Deep Complex Morphophysiological Dormancy in Seeds of Thaspium pinnatifidum (Apiaceae)

Abstract

Seeds of Thaspium pinnatifidum (Buckl.) Gray (Apiaceae) were dormant at maturity in early autumn. Embryos in fresh seeds were 0.7 mm long, but by the time germination began in early February they had grown to 3.6 mm. Seventy-six percent of the seeds sown in autumn in a nonheated greenhouse germinated the following late winter and early spring, with the peak occurring between February 4 and 11, when mean daily maximum and minimum air temperatures were 13.3 and 8.7 C, respectively. An additional 15% germinated the second season. Seeds cold stratified at 5 C for 12 wk germinated to 69% and 64% in light and darkness, respectively, at 5 C. After 4 wk at 5 or 15/6 C, embryos in seeds were 1.5 mm and 2.3 mm in length, respectively. Seeds transferred from 5 to 15/6 C germinated to 61% after 4 wk, whereas those kept at 15/6 C for 8 wk germinated to only 2%. Thus, cold stratification was required to break physiological dormancy and stimulate growth of the underdeveloped embryos. Since gibberellic acid did not substitute for cold stratification and dry, room-temperature laboratory storage did not reduce the length of the cold stratification period required to break dormancy, seeds have deep complex morphophysiological dormancy.