Intrapopulation genetic variation for seed dormancy in India ricegrass

Indian ricegrass (Achnatherum hymenoides [Roem. & Schult.] Barkw. = Oryzopsis hymenoides [Roem. & Schult.] Ricker = Stipa hymenoides Roem. & Schult.) may buffer its seed banks over time via morphological (lemma and palea) and physiological (seed coat) seed dormancy. However, Indian ricegrass seed dormancy has usually not been examined from a genetic perspective. Because a positive relationship between seed dormancy and seed size has long been noted within Indian ricegrass populations we wanted to determine if genetic variation for seed dormancy was present among seed morphs. We also wanted to determine if genetic variation for seed dormancy was present in material without polymorphism. The T-593 population from McKinley Co., N.M., has 3 seed morphs produced on genetically distinct plants, 'elongate' (2.24 mg/seed), 'globose' (3.00 mg/seed), and 'jumbo' (8.70 mg/seed). Following a 3-week prechill, elongate seed showed higher germination (66%) than globose seed (20%) over 6 tests (pairs of seed lots), while jumbo seed did not germinate without scarification. Jumbo seed had thicker (181 microgram) lemmas than globose (93 microgram) or elongate (52 microgram) seed. Individual plants of the nonpolymorphic cultivar, Rimrock, were selected for high or low germination following a 3-week prechill. The spring following seed harvest, germination with prechill was greater for progeny lines of the high-germination selections (45.5%) than low-germination selections (3.8%) with Rimrock intermediate (11.8%). This heritable difference in germination was accompanied by only small differences in lemma and palea thickness and no difference in seed mass. Genetic variation in seed dormancy may be found both between morphs (interpreted as variation for morphological dormancy) and within morphs (interpreted as variation for physiological dormancy). Genetic variation for seed dormancy can be as great within a population as between populations.