Preservation of seed viability during 25 years of storage under standard genebank conditions

Maintaining sufficient viability is critical to the sustainability of ex situ conserved seed collections. For this reason, accessions are regenerated when viability falls below a predefined threshold. Viability is monitored by determining the germination ability of accessions at predefined time intervals. Optimizing the frequency of these germination tests, in order to avoid waste of resources, is hampered by the scarce availability of data about seed longevity, particularly for material maintained under genebank conditions. Here we report on the analysis of nearly 40,000 germination test results collected for a wide range of crop species over a 25-years period by the centre for genetic resources, the Netherlands (CGN), where seeds of genebank accessions are dried to 3–7 % moisture content and stored for the long term under near-vacuum in aluminium foil bags at ?20 °C. The results indicate that seed viability is well maintained for the large majority of seed lots during the first 25 years after regeneration as only 3.3 % of the monitoring tests revealed below-threshold germination values. It is argued that the majority of these sub-standard seed lots are due to other causes than seed ageing, including dormancy problems and estimation error in germination testing. For material, maintained under the seed management procedures and storage conditions practiced by CGN, it is therefore recommended to delay the first germination monitoring tests to 25 years after regeneration.     

Medium-term seed storage of 50 genera of forage legumes and evidence-based genebank monitoring intervals

Genebanks maintaining seeds for long-term genetic resources conservation monitor seed lots to detect early loss in viability. Monitoring is costly and depletes valuable seed. Three decades of genebank seed germination test results of diverse forage species from 50 legume genera in the International Livestock Research Institute’s medium-term store (circa 8 °C with 5% moisture content) were analysed to determine whether advice on seed monitoring intervals could be derived. Cumulative normal distributions were fitted by probit analysis for each seed lot and compared within each genus. Six patterns of within-genus variation were identified: no detectable trend in germination test results during storage (4 genera); detectable trends, but variable (positive to negative) amongst lots (5); consistent slope of loss in viability amongst lots (17); consistent slope of increase in ability to germinate amongst lots (21); common loss in viability amongst lots (2); common increase in ability to germinate amongst lots (1). Seed lot monitoring intervals for the medium-term store were derived for each of 19 genera with consistent loss in viability across seed lots: three genera provided comparatively rapid deterioration, five met the general expectations for a medium-term store (2–10 years’ maintenance of high viability), whilst 11 provided much better survival. Moreover, 26 further genera provided no evidence as yet of seed deterioration; of these, 22 improved in ability to germinate during storage indicating confounding of hardseededness with viability in germination tests.     

Intercluster correlations for binomial data: An application to Seed Testing

Certification of crop seeds from a seed lot requires determination of the seed germination rate through tests governed by the International Seed Testing Association (ISTA) and the Association of Official Seed Analysts (AOSA). The results from four tests of 100 seeds each are compared with published tolerances to determine whether seed lots concur with a labeled germination rate. Examination of results from numerous corn and soybean seed lots sent to more than 30 member laboratories of the AOSA and the Society of Commercial Seed Technologists (SCST) suggested that, in aggregate, counts reported by the laboratories frequently show less sample variability than expected under independentbinomial sampling due to positive correlation among the individual test results. Whereas much of the recent literature on correlated binomial data is concerned with efficient methods for estimating the binomial success probabilities, comparatively little attention is paid to the problem of diagnosing whether correlations exist and are significant. Considering the replicate tests as clusters, we propose an estimator for the intercluster (interreplicate count) correlation coefficient and examine its statistical properties. Results from applying the estimator in unblinded and blinded seed tests are presented. The results are revealing; the estimates tend to be larger and significant in the unblinded seed tests.     

Vermicompost Leachate as a Promising Agent for Priming and Rejuvenation of Salt-Treated Germinating Seeds in Brassica Napus

Salinity is a major constraint hampering germination and early seedling growth, especially in aged seed lots. Any rejuvenation treatment improving salt resistance at these crucial developmental stages will be of special interest. Two sets of experiments were performed in Brassica napus to precise the impact of vermicompost leachate (VCL) on seed germination in the presence of NaCl and to analyze its putative interest as seed priming agent before NaCl exposure. Two seed lots were used: one old seed lot (cv. Libomir) and a recent one (cv. Harry). VCL increased the germination percentage of aged seeds in the absence of NaCl and increased seedling length in both cultivars. VCL had only a minor impact when directly added to the NaCl-containing germinating solution. In contrast, priming with VCL strongly improved subsequent germination in the presence of NaCl in relation to a more efficient management of oxidative stress in both cultivars. The improvement of salinity resistance provided by VCL priming was not due to modification in ion or proline content. It is concluded that VCL may act as a rejuvenation agent invigoring old seed lots and as an efficient priming agent for improvement of salinity resistance at the germination stage. Valuable properties of VCL are discussed in relation to the simultaneous presence of several protecting compounds.     

Evaluating homogeneity of LL601 rice in commercial lots using quantitative real-time PCR

Homogeneity analysis was performed on four distinctive commercial lots, derived from the 2006 rice harvest in the United States. Lots that had previously been tested and suspected to have some level of LL601 were selected to determine lot homogeneity. LL601 infiltration in the lots was low and estimated to contain <0.01% (sigma = 0.026), 0.014% (sigma = 0.020), 0.054% (sigma = 0.043), and 0.074% (sigma = 0.031) LL601. Lots were analyzed statistically as a one-way classification, or one-factor experiment, to assess the presence of strata within the lot. A p value of 0.05 or lower is needed to declare statistical significance and would suggest significant differences among the samples. The data revealed p values ranging between 0.105 and 0.607. The calculated p values for all lots were greater than the critical value of 0.05. Samples taken from different locations throughout these four commercial lots did not show statistically significant stratifications within the lot.     

Viability of Oryza sativa L. seeds stored under genebank conditions for up to 30 years

Germination ability, equilibrium relative humidity (eRH), and moisture content of ‘control’ seed samples representing 183 rice accessions stored in the active (2–4 °C) and base (?10 °C until 1993, then ?20 °C) collections of the T. T. Chang Genetic Resources Center were determined after storage for 20.5–30.5 years. Germination of seeds that had been stored in the base collection was generally high (>70 %), whereas germination was more variable for seeds stored in the active collection. Samples with lower viability after storage in the active collection were likely to have lower viability after storage in the base collection. There were significant differences in the moisture content-eRH relationship of the seeds depending on whether the seeds had been stored in the active or base collection. Based on re-test data for regular seed samples regenerated in 1979–1980 and stored in the active collection for up to 31 years, estimates of the time for ability to germinate to fall to 50 % (p ₅₀) ranged from 54 to 997 years. For the same seed samples stored in the base collection for approximately 31 years, ability to germinate has been maintained and germination increased due to improved procedures. The ability to germinate of base collection samples was also generally higher than that of ‘safety duplicate’ samples of the same seed lots that had been sent to the National Center for Genetic Resources Preservation, USA in 1981 and stored at ?18 °C. This may have been due to uptake of moisture either during processing for dispatch or as a consequence of poor packaging material. The results are discussed in relation to long-term seed storage and genebank management.     

Interactions calcium ‐ potassium ‐ magnesium chez le sorgho‐grain

Abstract

Absorption and accumulation of calcium in hydro— ponic solutions, deficient or not in calcium, are studied on whole plants of Sorghum (Sorghum dochna F.), In deficient lots, calcium is replaced either by magnesium (Ca/Mg lot), or by potassium (Ca/K lot). The limit threshold of defiency retained, does not modify, on the 26 day of culture (end of the experience) the yield of different lots compared with the control. The principal modifications in cation content are noted in leaves: plants grown in the Ca/Mg solution show a higher Ca content than plants in a Ca/K solution. As a consequence of saturation with potassium the substitution of Ca in the two deficient lots is effected by magnesium.     

Variability Among Maize (Zea mays L.) Inbred Lines for Seed Longevity

Genotypes conserved in active collections may suffer genetic erosion and modifications. The objective of this work was to investigate changes in germination and vigour in maize (Zea mays L.) inbred lines during cold storage in an active collection. Seeds of 16 maize inbreds produced along 16 years were evaluated for emergence and seedling vigour in a growth chamber. Linear and quadratic regressions of vigour and viability-related traits over seed age were calculated and tested for homogeneity. The seed of five production years of five inbreds that behaved differently in the regression analysis was multiplied in 1998, and original and renewed seed were evaluated in a growth chamber in 1999. Viability and vigour decreased linearly with age for most inbreds, particularly for B84 and EP10, varied at random for a few inbreds, and remained high for EP56 and A295. Aging caused reduction of vigour and loss of viability in most inbreds. There was variability for seed longevity among inbred lines; longevity was highest for inbred EP56. During storage, some seeds of each inbred died, while enduring seeds, when multiplied, produced new seed with enhanced viability and vigour compared to the average seed of the inbred, suggesting natural selection for viability and vigour during storage within inbred lines.     

Seed nitrogen accelerates the rates of germination,emergence, and establishment of rice plants

We examined the effect of seed nitrogen content on the rates of germination, emergence, and establishment of rice plants. Several seed lots with various nitrogen contents were obtained from the parent plants grown under 3 planting densities and 4 rates of nitrogen application. There was a clear negative correlation between the seed nitrogen content and germination time (R =0.88), whereas the correlation between the seed dry weight and germination time was very low (R=0.23). The seed lot with a high nitrogen content absorbed water faster than the seed lot with a low nitrogen content, especially on the first day after soaking, and also showed a faster emergence, exsertion of the fourth leave, and a more uniform germination. Moreover, the increase of seed nitrogen content as well as the prolongation of soaking time resulted in a uniform emergence. Therefore, seed vigor is likely to be enhanced by the increase of seed nitrogen content, which may be achieved by an adequate application of a large amount of nitrogen to parent plants. Consequently, it may be possible to improve and stabilize the establishment of directly sown rice plants by the sowing of vigorous seeds with a high nitrogen content.     

Modelling subalpine forest dynamics as influenced by a changing environment

FORSUM, a forest succession model of the JABOWA/FORET type was applied to simulate possible impacts of environmental changes on subalpine forest ecosystems and compared with the model FORECE (Kienast, 1987). The model used is based on approaches of Botkin et al. (1972), Shugart (1984) and Kienast (1987) and has been improved by implementing soil water movement calculations based on a user-defined one-dimensional nonhomogeneous soil profile. The influence of a possible climatic change on subalpine ecosystems was investigated for three different sites in the Grisons (Switzerland). The scenarios used are based on climate change predictions of General Circulation Models. A temperature increase of 3? C would cause important changes in species composition. Deciduous trees would invade today's subalpine belt causing a displacement of various conifers in this zone. Some coniferous species might eventually migrate into today's alpine zone which would consequently become afforested. Comparing the vegetation changes as predicted by the model FORSUM and FORECE we found that the models generate the main general patterns. However under global warming and a concurrent precipitation decrease total biomass production seems to be overestimated by FORECE. Information about seed dispersal rates (horizontal and vertical), seed availability and soil formation processes should be implemented in these models to improve the reliability of the predictions.     

Spring camelina N rate: balancing agronomics and environmental risk in United States Corn Belt

Camelina (Camelina sativa (L.) Crantz) seed oil has desirable properties for producing advanced biofuels and as a healthy cooking oil. It has been grown for centuries, but basic recommendations for nitrogen (N) fertilizer requirements are still needed to support widespread industrial cultivation across North America. A replicated N-response plot-scale study was conducted on a northern Mollisol soil for two growing seasons to 1) determine seed and oil yield, seed oil content, and vegetative response; 2) determine indices of N use efficiency; and 3) measure post-harvest residual inorganic soil N as an index of environmental risk. Seed and oil yield response to N fertilization was described with a quadratic function, which predicted maximum seed yield (1450 kg ha^?1) and oil yield (580 kg ha^?1) at about 130 kg N ha^?1. However, seed and oil yield did not differ significantly among N-rates above 34 kg N ha^?1. Seed oil content averaged 400 g kg^?1 among all N rates. Agronomic efficiency declined above 34 kg N ha^?1, which coincided with an increase of post-harvest soil nitrate-N plus ammonium-N (residual N). Considering N use efficiency, simple cost analysis, and risk associated with residual N, a rate of 34 kg N ha^?1 is recommended.     

Light- and Temperature-Dependent Dormancy in Stored Seed of Poa pratensis L. from Northern Norway

Abstract

Seed dormancy and slow germination often cause poor establishment of Poa pratensis L. in lawns and pastures. This study was conducted to determine whether persistent dormancy occurs and the influence of light and temperature on germination of Poa pratensis L. strains from Northern Norway. Seed from 23 different genotypes and seed lots was germinated in various phytotron chambers during the winters of 1986 and 1990. At 21°C constant temperature, dormancy was evident even after seven years of storage in a dry room at 0–10°C. By contrast, alternating temperatures (21/12°C) elicited 80–100% germination of viable seed of nearly all genotypes and seed lots. Light treatment had no impact on germination after 28 days at 21/12°C, but continuous darkness and continuous fluorescent light were both inferior to 8 h light/16 h dark illumination cycles at 21°C constant temperature. Seed of the commercial cultivar Lavang produced in Southern Norway developed the same long-term, temperature-dependent dormancy as seed produced in Northern Norway. One lot of the cultivar Holt showed a higher ability to germinate at low temperatures than any of the other genotypes.     

Effects of phosphorus nutrition on growth,fruit abscission and seed yield of the cowpea (Vigna unguiculata L.)

In pot experiments, cowpea cultivars, ?Adzuki”?, ?Ife Brown”? and ?New Era”?, were raised in soil fertilized with phosphorus at 0, 20, 40 and 80 kg/ha levels. Seed yield was enhanced in ?Adzuki”? mainly by the maintenance of functional pods, that ist by enhancement of fertility (defined as percent of floral buds that developed into mature functional, seed-bearing pods). In ?New Era”?, seed yield increase was due more to increased diversion of dry matter into the seed than by increased fertility. Harvest index (defined as the proportion of whole plant dry weight constituted by seed dry weight) was significantly enhanced more in ?New Era”? than in ?Adzuki”?. A P dressing equivalent to 40kg P/ha proved the nearest-optimal P level for seed production in ?New Era”?. Corresponding critical P level for ?Adzuki”? and ?Ife Brown”? were not specifically at any of the P regimes studied.     

Cd对油菜种子发芽与幼苗生长的生态毒性

通过水培实验研究了Cd胁迫下,油菜种子发芽及幼苗生长状况。结果表明:Cd胁迫下,发芽率、发芽势、发芽指数以5 mg L-1Cd浓度为阈值呈现低促高抑现象,发芽指数与Cd浓度曲线相关性好于发芽率和发芽势;活力指数、总长、芽长、根长、总重、芽重、根重表现为单抑现象。Cd对根生长抑制作用大于芽,逐步回归发现,Cd主要通过抑制根生长达到对幼苗生长抑制。种子电解质外渗率和根细胞有丝分裂指数分别与Cd浓度成极显著相关,相关系数分别为0.603**和-0.571**。因子分析发现,根长较其它指标对Cd敏感,可用于Cd污染的监测指标。     

Modelling of sinkage tests in tilled soils for mobility study

The study of the mechanical behaviour of breached surface soils allows the optimization of the running gear of the vehicles for the off-road mobility.The sinkage of the running gear causes a motion resistance which is opposed to the tractive capacity of the vehicle. In a homogeneous soil, the sinkage is predicted by the interpretation of plate sinkage tests. In order to make possible and easier the sinkage prediction of a vehicle going in a tilled soil, the article has for objective to present a method to model pressure–sinkage curve for a tilled soil with the pressure–sinkage curve of the same soil before tillage.The tilled soil is considered as two layers of the same soil whose density is lower for the upper layer than for the sub-base. The two-layered soil behaviour is modelled as the combination of the behaviour of the loose soil layer and the behaviour of the dense soil. The link between these two behaviours is a critical depth defined as the depth of the plate when the layer of soil in a critical density reaches the limit between the two layers.Sinkage tests with circular plates were carried out on four soils chosen to represent the mechanical properties of a range of soils: a sand for frictional soils, a silt for cohesive soils and a silty sand and a sandy loam for cohesive frictional soils predominant in the agricultural soils. The soils were tested in one-layered and two-layered configurations in small and large bins with well-known and controlled soil conditions.A theoretical approach allows the calculation of the critical depth with a deformation process of the soil below the plate. The critical depth depends on the density of the soil, the tillage depth, the diameter of the plate and the angle of friction of the soil.The critical depth allows the modelling of the pressure–sinkage curve for the tilled soils using the one-layered soil data. The comparison with the experimental tests in tilled soil validate the approach.     

离心式高速玉米精量排种器T形槽型孔设计与试验

针对离心式高速玉米精量排种器双粒种子并排填充导致重播严重的问题,该研究提出利用型孔槽对称凸台结构降低玉米种子并排填充概率的方法,设计了一种T形槽型孔。通过构建充种阶段玉米种子的力学模型,并结合玉米种子的形状特征确定了T形槽型孔基本结构参数。借助EDEM离散元仿真软件,以型孔槽前端长度、型孔槽后端面倾斜角以及型孔槽底部倾斜角为因素,以合格指数、重播指数与漏播指数为评价指标,设计二次正交旋转回归组合仿真试验。仿真试验结果表明：在作业速度18 km/h条件下,型孔槽前端长度为9.31 mm,型孔槽后端面倾斜角为43.37°与型孔槽底部倾斜角为70.5°时,排种质量最优,排种合格指数、重播指数与漏播指数分别为94.03%、1.72%与4.25%。台架验证试验结果表明：作业速度18 km/h时,T形槽型孔的合格指数为94.54%,与仿真试验结果的相对误差为0.54%,仿真优化试验结果可靠;作业速度为15 km/h时,排种器作业性能最佳,合格指数为95.16%,重播指数为1.42%,漏播指数为3.42%,满足高速精量播种要求;作业速度范围在12 ～ 21 km/h内时,T形槽型孔相较于矩形槽型孔的合格指数提升2.1个百分点以上,重播指数降低2.1个百分点以上,相较于蹄形槽型孔的合格指数提升1.4个百分点以上,重播指数降低2.1个百分点以上。该研究可为离心式高速玉米精量排种器优化提供参考。     

Patterns of SSR variation in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) seeds under ex situ genebank storage and accelerated ageing

Maintaining seed viability and germplasm integrity is a challenging task in conservation of plant genetic resources, as seeds under storage will lose viability and genetic changes will occur. Attempt was made to analyze the patterns of genetic changes in wheat germplasm under ex situ genebank storage and accelerated ageing treatments. A set of 16 naturally aged wheat accessions under ex situ genebank storage since 1994 were sampled. Four recently regenerated wheat accessions were selected, four random seed samples were chosen from each accession, and three of them were exposed to three different accelerated ageing treatments. These 32 seed samples in two germplasm sets displayed a range of germination rates from 4 to 98 %. Thirty-seven microsatellite markers representing 21 wheat chromosomes were applied to screen 12 seeds of each sample and 449 SSR alleles were scored. Large SSR variation was found in each germplasm set. There was 73.1 % of the total SSR variation present among the naturally aged samples and 78.2 % present among the accelerated ageing samples. Several analyses for genetic association consistently revealed no clear genetic separations among samples of high or low germination rates in both germplasm sets. Samples under different accelerated ageing treatments did not show much genetic differentiations from the original sample of each accession. Mantel tests revealed non-significant associations between SSR variability and sample germination rates for both germplasm sets. These findings are useful for understanding seed deterioration under different ageing conditions and suggest that genome-wide SSR variability may not provide sensitive markers for the monitoring of wheat seed viability.     

Prediction of the water sorption isotherm in air dry soils

Within this work we present a revised pedotransfer function (PTF) that predicts water sorption isotherms for dry soils based on the clay content of the soils. When the water sorption isotherm is plotted as a water retention curve (log water potential plotted against the water content) it typically results in a log linear function as described by Campbell and Shiozawa (1992). The linear function is defined by its slope and a fixed endpoint at zero water content. The reciprocal of the slope shows a strong correlation with the clay fraction. For the calibration of a PTF we measured water sorption data for 18 soils with clay contents from 2% to 61%. The final predictions of the water sorption isotherms from the clay mass fraction were very good if the clay content was higher than 7%. The use of a revised theoretical endpoint at the dry end of the WRC did improve the prediction as compared to the endpoint that has been used in the literature before. In addition Literature data for 22 soils and 3 pure clay minerals were used for validation. The good performance of the PTF only occurred if the clay fraction was dominated by 2:1 clay minerals. The water retention isotherm of soils rich in the 1:1 clay mineral kaolinite could not be predicted by this approach; the actual water content was strongly over-predicted and the water retention curve did not follow a log linear relationship.     

Triage for conserving populations of threatened species: The case of woodland caribou in Alberta

Prioritization of conservation efforts for threatened and endangered species has tended to focus on factors measuring the risk of extirpation rather than the probability of success and cost. Approaches such as triage are advisable when three main conditions are present: insufficient capacity exists to adequately treat all patients, patients are in a critical state and cannot wait until additional capacity becomes available, and patients differ in their likely outcome and/or the amount of treatment they require. The objective of our study was to document the status of woodland caribou (Rangifer tarandus) herds in Alberta, Canada, with respect to these three conditions and to determine whether a triage approach might be warranted. To do this we modeled three types of recovery effort - protection, habitat restoration, and wolf control - and estimated the opportunity cost of recovery for each herd. We also assessed herds with respect to a suite of factors linked to long-term viability. We found that all but three herds will decline to critical levels (<10 animals) within approximately 30 years if current population trends continue. The opportunity cost of protecting all ranges by excluding new development, in terms of the net present value of petroleum and forestry resources, was estimated to be in excess of 100 billion dollars (assuming no substitution of activity outside of the ranges). A habitat restoration program applied to all ranges would cost several hundred million dollars, and a provincial-scale wolf control program would cost tens of millions of dollars. Recovery costs among herds varied by an order of magnitude. Herds also varied substantially in terms of their potential viability. These findings suggest that woodland caribou in Alberta meet the conditions whereby triage should be considered as an appropriate conservation strategy.     

东北黑土区旱作农田土壤CO2排放规律

为研究农田土壤CO2排放规律,调控农田碳平衡,通过对东北黑土区旱作农田土壤CO2排放的定位连续观测,研究了玉米、大豆农田土壤CO2排放的季节变化规律;并估算了农田碳平衡。结果表明:1)农田土壤CO2排放通量随季节呈单峰曲线变化,7月份出现最大值;秸秆覆盖还田明显增加了农田土壤CO2排放;玉米或大豆生长发育对土壤CO2排放影响较小。2)地温的季节变化与土壤CO2排放通量季节变化规律一致,用指数方程和二次方程均可很好地模拟土壤CO2排放通量与地温之间的关系,但指数方程优于二次方程,以20cm土层地温的相关性最高,5cm土层地温的相关性最低。3)玉米、大豆农田在通常情况下为大气CO2的"汇",玉米-玉米-大豆轮作周期(3a)的碳汇年平均为4.53t/hm2,该碳汇可为固碳减排提供参考。