Changes inSenna obstuifoliaGermination Requirements over 12 Months under Field Conditions

Senna obtusifolia seeds were collected in Fall 2003 and immediately field sown to assess dormancy alleviation and effect of after-ripening over a 12-month period on light and temperature requirements for germination. Seeds did not exhibit physical dormancy at maturation and readily germinated over a broad range of light and thermal conditions. Dormancy gradually increased during Winter months, resulting in only a small fraction of the population capable of germination by early Spring. Dormancy break did not occur at a specific time of the year nor did dormancy alleviation increase over the 12-month period following maturation. Conditions during Spring and Summer coincided with thermal requirements for germination of the nondormant fraction of the population. Senna obtusifolia seeds were nonresponsive to red and far-red lights, and seeds did not acquire a light requirement following burial for 6 months