Germination Proportion Research Articles

Dormancy and Germination Pre-Treatments in Willamette Valley Native Plants

Seeds from 30 species of grasses and forbs native to Pacific Northwest prairies were tested for physical and physiological dormancy. The physical dormancy was determined by mechanically and chemically scarifying seeds. Physiological dormancy was evaluated with cold stratification before germination. Experiments were analyzed individually with ANOVA analysis, and by seed lots through time using multiple regression. Three of the tested species had too little germination to determine what kind of dormancy was present. Physical dormancy was found in three legumes that required a treatment to break the hard seed coat. These species, Lotus unifoliolatus, Lupinas albicaulis, and Trifolium willdenovii also had increased germination following cold stratification. This can be taken as evidence of physiological dormancy. Physiological and physical dormancy together is considered combinational dormancy. Another eight species had increased germination after cold stratification. This included both species that did not germinate without cold stratification (Aquilegia formosa, Camassia leichtlinii, C. quamash, Heracleum maximum, Lomatium nudicaule, Perideridia oregona, and Sidalcea campestris), and species with germination proportions that increased following stratification (Eriophyllum lanatum, and the legumes). Four annual forbs (Clarkia purpurea, Collomia grandiflora, Gilia capitata, and Madia gracilis) had increased germination when seeds were cold stratified, but the response was more consistent with a low temperature requirement for germination than physiological dormancy. The remaining 12 species germinated with no pretreatments. Understanding the germination requirements of these species will aid in their propagation for restoration and the provisioning of ecosystem services and may help explain the ecology of these species on the landscape.

Parental overwintering history affects the responses of Thlaspi arvense to warming winters in the North

The overwintering conditions of northern plants are expected to change substantially due to global warming. For perennial plants, winter warming may increase the risk of frost damage if the plants start dehardening prematurely. On the other hand, evergreen plants may remain photosynthetically active and thereby benefit from milder winters. The positive and negative effects of mild winters on annual plants remain, however, largely unknown. We postulated that summer annuals may be susceptible to frost damage if the seeds germinate during a mild spell in winter. Winter annuals may utilize a warm period for photosynthesis. These questions were addressed in two consecutive experiments in which pot-grown individuals of Thlaspi arvense that overwintered in the field were exposed to an elevated temperature for 8 days in growth chambers in mid-winter. No premature germination was observed in summer annuals. However, in accordance with our hypothesis, winter annuals started photosynthesising very rapidly upon exposure to elevated temperature. The winter warming treatment affected neither the total number of seeds produced nor the mean seed weight. These seeds, possessing divergent parental overwintering histories, were used as starting material for the second experiment. Seeds originating from both summer and winter annual plants germinated both in the autumn and in the following spring. We observed a major parental effect associated with the winter warming treatment. The warm spell experienced by the mother plant (either as a winter annual rosette or as a summer annual seed) reduced the proportion of autumn germination in the next generation. Only 43% of the seeds of summer annuals possessing a parental warming history germinated before the winter, whereas the germination percentage of seeds with no previous winter warming history was 71%. In the case of seeds collected from winter annual plants, 4% of the seeds germinated in autumn if the mother plants experienced the warming treatment during the previous winter, whereas the corresponding value was 37% if the mother plants did not experience warming. Our results show that summer and winter annual individuals show diverse responses to warm spells in winter. Since the responses are not limited only to the generation that actually experiences the warm spell, but also appear in their offspring, long-term studies consisting of several generations are called for.

Seed germination traits of two plant functional groups in the saline deltaic ecosystems

Aims Salt stress resulting from soil salinization is one of the driving forces of the land degradation throughout the world. The modern Yellow River delta is one of the most saline areas in China. Phytoremediation can be an effective way to restore the salinized ecosystems, which requires selecting appropriate plant species. This study explored the germination responses of common plant species from contrasting habitats in the Yellow River delta to varying salinity, offering experimental information for ecosystem restoration in the Yellow River delta. Methods In this study, 15 common plant species from the Yellow River delta were divided into two groups (high-salinity and low-salinity groups) by their natural habitats using Canonical Correlation Analysis. Seeds of each species were treated with five salinity levels (0, 5, 10, 20 and 30 ppt), using a randomized complete block design, and germinated seeds were counted and removed daily for 28 days to calculate the final germination proportion and mean time to germination. The germination responses of seeds to salinity treatments were compared between the two groups. Important Findings In relation to salinity, seed germination behavior of the test species was closely related to the salinity level of the habitats over which they were distributed. Species from the habitats with higher salinity had generally higher final germination proportion but shorter mean time to germination than those from the habitats with lower salinity in all of five salinity treatments used. The final germination proportion and mean time to germination of low-salinity group species were more sensitive to salinity than those of high-salinity group species. Selecting the species with high final germination proportion and short mean time to germination is important for restoration of salinized land.

The role of avian frugivores on germination and potential seed dispersal of the Brazilian Pepper Schinus terebinthifolius

Frugivorous birds play a key role in seed dispersal and establishment of a range of plant species, including invasive weeds, such as the Brazilian Pepper Schinus terebinthifolius. The potential of seed dispersal of Schinus by birds with varied feeding behaviours was studied through seed-viability tests and germination experiments using seeds obtained from birds in the field and birds kept in captivity. It was found that seeds collected after gut passage in five bird species in the field had higher proportion of germination as well as higher germination rates compared to the control seeds. Viability of seeds ingested by the Blue-and-yellow Tanager Thraupis bonariensis, which mandibulates seeds before ingesting, was significantly lower than control seeds, while reduction in viability of seeds ingested by the Creamy-bellied Thrush Turdus amaurochalinus was nonsignificant. Seeds ingested by birds in captivity germinated earlier than the control seeds, within 1-2 weeks, and had proportion and germination rates higher than controls. Probably both mechanical and chemical effects play a role in enhancing germination of seeds. In Brazil where both Schinus and avian frugivores had evolved together, the dependence of Schinus on generalist frugivores had been demonstrated in this study, similar to other countries where the invasive Schinus is dependent on native or introduced avian species for its spreading. This finding has important implications for the restoration of human-altered areas in South America, were Schinus is a native pioneer species, as well as for the management and restoration of areas invaded by Schinus elsewhere.

Effects of light on urediniospore germination, appressorium formation and infection efficiency of Phakopsora pachyrhizi, causal agent of soybean rust

Effects of light on infection efficiency, germination, and appressorium formation of urediniospores of Phakopsora pachyrhizi Sydow, the causal agent of Asian soybean rust, were investigated in three experiments separately conducted in China and the USA during 2006–2008. To examine infection efficiency, in Experiments 1 and 2, detached soybean leaves at the V3-V4 stages were inoculated with urediniospores of P. pachyrhizi, and then exposed to different periods of darkness (0, 4, 8 or 12 h ). General linear model analysis indicated that infection efficiency of the urediniospores increased significantly with a longer period of darkness. In Experiment 3, urediniospores treated with different light/darkness periods were examined at 2, 4, 6 or 8 h after incubation for germination and appressorium formation. Multiple comparison and orthogonal contrast analyses indicated significant reduction in spore germination and appressorium formation in the treatments of light contrasted to the treatments of darkness. Within 8 h, proportions of urediniospores appressorium formation were up to 0.35 in darkness and 0.1 under light, which was a more significant relative difference, compared with that of the germination proportions (as high as 0.7 under light and 0.8 in darkness). These results suggest that light was detrimental to germination and infection of P. pachyrhizi and may suppress the development of soybean rust. They may provide an explanation for late season occurrences of this disease in high latitude regions in the northern and southern hemispheres.

Seed Dispersal by Golden‐headed Lion TamarinsLeontopithecus chrysomelasin Southern Bahian Atlantic Forest, Brazil

ABSTRACTSeed dispersal by small primates may be particularly relevant in areas where populations of larger frugivores have been reduced or extinguished by hunting and/or habitat disturbance. In this context, the aim of this study was to evaluate the role of the golden‐headed lion tamarinLeontopithecus chrysomelasas a seed disperser in Atlantic forest remnants in Brazil. To this end, we opportunistically collected feces deposited during observations on the feeding behavior of two groups of golden‐headed lion tamarins ranging in the degraded areas of the Una Biological Reserve, Bahia, Brazil, from February 2006 to January 2007. We collected 587 fecal samples, of which 524 contained seeds from 24 plant species, distributed over 13 families. Disregarding seeds of<3 mm, the majority of seeds recovered were bromeliad seeds. In general, ingestion of seeds by golden‐headed lion tamarins did not improve the germination proportion or decrease the germination delay of seeds, with the exception ofAechmeaspp. seeds. The tamarins encountered different habitats during their daily activity period, while feeding and defecating. Consequently, some seeds were transported to different habitats including disturbed areas. Thus, the role of seed dispersal in combination with the daily movement pattern ofL. chrysomelascontributes to the persistence of fruit plants and epiphyte species and to the natural regeneration process within Atlantic forest remnants.

Germination responses of an invasive species in native and non-native ranges

Studying germination in the native and non-native range of a species can provide unique insights into processes of range expansion and adaptation; however, traits related to germination have rarely been compared between native and nonnative populations. In a series of common garden experiments, we explored whether differences in the seasonality of precipitation, specifically, summer drought vs summer rain, and the amount and variation of annual and seasonal precipitation affect the germination responses of populations of an annual ruderal plant, Centaurea solstitialis, from its native range and from two non-native regions with different climates. We found that seeds from all native populations, irrespective of the precipitation seasonality of the region in which they occurred, and non-native populations from regions with dry summers displayed similarly high germination proportions and rates. In contrast, genotypes from the non-native region with predominantly summer rain exhibited much lower germination fractions and rates. Also, percent germination was strongly correlated with variation in precipitation in winter, the season that follows germination for C. solstitialis. Specifically, germination was lower for native and non-native populations experiencing greater variation in winter precipitation. This correlation, however, was greatly influenced by the non-native region with summer rain, which also exhibited the greatest variation in winter precipitation among studied regions. These results suggest that rather than general climatic patterns, the degree of risk experienced at early developmental stages could exert an important control over the germination strategy of C. solstitialis populations in both native and non-native ranges. Also, these findings reveal a largely unique germination response in C. solstitialis genotypes growing in the non-native region with summer rain and high variation in winter precipitation. Our work raises the possibility that rapid adaptive changes in germination strategies may contribute to the success of globally distributed invaders.

Quantitative Trait Loci for Cold Tolerance in the Maize IBM Population

B73 and Mo17 represent the main families of elite maize (Zea mays L.) inbred lines. B73 and Mo17 significantly differed in their proportion of germination under low‐temperature conditions, and the IBM population derived from the cross $$\mathrm{B}\,73\times \mathrm{Mo}\,17$$ provides breeders a great opportunity for locating quantitative trait loci (QTLs) for cold tolerance in elite maize germplasm, the objective of this study. Under low‐temperature conditions, the recombinant inbred lines significantly differed for all traits except vigor. No QTLs were detected at optimal conditions, but two QTLs involved in leaf color at low temperature were located in the short arm of chromosome 3 and the long arm of chromosome 6. The final fit for QTLs detected in our study explained 14.2% of phenotypic variance and 28.2% of genetic variance. However, in cross‐validation analysis, QTLs detected in chromosomes 3 and 6 were detected in only 12.3% and 25.7% of all cross‐validation runs, respectively, and explained 3.7% of the genetic variance. Although Mo17 could bring some favorable alleles, marker‐assisted selection is not advisable because differences between allelic variants are small and explain a low proportion of genotypic variance. The locus luteus11 is proposed as a candidate gene for the QTL located in chromosome 6, while the QTL located in chromosome 3 probably corresponds to an unknown gene.

Burning seeds: germinative response to heat treatments in relation to resprouting ability

Summary In Mediterranean fire‐prone ecosystems, plant species persist and regenerate after fire by resprouting, by recruiting new individuals from a seed bank (post‐fire seeding), or by both resprouting and post‐fire seeding. Since species with resprouting ability are already able to persist in fire‐prone ecosystems, we hypothesize that they have been subjected to lower evolutionary pressure to acquire traits allowing or enhancing post‐fire recruitment. Consequently, we predict that the germination of non‐resprouters is more likely to be increased or at least unaffected by heat than the germination of resprouters. To test this hypothesis we compiled published experiments carried out in Mediterranean Basin species where seeds were exposed to different heat treatments. We compared the probability of heat‐tolerant germination (i.e. heated seeds had greater or equal germination than the control), the probability of heat‐stimulated germination (i.e. heated seeds had greater germination than the control) and the stimulation magnitude (differences in proportion of germination of the heated seeds in relation to the untreated seeds, for heat‐stimulated treatments) between resprouters and non‐resprouters. Non‐resprouters showed higher probability of heat‐tolerance, higher probability of heat‐stimulation and higher stimulation magnitude even when phylogenetic relatedness was considered. Differences between life‐forms and post‐fire seeding ability do not explain this pattern. Non‐resprouters appear to have a greater capacity to both (i) persist after fire by means of recruiting (greater heat‐tolerance) and (ii) increase their population after fire (greater heat‐stimulated germination), than resprouters. Synthesis. Our results contribute to understanding the factors that condition the evolution of fire‐persistence plant traits and support the hypothesis that resprouting and post‐fire recruitment are negatively associated in Mediterranean Basin flora.

Efeito da temperatura e de regimes de luz no crescimento do micélio, germinação de conídios e esporulação de Stenocarpella macrospora e Stenocarpella maydis

O objetivo deste trabalho foi avaliar a influência da temperatura (5 a 45 ºC) e do regime de luz no crescimento radial do micélio, na germinação dos conídios e na esporulação (produção de cirros) de Stenocarpella macrospora e de S. maydis. Foram utilizados um isolado monospórico de cada uma das espécies de Stenocarpella obtidos na área experimental da Universidade de Passo Fundo RS, a partir de colmos de milho infectados. A faixa de temperatura entre 23 e 28 ºC proporcionou crescimento do micélio mais rápido para os dois isolados, tanto sob luz contínua como sob fotoperíodo de 12 h. Não se observou crescimento do micélio nas temperaturas de 5 a 45 ºC. Considerando o período de luz, verificou-se que o crescimento do micélio de ambas espécies foi maior no fotoperíodo de 12 h. Os conídios de S. macrospora e S. maydis não germinaram mesmo após 24 h de incubação nas temperaturas de 5 e 45 ºC, independentemente do regime de luz. As temperaturas entre 28 e 33 ºC propiciaram a maior porcentagem de germinação dos conídios de S. maydis, enquanto os conídios de S. macrospora apresentaram maior germinação na faixa de temperatura entre 26 e 29 ºC. Os conídios de ambos isolados apresentaram uma maior velocidade de germinação na presença da luz. Ambos isolados apresentaram maior esporulação em colmos de milho na faixa de temperatura entre 30 e 35 ºC e sob regime de luz contínua.

The Effect of Solar Irradiance on the Mortality of Phakopsora pachyrhizi Urediniospores.

Soybean rust, caused by Phakopsora pachyrhizi, may be the most important foliar disease of soybean. Within the last 10 years, the fungus has moved to many new geographical locations via spread of airborne urediniospores. The objective of this study was to determine the relationship between urediniospore viability and exposure to solar radiation. Urediniospores of P. pachyrhizi were exposed in Capitán Miranda, Paraguay, to determine the deleterious effects of sunlight. Concomitant total solar (0.285 to 2.8 μm) and ultraviolet (0.295 to 0.385 μm) irradiance measurements were used to predict urediniospore germination. Urediniospores exposed to doses of solar and ultraviolet (UV) radiation ≥27.3 MJ/m2 and ≥1.2 MJ/m2, respectively, did not germinate. The proportions of urediniospores that germinated, normalized with respect to the germination proportion for unexposed urediniospores from the same collections, were a linear function of solar irradiance (R2 = 0.83). UV measurements predicted normalized germination proportions equally well. Results of inoculation experiments with exposed P. pachyrhizi urediniospores supported the results of the germination trials, although the effects of moderate levels of irradiance varied. The relationship between urediniospore viability and exposure to solar radiation has been incorporated into the U.S. Department of Agriculture's soybean rust aerobiological model that provides North American soybean growers with decision support for managing soybean rust.

Agamospermous seed production of the invasive tussock grass Nardus stricta L. (Poaceae) in New Zealand – evidence from pollination experiments

The breeding system of the European tussock grass Nardus stricta L. (Poaceae) was investigated with pollination experiments. Plants were sampled from two populations at Lake Pukaki, Canterbury, New Zealand, where the species is recognised as an alien invader. Bagging of flowers with king-sized cigarette paper and hand-pollination were used to test for three modes of reproduction in the greenhouse: (1) agamospermy (apomixis), (2) autogamy and self-compatibility, and (3) allogamy (outcrossing). Two control groups without experimental treatments were further tested for seed set under (1) greenhouse and (2) field conditions. The success or failure of all experimental treatments was assessed with seed set and germination trials. All agamospermy treatments showed high seed set and germination proportions arguing for an apomictic mode of reproduction in Nardus stricta. Cross-pollination treatments were also successful making it difficult to estimate the degree of outcrossing, selfing, and agamospermous seed production in Nardus stricta. Fecundity in field populations was considerably reduced, possibly due to environmental factors acting upon seed development during maturation. The reproductive strategy of Nardus stricta might be particularly beneficial during invasion because single tussocks can form reproducing colonies and high reproductive output is ensured even in the absence of pollination. Genetic studies in combination with pollination experiments would be necessary to gain deeper insights into the breeding strategy of Nardus stricta.

Ephemeral wetland vegetation in irregularly flooded arable fields along the northern Upper Rhine: the importance of persistent seedbanks

Along the northern Upper Rhine ephemeral wetland vegetation is not confined to primary habitats such as the fringes of backwaters and river banks, but is also found in irregularly flooded arable fields. Within these highly variable environments, where disturbance is not only by flooding but also by agricultural management, we assessed the role of seedbanks for the persistence of ephemeral vegetation. In order to achieve this, we analysed the floristic composition of the above-ground vegetation and the correspond- ing soil seedbank of arable fields after a long-lasting spring and early summer flood in 2001. Moreover, we compared our vegetation data with other phytosociological studies from primary and secondary habitats along the northern Upper Rhine. The comparison between primary and secondary habitats of mudflat species revealed differences in species composition. While primary habitats were characterised by the pre- dominance of species of Isoeto-Nanojuncetea and B identetea, secondary habitats contained additionally species of the classes Agrostietea and S tellarietea. The studied soil seedbanks were dominated by species typical of both, mudflat and agri- cultural habitats. Most species found in the seedbank were characterised by short life cycles and the ability to rapidly exploit periods of favourable conditions for germination and growth. The flooding treatments that were applied prior to the third season of seed- bank analysis almost generally resulted in a high proportion of additional germination of mudflat species, even two years after the start of the analysis. The emergence of some mudflat species such as Gnaphalium uliginosum, Veronica peregrina and semi-aquatic helophytes such as Alisma lanceolatum and A. plantago-aquatica was actually confined to the flooding treatment. Seed densities were exceptionally high and increased with the duration and frequency of inundation at the sampling sites. Juncus bufonius, Ranunculus sceleratus and Veronica catenata were the most abundant species. For Juncus bufonius we found a maximum seed density of 707,072 seeds m Ð2 , which is to our knowledge the highest seed concentration that was ever found in a higher plant. The large persistent soil seedbanks proved to be of outstanding importance for the emergence of ephemeral wetland vegetation after flood disturbances in arable fields. This was also reflected by the relatively high similarity be- tween the seedbank and the established vegetation directly after flooding. Our study highlights the importance of irregularly flooded arable fields as a secondary habitat for the conservation of ephemeral wetland species. At these sites, not only im- proved drainage and landfill threatens the occurrence of mudflat vegetation but also the replenishment of the seedbank is often prevented by early re-ploughing of the fields.

Germination and seed bank depletion of holly (Ilex aquifolium L.) in four microhabitat types

The germination dynamics ofIlex aquifoliumL. were studied in central Spain using a 3-year field sowing experiment. Ten triads of bags (n= 30 seeds per bag) were buried randomly in four different microhabitats: inside the holly woodland, along the forest edge, in open grassland and under isolated shrubs. Bags were harvested annually, and seeds were analysed for seed viability, embryo development changes and germination. Holly seeds did not germinate until the second year. Embryo development and seed germination were faster at the forest edge, with a total germination proportion of 63% of sown seeds. Germination in the holly woodland (48%), under the shrubs (46%) and in grassland (46%) were very similar. Thus, recruitment ofIlexpopulations in this region is not limited by requirements for germination. After the third year, the seed bank was reduced by 80–90% of the initial seeds, so it can be considered as a short-persistent seed bank. Holly seed behaviour can enhance recruitment in semi-open areas, such as forest edges. Linked to the short persistence of its seed bank, this species can be considered an intermediate strategist between mature forest specialists and early successional species. This work contributes to a deeper knowledge of the germination ecology ofI. aquifolium, in an effort to determine the relative importance of germination/ dormancy processes within holly population dynamics.

Dispersal and germination of big and small nuts of Quercus serrata in a subtropical broad-leaved evergreen forest

Few studies have concerned with the differences in seed dispersal, germination and seedling establishment between big and small seeds within a tree species. In this study, the dispersal and fates of big and small nuts (labeled with coded tin-tags) of Quercus serrata (a dominant canopy tree species) were monitored at two stands (a primary stand and a secondary stand) in a subtropical broad-leaved evergreen forest in the Dujiangyan Region, Sichuan Province, China. We also examined the differences in germination of big and small nuts of Q. serrata without predation by sowing nuts on the ground surface or in the soil. We found that, the big nuts were better survived with longer cache lifetime, longer dispersal distances and higher proportion of emerged seedlings (2% at primary stand, 0.5% at secondary stand) than small nuts. We also found that, there was a marginally physiological difference in germination (germination proportion and seedling height) between big and small nuts. Burial obviously improves germination of both big and small nuts. It is suggested that small rodents may act as an important selective force to affect seed fates, seed shadows and seedling establishment for big and small nut of Q. serrata.

Correlation of morphological traits with molecular markers in radish (Raphanus sativus)

Radish (Raphanus sativus L.) is an important vegetable crop in Asia. Lack of uniformity in the crop at harvest is due to genetic variability and environmental conditions. Molecular markers associated with morphological traits of seed and seedlings were identified. Seed (100) of radish cvv. Fire Ball and Long White Chinese from Australia and Mino Early, Pyuthane Red, Tokinasi, White Neck and 40 Days from Nepal. The seed was germinated between paper (20°C, 6 days) and seedlings were grown in pots under glasshouse conditions (20°C, further 3 weeks). Morphological characters were measured in seed and seedlings at 6 days and 4 weeks after germination. Deoxyribonucleic acid was extracted from selected samples and Random Amplified Polymorphic DNA (RAPD) markers were identified using 10 primers. Multivariate analysis based on principle coordinates analysis was used to correlate morphological traits with molecular markers within and across cultivars. Several markers associated with high or low seed weight, germination proportion, seedling length and fresh weight were identified. This new method for identifying potential RAPD markers may be useful for marker assisted breeding and selection of improved radish varieties.

Effects of seed production and storage conditions on blackgrass (Alopecurus myosuroides) germination and shoot elongation

Blackgrass is a common winter annual grass weed in autumn-sown crop rotations in Atlantic European countries. Control with a minimum amount of herbicides in integrated cropping systems would be facilitated by modeling the effect of cropping systems on its demography. To develop the submodel relating weed seed bank to emerged seedlings, laboratory experiments were conducted to analyze and quantify seed germination and shoot elongation. These processes were studied as a function of environmental conditions during seed production (nitrogen availability, water deficit, plant density, and crop) and of seed characteristics (seed weight, harvest date, storage length, and dry-stored/soil-buried). Nonlinear equations relating germination and shoot elongation to time calculated as cumulated degree-days were fitted to the observed germination and shoot elongation data. These were used to estimate parameters for germination proportion and rate, as well as final shoot length and elongation rate. Recently harvested seeds germinated best and fastest when they were collected in spring crops compared with winter crops. Germination proportion and rate increased with seed storage length, especially for seeds collected in winter crops. Midgermination time decreased with seed weight and water deficit during seed production; it increased with nitrogen amounts available to the mother plants. Maximum shoot length increased with seed weight and plant density during seed production. It decreased with nitrogen availability to mother plants and with storage length, irrespective of whether the seeds were dry-stored or buried in soil. Elongation rate was highest for early- and fast-germinating seeds. Time to midelongation increased with maximum shoot length. These germination and preemergence growth models can now be combined with other submodels to develop a blackgrass emergence model.

The influences of temperatures on seed germination rate in Himalayan elm (Ulmus wallichiana)

The germination response of U. wallichiana seeds from three sources to constant temperature was investigated over the range 14-34°C on a thermo-gradient system. Difference between seeds in proportion and rate of germination, cardinal temperatures and thermal time required for germination was observed. The three cardinal temperatures viz., the base (T b ), the optimum (T o ) and the maximum (T m ) for germination rate varied slightly between seed lots as well as different percentiles of germination in a particular seed lot. The mean cardinal temperatures i.e., T b , To and T m were estimated as 11.3, 26.3 and 34.2°C for Chakrata, 11.6, 26.5 and 34.7°C for Manali and 12.7, 25.3 and 34.1°C for Sangla valley seed lots respectively. The seeds from the inner Himalayan range (Sangla valley) had slightly lower T o as compared to seeds from the outer Himalayan ranges (Chakrata and Manali). The mean thermal time at sub-optimal temperature for germination was estimated as 74.9, 64.9 and 71.9°Cd (degree-days), while at supra-optimal temperatures it was 35.1, 33.8 and 50.1°Cd respectively for seeds from Chakrata, Manali and Sangla valley. The thermal time both at sub and supra-optimal temperatures increased linearly as the values of the percentile germination increased in all three seed sources. The seeds germinated at supra-optimal temperatures required less thermal time to germinate than at sub-optimal temperatures.

Effect of environmental conditions on Alopecurus myosuroides germination. I. Effect of temperature and light

Summary Control of Alopecurus myosuroides with a minimum amount of herbicide may be improved by models describing the impact of cropping system effects on the weed's demography. In order to develop the submodel relating the weed seedbank to the emerged seedlings, a series of laboratory experiments was set up to analyse and quangify the effects on A. myosuroides germination of temperature, storage location, seed age and light incidence for various seed populations. The minimum temperature requirement for germination was estimated at 0 °C, and it did not depend on seed population or weight. In the subsequent experiments, a four-parameter non-linear equation depending on accumulated day-degrees was fitted to the observed germination data, resulting in the estimation of parameters quangifying germination proportion and rate. Storage location had little influence on germination. Germination proportion and rate increased with seed age and were higher in light than in darkness. The later the germinating seeds were submitted to light, the less was their germination stimulated. These observations were synthesized by a series of equations quangifying the relative variation in germination parameters as a function of storage and light conditions, independent of seed population.

Effect of environmental conditions on Alopecurus myosuroides germination. II. Effect of moisture conditions and storage length

Summary More effective control of Alopecurus myosuroides with a minimum amount of herbicide may be achievable by using models describing the impact of cropping system effects on the weed's demography. In order to develop the submodel relating the weed seedbank to the emerged seedlings, a series of laboratory experiments was set up to analyse and quangify the effects on A. myosuroides germination of length of seed storage in dry conditions, soil water potential and dryness during imbibition. The base soil water potential for germination was estimated at −1.5 MPa. A four-parameter non-linear equation depending on accumulated day–degrees was fitted to the observed germination data, resulting in the estimation of parameters illustrating germination proportion and rate. Germination proportion and rate increased with seed storage length, and were increased by short and decreased by long dry periods occurring after imbibition. These results showed that, in contrast to crop species, A. myosuroides germination cannot be expressed simply as a function of hydrothermal time, but also requires the determination of the proportion of non-dormant seeds as a function of seed age and environmental conditions.