Morphophysiological dormancy in seeds of Convallaria keiskei and a proposal to recognize two types of double dormancy in seed dormancy classification

Convallaria majalis has double dormancy and hypogeal germination, but no information is available on embryo growth or on the effects of light and gibberellic acid (GA(3)) on germination in this genus. Therefore, we investigated embryo growth and other germination features in seeds of Convallaria keiskei and compared the data with those of Trillium camschatcense in another study. Until now, in seeds with double dormancy, embryo growth and germination (epigeal) have been studied in detail only for seeds of Trillium camschatcense. Phenology of embryo growth and emergence of cotyledonary petiole/root (hereafter root) and shoot in seeds of Convallaria keiskei were monitored outdoors. Effects of temperature, light and GA(3) on embryo growth and root and shoot emergence were tested under laboratory conditions. Roots emerged the first spring following seed dispersal in autumn. The embryo grew soon after root emergence, and germination was hypogeal. Seeds with an emerged root formed buds from which a shoot (leaf) emerged above ground during the second spring. Alternating temperatures and light had negative effects on root emergence, and GA(3) did not substitute for cold stratification in root emergence. Seeds of Convallaria keiskei have double dormancy, but it differs from that in Trillium camschatcense. Based on differences in embryo growth before (Trillium camschatcense) versus after (Convallaria keiskei) root emergence, and on epigeal (Trillium camschatcense) versus hypogeal (Convallaria keiskei) germination, we suggest that two types of deep simple double morphophysiological dormancy (MPD) be recognized. Since embryo growth in Convallaria keiskei does not fit the standard definition of MPD, we propose to expand this definition.