Epicotyl morphophysiological dormancy and a rare case of epigeal cryptocotylar seed germination in Goniothalamus wynaadensis (Bedd.) Bedd., a tropical threatened endemic tree species of the Western Ghats

Abstract

Goniothalamus wynaadensis (Bedd.) Bedd. is a threatened indigenous tree species found in the Western Ghats and possesses significant medicinal value. This species belongs to the primitive family Annonaceae. However, there is a lack of information regarding seed germination in this species. We conducted experiments on seed germination using various media and found that the species exhibits epicotyl morpho-physiological dormancy (eMPD), marking the first such record in Annonaceae. GA3 at a concentration of 500 ppm and warm stratification at 20 °C for one week proved effective in enhancing embryo growth and radicle emergence. The epicotyl emergence was observed only at 30±2 °C. Because warm stratification promotes both radicle and shoot emergence in G. wynaadensis, the level of eMPD is non-deep and simple. Hence, dormancy in G. wynaadensis can be described as C1b Bb (radicle)- C1b Bb (epicotyl); i.e., the embryo is underdeveloped and grows before radicle emergence and epicotyl emergence under warm temperatures (Bb) and both the radicle and epicotyl have non-deep simple physiological dormancy broken by warm temperatures (C1b). Consequently, G. wynaadensis seed dormancy is phenologically well- adapted to the seasonal climate of Wayanad. Additionally, the species was found to display epigeal cryptocotylar seed germination—a rare occurrence in the development of angiosperm seedlings and this is the first record of such a phenomenon in the genus Goniothalamus.