Differences In Germination Responses Research Articles

Bromus tectorum seed germination: between-population and between-year variation

Cheatgrass (Bromus tectorum L., Poaceae), an introduced winter annual, has invaded a variety of habitats in western North America. This study examines variation in cheatgrass germination response and after-ripening patterns that are related to differences in habitat and to yearly differences in weather conditions during seed maturation. Seeds collected from five contrasting populations in 1992 and 1993 were subjected to controlled dry storage and then incubated across a range of temperatures. Recently harvested seeds were dormant and germinated slowly, while fully after-ripened seeds were nondormant and germinated rapidly. The optimal incubation temperature for mean germination time shifted from 5:15 to 20:30 °C as a result of after-ripening. Between-population differences in germination response appear to be related to the potential risk of precocious summer germination. The results from this 2-year study suggest that the more extreme yet predictable environments select for seed germination and after-ripening patterns that are genetically fixed, while populations from more favorable environments tended to show more between-year variations, suggesting more phenotypic plasticity. Germination percentage showed greater between-year variation than mean germination time. Between-year differences could not be explained simply by differences in maximum temperature or total precipitation during maturation. Adaptive germination responses in cheatgrass populations from contrasting habitats may have both genetic and environmental components, thus explaining why this species can become established in such a variety of habitats. Keywords: after-ripening, invading species, dormancy, mean germination time, cheatgrass, downy brome.

Potential for Persistence of Genes Escaped from Canola: Germination Cues in Crop, Wild, and Crop-Wild Hybrid Brassica rapa

Seeds of two wild populations, a crop type (canola) and reciprocal crop-wild hybrids of Brassica rapa were exposed to a factorial combination of light, nutrient and stratification treatments in a growth chamber study to test differences in germination responses to environmental cues. The effects of seed density and nutrient treatment on germination were tested in a separate study. Germination of each type differed in response to treatment combinations. Canola had higher levels of germination than the wild populations. Hybrid germination more closely resembled that of the maternal parent than that of the reciprocal hybrid or paternal parent. Seeds from agricultural and non-agricultural wild populations differed in germination responses to treatments (...)

Seed Germination Physiology of Eucalyptus delegatensis R. T. Baker in Tasmania

The seed germination response of seedlots from five geographically disparate provenances of Eucalyptus delegatensis to temperature, stratification, soil matric potential, relative humidity and interrupted imbibition was examined. The species was found to have a distinct temperature optimum of between 15 and 20°C, and a minimum temperature for germination of approximately 2°C. Short periods of exposure to high temperatures did not substantially affect germination performance. Stratification greatly increased the range of temperatures over which a high proportion of the seed germinated. Increases in the rate of germination with stratification are related to accrued thermal time during stratification. Pre-imbibing seeds at water potentials down to -2 MPa increased the rate of germination; however, no advantage was found after pre-imibibing at -3 MPa. This increased germination rate was associated with a shortening of the time to commencement of germination and more synchronous germination. Germination rate and germination capacity were impeded by soil matric potentials below -0.01 MPa, and germination was totally inhibited by soil matric potentials below -0.5 MPa. Soil matric potential and temperature interacted in their effects on germination capacity, and seeds germinating at near optimum temperatures were less sensitive to soil moisture stress. Seeds survived dehydration within 60 h of the commencement of imbibition, but were increasingly affected by dehydration thereafter. The rate of imbibition was influenced by the ambient temperature and solution water potential. At modest levels of water stress, imbibition was not impeded and the reduction in germination capacity was probably due to the inhibition of growth related processes. Differences in germination response were detected between the seedlots and these could be related to the geographic origin of the seedlots.

Salinity and germination of annual Melilotus from the Guadalquivir delta (SW Spain)

The germination response to NaCl treatments has been studied in Melilotus seed populations collected from saline and non-saline soils in the Guadalquivir delta. The rank orders for salt tolerance and seed weight were the same in the threeMelilotus species living in this area:Melilotus messanensis>M. segetalis>M. indica. Within the species, differences in germination response to salinity were found inM. indica (6 populations) andM. segetalis (8 populations). The relationship between salt tolerance during germination and salinity of maternal habitat is discussed.

Germination and Phenology of Seven Introduced Thistle Species in Southern Australia

Seeds of seven introduced thistle species, common and widespread in southern Australia, were germi- nated over a range of different day!night temperatures and water potentials. The thistles were Carduus nutans L. (nodding), C. pycnocephalus L. and C. tenuiflorus Curtis (slender), Carthamus lanatus L. (saffron), Cirsium vulgare (Savi) Ten. (spear), Onopordum aff. illyricum (illyrian) and Silybum marianum J. Gaertn. (variegated). Fresh seed of all thistle species germinated over a wide temperature range (15/5° to 40/30°C). Differences between taxa were expressed mainly at low temperatures (15/5° and 15/0°C), at which C. pycnocephalus germinated well and Onopordum only minimally. Germination of C. lanatus seeds was the most sensitive to moisture stress and that of C. nutans and C. vulgare the least. Radicle elongation of germinating seedlings differed at different water potentials, with C. tenuiflorus being the most sensitive to low water potential and that of C. lanatus the least, even at a water potential of - 1.5 MPa. The seven thistle species were separated into three groups based on the patterns of their phenological responses over two seasons when grown in a common environment. Carduus pycnocephalus and C. tenuiflorus behaved as short-season annuals, C. vulgare and Onopordum showed a strongly biennial response, and the other species were annual except for C. nutans, which behaved as an annual or a biennial depending on time of establishment. We conclude that the differences in germination responses to temperature and water potential between the different introduced thistles are minor. In combination with the major differences in phe- nology revealed in this study some of these differences may help to explain the predominance of the seven thistles in different regions of southern Australia. Other factors will largely determine their weediness in any one region.

LEAF‐CANOPY‐INDUCED SEED DORMANCY IN A GRASSLAND FLORA

SUMMARYThe germination of 27 species from calcareous grassland was tested in three light treatments in the laboratory: in darkness, under tungsten lamps and under a leaf‐canopy. Germination was significantly lower under a leaf‐canopy than in the dark in 17 species. The phenomena of leaf‐canopy induced dormancy was not associated with the life‐span of species, though there was a weak, negative relationship with seed weight amongst 20 perennials in the sample. It is suggested that the co‐existence of species at high density in calcareous grasslands may, in part, be explained by differences in germination response to fine‐grained variations in the light environment at the soil surface.

Differences in germination response of spores of several species of rust and smut fungi to nonanal, 6-methyl-5-hepten-2-one, and related compounds.

Differences in germination response of spores of several species of rust and smut fungi to nonanal, 6-methyl-5-hepten-2-one, and related compounds.