Germination of prechilled mechanically scarified and unscarified Indian ricegrass seed

Abstract

Seed dormancy typically limits stand establishment of Indian ricegrass [Oryzopsis hymenoides (Roem. and Schult.) Ricker]. The mechanical and physiological mechanisms that contribute to dormancy must both be overcome before germination. Our objective was to study potential interactions between the breaking of mechanical dormancy and breaking of physiological dormancy. Germination of 13 seedlots of 'Nezpar', 'Paloma', and PI 478833, ranging in age from 4 to 19 years and in viability from 67 to 96%, was tested. Seed was scarified with an air-gun scarifier to reduce mechanical dormancy approximately 2 1/2 years before testing, or left unscarified. Over 77% of seeds remained intact following scarification. Seed was moved from 5 degrees C to room temperature 1 year before testing to reduce physiological dormancy, or left refrigerated. Seed was also prechilled for 3 weeks at 5 degrees C to reduce physiological dormancy, or left nonprechilled. Germination was determined after 2-week and 3-week 15 degrees C germination periods for prechilled and nonprechilled treatments, respectively. Scarification improved germination of undamaged seed in 12 of the 13 seedlots from 9.5 to 29.7%. Prechilling improved germination of 10 of the 13 seedlots from 8.0 to 22.8%. Room-temperature storage improved germination of 5 seedlots from 4.9 to 12.8%. In 9 seedlots prechilling improved germination of scarified seed 13.1% less than unscarified seed. In 4 seedlots room-temperature storage improved germination of scarified seed 6.5% less than unscarified seed. Depending on the vigor of the seedlot, such effects may be related to a greater reduction of either physiological dormancy or viability in scarified seed than in unscarified seed.