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     

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     

The Low-moisture-content Limit to the Negative Logarithmic Relation Between Seed Longevity and Moisture Content in Three Subspecies of Rice

The lower limit to the negative logarithmic relation betweenseed longevity and moisture content was determined in threesubspecies of rice (Oryza satwa L.) by storing seeds of fivecultivars at 65 °C with 11 different moisture contents (1.5–15.3%f. wt) for various periods up to 150 d and then testing forgermination. The estimates of the low-moisture-content limit(m_c) were 4.3% for subsp. indica, 4.4% for subsp. japonica,and 4.5% for subsp. javanica. These moisture contents were inequilibrium with 10.5—12.0% r.h. No significant effectof moisture content between 1.5% and m_c on longevity was detected(P > 0.05), while between m_c and 15.3% there were negativelogarithmic relations between longevity and moisture content.There were no significant differences in the relations betweenlongevity and moisture either above or below m_c between thetwo japonica cultivars or between the two javanica cultivars(P > 0.10). There was also no significant difference in theslope of the negative logarithmic relation between longevityand moisture above m_c among the three subspecies (P > 0.25).However, there were significant differences in the standarddeviation of the frequency distribution of seed deaths in timeat any one moisture content, both above and below m_c; this isa measure of seed longevity which is independent of pre-storageenvironment, and the differences observed show that there aregenetically determined differences in longevity among the threesubspecies (P < 0.005), indica being the longest and japonicathe shortest lived. The results provide no evidence for intra-specificvariation in m_c and support the view that the maximum seed storagemoisture content which provides the maximum longevity is thatwhich is in equilibrium with about 10–11% r.h. It is concludedthat while the seed viability constant C_w of the seed viabilityequation is species specific and therefore applies to most,if not all, cultivars of rice, variation in the value of K_Eis the source of the differences in potential longevity of thethree subspecies. Rice, Oryza sativa L, seed storage, seed longevity, seed moisture, viability equation     

Constant, Fluctuating and Effective Temperature and Seed Longevity: a Tomato (Lycopersicon esculentum Mill.) Exemplar

Tomato seeds with a moisture content of 16.4% were stored hermeticallyat one of five constant temperatures (10, 20, 30, 40, 50 °C)or in one of nine alternating temperature (24 h/24 h) regimes(10/30, 10/40, 10/50, 20/30, 20/40, 20/50, 30/40, 30/50, 40/50°C) for up to 224 d. In each regime, seed survival conformedto cumulative negative normal distributions and all 14 survivalcurves could be constrained to a common origin. Estimates ofthe constants C_Hand C_Qof the viability equation determined atconstant temperatures were 0.0346 (s.e. 0.0058) and 0.000401(s.e. 0.000096), respectively. The effective temperature forseed survival of each alternating temperature regime was alwaysmuch higher than the mean. Tomato seeds were also stored hermeticallyat 15.9% moisture content at 40 °C for 0, 7, 14, 21 or 28d before transfer to 50 °C. This investigation showed thatthe standard deviation of the subsequent survival curves at50 °C was unaffected by the duration of previous storageat 40 °C. The results of both investigations were consistentwith the hypothesis that loss in probit viability is solelya function of the current storage environment, with no effectof change in temperature per se. The application of the viabilityequation to seed survival in fluctuating environments was validatedagainst independent observations for rice in uncontrolled storageconditions. Copyright 2001 Annals of Botany Company Temperature, seed storage, longevity, moisture content, viability equation, tomato, rice     

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     

The effect of temperature and CO2 on seed quality development in wheat (Triticum aestivum L.)

Winter wheat (Triticum aestivum L.) cv. Hereward was grown inthe field in two double-walled polyethylene-covered tunnelswithin each of which a temperature gradient was superimposedon diurnal and seasonal fluctuations in temperature. The meantemperature between anthesis and harvest maturity varied from14.3 to 18.4C among plots within these tunnels. The CO₂ concentrationwas controlled at different values in each tunnel; seasonalmean concentrations were 380 and 684 µmol CO₂ mol^–1air. Crops were also grown outside the tunnels at ambient temperaturesand CO₂. Samples of seeds were harvested sequentially from eachplot between anthesis and harvest maturity. Seed germinationand seed survival during subsequent air-dry storage were determinedfor each sample. The onset of both ability to germinate anddesiccation tolerance (ability to germinate after rapid desiccationto 10–15% moisture content and subsequent rehydration)coincided in all environments. Full germination capacity (>97%, determined at 10C) was reached 4–18 d before theend of the seed-filling phase (mass maturity) in most cases.There was little or no decline in germination capacity duringsubsequent seed development and maturation. Differences in seedquality were evident, however, throughout seed development andmaturation when seed survival curves during subsequent storagewere compared. Potential longevity in air-dry storage (assessedby the value K₁ of the seed viability equation) improved consistentlyboth before and after mass maturity. There was a significantpositive relation between the rate of increase in potentiallongevity (dK₁Idt) and temperature (the minimum temperaturefor seed quality development was 4.8 C), but neither CO₂ concentrationnor production within the polyethylene tunnels affected thisrelation. Key words: Wheat, Triticum aestivum L., seed development, seed longevity, carbon dioxide, temperature     

Seed Longevity of Rice Cultivars and Strategies for their Conservation in Genebanks

Changes in seed quality during ripening were studied in sixteencultivars of rice, representing the three ecogeographic racesofOryza sativa, and one cultivar ofO. glaberrima, grown duringone dry season (Nov. –May) 1992 –1993 at Los Baños, Philippines. Mass maturity (defined as the end ofseed filling period) among the cultivars was attained between18.5 and 21.6d after anthesis (DAA). The seed moisture contentat mass maturity varied between 24 and 40%. Germination abilityof seeds in the early stages of development varied significantly,but as mass maturity approached, germination increased to themaximum and no significant differences were found among cultivars.The seeds were stored hermetically at 35 °C with 15±0.2%moisture content and the resultant seed survival data were analysedby probit analysis. Potential longevity (quantified by the valueof seed lot constantK_iof the seed viability equation) was greatestbetween 33 and 37 DAA, i.e. about 2 weeks after mass maturity.The stage during development at which seeds achieve maximumpotential longevity is described by the term storage maturity.Lowlandjaponicacultivars, large seeded accessions (seed mass40mg) andO. glaberrimahad shorter storage longevity ( , standarddeviation of the frequency of seed deaths in time=1.47 weeks)while cultivars with purple pericarp survived longer than othercultivars ( =2.33 weeks). The initial germination of thejaponicacultivarsat storage maturity was high (99 –100%) and the estimatesof maximum potential longevity (K_i) which ranged between 3.3(Shuang cheng nuo) and 4.4 (Minehikare) were close to thoseof theindicacultivars. This research suggests that seed production environment betweenNov. and May at Los Ba ños is benign for the temperatejaponicacultivars.The implications of these results on management of rice geneticresources are discussed. Oryza sativaL.; rice; germplasm conservation; seed production environment; seed development; seed longevity     

A Low-Moisture-Content Limit to Logarithmic Relations Between Seed Moisture Content and Longevity

Seeds of quinoa (Chenopodium quinoa Willd.), sunflower (Helianthusannuus L.) and linseed (Linum usitatissimum L.) showed negativelogarithmic relations between longevity and moisture contentsbetween 4.4 and 15.4, 3.2 and 13.0, and 3.2 and 15.5%, respectively,in hermetic storage at 65 °C. However, between 1.8 and 3.1,1.1 and 1.9, and 1.1 and 2.1%, respectively, longevity did notvary. The critical moisture content, below which further reductionin moisture content no longer increased longevity in hermeticstorage at 65 °C, for each species was 4.1, 2.04 and 2.7%,respectively. Quinoa, Chenopodium quinoa Willd., sunflower, Helianthus annuus L., linseed, Linum usitatissimum L., seed storage, improved viability equation, seed longevity, seed moisture content     

Theoretical Basis of Protocols for Seed Storage III. Optimum Moisture Contents for Pea Seeds Stored at Different Temperatures

In previous work, we demonstrated that there was an optimummoisture level for seed storage at a given temperature (Vertucciand Roos, 1990), and suggested, using thermodynamic considerations,that the optimum moisture content increased as the storage temperaturedecreased (Vertucci and Roos, 1993b). In this paper, we presentdata from a two year study of aging rates in pea (Pisum sativum)seeds supporting the hypothesis that the optimum moisture contentfor storage varies with temperature. Seed viability and vigourwere monitored during storage under dark or lighted conditionsat relative humidities between 1 and 90%, and temperatures between-5 and 65°C. The optimum moisture content varied from 0·015g H₂O g^-1 d.wt at 65°C to 0·101 g H₂O g^-1 d.wt at15°C under dark conditions and from 0·057 at 35°Cto 0·092 g H₂O g^-1 d.wt at -5°C under lighted conditions.Our results suggest that optimum moisture contents cannot beconsidered independently of temperature. This conclusion hasimportant implications for 'ultra-dry' and cryopreservationtechnologies.Copyright 1994, 1999 Academic Press Seed storage, seed aging, seed longevity, water content, temperature, glass, desiccation damage, ultradry, Pisum sativum L., pea, cryopreservation     

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     

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     

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     

The Effect of Temperature and Moisture Content on the Longevity of Seed of Ulmus carpinifolia and Terminalia brassii

Seeds of the Smooth-leafed Elm (Uimus carpinifolia) and of thetropical forest tree Terb (Terminalia brassii) were stored hermeticallyand sampled at intervals for periods of up to two years. Bothspecies possess ‘orthodox’ seed (increasing longevityis observed as either moisture content or temperature are reduced)within the temperature ranges from — 13 to 52°C (Elm)and from —4 to 42°C (Terb) and within the moisturecontent ranges from 3 to 19 per cent (Elm) and from 5 to 14per cent (Terb) on a fresh weight basis. Elm seed stored at—75°C showed the expected relationship between longevityand moisture content, but did not differ significantly in longevityfrom seed kept at — 13°C when moisture contents wereheld constant. Probit analysis of the relationship between germinationpercentage and time was performed for each storage environment,yielding a slope from which the standard deviation of the distributionof seed deaths over time () was calculated. Standard deviationvalues were used in turn to determine the values of constantsin a viability equation which had previously been applied toseed of barley, chickpea, cowpea and soybean. The equation,which gave a good fit to the results obtained, can be used topredict viability for seed in storage over a wide range of environmentalconditions. Some limitations to the applicability of the viability equationwere defined. At 22 per cent and higher moisture contents Elmseed survived longer than predicted. Furthermore, all Elm andTerb seed was killed quickly on placing in —75°C at22 and 20 per cent moisture content respectively, but high viabilitywas retained for several days at 19 and 17 per cent respectively.Practical implications of the results are discussed. Uimus carpinifolia Gleditsch, Smooth-leafed Elm, Terminalia brassii Exell, Terb, seed longevity, seed storage, moisture content, temperature     

Temperature and Seed Storage Longevity

Seed survival data for eight diverse species, namely the cerealbarley (Hordeum vulgare L.), the grain legumes chickpea (Cicerarietinum L.), cowpea [Vigna unguiculata (L.) Walp.] and soyabean [Glycine max (L.) Merr.], the timber trees elm (Ulmus carpinifoliaGleditsch.), mahogany (Swietenia humilis Zucc.), and terb (Terminaliabrassii Exell.), and the leaf vegetable lettuce (Lactuca sativaL.) were compared over a wide range of storage environments(temperatures from –13 °C to 90 °C, seed moisturecontents from 1.8 to 25% f. wt) using a viability equation developedpreviously. In accordance with that equation, the effect oftemperature on seed longevity was dependent upon the temperaturerange. The temperature coefficients of the viability equationdid not differ significantly (P > 0.05) among the eight speciesdespite their contrasting taxonomy. Thus the quantitative relationbetween seed longevity and temperature does not vary among diversespecies. The same conclusion was obtained for the coefficientsof a proposed alternative model of the relation between seedlongevity and temperature. The implications of the two temperaturemodels in the viability equation for extrapolations to low andvery low temperatures are discussed. Seed storage, seed longevity, seed moisture, temperature, viability equation, genetic resources conservation, Cicer arietinum L., Glycine max (L.) Merr., Hordeum vulgare L., Lactuca sativa L., Swietenia humilis Zucc., Terminalia brassii Exell., Ulmus carpinifolia Gleditsch., Vigna unguiculata (L.) Walp     

The Influence of Genotype, Temperature and Moisture on Seed Longevity in Chickpea, Cowpea and Soya bean

Seed of three chickpea (Cicer arietinum L.), three cowpea [Vignaunguiculata (L.) Walp.] and four soya bean [Glycine max (L.)Merr.] cultivars were hermetically stored for up to 2 yearsin various constant environments which included temperaturesfrom —20 to 70 °C and moisture contents (fresh weightbasis) from 5 to 25 per cent. In all cases the survival curvescould be described by negative cumulative normal distributions.The longevity of the various seed lots differed but the valueof the standard deviation (the reciprocal of which gives theslope of the survival curve when percentage germination is transformedto probit) was the same for all cultivars within a species whenstored under similar conditions. Within each species the relativeeffects of moisture and temperature on longevity did not differsignificantly between cultivars. In all three species therewas a negative logarithmic relationship between seed moisturecontent and longevity, but the relative effect of moisture contentdiffered between the species: differences in the longevity ofsoya bean seed as a function of moisture content were less thanfor either cowpea or chickpea. The relative effect of temperatureon seed longevity did not differ between the three species,and the seed of all three species showed increasing temperaturecoefficients for the change in rate of loss of viability withincrease in temperature. The complete pattern of loss in viabilityin all three species can be described by a single equation whichwas developed for barley and has also been shown to apply toonion seed. The constants applicable to the three grain legumeshave been calculated so that it is now possible to predict percentageviability of any seed lot of these species after any storageperiod under a very wide range of storage conditions. Cicer arietinum L., chickpea, Glycine max (L.) Merr., soya bean, Vigna unguiculata (L.) Walp., cowpea, seed longevity, seed storage, moisture content, temperature     

Desiccation Tolerance and Potential Longevity of Developing Seeds of Rice (Oryza sativa L.)

The longevity and desiccation tolerance of samples of seedsof a japonica rice (Oryza sativa L.) harvested serially duringdevelopment from plants grown in two temperature regimes, viz28/20 °C and 32/24 °C (12/12 h) were determined. Massmaturity (defined as the end of the seed-filling phase) occurred19·7 and 18·3 d after 50% anthesis, respectively.Longevity (determined at 40 °C with 15% moisture contentand quantified by the value of the constant K_i of the seed viabilityequation) improved during seed development and maturation until17 and 14 d after mass maturity in the cooler and warmer regimes,respectively, but declined thereafter. Changes in K_i with timewere similar in the two environments until mass maturity, butthe increase in K_i values after mass maturity was much greaterin the cooler regime. Tolerance of desiccation to low (4%) moisturecontents improved until 22 and 14 d after mass maturity in thecooler and warmer regimes, respectively, when maturation dryinghad reduced seed moisture contents naturally to 24 and 32% moisturecontent, respectively. Further delays to seed harvest reduceddesiccation tolerance, particularly in the warmer environment.Comparison among 15 samples of seeds harvested at differenttimes in the two environments showed a strong correlation (r= 0·947, P < 0·01) between longevity (K_i) anddesiccation tolerance (to 4% moisture content). Hence, it issuggested that the regulation of desiccation tolerance to lowmoisture contents and potential air-dry longevity during seeddevelopment and maturation determined here may have a commoncause.Copyright 1994, 1999 Academic Press Oryza sativa L., rice, desiccation tolerance, genebanks, seed development, seed longevity, temperature     

The Dry Storage of Citrus Seeds

The survival of seeds of lemon (Citrus limon L.), lime [C. arantifolia(Christm.) Swing.] and sour orange (C. aurantium L.) was examinedunder a wide range of constant moisture contents and temperatures.Seed longevity was increased by decreasing the moisture contentand temperature of the storage environment. Maximum viabilitywas maintained in the combination of storage conditions includingthe lowest moisture content (5 per cent) and lowest temperature(–20 °C) investigated. The practicality of dry storageof citrus seed for genetic conservation is discussed. Citrus limon L., lemon, Citrus aurantifolia (Christm.), Swing, lime, Citrus aurantium L., sour orange, dry storage, moisture content, temperature, seed viability, seed longevity     

Limits to the Negative Logarithmic Relationship Between Moisture Content and Longevity in Conidia ofMetarhizium flavoviride

Conidia ofMetarhizium flavoviridewere hermetically stored at50 °C and 14 moisture contents between 2.5 and 31.8% (freshweight basis) for up to 146 d, and tested for germination onSabouraud Dextrose Agar at 25 °C for 24 h. Survival of conidiaconformed to cumulative negative normal distributions and all14 survival curves could be constrained to a common origin.There was a negative logarithmic relation between longevityand conidia moisture content, but limits to the relation weredetected: the lower-moisture-content limit was 4.6% [in equilibriumwith 10.7% relative humidity (RH) at 20 °C], below whichvalue further reduction in moisture content did not increaseconidia longevity; and an upper-moisture-content limit betweenabout 21.2 and 31.8% moisture content (between 77 and 90.0%equilibrium RH at 20 °C) above which conidia longevity nolonger decreased. The observations could also be described bya negative semi-logarithmic relation between conidia longevityand equilibrium relative humidity. In this model, each reductionin equilibrium relative humidity by 11.2% within the range 10.7to 80% RH doubled conidia longevity. The similarities in theserelations, and the limits to these relations, between the conidiaof this entomopathogenic fungus and the orthodox seeds of higherplants are discussed.Copyright 1998 Annals of Botany Company Conidia longevity, equilibrium relative humidity,Metarhizium flavoviride, moisture content, hermetic storage, viability equation     

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     

Seed Production Environment, Time of Harvest, and the Potential Longevity of Seeds of Three Cultivars of Rice (Oryza sativa L.)

Changes in seed quality (assessed by potential longevity, i.e.the value of the seed lot constant K₁ of the seed viabilityequation) in three contrasting cultivars of rice (Oryza sativaL.) were monitored during seed development and maturation intwo temperature regimes, viz 28/20°C and 32/24°C (12/12h), provided by controlled environments. Mass maturity (definedas the end of the seed-filling phase) varied only between 18and 20 d after 50% anthesis. In five of the six treatment combinationsmaximum potential longevity was not achieved until 12-19 d aftermass maturity. In contrast, the maximum potential longevityof seeds of a japonica rice cultivar produced in the warmerregime was obtained in the first harvest after mass maturity.After mass maturity, the potential longevity of the japonicarice seed lots produced in the warmer environment was much lessthan that for the cooler environments. Maximum potential longevitywas also consistently greater in the cooler than the warmerregime for the two indica cultivars, although the differencein K₁ was small (0·3-0·5). The deleterious effectof increase in temperature on seed quality development was notdetected until after mass maturity. Maximum potential longevityin the cooler regime was greatest in the glutinous indica (K₁= 3·9) and least in the japonica cultivar (K₁ = 3·1).It is concluded that the japonica cultivar is not as well adaptedto warm seed production regimes as the indica cultivars. Consequently,subject to confirmation, this research suggest that the seedproduction of japonica cultivars for long-term genetic conservationshould be undertaken, whenever possible, in warm temperate environments.Copyright1993, 1999 Academic Press Oryza sativa L., rice, genebanks, seed development, seed storage, seed longevity, temperature