of 3–11 and varying light and dark hours did not significantly influence seed germination. A decrease in seed germination was observed from 79% to 57% with the increase in salt concentration from 0 to 50 mM. Similarly, germination was highest at 0 MPa (78%), but it dropped by nearly half to 40% with an increase in osmotic stress to −0.1 MPa. A lower rate of cereal rye cover crop residue (2 t ha −1 ) recorded greater seedling emergence compared to no cover crop. Varying levels of soil moisture also influenced seedling emergence, in which 100% and 75% field capacity (FC) produced maximum seedling emergence (85% each), followed by a 37% seedling emergence at 50% FC. The ability to emerge under high salinity and a wide range of pH along with the high invasive tendency makes Palmer amaranth a troublesome weed.