EFFECT OF TEMPERATURE ON SEED-GERMINATION RATE OF STRIGA-HERMONTHICA (DEL.) BENTH

The effect of a range of constant temperatures (15-45 degrees C) on th e germination of S. hermonthica (Del.) Benth. seed was investigated on a temperature gradient plate to quantify the relationship between tem perature and the rate of seed germination and to study the effect of c onditioning temperature on the relationship. Seeds were conditioned on moist filter paper either at 30 degrees C for 14 days or 20 degrees C for 15 days in an incubator. A synthetic stimulant, GR-7, was applied to conditioned seeds prior to exposure to the various temperatures. N o seeds of S. hermonthica conditioned at 30 degrees C, germinated at < 20 degrees C or > 42.5 degrees C within 312 h. For seeds conditioned a t 20 degrees C, germination occurred at temperatures between 25 and 42 .5 degrees C within 312 h. The base (Tb, estimated from extrapolation, optimum (T-o) and ceiling (T-c) temperatures determined were: T-b = 2 2.7 degrees C, T-o = 40 degrees C and T-c > 42.5 degrees C for seeds c onditioned at 20 degrees C compared with T-b = 18.9 degrees C, T-o = 3 2-35 degrees C and T-c > 42.5 degrees C for seeds conditioned at 30 de grees C. Positive linear relationships were established between the ra te (reciprocal of time taken) of germination of 90% of the final germi nation percentage and temperature up to the respective optimal tempera tures. The rate of germination for seed conditioned at 20 degrees C wa s lower (P<0.0001) than for seed conditioned at 30 degrees C. Similarl y base and optimum temperatures were lower (P<0.0001) for seed conditi oned at 30 degrees C. The base temperatures reported here are about tw ice those reported for the host crops of maize, sorghum and millet. (C ) 1998 Elsevier Science Ltd. All rights reserved.