Effects of Temperature On Sweet Basil (Ocimum basilicum L.) Germination.

Sweet basil (Ocimum basilicum L.) is a warm season herb usually propagated from seeds. But establishment of the plant is somewhat difficult as seed germination may be limited, particularly during field seeding at cold soil temperature. The germination of six cultivars of sweet basil seeds were tested on a one dimensional thermo-gradient table over temperatures ranging from 0 to 50 °C. Germination of all cultivars ceased at temperatures 45°C. At temperatures below 20°C, germination among cultivars was more variable and the mean time to germination (MTG) increased to greater than 25 days for some cultivars. The base temperature for germination was 11.8°C. The optimal and ceiling temperatures for germination were similar and did not vary among the cultivars compared in this study. The optimal temperature was 35°C, and the ceiling temperature was 43.0°C, respectively. Aged seeds (>5 years) had lower seed vigor and lower germination percentage, also lower ceiling temperature compared with the fresh seeds of same cultivar, but the base and optimal temperatures for germination did not change.