Ecophysiology of germination in the aromatic plants thyme, savory and oregano (Labiatae)

Abstract

Ecophysiological aspects of seed germination were investigated in the widely distributed Mediterranean-endemic, aromatic plants thyme (Coridothymus capitatus), savory (Satureja thymbra) and oregano (Origanum vulgaresubsp.hirtum). Thyme seed germination is light indifferent, whereas oregano seeds have an absolute light requirement; their germination can be promoted even by green safelight or far-red light. In savory, a portion of the seeds germinates in the dark and germination can be either increased or decreased by the appropriate illumination. All three species show more germination at a relatively low temperature range, a Mediterranean characteristic, with an optimum around 15–20°C. The rate of germination is considerably higher in the tiny seeds of thyme and oregano than in the larger seeds of savory. In the latter species, germination is also dependent upon the age of the seeds; old seeds germinate to a higher percentage than fresh ones, as already observed by Theophrastus, possibly as a result of the volatilization of the essential oils present on the nutlet coat. Seeds of thyme, savory and oregano are dispersed within the persistent fruiting calyces and the seeds eventually germinate within it. Essential oils in the calyx strongly inhibit germination of the enclosed seeds; germination is much suppressed in thyme and to a lesser extent in savory and oregano. This diaspore dormancy caused by essential oils apparently is overcome under natural conditions by leaching of the inhibitors with rainwater. It is suggested that this dormancy operates as an adaptation strategy that delays germination by acting as a rain gauge. In this way, seed germination and subsequent seedling establishment are prevented during the early phase of the rainy period, which is usually interrupted by drought spells in the Mediterranean climate.

Seed germination of Phillyrea angustifolia L., a species of difficult propagation

“…Regarding the effects of temperature, the highest germination percentage was obtained at 15 ºC. These results are in agreement with those of Thanos et al (1992Thanos et al ( , 1995, who found that the optimal germination temperature for most Mediterranean shrub species ranges between 15 ºC and 20 ºC, and with previous data on P. angustifolia seeds collected at a different geographical location (Mira et al, 2015b).…”

Seed germination characteristics of Phillyrea angustifolia L. and P. latifolia L. (Oleaceae), two Mediterranean shrub species having lignified endocarp

“…Also, temperature regime for P. latifolia was very restrictive, since seeds did not germinate at either 25 ºC or 25/15 ºC. These results are in agreement with optimal germination temperature for most Mediterranean shrub species ranging between 15 ºC and 20 ºC (Thanos et al 1992(Thanos et al , 1995. Alternating temperatures (20/7 ºC and 25/15 ºC) resulted in low germination percentages, although previous works stated that Phillyrea seeds germinated a 90% after 60 days at 20/7 ºC (Herranz et al 2006), or a 90%…”

Effect of pre-treatments on the germination of jasmin box (Phillyrea latifolia) seeds in Greece

“…After two months they started to germinate. Other studies on germination temperatures for most Mediterranean shrub species suggest 15-20 °C as optimal temperature (Thanos et al 1992(Thanos et al , 1995. Concerning stratification, the cold stratification at 2-4 °C for all the combinations of chemical pre-treatments resulted in zero germination, while warm stratification at 15°C significantly increased the germination.…”