Germination of Opuntia tomentosa seeds collected during 1998 was evaluated using treatments of scarification (H2SO4), gibberellic acid (GA3), dry heat, soaking, light, after-ripening and stratification at constant and alternating temperatures. Seeds were positive photoblastic, germinated best at constant temperatures, and showed a combined dormancy (physiological and physical). Acid scarification, GA3, and heating induced germination, soaking and stratification did not. After 15 and 18 months, GA3 inhibited germination. Dormancy of seeds collected during 2000 was overcome with a short scarification. Differences between baths could be due to 1998 was very dry due to “El Niño”. It is important to identify maternal effects.

Laboratory trials were performed to test germination and emergence characteristics of jimsonweed (Datura stramonium L.) seeds buried in 10 different soil types (with or without the control of soil external gas environment) with pronounced sandy or clay texture. The aim of the experiments was to investigate if the physical characteristics of the soils were involved in both buried-seed ecology and emergence dynamics. Germination inhibition due to burial depth was found to be directly proportional to clay content and inversely proportional to sand content. Measurement of soil air permeability showed a close relation between gas exchange potential and depth-mediated germination inhibition. Comparative analysis of the germination response in nonsoil and soil hypoxia suggested that inhibition is caused not so much by hypoxia per se as by the presence of fermenting metabolites that could not easily be eliminated due to decreased respiratory activity. In situ inspection of buried seeds also revealed that the increased time required for emergence in clay soils is primarily due to increased mean germination time rather than greater difficulty in seedling penetration upwards through the soil before emergence. Partial removal of germination inhibition of buried seeds was facilitated by elevated air oxygen availability but only with sandy soils, showing that inhibition is closely linked to soil ability to induce gas exchange with external air. At excessive burial depth (12 cm), seeds exhibited induction of secondary dormancy independent of soil texture. In conclusion, these experiments demonstrated that soil physical properties have a strong effect on buried-seed ecology and consequently on seedbank dynamics in the agroecosystem.

Accelerated aging is a physical stress commonly used in order to obtaininformation on seed vigor within a short period of time. The present studyaimed to assess the effects of temperature and duration of accelerated agingon the germination behaviour, expressed as final germination percentage andgermination rate, of seeds of the cosmopolitan weed Chenopodium album. Seedswere aged by incubating them inside sealed boxes with distilled water at 45,55 and 65 degree C for periods of time ranged between one and six days.Seed germination was tested at three incubators. Accelerated agingsignificantly reduced both final germination percentages and germinationspeed. The overall germination after one, two, three and six days of agingdecreased by 46%, 88.7%, 85% and 83%, respectively, from that of unaged seeds.Germination was completely inhibited after aging of the seeds at 65 degree C.The results discussed in the light of employing accelerated aging technique inobtaining information about the most effective temperature and duration thatare required to deteriorate seeds of weeds during the soil solarization.

The effect of kernel size and texture of kernels on the malting properties of sorghum was investigated. Twelve sorghum cultivars were used for the study. The physical features of the kernels that were determined included the endosperm texture, endosperm type and kernel size. Also determined were the germination energy and germination capacity. To monitor the malting properties, the malting loss, hot water extract, cold-water extract and diastatic power were determined. The effect of duration of germination on the root and shoot lengths of kernels was also investigated. Two of the cultivars were floury while the other cultivars were corneous. All the cultivars were non-waxy. The mean percentage values of the germination energy and germination capacity were 84.92% and 91.75% respectively. As the germination period increased, root and shoot lengths of all the twelve cultivars also increased. The greatest change in the root and shoot lengths was observed between the second and third day of the germination period. The malting loss increased with the germination period and ranged between 15.5-33.0%. The malting loss for all cultivars reached its peak between the second and third day of germination. Malting loss was least for floury endosperm. The diastatic activity increased throughout the duration of germination. The diastatic activity was positively correlated with the cold water extract (r = 0.99) and hot water extract (r = 0.29). The cold water extract increased as the diastatic activity increased. The corneous grains were relatively high in diastatic activity but no correlation was obtained between the size indices and malting properties of the cultivars.

It was observed that as the screen size increased the recovery percentage, bulk density, angle of repose and mechanical damage decreased while true density, equivalent seed diameter, 1000 seed weight, physical purity, germination percentage and vigour index increased. The variety JS 335 screened with 4.00 mm screen had shown all physical properties and quality parameters of seed to be superior to that of the varieties MACS-13, MACS-24 and MACS-58.

The effect of matriconditioning, the physiological presowing seed technique, using Micro-Cel E on Allium cepa L. cv. Czerniakowska seed quality was studied. Several ratios of seeds, carrier, water and time of priming were tested. The most effective treatment for improving onion seed germination at most tested temperatures was priming to a ratio of 2 g seed:1 g Micro-Cel:3 g water for 5 days in light at 15°C. Matriconditioning greatly improved the germination and emergence percentage, seedling fresh and dry weight and reduced electrolyte leakage compared to that of untreated seeds; this beneficial effect was especially evident at suboptimal temperatures. Matriconditioning improved the germinability of aged seeds, the effect being more pronounced in the more aged seeds. No significant differences in ethylene production by primed and non-primed seeds were observed in the absence of its precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), but its presence during imbibition caused an increase in ethylene production; an enhanced activity of in vivo ACC oxidase in Allium cepa matriconditioned seeds in comparison to untreated seeds, indicates that the endogenous level of ACC is a limiting factor of ethylene production. Likewise, the activity of ACC oxidase isolated from matriconditioned seeds was higher than that from untreated seeds. Higher endo-β-mannanase and total dehydrogenase activities were observed in primed air-dried seeds in comparing to non-primed seeds.

β-1,3-Glucanase (βGlu) expression in seeds plays important roles in the regulation of seed germination, dormancy and in the defence against seed pathogens. A thick β-1,3-glucan layer is typical for the seed envelope of cucurbitaceous species, confers seed semipermeability and is degraded during germination. In many species with coat-imposed dormancy, the seed envelope confers a physical constraint to radicle emergence. In the solanaceous species, the micropylar endosperm and testa have this function, and endosperm weakening appears to be a prerequisite for germination. Class I βGlu is transcriptionally induced in the micropylar endosperm of tobacco, tomato and other solanaceous seeds just prior to radicle emergence. βGlu induction and germination are tightly linked in response to plant hormones and environmental factors, e.g. they are both promoted by gibberellins and inhibited by abscisic acid (ABA). Sense and antisense transformation of tobacco reveals two sites of βGlu action: after-ripening-mediated release of testa-imposed dormancy and endosperm rupture during germination. The use of an ABA-inducible chimeric sense-transgene resulted in overexpression of class I βGlu in seeds and provided direct evidence that βGlu contributes to endosperm rupture. A model integrating βGlu, seed dormancy, after-ripening and germination is presented, and possible mechanisms for βGlu action are discussed. It is proposed that βGlu not only helps defend seeds against pathogens, but is also a key factor in regulating coat-imposed dormancy and germination of seeds in response to environmental and hormonal cues.

Physical changes and flows of energy at the interface between two contrasting ecosystems affect the distribution of species across the ecotone. The maintenance and stability of the, often abrupt, transition between Australian rainforest and non-rainforests is often attributed to fire. We use pre-germination treatments of smoke and heat on soil seed bank samples to determine plant distributions across the edge between subtropical rainforest and an adjacent eucalypt-dominated wet sclerophyll forest. Soil seed bank collections at 15 m within the eucalypt forest had both significantly higher density and diversity of seedlings than those at 30 m, at the edge itself or at any site within the rainforest. This response was most apparent when a pre-germination smoke treatment was applied. We suggest that smoke is an important germination trigger for species regenerating at this interface. Our results confirm the importance of fire in determining and maintaining the nature of this ecotone.