Prehydration and Priming Treatments that Advance Germination also Increase the Rate of Deterioration of Lettuce Seeds

The influence of prehydration in water or priming in –1.5 MPa polyethylene glycol 8000 solution for various periods,followed by redrying, on germination rate and longevity of lettuce(Lactuca sativa L.) seeds (achenes) was determined during controlleddeterioration at 10% moisture content (fresh weight basis) and40°C. Short prehydration treatments (up to 1 h) had littleeffect on either germination rate or longevity, but significantlyimproved root growth rates. Increasing durations of prehydrationor priming reduced the mean time to germination by up to 61%relative to untreated seeds, but also reduced mean seed longevityby as much as 84% Prehydration and priming altered the relationshipsbetween germination rate and viability and between normal andabnormal seedlings during ageing. Prehydration in abscisic acidor at a temperature inhibitory to germination did not preventthe reduction in longevity under controlled deterioration conditions.While prehydration or priming treatments effectively acceleratesubsequent germination rates of lettuce seeds, the redried seedsare nonetheless highly susceptible to deterioration in storage. Key words: Lettuce, Lactuca sativa L., seed priming, seed deterioration, germination rate     

The Survival of Germinating Orthodox Seeds after Desiccation and Hermetic Storage

Seeds of barley (Hordeum vulgare L.) and mung bean (Vigna radiata(L.) Wilczek), with orthodox seed storage behaviour, were imbibedfor between 8 h and 96 h at 15 °C and 25 °C, respectively,while barley seeds were also maintained in moist aerated storageat 15 °C for 14 d. These seeds and seedlings, together withcontrols, were then dried to various moisture contents between3% and 16% (wet basis) and hermetically stored for six monthsat —20°C, 0°C or 15°C. In both species, neitherdesiccation nor subsequent hermetic storage of the control lotsresulted in loss in viability. The results for barley seedsimbibed for 24 h were similar to the control, but desiccationsensitivity increased progressively with duration of imbibitionbeyond 24 h in barley or 8 h in mung bean; these treatmentsalso reduced the longevity of the surviving seeds in air-drystorage. Loss in viability in barley imbibed for 48 h was mostrapid at the two extreme seed storage moisture contents of 3·6%and 14·3%, and in both these cases was more rapid at15 °C than at cooler temperatures. Similarly, for mung beanimbibed for 8 h, loss in viability was most rapid at the lowest(4·3%) moisture content, but in this case it was morerapid at –20 °C than at warmer temperatures. Thus,these results for the storage of previously imbibed orthodoxseeds conform with the main features of intermediate seed storagebehaviour Key words: Barley, Hordeum vulgare L., mung bean, Vigna radiata (L.) Wilczek, desiccation sensitivity, seed longevity, seed storage behaviour     

Low Moisture Content Limits to Relations Between Seed Longevity and Moisture

Discontinuities at low moisture contents in the otherwise logarithmicrelations between seed longevity and seed moisture content (%,f. wt basis) in hermetic storage at 65 °C were detectedat 2–0% in groundnut (Arachis hypogaea L.), 3·5%in onion (Allium cepa L.), 4·5% in sugar beet (Beta vulgarisL.), 4·6% in barley (Hordeum vulgare L.), 5·3%in chickpea (Cicer arietinum L.) and wheat (Triticum aestinumL.), and 5·6% in cowpea [Vigna unguiculata (L.) Walp.].In contrast, the equilibrium relative humidity of seeds at thesevalues was similar, varying between 9·9% (onion and sugarbeet) and 11·5% (wheat). The mean value was 10·5%r.h. (s.e. 0.2). There was no significant (P > 0·05)effect of further reduction in seed moisture content below thesecritical values on longevity, except in wheat (P < 0·005),in which there was a further increase in longevity. In soyabean [Glycine max (L) Merrill], the logarithmic relation continueddown to the lowest moisture content investigated, 3·3%(11·4% equilibrium relative humidity). Above the criticalvalue, seed longevity in groundnut showed the least sensitivityto increase in percentage moisture content, while barley showedthe greatest, the values of the viability constant C_w (slopeof the negative logarithmic relation between longevity and moisture)being 4·089 (s.e. 0·278) and 5·966 (s.e.0·325), respectively. These differences in the valueof C_w among the eight crops were significant P < 0·005),whereas the relative sensitivity of seed longevity to changein equilibrium relative humidity above the critical moisturecontent did not differ significantly among the eight (P >0·10) and was equivalent to a doubling of longevity foreach 8·7% reduction in equilibrium relative humidity.Accordingly it is concluded that the relative effect of waterpotential on seed longevity can be considered to be the samefor these and probably also for many other orthodox species. Barley, chickpea, cowpea, groundnut, onion, soya bean, sugar beet, wheat, seed storage, seed longevity, seed moisture content, viability equation, water relations     

An Intermediate Category of Seed Storage Behaviour?: I. COFFEE

Seeds of four cultivars of arabica coffee (Coffea arabica L.)were tested for germination following hermetic storage for upto 12 months at several different combinations of temperaturesbetween –20 °C and 15 °C and moisture contentsbetween 5% and 10% (wet basis). Most of the seeds from one cultivarwithstood desiccation to between 5% and 6% moisture content,a seed water potential of approximately –250 MPa, butthose of the remaining three cultivars were much more sensitiveto desiccation damage. Moreover, in all four cultivars, seedlongevity at cool and sub-zero temperatures, and at low moisturecontents did not conform with orthodox seed storage behaviour:viability was lost more rapidly under these conditions thanat either warmer temperatures or higher moisture contents. Theresults confirm that coffee seeds fail to satisfy the definitionsof either typical orthodox or recalcitrant seed storage behaviour.These results, therefore, point to the possibility of a thirdcategory of storage behaviour intermediate between those oforthodox and recalcitrant seeds. One of the main features ofthis category is that dry seeds are injured by low temperatures. Key words: coffee, Coffea arabica L., seed storage, seed longevity, desiccation, temperature     

The Effect of Chilling and Moisture Status on the Germination, Desiccation Tolerance and Longevity ofAesculus hippocastanumL. Seed

Effects of 2 °C chilling on the threshold moisture contentsand water potentials for various physiological processes wereestimated forAesculus hippocastanumL. seed. Seed harvested atthe time of maximum seed fall exhibited a dual response to drying:partial drying from near 50% to 32–40% moisture contentprogressively increased germination percentage (at 16 °C)up to various peak values; further desiccation was detrimental,confirming that the seeds are ‘recalcitrant’. Themoisture content for optimum germination was increased by atleast 10% as the chilling period was raised from 0 to 9 weeks.A negative linear relationship was found between log₁₀mean timeto germinate and probit final germination, regardless of pre-treatment,indicating that partial desiccation and chilling are interchangeablein promoting germination of hydrated seed. For nearly fullyhydrated seeds, increasing the chilling period from 6 to 26weeks increased the viability-loss onset point for desiccationinjury from near 40% to about 48% moisture content without alteringthe drying rates of seed tissues. Extending moist chilling invarious seed lots from 0 to 26 weeks decreased subsequent longevityat 16 °C. For 26-week-chilled seeds longevity (the periodto lose one probit of germination) differed above and belowa threshold moisture content of 48%. It remained constant inthe moisture-content range 48–38%, but increased progressivelyas moisture content was raised above 48%. This threshold moisturecontent coincided with the value above which chilled seed pre-germinatedin storage. The results indicate that post-harvest desiccationand chilling alter the water relations of various physiologicalprocesses and a schematic summary is presented which relatesthe results to an axis water sorption isotherm.Copyright 1998Annals of Botany Company Aesculus hippocastanumL., horse chestnut, chilling, moisture content, water potential, desiccation tolerance, longevity, recalcitrant seed, embryo axis, maturation, germination.     

Phenotypic Mutations Induced During Storage in Barley and Pea Seeds

Previous work on chlorophyll-deficiency mutations in pea andbarley has shown that a significant increase in mutations isinduced by storing seeds under various conditions which leadto losses of viability to about 50 per cent. The work here showsthat a detectable increase in mutation frequency is also associatedwith much smaller losses of viability. Pea seeds were storedat 35 °C and 16.5 per cent moisture content for 40 and 57d when viability fell from 99 to 93 and 82 per cent, respectively.At the same time mutation frequency (percentage of seeds containingrecessive point mutations) increased from 1.62 per cent in thecontrol treatment to about 3 to 4 per cent. Barley seeds at15.5 per cent moisture content were stored at 50 °C for42 and 54 h, and at 35 °C for 28 and 39 d. During theseageing treatments viability fell from 98 to 75, 26, 93 and 48per cent respectively and the mutation frequency increased fromzero to between about 0.3 to 0.9 per cent. In both species theinduction of mutation by ageing treatments was significant butthe differences between the various ageing treatments were not.It is concluded that there is probably no safe threshold lossof viability which completely avoids mutation, and these resultssupport the view that for genetic conservation seeds shouldbe stored under conditions which minimise loss of viability. Pisum sativum L., pea, Hordeum distichum L., barley, mutation frequency, seed storage, seed viability     

Moisture Content and the Longevity of Seeds of Phaseolus vulgaris

The lower limit to the negative logarithmic relation betweenseed longevity and moisture was determined in bean (Phaseolusvulgaris L.). Sub-lots of seed were hermetically stored at 65°C and 11 moisture contents (3.26–13.6% f. wt) forup to 80 d, tested for germination and the seedlings evaluated.In accordance with the seed viability equation, there was anegative logarithmic relation between moisture content (%, f.wt) and longevity. Two different criteria for estimating theslope constant of this relation gave similar values of 4.76(s.e. 0.26) and 4.82 (s.e. 0.24). The calculated lower moisturecontent limits to the relation were 5.7 and 5.6%, respectively,values at equilibrium with 10.6–10.8% relative humidity(rh). Further drying to 3.26% had little additional effect onlongevity, but initial germination was slightly reduced. Theresults are discussed in relation to water potential and comparedwith other crops. Arguments against transforming germinationvalues to disregard the seeds initially failing to germinateare emphasized. Common bean, Phaseolus vulgaris L. cv. Provider, seed storage, seed longevity, seed moisture, viability equation, water relations     

Responses of Vegetable Seeds to Controlled Hydration

Leek, onion and carrot seeds were imbibed in water and in solutionsof polyethylene glycol (PEG) 6000 over the range –0.5to –4.0 MPa osmotic potential, for periods up to 28 dat 15 C. Seeds started to germinate after 7 and 14 d at –0.5MPa and –1.0 MPa PEG, respectively, but in the lattercase, germination did not exceed 5%. No germination occurredin solutions of lower (more negative) osmotic potential. Seedmoisture content increased with osmotic potential in all threespecies and the relationships were unaffected by the durationof imbibition in solutions of –1.0 to –4.0 MPa,though leek seeds had higher moisture contents than the otherspecies for any given osmotic potential. Linear relationships between response to priming (differencebetween mean germination times of primed and untreated seeds)and seed moisture content were obtained for each species, positiveresponses being obtained above 30–35% seed moisture contentwith optima at 46, 44.5 and 44% seed moisture contents in leek,onion and carrot, respectively. Priming had no effect on embryovolume or cell number per embryo in leek and onion. Carrot embryovolume increased by 43% and cell number per embryo doubled inprimed compared with untreated seeds, whereas seeds imbibedin water showed only a slight increase in cell number per embryoat the stage when radicles were beginning to penetrate the seedcoat. Allium cepa L. cv. Rijnsburger Robusta, onion, Allium porrum L. cv. Winterreuzen, leek, Daucus carota L. cv. Nantaise, carrot, germination, priming, polyethylene glycol, seed moisture, cell number, embryo volume     

Improved Equations for the Prediction of Seed Longevity

Equations for predicting seed longevity in storage have beenimproved so that they now take into account variations withina species in initial seed quality—which is affected bygenotype and pre-storage environment—and so that theyare more accurate over a wider range of storage environmentsThese improvements have been incorporated into a seed viabilitynomograph for barley (Hordeum distichum L.) which may be usedto predict percentage viabihty of any seed lot after any timein any storage environment within the range –20 to 90°C and 5–25 per cent moisture content. Applicationsof the improved equations to seed drying and to long-term seedstorage for genetic conservation are discussed. Hordeum distichum L., barley, seed viability, seed longevity prediction, seed storage, seed drying, storage temperature, seed moisture content, genetic resources conservation     

Effects of Moisture Content on Germination of Seeds of Hancornia speciosa Gom. (Apocynaceae)

Seeds of Hancornia speciosa germinated best at a temperatureof 20–30 °C. The viability of the seeds during storagewas short and the best storage conditions for viability entailedkeeping the seeds in polyethylene bags. Seed viability was maintainedonly when the seeds were stored at a moisture content above30%; storage conditions which allowed dehydration resulted ina rapid loss of viability (the seeds showed recalcitrant behaviour). Low temperature during storage did not improve longevity. Arelationship between germination and moisture content was established,but when the moisture content fell below 25% there was a drasticreduction of germination. After 9 weeks of storage, even athigh moisture content, seeds lost viability. Loss of seed viability during seed dehydration was associatedwith increased leakage of electrolytes and organic solutes,and reduced tetrazolium staining during subsequent imbibition. Hancornia speciosa, germination, recalcitrant seeds, storage, moisture     

The Effects of Temperature and Moisture on the Induction of Genetic Changes in Seeds of Barley, Broad Beans, and Peas during Storage

Seeds were ‘aged’ by treatments with various combinationsof temperature and moisture content so that viability was reducedto about 50 per cent. It was shown that such treatments inducednon-heritable morphological abnormalities in about 10 per centof the bean plants and 5 per cent of the pea plants; but nonon-heritable morphological abnormalities were observed in thebarley plants. In all species there was an increased frequencyof pollen abortion in the plants produced from ‘aged’seeds. From the examination of second and third selfed generationsit was shown that single-recessive and double-recessive chlorophyll-deficiencymutations of various types were usually induced in sectors ofabout 1–3 per cent of the plants grown from treated seeds. The evidence from pollen-abortion supports previous cytologicalevidence that, under most storage conditions, for a given lossof viability, a predictable amount of chromosome damage is foundin the surviving seeds, irrespective of how fast viability waslost or which environmental factor was mainly instrumental inthe loss of viability. A comparison of the frequency of chlorophyllmutations produced under different storage treatments was notas quantitatively precise, but this evidence also is at leastcompatible with the thesis that loss of seed viability is associatedwith chromosome damage which is reflected in gene mutation.It is concluded, therefore, that percentage seed viability isa good index of the loss of genetic purity resulting from mutationswhich accumulate during storage.     

Seed Viability Constants for Lettuce

Seeds of two lettuce cultivars (Lactuca sativa L., cv. Meikoninginand cv. Grand Rapids) were hermetically stored with constantmoisture contents ranging between 3.6 and 17.9 per cent (freshweight basis) at constant temperatures ranging between 5 and75 °C. The decline with time in percentage germination andpercentage normal seedlings was determined for each storagetreatment. The data were fitted to an equation which containsthe constants: K₁, the probit of the initial percentage germinationor normal seedlings; K_E, a species constant; C_W, the constantof a logarithmic moisture term; C_H, the constant of a lineartemperature term and C_Q, the constant of a quadratic temperatureterm. Regression analysis of data from storage periods up to5.5 years at temperatures of 5–75 °C and seed moisturecontents of 3.6–13.6 per cent yielded the following values:K_E= 8.218, C_W=4.797±0.163, C_H=0.0489±0.0050 andC_Q=0.000365±0.000056. Although this equation consistentlyprovided a better fit, simplified equations, assuming eithera log-linear relationship between seed longevity and temperature,or a log-linear relationship between seed longevity and bothmoisture content and temperature, accounted for more than 94per cent of the variation at the restricted temperature rangeof 5–40 °C. Longevity of the same seed lots at sub-zero temperatures (–5,–10 and –20 °C) was studied in separate tests.Freezing damage, resulting in abnormal seedlings in the germinationtest, occurred at –20 °C when the moisture contentof the seeds exceeded 12 per cent. No decline in percentagenormal seedlings was observed after a storage period of 18 monthsor longer at –20 °C, provided the seed moisture contentdid not exceed 9.5 per cent. For seeds stored at –5 and–10 °C with 9.6–12.5 per cent moisture content,the observed rate of decline of percentage normal seedlingswas adequately predicted by the viability equation, using theabove values for the constants. This suggests that for low moisturecontents the viability equation can be applied to estimate longevityat sub-zero temperatures. Lettuce, Lactuca sativa (L.), seed longevity, seed storage, viability constants, storage conditions     

A Comparison of the Quantitative Effects of Seed Moisture Content and Temperature on the Accumulation of Chromosome Damage and Loss of Seed Viability in Lettuce

The rate of accumulation of cells containing chromosome aberrationsin lettuce (Lactuca sativa L.) seeds is a positive functionof temperature and moisture content. It may be described byan equation similar to that for loss of seed viability. Therelative effect of temperature on the rates of loss of viabilityand accumulation of chromosome aberrations is the same. In contrast,the relative effect of moisture on the rate of loss of viabilityis greater than that for the rate of accumulation of aberrations.Hence considerably more chromosome damage accumulates beforedeath in drier lettuce seeds. Lactuca sativa, lettuce, seed storage, seed viability, seed longevity, chromosomal aberrations temperature, moisture content     

Water Status Changes During Development in Relation to the Germination and Desiccation Tolerance of Aesculus hippocastanum L. Seeds

Seed growth characteristics of Aesculus hippocastanum were examinedin detail during development from about 70 to 140 d after anthesis(DAA), mainly in 1988 and 1989. Mean fresh and dry weights increasedfor both the axis and the whole seed up to the time of peakseed fall at 135 DAA with no cessation before fruit abscission.Water per seed increased up to 100 DAA, after which no furtherincrease occurred; moisture content declined for the embryonicaxis and whole seed respectively from above 75 and 65% at 95DAA to 65 and 50% at 130 DAA. At fruit shedding in 1990 waterpotential values of -1·2, -2·6 and -1·1MPa were observed for the testa, cotyledon and axis tissuesrespectively; relevant sorption isotherms are presented. Decreases in seed moisture content during development were accompaniedby increases in desiccation tolerance and in germinability,both reaching their maximum at the time of peak seed fall. Atmaturity, only about 10% viability was retained on drying seedto 20% moisture content; it is confirmed that the seeds are'recalcitrant'. The exact relationship between moisture contentand germination during development was dependent on the deptof dormancy, as judged by the period of chilling required; eachduration of chilling at 2°C within the range 3-12 weeksyields a curve of sigmoid shape. No germination occurred at26°C without chilling, but nearly full germination can beobserved for samples collected at 6 weeks before maximum seedfall with 12 weeks chilling. The rate of moisture loss duringdesiccation at 15°C and 15% rh becomes reduced during development.The ontogeny of these 'recalcitrant' seeds is compared withthat of 'orthodox' seeded species and the implication of sigmoid-shapedcurves for the relationship between seed moisture content andgermination are considered.Copyright 1993, 1999 Academic Press Aesculus hippocastanum L., horse chestnut, seed development, water status, germination, desiccation intolerance, desiccation rate     

The Viability of Cereal Seed in Relation to Temperature and Moisture: With eight Figures in the Text

Critical examination of previous work on the viability of cerealseeds shows that there is a simple mathematical relationshipbetween temperature, moisture content, and period of viability.There is evidence that this relationship is similar for wheat,barley, and oats. If the moisture content and temperature ofthe seed is known it is possible to predict the expected lifeof the seed; or alternatively, it is possible to predict variouscombinations of storage conditions necessary to achieve a requiredperiod of viability. These results are discussed in relationto current theories concerned with factors which cause lossof viability in seeds.     

The Influence of Temperature and Moisture on Seed Viability Period in Barley (Hordeum distichum L.)

Storage experiments were carried out on barley seed (Hordeumdistichum L.) lasting from 1 min to 926 days, including 52 hermeticstorage environments covering a range of temperatures from 3to 90 °C and 5·5 per cent to 24·6 per centmoisture content (f. wt basis). Over the entire range of conditionssurvival curves conformed to negative cumulative normal distributionsand, for any given measure of longevity, e.g. half-viabilityperiod, longevity was roughly proportional to the negative exponentof both temperature and moisture content. Although previouslyreported viability equations were adequate to describe theserelationships over restricted ranges of environments, over theextended range of conditions tested here it was shown that therelationship between log seed viability and temperature is infact slightly convex, whilst that between log seed viabilityand moisture content is slightly concave. An improved viabilityequation was applied which takes into account those curvaturesand, at the same time takes into account the initial viabilityof a seed lot which reflects pre-storage deterioration. Thefit was excellent and thus it is now possible to predict percentageviability of any lot of barley seed after any storage periodunder a very wide range of conditions. Hordeum distichum L., barley viability, seed longevity, seed storage, moisture content of barley seed, temperature, influence of seed viability     

Osmoconditioning and Ageing of Pepper Seeds During Storage

The effects of osmoconditioning on the germination at 15 and25 °C of pepper (Capsicum annuum L.) seeds were studiedover a 3-year period with respect to temperature of storage.Untreated seeds stored at 5 °C showed high germinabilitythroughout the entire storage period, whereas untreated seedsstored at 25 °C showed a progressive decline in germinability,especially when assayed at 15 °C. Seeds that had been osmoconditionedprior to storage retained a high level of germinability irrespectiveof either storage or germination temperatures. When seeds thathad been stored at 25 °C were osmoconditioned after storage,there was a significantly higher germinability (assayed at 15 °C) in comparison with the corresponding untreated seeds.Seeds that were osmoconditioned twice (prior to and after storage)germinated in a similar way to those that had been osmoconditionedonce only Lactuca saliva L., lettuce, Hordeum oulgare L., barley, seed storage, moisture content, relative humidity, water potential, temperature, oxygen     

Time to Seed Death as a Function of the Gibbs Free Energy of Water Vapour: Practical and Theoretical Implications

Time (t) to loss of seed viability (e.g. log t or log ) is modelledin the literature as the sum of a moisture term and a quadratictemperature term, f(T,T²). The coefficients inf(T,T²) have beenshown to be ‘identical’ in orthodox seeds. I postulatethat this identity is due to a parameter common to all seedsand, consistent with that hypothesis, report a close correlation(R²=0.9998) between f(T,T²) and the Gibbs free energy of watervapour, G, over the temperature range 0–90 °C. Thehypothesis has the statistical advantage of reducing the numberof independent variables from two to one, without changing thefit. This is demonstrated from analysis of data for lettuceand barley. An explanation for this correlation of time to seeddeath with G is that water vapour is the proximate source ofenergy leading to decomposition of individual molecules, withthe ultimate result of seed death. Copyright 1999 Annals ofBotany Company Seed longevity, temperature effect, Gibbs free energy of water vapour, moisture-temperature interactions, Hordeum vulgare L., barley, Lactuca sativa L., lettuce.     

Logarithmic Relationship between Moisture Content and Longevity in Sesame Seeds

The relationship between seed moisture content and seed longevityin sesame (Sesamum indicum L.) in hermetic storage at 50 °Cis logarithmic. The logarithmic relationship is maintained from15 per cent down to 2 per cent – the lowest moisture contenttested — but above 15 per cent this ‘air-dry’relationship no longer holds since further increase in seedmoisture content does not reduce longevity. Tentative estimatesof constant values for the improved seed viability equationare provided, and implications for long-term storage are discussed. Sesame, Sesamum indicum L., seed storage, improved viability equation, seed moisture content, seed longevity prediction