Dynamics of Dormancy-Status Subpopulations of Indian Ricegrass Seed Held in Dry Storage

Germination of Indian ricegrass (Achnatherum hymenoides [Roem. & Schult] Barkworth), a rangeland species native to western North America, is limited by persistent seed dormancy. We previously identified high-dormancy (HD) and low-dormancy (LD) genotypes from within the genetically heterogeneous cultivar Rimrock. Seed was produced in 2000 and 2001 in a common garden, stored in paper-can containers at room temperature, and tested every 3 mo with and without prechill through 2005. In 2005, tetrazolium viability of all four lots was 99%, reflective of this species' extensive seed longevity. Over this time period, germination of nonprechilled seed increased from 1% to 53% for HD and from 15% to 79% for LD, whereas corresponding increases for prechilled seed were from 8% to 56% for HD and from 61% to 76% for LD. At first, the great majority of seeds of HD (99%) and LD (86%) were dormant, but this majority was overwhelmingly prechill nonresponsive for HD (92%) compared to roughly equal portions of prechill-nonresponsive (39%) and prechill-responsive (46%) seed for LD. At the end of the trial, most seeds of both HD (53%) and LD (79%) were nondormant, but more prechill-nonresponsive seeds were present in HD (44%) than LD (24%). Over the course of the study, the prechill-nonresponsive subpopulation declined more for HD (by 32%), the prechill-responsive subpopulation declined more for LD (by 45%), and overall dormancy (sum of the two subpopulations) declined more for HD (by 13%). The prechill-responsive subpopulation was depleted more quickly than the prechill-nonresponsive subpopulation for both genotypes. Both HD and LD genotypes were responsive to room-temperature storage without loss of viability over a 4–5-yr period. These data highlight the utility of long-term storage as a technique to improve germinability, and consequently establishment, success of Indian ricegrass.