Nitrogen (N) fertilization affects wheat yield and grain protein concentration; however, its mismanagement can increase plant lodging. While the use of plant growth regulators such as trinexapac-ethyl (TE) can mitigate plant lodging, their effects on seed physiological quality are not well known. The aim of this study was to evaluate the effects of N fertilization and TE on wheat yield, lodging and seed quality of spring wheat varieties. It was carried out in the 2018 growing season in the environments of Londrina and Ponta Grossa, Brazil. A randomized complete block design was used with a 2 × 3 × 3 factorial arrangement to evaluate two wheat genotypes (WT 15008 and WT 15025), three top-dressing N rates (0, 40 and 120 kg ha−1), and three TE rates (0, 50 and 100 g ha−1). Agronomic characteristics related to wheat productivity (hectolitre weight, thousand-grain weight, density of fertile spikes, plant height, lodging and grain yield) and seed physiological quality (seed germination and vigour; length and dry matter of normal seedlings) were evaluated. Increasing N rates up to 120 kg ha−1 increased plant lodging up to 26.4 percentage points for WT 15025 in Londrina. TE impaired some traits of seed physiological quality. Spraying 100 g ha−1 TE on the plants reduced seedling length by 9.4% in the seeds of WT 15008 harvested in Ponta Grossa compared to the TE control (0 g ha−1). The dry matter of the seedlings from the seeds harvested in Londrina declined by 7.2% due to the application of 100 g ha−1 TE, compared to the control. However, a lower rate of TE (50 g ha−1) might be enough to minimize plant lodging without impairing the physiological quality of the seeds, depending on the rate of N fertilization. This study is the first step in providing empirical evidence for the detrimental effects of TE in combination with N on wheat seed quality, suggesting that seed producers should exercise caution in managing TE and N fertilization.

A low-cost technique named ‘on-farm’ seed priming is increasingly being recognized as an effective approach to maximize crop establishment. It consists of anaerobically soaking seeds in water before sowing resulting in rapid and uniform germination, and enhanced seedling vigour. The extent of these benefits depends on the soaking time. The current determination of optimal soaking time by germination assays and mini-plot trials is resource-intensive, as it is species/genotype-specific. This study aimed to determine the potential of the seed respiration rate (an indicator of metabolic activity) and seed morphological changes during barley priming as predictors of the priming benefits and, thus, facilitate the determination of optimal soaking times. A series of germination tests revealed that the germination rate is mostly attributable to the rapid hydration of embryo tissues, as the highest gains in the germination rate occurred before the resumption of respiration. Germination uniformity, however, was not significantly improved until seeds were primed for at least 8 h, that is, after a first respiration burst was initiated. The maximum seedling vigour was attained when the priming was stopped just before the beginning of the differentiation of embryonic axes (20 h) after which vigour began to decrease (‘over-priming’). The onset of embryonic axis elongation was preceded by a second respiration burst, which can be used as a marker for priming optimization. Thus, monitoring of seed respiration provides a rapid and inexpensive alternative to the current practice. The method could be carried out by agricultural institutions to provide recommended optimal soaking times for the common barley varieties within a specific region.

Seed is a fertilized mature ovule, which possesses an embryonic plant. When the dry, mature seeds are subjected to imbibition, they release a wide range of organic substances, which include low molecular weight carbonyl compounds (gases and volatiles) and water-soluble organic substances (enzymes and polysaccharides). The volatile organic compounds (VOCs) are molecules of low molecular weight (300 g mol−1) and high vapour pressure (0.01 kPa at 20°C) and include diverse chemical compounds. The nature and emission kinetics of volatiles produced from seeds vary, depending on the moisture content of the seeds. Orthodox seeds stored at ‘low seed moisture content’ undergo seed deterioration, predominantly due to lipid peroxidation, initiated by autoxidation or enzymatic oxidation of unsaturated or polyunsaturated fatty acids. This peroxidation leads to emission of volatile compounds. The quantity of VOCs emitted is positively correlated with the advancement of seed deterioration. With respect to the seed germination process, exposure of seeds to ‘high moisture conditions’ leads to increased respiration, triggers glycolysis and mobilization of storage reserves, resulting in the emission of volatile metabolic products. The quantity of VOCs emitted on commencement of metabolic activity in germinating seeds depends on (1) vigour status and (2) amount of storage reserves. Since it has been established that there is a significant difference between high and low vigour seeds with respect to quantity and profile of VOCs emitted, there is great potential for utilizing the VOC profile to obtain a quick and reproducible test of vigour status of crop seeds. In order to harness the VOC profile for quick assessment of vigour status of seeds, research has to be taken up to develop standard protocols for fingerprinting of VOCs for the purpose of seed vigour assessment and to fix the standard volatile biomarker(s) specific to crop and vigour status of seeds.

Suaeda salsa is an annual herbaceous euhalophyte in the family Chenopodiaceae that produces dimorphic seeds on the same plant under natural conditions. In order to determine the effect of salinity on seed quality traits during seed formation, seeds from plants grown under control conditions and on 200 mM NaCl were used to investigate the effect of NaCl on seed production and seed germination. Results showed that size and weight of both black and brown seeds generated from 200 mM NaCl-treated plants were markedly greater than those from controls. The germination percentage of brown seeds from both control and NaCl-treated plants was higher than that of black seeds. Furthermore, the germination percentage of the black seeds generated from 200 mM NaCl-treated plants was significantly higher than that of the control at different concentrations of NaCl, although germination percentage declined with the increase NaCl concentration. Surprisingly, NaCl did not affect germination of the brown seeds. The germination index and vigour index of both black and brown seeds from the control plants were significantly lower than those of seeds from the different NaCl treatments. Seed starch, soluble sugar, protein and lipid content of both black and brown seeds generated from the 200 mM NaCl-treated plants were significantly higher than those from the control. These results suggest that a certain concentration of NaCl plays a pivotal role in seed vitality of the euhalophyte S. salsa through increasing seed weight and contents of storage compounds such as protein, starch and fatty acids.

The physically dormant seeds of Ipomoea lacunosa and of I. hederacea undergo sensitivity cycling (insensitive ↔  sensitive) to dormancy-breaking treatment. Sensitivity cycling is important to seeds with physical dormancy in sensing appropriate environmental conditions for germination. Seed vigour is also important to seedling establishment, but no study has compared changes in vigour (or not) with changes in sensitivity. This study was conducted to determine the relationship between sensitivity cycling and seed vigour in I. lacunosa and I. hederacea. The seed moisture contents of insensitive and sensitive seeds of I. lacunosa and of sensitive seeds of I. hederacea were measured, and several vigour tests were performed. Vigour of sensitive seeds of I. lacunosa decreased more rapidly than that of insensitive seeds. No significant change in vigour was observed in either permeable or impermeable seeds of I. hederacea. We conclude that sensitivity cycling to physical dormancy break is important in maintaining vigour of I. lacunosa seeds in the soil seed-bank.

The sorption isotherm for excised embryonic axes of recalcitrant (i.e. desiccation-sensitive) Quercus robur L. acorns was determined to find the relation between moisture content and water potential. Subsequently, physiological studies on the effect of desiccating the axes to a range of water potentials were undertaken. The respiratory capacity declined steeply after short exposure to water potentials from −5 to −30 MPa. The leachate conductivity increased significantly after exposure to −5 MPa and rose steeply after exposure to between −12 and −40 MPa. Axes were equilibrated at different relative humidities and the proline content showed a 15-fold increase with a peak value at −10 MPa. It was concluded that the critical water potential for initiation of damage was −5 MPa, and that axes accumulated proline as a response to desiccation stress. The embryonic axes from Q. robur behave more like typical vegetative tissue of angiosperms than like orthodox seeds.

Some of the seed-evolved volatiles, which were mainly composed of methanol, acetaldehyde, ethanol and acetone, caused the loss of seed germinability during storage. In general, the deleterious effects of the volatiles increased with increasing RH and temperature during storage. Acetaldehyde had the strongest deleterious effect regardless of RH and temperature, while ethanol caused seed deterioration only at high RHs. Acetone was slightly deleterious to some species, while methanol was almost inert in most seeds. Various aldehydes applied during storage showed some toxicity to seed germinability, which decreased, except for 3-methylbutanal, with increasing molecular size, suggesting that the endogenous volatile compounds with an aldehyde group cause seed deterioration. On the other hand, the contents of volatile compounds in seeds were higher when they were stored at 44% RH (water sorption zone 2), than when stored at 12% RH (water sorption zone 1). Acetaldehyde, the most deleterious volatile, was more abundantly accumulated within the seeds stored at −3.5°C than at 23°C. Based on these facts, it is suggested that endogenous volatiles, especially acetaldehyde, may be an important factor that accelerates seed deterioration which often occurs under lower RHs and/or temperatures throughout long-term storage.

The rate of oxygen consumption by cabbage seeds increased on imbibition and there was a further sharp increase on germination. This was delayed in artificially aged seeds of low vigour. The increases in oxygen consumption reflect the increased oxidation of carbohydrates via respiratory pathways. The activities of key regulatory enzymes of glycolysis and the oxidative pentose phosphate pathway were measured in aged and unaged seed lots of cabbage. Differences in the activities of glucose 6-phosphate dehydrogenase and pyrophosphate:fructose 6-phosphate 1-phosphotransferase were correlated with the rate of germination (T50) in seed lots with large differences in seed vigour induced experimentally by artificial aging. However, the activities of these enzymes could not be used to distinguish between untreated seed lots which had smaller vigour differences apparent only under stress. The enzymes are presumably not controlling and determining seed vigour, but merely reflecting actual seed performance under the current conditions.

When seeds deteriorate, they lose vigour and become more sensitive to stresses upon germination. Eventually seeds lose the ability to germinate. The factors which determine the rate of this ‘aging’ are the temperature and moisture content at which seeds are stored and an ill-defined parameter, seed quality. While it has been known for many years that manipulation of these factors influences the longevity of seeds, the precise interactions among them are so poorly understood as to preclude the prediction of longevity for a particular seed lot. Concepts from studies of materials and food stability can be applied to seed aging research, and this may help us take a more integrative approach to understanding the kinetics of seed deterioration. These concepts describe the physical environment of the seed matrix in response to changing water contents and temperature. Water activity models describe the state of water in the seed, while the glass models describe the state of the aqueous solution. Both models presume that changes of state affect the nature and kinetics of chemical reactions. Thus, the physical and chemical environment within the seed are inextricably linked.

Profiles of proteins synthesized in vivo in radicle tips were compared among unaged, artificially aged (controlled deterioration: 10% moisture content at 42°C for 3 weeks), osmoprimed (−1.5 MPa polyethylene glycol 6000 at 20°C for 1 week), and artificially aged and subsequently osmoprimed cauliflower (Brassica oleracea L.) seeds. Germination and initiation of incorporation of 35S-methionine into radicle tips were delayed by controlled deterioration. Osmopriming accelerated these processes and also alleviated the delays. The labelled proteins were analysed by two-dimensional gel electrophoresis and fluorography. Proteins were found whose expression correlated with the rate of germination, and was reduced by controlled deterioration but enhanced by osmopriming. Subsequent osmopriming reversed the effect of controlled deterioration and even caused an enhancement up to the level of unaged osmoprimed seeds. These proteins appeared to be related to processes preceding visible germination. In unaged seeds, formation of the proteins in the radicle tip began upon imbibition but decreased towards visible germination. On silver-stained gels, one of the proteins was shown to be mobilized by the time of radicle protrusion, while all were found in dry seeds. Proteins whose pronounced expression was observed only after both treatments were also found.

The effect of natural and artificial seed ageing has been compared in terms of physiological and biochemical responses of several maize genotypes. The physiological parameters were: viability, germinability, emergence in sand and dry matter accumulation. The biochemical parameters were: DNA synthesis and DNA polymerase activity. A close and direct relationship was found between seed deterioration and DNA metabolism in all maize materials which responded to ageing according to their genetic constitution; i.e., vigorous genotypes suffered less severe damage or recovery was faster than in the low-vigour genotypes. Coordination of events at appropriate times would seem a critical factor for proper seed germination.

Artificial aging of wheat grains (Triticum aestivum cv. Mercia) for 3 d resulted in the gradual loss of seed vigour without loss of viability, but the latter decreased rapidly over the next 24 h. Loss of vigour was expressed as a delay in germination i.e. an increasing ‘lag’ period with aging before the onset of radicle emergence, but the subsequent rate of seedling growth was not affected. There was an overall decrease in the incorporation of 35S-methionine into protein in aged embryos, and associated with the aging-induced delay in the completion of germination (i.e. start of radicle emergence) there was a delay in the production of certain polypeptides. In embryos of both non-aged and aged seeds these polypeptides appeared just prior to radicle emergence but several of these were never synthesized in embryos from non-viable seeds. The synthesis of mRNA coding for in vitro translated polypeptides, or groups of polypeptides, was similarly delayed in lowvigour embryos. Furthermore, some polypeptides were identified which were induced by the accelerated aging treatment. It is concluded that a reduced level of protein and mRNA synthesis in the embryos of low-vigour seeds may result in the delay in the accumulation of specific of mRNAs and polypeptides which are needed for the normal completion of germination, i.e. radicle emergence.

Plants respond to sub-optimal conditions by the synthesis of specific ‘stress’ proteins, and these are thought to play a role in stress tolerance. Some of these proteins accumulate during late seed development, arguably to protect against damage during post-maturation drying and subsequent imbibition, prior to germination. Seed vigour is also determined during this late stage of seed development. High vigour seeds are those that can withstand the desiccation required for storage and successfully germinate under sub-optimal conditions to establish healthy seedlings. If stress proteins are involved in tolerating stress conditions, then they are likely to be important determinants of seed vigour. In this work the relationship between seed vigour (measured by seed germination performance following rapid aging, or under water stress) in Brassica oleracea var. capitata and the content of two classes of stress protein (dehydrins and a low molecular weight heat shock protein HSP17.6) at maturity was examined. Dehydrins did not show a positive relationship with seed performance. However, the protein HSP17.6 showed a positive correlation with seed performance, and a treatment that reduced the amount of this protein in the seed also caused a reduction in subsequent seed performance.

Cotyledon length in onion (Allium cepa, cv. White Lisbon) was linearly related to time from radicle emergence until the formation of the cotyledon hook, but thereafter increased exponentially with time. Within each phase the rate of cotyledon elongation was linearly related to temperature, and these relations were similar among seeds from several percentiles of the germinating populations of three contrasting seed lots. The mean base temperature was 1.4°C. These thermal time relations closely predicted the elongation of cotyledons of seedlings from cohorts of early- and lategerminators from a further lot of this cultivar at two suboptimal temperatures. Eleven cohorts of seedlings from seeds of differing quality were transplanted to the field on both the same date and at the same time from visible germination. The plants were harvested 59 days later. No effect of seed quality on mean plant weight, mean bulb diameter, or interplant variation in bulb diameter was detected. It is concluded that the rate of pre- and post-emergence seedling growth in onion is independent of environmentally induced differences in seed quality (seed vigour). Thus, any effect of this factor on plant size or crop yield, at a given density, is solely a function of time to germinate.

The involvement of ethylene in determining the time to radicle protrusion was investigated in ethylene-insensitive gain-of-function (GOF) receptor mutants in tomato and Arabidopsis, as well as in single and double loss-of-function (LOF) receptor mutants in Arabidopsis. Because ethylene evolution from seeds is coincident with radicle protrusion, and the ability to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene is diagnostic for seed vigour, it was hypothesized that ethylene-insensitive mutants would require more time to complete germination compared to wild-type seeds. Mutant Never Ripe (Nr) tomato seeds from two genetic backgrounds refuted this hypothesis, while experiments with wild-type seeds, treated with the ethylene action inhibitors, 2,5-norbornadiene or silver thiosulphate, supported it. However, reciprocal crosses between wild-type and Nr demonstrated that ethylene insensitivity during seed development determined subsequent time to complete germination, rather than the ability of the embryo/endosperm to perceive ethylene in the mature seed during germination. Additionally, seed quality, determined by standard vigour tests, was reduced in Nr compared to wild-type seeds, establishing a disconnection between rapid completion of germination and seed vigour. In Arabidopsis, all ethylene-insensitive GOF, and five of six single LOF mutants, required more time to complete 50% radicle protrusion, while double LOF mutants required the same, or less, time to complete germination compared to wild-type seeds. These findings support a role for ethylene perception in determining the length of time Arabidopsis seeds remain in the lag phase prior to radicle protrusion.

The aim of this study was to investigate whether there was a relationship between growth of sunflower seedlings at 15°C in the dark and activities of enzymes involved in scavenging of reactive oxygen species (ROS), especially superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR), or in production of free radicals, namely lipoxygenase (LOX). Untreated control seeds were compared with seeds exposed to accelerated ageing (5 d at 45°C and 100% relative humidity), osmopriming (7 d at 15°C with a polyethylene glycol (PEG) solution at –2 MPa) and accelerated ageing followed by priming. Accelerated ageing decreased seed germinability and slowed down hypocotyl growth, whereas priming resulted in an increase in germination rate and enhanced seedling development. Osmopriming of aged seeds almost completely restored the initial rate of germination and seedling growth. The activity of all the enzymes studied increased during seed germination and seedling development, except that of SOD. Seed imbibition or radicle protrusion were related mainly with an increase in CAT activity and, to a lesser extent, in GR activity. Increase of LOX activity was clearly associated with the onset of hypocotyl elongation. However, in all cases, malondialdehyde measurements did not reveal intense lipid peroxidation. Priming induced a marked stimulation of CAT and GR during seed imbibition or very early during seedling development, as compared to the control seedlings and particularly to the seedlings generated by aged seeds. Hydrogen peroxide (H2O2) contents of seeds and seedlings were closely correlated to the activities of CAT and GR and to the kinetics of seedling development. The results obtained establish a clear relationship between sunflower seed vigour and ROS scavenging.

The ability of seeds to germinate and establish seedlings in a predictable manner under a range of conditions has a direct contribution to the economic success of commercial crops, and should therefore be considered in crop improvement. We measured traits associated with seed vigour and pre-emergence seedling growth in a segregating population of 105 doubled haploid Brassica oleracea lines. The germination traits measured were: mean germination times for unstressed germination; germination under water stress or germination after a heat treatment; and conductivity of seed leachate. The seedling growth traits measured were: seed weight; seedling growth rate; and seedling size at the end of the exponential growth phase. There were some correlations, notably among germination traits, and between seed weight and pre-emergence seedling growth. Heritability of the various traits was typically in the 10–15% range, with heritability of conductivity and mean germination time under water stress 25 and 24% respectively. Collectively the results indicate that germination and pre-emergence seedling growth are under separate genetic control. Quantitative trait loci analyses were carried out on all measurements and revealed significant loci on linkage groups O1, O3, O6, O7 and O9. We suggest that genes at these loci are important in determining predictable seed germination and seedling establishment in practice.