Submitted to: Rangeland Ecology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/24/2009
Publication Date: 5/1/2009
Citation: Jones, T.A. 2009. Dormancy-Status Pool Dynamics in Indian Ricegrass. Rangeland Ecology and Management. 62:284-289. Interpretive Summary: Indian ricegrass is primarily seeded for rangeland restoration efforts in western North America. Rapid germination is desirable for successful seeding establishment, but this perennial must also be able to propagate itself indefinitely as a wild species. Thus, a better understanding of the dynamics of dormancy in seed lots held in dry storage is desired. Two genotypes were selected from the cultivar Rimrock for the extremes of high and low seed dormancy. This study monitored changes between three fluctuating dormancy-status pools (mechanically dormant, physiologically dormant, and non-dormant) in seed lots of the two genotypes held in dry storage over a 4- to 5-year period. At the beginning of the experiment, seeds of the high-dormancy line were overwhelmingly mechanically dormant (92%), while for the low-dormancy line mechanically dormant (39%) and physiologically dormant (46%) pools were about the same size. By the end of the experiment, 53% and 79% of seeds were non-dormant for the high-dormancy and low-dormancy lines, respectively, and mechanical dormancy was 20% greater for the high-dormancy line. An understanding of the relative sizes of the three pools and their changes over time in storage will help land managers manage their seed stocks to maximize germination for rangeland seedings.
Technical Abstract: Germination of Indian ricegrass (Achnatherum hymenoides [Roem. & Schult] Barkworth) (Poaceae), a rangeland species native to western North America, is limited by persistent mechanical and physiological dormancy. We previously selected high (HD 3-15) and low-dormancy (LD 6-6) lines from the cv. Rimrock. Seed was produced in 2000 and 2001 in a common garden, stored in paper-can containers at room temperature, and tested every three months with and without prechill (PC) through 2005. In 2005, tetrazolium viability of all four lots was 99%, reflective of the seed longevity of this species. Over this time period, germination on non-PC seed increased from 1 to 53% for HD 3-15 and from 15 to 79% for LD 6-6, while corresponding increases for PC seed were from 8 to 56% and from 61 to 76%, respectively. At first, the great majority of seeds of HD 3-15 (99%) and LD 6-6 (86%) were dormant, but this majority was overwhelmingly PC-non-responsive for HD 3-15 (92%) compared to roughly equal portions of PC-non-responsive (39%) and PC-responsive (46%) for LD 6-6. At the end of the trial, most seeds of both HD 3-15 (53%) and LD 6-6 (79%) were non-dormant, but more PC-non-responsive seeds were present in HD 3-15 (44%) than LD 6-6 (24%). Thus, mechanical dormancy was more persistent than physiological dormancy. Over this time period, the PC-non-responsive pool declined more for HD 3-15 (by 32%), the PC-responsive pool declined more for LD 6-6 (by 45%), and overall dormancy (sum of the two pools) declined more for HD 3-15 (by 13%).