Characterization and germination of chasmogamous and basal axillary cleistogamous florets of Texas wintergrass

Abstract

Texas wintergrass (Stipa leucotricha Trin. & Rupr.) is an important cool-season, perennial forage grass in Texas. Seed handling problems and a limited knowledge of germination and establishment requirements have severely limited its use in revegetation programs. This study was designed to characterize floret morphology and investigate the effects of different temperature × water potential regimes on germination responses of chasmogamous and basal axillary cleistogamous florets from 2 Texas wintergrass populations in central Texas. Germination responses were evaluated at polyethylene glycol-induced water potentials of 0, -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 environment chambers. Awns contributed most to the weight of chasmogamous florets, while caryopses contributed most to the weight of cleistogamous florets. Cleistogamous florets generally had higher cumulative germination percentages and slower germination rates than chasmogamous florets in the various temperature × water potential regimes. Cumulative germination percentages of both floret types were greatest at substrate water potentials of 0 and -0.25 MPa in the 10/20 degrees C temperature regime, and mean germination times were most rapid at the 0 MPa substrate water potential in the 15/25 degrees C temperature regime. Based upon seasonal temperature and moisture conditions in central Texas, germination from natural seed banks or artificial seedings should occur primarily between late September and mid-November, and occasionally from December through February during mild winters.