Impact of temperature, light and seed depth on emergence and germination of Conyza bonariensis e Conyza canadensis resistant to glyphosate

Intense glyphosate use either in orchards or specially no-tilled glyphosate-resistant soybeans, has selected resistant biotypes of both Conyza bonariensis and C. canadensis. Studies of the species biology could provide insight for integrated weed management. A research program was designed to evaluate how seed germination of both species was affected by the following factors: biotype, substrate composition, soil depth, temperature and light. A factorial arrangement of the treatments was established for the first experiment, where factor A consisted of biotypes (two from each species);factor B was substrate composition (soil, sand, soil: sand): and factor C was substrate depths (0, 0.5, 1, 2, 5 cm). The second experiment included the first factor; plus factor B as temperature (constant 20, 25, or 30 degrees C, and alternating 20/30 degrees C), and factor C as light conditions (light, dark). In a third experiment, factors consisted of species and temperature (10, 15, 20, 25, 30 degrees C). Seedling emergence or seed germination were assessed at 12 days after treatments. All biotypes from both species had similar seedling emergence in relation to soil depth. Increasing soil depth reduced seedling emergence. Sandy substrate facilitated seed germination at 0.5 and 1.0 cm depth. The species are positive photoblastic. Optimum temperature for seed germination for both species was 20 degrees C, but C. canadensis germinates better at temperatures below the optimum and C. bonariensis germinates better at temperatures above the optimum.