Influence of Matric Potential and Substrate Characteristics on Germination of Nezpar Indian Ricegrass

Abstract

Intact seeds (caryopses) of Indian ricegrass [Oryzopsis hymenoides (R. & S.) Ricker] are generally reported to exhibit poor germination. The cultivar Nezpar was evaluated to determine if substrate matric potential and substrate physiochemical properties influence germination. Matric potentials ranged from 0 to -1.5 MPa. Substrate variables included: 2 kinds of germination paper, the A horizon of a dune sand, and a commercial washed silica sand. Seeds of Indian ricegrass had low germination (< 5%) with an oversaturated substrate. Germination increased significantly (P less than or equal to 0.05) between -0.005 and -0.10 MPa tension (30 to 70%), then decreased at more negative matric potentials. As compared with paper substrates, the dune sand showed significantly greater (P less than or equal to 0.05) germination at matric potentials more negative than -0.30 MPa. Standard germination screening procedures, especially at high water contents, do not adequately predict the maximum germination characteristics of Indian ricegrass; thus, substrate matric potential is a critical variable to control in germination tests. Moreover, physicochemical differences among common laboratory germination substrates may lead to significantly different termination responses. Microscopic examination of cross-sections of caryopses suggests the mechanism for reduced seed germination at saturated and oversaturated conditions may be the presence of a void between the lemma and palea which, when water-filled, retards oxygen diffusion to the embryo.