THE ROLE OF LIGHT DURING PHLOX-DRUMMONDII HOOK - SEED-GERMINATION

The role of light on phlox germination and radicle emergence was studied. Neither light level nor duration affected total germination (G) percentages, which ranged from 93% to 98%. Increasing light level and lengthening light duration delayed achieving 50% of final germination (T50) and increased the span in days between 10% and 90% germination (T90-T10). Increasing light duration from 0 to 24 hours during germination at 0.15 mumol.s-1.m-2 progressively increased T50 from 3.5 to 7.1 days and T90-T10 from 2.6 to 13.1 days. Similarly, lengthening light duration from 0 to 24 hours at 1.5 mu Mol.S-1.M-2 light increased T50 from 3.7 to 10.8 days and T90-T10 from 2.8 to 13.4 days, whereas 15 mumol.s-1.m-2 increased T50 from 3.9 to 21.9 days and T90-T10 from 2.9 to 29.2 days. Increasing the number of days in darkness from 0 to 6 decreased T50 from 14.8 to 4.3 days and T90-T10 from 20.2 to 3.5 days. Increasing the number of days in light from 0 to 6 increased T50 from 4.0 to 8.9 days and T90-T10 from 3.8 to 8.2 days. Estimated rates of decline or increase in T50 and T90-T10 with each added day in darkness or light were measured by fitting regression equations. Seeds germinated in continuous darkness or in 24 or 48 hours of light followed by total darkness had similar G, T50, and T90-T10. The results indicate that initial phlox seed germination was not affected by light, but that light inhibited radicle extension in later germination stages.