Epicotyl dormancy in Viburnum acerifolium (Caprifoliaceae)

Seeds (true seed plus endocarp) of Viburnum acerifolium have underdeveloped linear embryos and deep simple epicotyl morphophysiological dormancy. Seeds mature and are dispersed in autumn, and radicles and epicotyls emerge the following autumn and late autumn-winter, respectively. Embryos in seeds incubated at 25/15 C became fully elongated in 16 wk, whereas those incubated at 5 C hardly grew at all. The optimum continuous temperature regime for both rate and percentage of radicle emergence was 25/15 C. At this regime, however, ≥20 wk were required for radicles to emerge in a high percentage of the seeds. GA₃ had little or no effect on radicle emergence. In seeds subjected to a winter → spring → summer → autumn temperature regime in controlled environments, radicles emerged in autumn in the 20/10 → 15/6 C portions of the sequence. In those subjected only to the summer → autumn portions of the sequence, radicles also emerged in autumn at 20/10 → 15/6 C. Thus, in nature, the cold winter season has no effect on dormancy-break. Radicles of seeds planted in a nonheated greenhouse in November 1998 emerged in October 1999, when mean maximum and minimum temperatures were about 19 and 9 C, respectively. The optimum continuous temperature regime for both rate and percentage of epicotyl emergence was 15/6 C. For seeds planted in the nonheated greenhouse in November 1998, rate of epicotyl emergence peaked in early January 2000, when mean maximum and minimum temperatures were about 10 and 5 C, respectively.