Germination Characteristics of Helianthus maximilianai Schrad. and Simsia calva (Engelm. and Gray) Gray

Abstract

Germination characteristics of Maximilian sunflower (Helianthus maximiliana Schrad.) and awnless bushsunflower {Simsia calva Engelm. & Gray) Gray were evaluated at water potentials of 0, -.25, -0.50, -0.75, and -1.0 MPa under alternating temperature regimes of 10/20, 15/25, and 20/30 degrees C in controlled environmental chambers. Cumulative germination was greatest for both species at water potentials of 0 and -0.25 MPa in the 15/25 degrees C temperature regime. Germination total and rate were depressed for both species in the 10/20 degrees C regime. The 20/30 degrees regime depressed total germination but increased germination rate. The adverse effects of more negative water potentials (-0.75 and -1.0 MPa) were more pronounced at low temperatures for awnless bushsunflower and high temperatures for Maximilian sunflower.