A comparative study of seed dormancy in five genera of Caprifoliaceae s.l (Germination)

This study investigated seed dormancy in Diervilla, Lonicera, Sambucus, Symphoricarpos, and Viburnum. The germination unit in Diervilla and Lonicera is the true seed and in Sambucus, Symphoricarpos, and Viburnum true seed plus endocarp. Mature seeds of Diervilla, Symphoricarpos, and Viburnum have underdeveloped linear embryos and those of Lonicera and Sambucus underdeveloped spatulate embryos. Contrary to previous reports, seeds of Sambucus and Symphoricarpos are not water impermeable. Seeds of Sambucus canadensis, S. pubens, and L. fragrantissima have deep simple morphophysiological dormancy (MPD). Embryos grew at warm temperatures (W), and W followed by cold temperatures (C) were required to break dormancy. GA3 was slightly effective in breaking dormancy. Seeds of Sambucus racemosa had intermediate complex MPD. Embryo growth and seed dormancy-break occurred at 5°C, and GA3 overcame dormancy. Some seeds of D. lonicera, L. maackii, and L. morrowii had morphological dormancy (MD) and others nondeep simple MPD. Seeds with MD germinated in ≤30 d at W in light, whereas those with nondeep simple MPD required >30 d of W ( D. lonicera, L. morrowii) or of either W or C ( L. maackii) to become nondormant. GA3 broke dormancy. Seeds of L. japonica have nondeep simple MPD. Embryos grew better at W than at C, and seeds required either W or C for dormancy-break. GA3 was moderately effective in breaking dormancy. Seeds of Symphoricarpos orbiculatus have nondeep complex MPD. Embryos grew at C only after they received W; thus, W followed by C were required for dormancy-break. GA3 did not break dormancy. Seeds of V. acerifolium have deep simple epicotyl MPD. W were required for radicle emergence and C for epicotyl emergence. GA3 did not break radicle dormancy; effect not tested on epicotyl dormancy. A graphical model was developed to explain the role of reentrance into dormancy, loss of viability, and afterripening in the decrease in germination percentages of L. japonica, L. maackii, and L. morrowii seeds that afterripened during dry storage and then lost the capacity to germinate. Evolutionary aspects of seed dormancy types in Caprifoliaceae are discussed.