SEED-GERMINATION RESPONSE TO TEMPERATURE, IN 2 ALTITUDINALLY SEPARATEPOPULATIONS OF THE PERENNIAL GRASS THEMEDA-TRIANDRA

The response of fresh (less than 8 weeks from seed shed) and after-rip ened (non-dormant) Themeda triandra (Forssk.) seed to temperature was assessed. Seed was collected at two sites of similar latitude situated at opposite extremes of an altitudinal gradient spanning the province of Natal, South Africa. The low-altitude population (90 m) was situat ed in the Umfolozi Game Reserve, and the high-altitude population (I 8 00 m) at the Cathedral Peak Forestry Research Station. At seed shed T. triandra seeds were dormant. A period of dry after-ripening was requi red to overcome dormancy. Seed from Cathedral Peak exhibited a deeper dormancy, and required a longer period in dry storage for dormancy to be lost. In both populations, limited germination of fresh seed occurr ed over a narrow range of temperatures. After-ripening widened the ran ge of temperatures over which germination subsequently occurred. The r ate of germination increased and optimum constant temperatures for ger mination decreased with after-ripening. Stratification partly overcame the after-ripening requirement of fresh seed, decreasing dormancy.