Intermediate Epicotyl Physiological Dormancy in the Recalcitrant Seed of Quercus chungii F.P.Metcalf with the Elongated Cotyledonary Petiole

Abstract

Control of seed germination and dormancy is important in seed plant adaptation and evolution. When studying seed dormancy of Quercus species, we observed a substantially delayed shoot emergence following a fast root emergence in Quercus chungii F.P.Metcalf. Since epicotyl physiological dormancy (PD) has not been reported in Quercus section Cyclobalanopsis, we examined seed morphology and germination in Q. chungii and aimed to document epicotyl PD in the seeds. The embryo was fully developed in fresh ripe seeds. The elongating cotyledonary petiole pushed the embryo axis out of the seed during germination, which differed from observations in other Quercus species. Shoots emerged from seeds with developing roots after 3 months of warm stratification (35/25 °C), reaching the highest percentage of shoot emergence in seeds after 5 months. Seeds were recalcitrant and displayed a yet unreported epicotyl PD type, for which we propose the formula Cnd(root) ‒ Cp’’ 2b(shoot). Early emergence and development of the root system in Q. chungii seeds with epicotyl PD appears to be a mechanism to maintain a constant water supply to the shoot during plumule development and emergence. Our documentation of seed germination will provide guidance for the conservation and restoration of this species from seeds.

Climate drives patterns of seed traits in Quercus species across China

“…Although only based on two CTB species, this pattern of rapid germination is consistent with previous literature for Q. chungii and Q. kerrii from the lineage (e.g. Xu et al, 2019;Sun et al, 2021).…”

“…prinus and Q . robur (McCartan et al ., 2015; Sun et al ., 2021), which occur in cold dry regions of North America and Europe.…”

The great diversity in kinds of seed dormancy: a revision of the Nikolaeva–Baskin classification system for primary seed dormancy

“…It should be noted that, in many oak species, the epicotyl is carried just outside the apex of the acorn via elongation of the cotyledonary petioles prior to shoot elongation (Rowlee and Hastings, 1898;Pammel and King, 1917;Korstian, 1927;Jones, 1959;Molinas and Verdaguer, 1993;Pascual et al, 2002;Sung et al, 2010;Yi et al, 2012Yi et al, , 2013Yi et al, , 2019. Furthermore, in some species of Quercus, including Q. chungii (Sun et al, 2021), Q. engelmannii (Snow, 1991), S. semecarpifolia (Troup, 1921;Shrestha, 2003) and Q. virginiana (Engelmann, 1880;Lewis, 1911;Coker, 1912), the cotyledonary tube (formed by fusion of cotyledonary petioles) carries/pushes the embryonic axis up to several centimetres from the apex of the acorn. Troup (1921) says that in Q. semicarpifolia '… the tube may thus attain a length of as much as 4 in [10 cm] or even more'.…”

“…Thus, it seems likely that the acorns of this species have epicotyl PD. Recently, Sun et al (2021) have clearly demonstrated that seeds of Quercus chungii from subtropical southern China have epicotyl PD.…”

Tree Regeneration by Seeds in Natural Forests

“…An important ecological adaptation is seed dormancy, which allows dispersal in time and space and which prevents the simultaneous germination of all new produced seeds [13]. Sun et al [14] examined both seed morphology and germination in Quercus chungii (syn. Cyclobalanopsis chungii) and they aimed to describe seed dormancy.…”