Dormancy inDioscorea: Differences of temperature responses in seed germination among six Japanese species

Abstract

Effects on seed germination of temperatures ranging from −2 C to +29 C were tested inDioscorea nipponica, D. tokoro, D. japonica, D. tenuipes, D. septemloba andD. quinqueloba which orginate in the temperate zone; they are distributed from northern cold areas to southern warm areas approximately in this order in Japan. After water imbibition of these seeds, chilling induced full germination, and high temperatures over 23 C induced a secondary dormancy, but sensitivities to the chilling and to the high temperatures differed with species. Cold-climate species germinated rapidly at higher temperatures after a short-term chilling or even without chilling, whereas warm-climate species required chilling of a rather long period for germination; thus, among 6 species tested, favourable temperatures for germination and climatic temperatures of distribution area were conversely correlated.

Seeds ofD. tokoro andD. japonica collected from several populations grown in different climates were also tested for germination at 11 to 29 C; seeds from warm climates germinated rather slowly compared to seeds from cold climates.

These inte- and intra-specific adaptation manners in the temperature members of the genusDioscorea are entirely different from those of many other plant genera reported by some workers.