Temperature effects on seed germination and early seedling growth of 225 American sloughgrass ( <i>Beckmannia syzigachne</i> ) populations

Abstract American sloughgrass [ Beckmannia syzigachne (Steud.) Fernald] is a troublesome weed in wheat ( Triticum aestivum L.). We tested the germination of B. syzigachne seeds under different temperatures in growth chambers (12-h dark/12-h light, 12,000 lx), simulating temperatures during the winter wheat sowing periods: early (25/15 °C), standard (20/10 °C), late (15/5 °C), and very late (5/0 °C). We also tested the accumulated temperatures required for seedling growth to the 2- to 5-leaf stages, using 225 populations collected from wheat fields in eastern China. The average 1,000-seed weight of the 225 populations was 1.2 ± 0.01 g. Overall, the populations tested did not show seed germination after 21 d of treatment (DAT) at 5/0 °C or constant 30 °C. At 14 DAT with 25/15, 20/10, and 15/5 °C, the mean germination rates were 85.4%, 6.4%, and 0.1%, respectively. These rates increased to 99.9%, 58.6%, and 21.7% at 21 DAT. Populations collected from lower-latitude regions germinated significantly faster (P &lt; 0.05) under optimal conditions. Accumulated temperatures required for growing the second, third, fourth, and fifth leaves were 139.0 ± 1.0, 127.8 ± 1.0, 115.6 ± 1.0, and 98.9 ± 0.7 °C, which showed a significant decreasing trend. The narrower optimal temperature range for B. syzigachne seed germination and higher thermal requirements for early seedling growth constrain its distribution, while the heterogeneous seed germination facilitates its infestations in wheat-planting areas in eastern China.