Effects of desiccation of seeds in nine species with morphophysiological dormancy on germination and embryo growth

Aims In species with morphophysiological seed dormancy(MPD),little is known about the effects of desiccation of imbibed seeds on embryo growth and germination.We studied seed responses to dehydration in nine species with different levels of MPD.Methods For each species,a control test was conducted by keeping seeds permanently hydrated and exposed to the optimal stratification-incubation sequenee to promote embryo growth.Simultaneously,tests were run in which seed stratification was interrupted for 1 month by desiccation at room temperature.Important Findings In Clematis vitalba and Ribes alpinum,with non deep simple MPD,desiccation affected neither embryo growth nor seed viability,but the desiccation led to a decrease of germinative ability in R.alpinum by 16%.The seeds of Narcissus pseudonarcissus subsp.munozii-garmendiae,with deep simple epicotyl MPD,tolerated desiccation in different embryo growth stages,but their germinative ability decreased slightly.The response of species with complex levels of MPD to desiccation was more variable:Delphinium fissum subsp.sordidum,with intermediate complex MPD,and Anthriscus sylvestris and Meum athamanticum,both with deep complex MPD,tolerated desiccation.In contrast,Ribes uva-crispa with nondeep complex MPD,Lonicera pyrenaica with intermediate complex MPD and Chaerophyllum aureum with deep complex MPD,had diminished germination ability by desiccation.Although seeds of the species with simple levels of MPD tolerated desiccation,those of some species with complex levels were also highly tolerant.Thus,desiccation did not induce secondary dormancy in late embryo growth stages.The desiccation tolerance of imbibed seeds of most of the nine species may show their adaptability to climate change in the Mediterranean region.

Discovering the type of seed dormancy and temperature requirements for seed germination of Gentiana lutea L.subsp.lutea(Gentianaceae)

Aims There are a number of mechanisms that regulate germination;among these,seed dormancy,one of the most important,is an adaptative mechanism in plants to promote survival by dispersing germination in space and time until environmental conditions are favourable for germination.The main goals of this study were to determine the tem-perature requirements for seed dormancy release and germination of Gentiana lutea subsp.lutea,to identify the class and level of seed dormancy and to suggest an optimal germination protocol.Methods Seeds belonging to two different localities were subjected to vari-ous pre-treatments,including cold stratification(0 and 5°C),warm stratification(25/10°C)and different combinations of these,and then incubated at a range of constant temperatures(5-25°C)and 25/10°C.Embryo growth during pre-treatments and incubation con-ditions were assessed at different times by measuring the embryo to seed length ratio(E:S ratio).The final germination percentage(FGP)and the germination rate(t50)were calculated.Important Findings Fleshy mature seeds of G.lutea subsp.lutea have linear under-developed embryos.Cold stratification at 0°C was effective in overcoming the physiological dormancy(PD)and promoted embryo growth and subsequent germination.After cold stratifica-tion at 0°C,both the root and the shoot emerged readily under a wide range of temperatures.G.lutea subsp.lutea seeds showed an intermediate complex morphophysiological dormancy(MPD).As regards the optimal germination protocol for this taxon,we suggest a period of cold stratification at ca.0°C followed by seed incuba-tion at 10-20°C.The optimal germination temperatures found for seeds of this taxon,as well as its pre-chilling requirement at 0°C,suggest that it is well adapted to a temperate climate;this behavior highlights an increasing threat from global warming for G.lutea,which could reduce the level of natural emergence in the field,prejudicing also the long-term persistence of the natural popula-tions in Sardinia.