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Action of Temperature and Light on the Control of Seed Germination in Alta Tall Fescue (Festuca arundinacea Schreb.)¹

Temperature, light, and their interactions were studied for their effects of germination of ‘Alta’ tall rescue (Festuca arundinaeea Schreb.) seeds. A thermogradient plate was used to study effects of 30 constant temperatures on germination in darkness. Germination was maximum at 12 through 18 C, although seeds germinated in varying number from 8 to 31 C during the 9-day test period. Rates of germination increased with temperature and were highest between 16 and 19 C. Seeds exhibited a high temperature sensitivity and became more dormant with increased temperature above 18 C and with increased periods at high temperatures. Studies of alternating temperature cycles revealed that germination was significantly reduced when seeds were held longer than 16 hours at 25, 8 hours at 30, and 4 hours at 35 C in daily cycles with 15 C.

The lowered germination at temperatures above 18 C was probably due to P_fr reversion and decay of total phytochrome (P). Seeds were more dormant at 30 than at 25 C. At 25 and 30 C a single saturating red light (R) treatment caused a germination increase of 25% above the dark controls. Repeated R irradiances caused significantly higher germination than one brief exposure at 25, but not at 30 C. However at 30 C, where reversion and decay of P would be greater, continuous R caused a significant increase in germination.

Seeds held for 7 days at 35 C and then germinated at 15 and 25 C showed the typical reversible P reaction. Single, brief R again increased germination about 25 to 30% above the dark controls. Recovery from the 35 C treatment was greater at 15 C than at 25 C as shown by germination in darkness of 63 and 3%, respectively. Apparent P synthesis, which is also temperature sensitive, probably occurs at 15 but not at 25 C.

The period required for P_fr action was 20 to 24 hours at 15 C. Germination of seeds following P conversion and P_fr action depended on temperature and was lower at 30 than at 25 C. Thus high temperature imposes a block to germination processes beyond that of P_fr action.

Key Words: Dormancy • Phytochrome • Seed testing • Thermogradient plate

² Senior instructor, Dep. of Agronomic Crop Science, Oregon State Univ., Corvallis, OR 97331; research plant physiologist, Seed Quality Laboratory, Agricultural Marketing Research Institute, NER, ARS, USDA, Beltsville, MD 20705.

Received for publication March 6, 1975.