Intermediate morphophysiological dormancy allows for life-cycle diversity in the annual weed, Turgenia latifolia (Apiaceae)

Our aim was to determine the seed dormancy-breaking requirements and type of life cycle of Turgenia latifolia in north-western China. At dispersal in July, only 0-9% of the seeds germinated at 5/2 degrees C, 15/2 degrees C, 20/10 degrees C and 25/15 degrees C; thus, 91% of the seeds exhibited physiological dormancy (PD) and 9% were non-dormant. Also, the embryo was underdeveloped and embryo length : seed length ratio increased from 0.38 in fresh seeds to 0.79 at germination. Seeds buried in dry soil at the four temperature regimes for 12 weeks germinated to >= 50% when tested in darkness at 5/2 degrees C, and those buried at 15/2 degrees C and 20/10 degrees C germinated to >= 50% when tested at 15/2 degrees C. Seeds have intermediate complex morphophysiological dormancy (MPD). PD was broken at high and/or low temperatures, but embryo growth was completed only at low temperatures; gibberellic acid (GA(3)) promoted germination. Seeds buried under natural conditions during summer germinated to similar to 70% and similar to 55% at 5/2 degrees C and 15/2 degrees C, respectively, in darkness in autumn. In a germination-phenology study, cumulative germination was similar to 20% and similar to 80% in autumn and spring, respectively. Intermediate complex MPD allows the species to behave as a winter annual and as a short-lived summer annual.