Changes in developing pea (Pisum sativum) seeds in relation to their ability to withstand desiccation

In two separate experiments in 1970 and 1971 the germination ability of seeds that had been rapidly desiccated following harvesting from glasshouse-grown pea plants improved with time after fertilization. In 1970 the germination of seeds directly after harvesting also improved with time. In both years the readiness with which electrolytes were leached from dried seeds decreased with seed age, measured as time after fertilization. The germination ability of desiccated seeds, and of undried seeds in 1970, improved after the cessation of seed moisture increase on the parent plant. This improvement coincided, in 1970, with a fall in the readiness with which electrolytes could be leached from seeds and with a decline in the rate of oxygen uptake of seeds directly after harvest. Vital staining of dried seeds from harvest samples indicated the viability of the samples as determined by germination tests. In both years, when the cotyledons first showed complete staining, the staining was very intense; in 1970 this occurred in a harvest sample with a greater than 50% germination level, but in 1971 it occurred in a sample that showed incomplete staining in the embryo axis and less than 5 % germination. In 1971 the comparative rates of moisture loss from seeds, measured with a sensor element diffusion porometer, were very low at 25 days after fertilization, increased up to a peak at 35 days and fell to a rate at the final harvest (44 days) which was nearly three times faster than the initial rate. Thus, during the period of dehydration, after 37 days, the seeds were able to lose moisture. When seeds were allowed to lose moisture slowly after harvest, before being desiccated rapidly, their eventual condition as measured by leaching improved. Also, the faster the initial water loss preceding rapid desiccation the more readily were the dried seeds leached. It is suggested that seeds can only withstand rapid desiccation after the cessation of moisture increase and after some slow dehydration, which is accompanied by a slowing down in physiological activity.     

Stress integrated tests and cytological analyses reveal Brassica villosa subsp. drepanensis seed quality decrease upon long-term storage

Under stress integrated germination test (SIGT), seeds undergo osmo-saline stresses, which enable to detect differences in vigour of long-term stored seeds with high germination percentage (G%). The quality of Brassica villosa subsp. drepanensis seeds stored in a genebank (at ? 20°C for 16 years) was compared with seeds at harvest by standard germination tests (GT), SIGT and cytogenetic analysis. No differences were detected in G% and mean germination time under GT. Conversely, SIGT performed with NaCl ? 0.9 MPa osmotic potential did not influence G% at harvest but reduced that of stored seeds, SIGT at ? 1.4 MPa reduced G% of both. Cytogenetic analysis showed reduction of mitotic index, appearance of chromosomal aberrations and smaller nucleoli in stored seeds compared with harvest seeds germinated in water. SIGT at ? 0.9 MPa had no effect on mitotic index, but increased chromosome aberrations and nucleoli number. SIGT at ? 1.4 MPa inhibited G% of harvest and stored seeds, reduced mitoses in harvest and completely prevented it in stored seeds. The results indicate that GT does not faithfully reflect the quality of stored seeds, with misinterpretation of their vigour, whereas SIGT and cytogenetical parameters are sensitive, reliable and inexpensive methods for early prediction of genetic erosion in germplasm banks.     

The effects of fluid drilling and seed covering medium on early carrot production under polyethylene mulch

Ungerminated seeds, fluid-drilled germinating seeds and fluid-drilled uniformly-germinated seeds were sown in furrows that were either uncovered or covered by soil and left unmulch ed or mulched with polyethylene sheet. The effects of these treatments on the emergence and growth of carrots for early harvest were examined. Leaving seeds uncovered or mulching them with polyethylene advanced seedling emergence and increased the percentage that emerged; leaving seeds uncovered also reduced the spread of emergence times and produced seedlings with larger cotyledons. Uniformly-germinated seeds emerged before germinating seeds and both emerged before ungerminated seeds. The best combination of treatments (i.e. mulched, uncovered uniformly-germinated seeds) reduced the mean number of days for emergence from the 52 required by traditionally sown seeds to 29. There was a more variable effect of seed treatments on the spread of emergence times and the percentage emergence. Earlier emergence generally led to roots reaching a marketable size earlier and more uniform emergence led to less variation in root weights at harvest.     

The effect of time of harvest on the viability and pre-emergence mortality in soil of pea (Pisutn sativum L.) seeds

A series of harvests from field plots of peas showed that the younger seeds were at the time of harvest the lower was their percentage viability and the greater their percentage mortality in soil. Young seed also showed a high degree of solute leaching into steep water and had a high moisture content at harvest compared with older seeds. Heavy rainfall just prior to harvesting reduced the percentage viability of the dried seed and increased the moisture content of the seed at harvest as well as the leaching of solutes from the dried seed into steep water. Comparisons of moisture content at harvest and seed condition after drying suggested that cotyledons and embryo axes were only able to withstand enhanced drying after removal from the plant if the seed moisture content had already begun to decline whilst the seed was still on the plant.     

Mechanisms of seed harvest by heteromyid rodents: soil texture effects on harvest rate and seed size selection

Summary Several lines of evidence show that soil texture plays an important role in the distribution of desert-dwelling heteromyid rodents. This is not surprising, since texture influences the energetic cost of digging burrows and of scratching at the soil surface to harvest buried seeds. Texture also may influence the efficiency with which seeds can be separated from the soil particles with which they are mixed. To explore mechanisms of particle separation by foraging heteromyids we measured seed harvest rates and size selection in the laboratory for a variety of seed sizes and soil textures. Harvest rate declined with increasing soil coarseness, and the preference for seeds of intermediate size that was apparent in fine soil disappeared when seeds were mixed with soil slightly coarser than the preferred seed size. In addition, there was evidence that particle separation efficiency is sensitive to the relative sizes of seeds and soil. A discontinity in the function relating harvest rate to soil texture occurred at finer soil textures for small seeds than for large seeds, suggesting that harvest techniques change once soil particle diameter equals or exceeds that of seeds. These results are consistent with the hypothesis that heteromyids use a combination of gravity-and rake-sorting mechanisms for particle separation.     

应用基因工程生产一次性使用的常规种子

美国公布的“植物基因表达调控”的专利技术,使经遗传改变的植物生产的下一代种子不能发芽。农民买了此一次性种子后,产量不受影响但不能留种用。种子公司把此技术作为开发新品种的一种手段。     

Endoreduplication in cucumber (Cucumis sativus) seeds during development, after processing and storage, and during germination

Flow cytometry was used to study endoreduplication in developing, stored and germinating seeds of cucumber ( Cucumis sativus ). Fruits growing in a commercial seed production field were collected every 7 days, starting 14 days after pollination (DAP) up to 63 DAP (commercial harvest time). Seeds were isolated and the proportion of nuclei with different DNA contents in the whole seeds and in the embryos was analysed. Germination capacity of fresh and dried seeds at 25°C was established. In addition, the same analyses were performed on the seeds after processing (fermentation, drying and cleaning), following 1 and 2 years of storage, and after imbibition for 3, 6 and 12 h. In the young developing seeds, endoreduplication up to 128C occurred but this decreased to 8C by maturity. The proportion of endosperm nuclei was the highest at 21 DAP (30%) and then decreased to below 14% at harvest and 8% after processing. In the mature processed seeds, the majority of embryo nuclei (about 80%) contained 2C DNA; however, about 2% of endoreduplicated (8C) nuclei were still present. Seeds did not show any germination capacity up to 21 DAP; then it gradually increased to reach 100% as early as 49 DAP, 2 weeks before commercial harvest time. The relationship between seed maturity, germination and cell cycle status is discussed. The mean C-value of the seed cells as well as the (4C + 8C + 16C)/2C ratio are recommended as markers of cucumber seed maturity and the advancement of germination/priming (the stage of germination sensu stricto ).     

Seed Vigour in Bean (Phaseolus vulgaris L. cv. Apollo) as Influenced by Temperature and Water Regime during Development and Maturation

Bean plants grown in a controlled temperature glasshouse athigh temperatures (33/28, 30/25, or 27/22 °C) during theperiod of seed development and maturation matured early andproduced small seeds. The seeds were of lower vigour than thosegrown at 21/16 or 18/13 °C. The detrimental effect of highmaturation temperatures was observed even on plants bearingwell-developed seeds (yellow, fleshy-pod stage). Seeds maturedat high temperatures were also more susceptible to deteriorationwith delay in harvest, and to mechanical damage. Heavy wateringof plants with seed ready to harvest caused a reduction in seedvigour. For optimum quality bean seed, it appears essentialthat the seed develops and matures at cool temperatures, ina dry environment.     

A mechanism for resource allocation among sympatric heteromyid rodent species

Summary Laboratory feeding experiments were conducted with Dipodomys ordii and Perognathus flavus in an attempt to discover a mechanism which might result in seed size selection. There was no marked difference in the proportions of four seed types collected whether the rodents foraged in the presence or absence of one another. However, analysis of the variability in weight of each of the seed types collected by the two species showed that when alone, the larger kangaroo rat was less effective at harvesting all of a uniformly distributed mixture of seeds. When in the presence of one another both species could harvest enough of the mixed, uniformly distributed seed to coexist indefinitely, but when the food source was presented as four large clumps the kangaroo rat's foraging effectiveness increased tremendously so that the pocked mouse was almost entirely unable to harvest any seed. These data, in light of mobility differences between large and small heteromyids, suggest a mechanism whereby the larger, more mobile kangaroo rats forage for the most readily available (large or clumped) seeds over a relatively large area. The smaller pocket mice, by virtue of their relative efficiency in harvesting seeds can utilize the less detectable seeds which are energetically too demanding for the larger kangaroo rats to harvest. Behavioral dominance of the larger animals may help prevent the smaller from utilizing the most readily available seeds. The patterns of seed size and foraging site selection described in the literature may be easily accounted for by this difference in foraging strategy.     

Exploring nitrogen remobilization for seed filling using natural variation in Arabidopsis thaliana

Nineteen Arabidopsis accessions grown at low (LOW N) and high (HIGH N) nitrate supplies were labelled using (15)N to trace nitrogen remobilization to the seeds. Effects of genotype and nutrition were examined. Nitrate availability affected biomass and yield, and highly modified the nitrogen concentration in the dry remains. Surprisingly, variations of one-seed dry weight (DW(1S)) and harvest index (HI) were poorly affected by nutrition. Nitrogen harvest index (NHI) was highly correlated with HI and showed that nitrogen use efficiency (NUE) was increased at LOW N. Nitrogen remobilization efficiency (NRE), as (15)N partitioning in seeds ((15)NHI), was also higher at LOW N. The relative specific abundance (RSA) in seeds and whole plants indicated that the (14)NO(3) absorbed post-labelling was mainly allocated to the seeds (SEEDS) at LOW N, but to the dry remains (DR) at HIGH N. Nitrogen concentration (N%) in the DR was then 4-fold higher at HIGH N compared with LOW N, whilst N% in seeds was poorly modified. Although NHI and (15)NHI were highly correlated to HI, significant variations in NUE and NRE were identified using normalization to HI. New insights provided in this report are helpful for the comprehension of NUE and NRE concepts in Arabidopsis as well as in crops and especially in Brassica napus.     

Biotic and abiotic factors that affect the quality of Schinopsis balansae Engl. and Aspidosperma quebracho-blanco Schltdl. seeds

Aspidosperma quebracho-blanco (white quebracho) and Schinopsis balansae (red quebracho) are distinctive trees of the South American Park in Argentina. Quebrachos are found in forests that have been exploited very intensively. The object of this work was the identification of biotic and abiotic factors specially fungal pathogen that affect the quality of both species and its relation with germination. Seeds where evaluated through germination test and the percentage of the incidence of fungal agents in two different years of harvest was determined. In S. balansae the germination rate was 77% and of 27% in 2000 and 2001 harvests, respectively. Associations fungi-germination were found in 2001 for Alternaria spp., Curvularia spp., and Fusarium spp., showing an coefficient of correlation = -0.84; -0.85 and -0.73 (p < 0.00004), respectively. A high percentage of vane seeds (55%) was also found in 2001 harvest, due to adverse environmental factors, specifically higher precipitations during flowering. In A. quebracho-blanco seeds, the germination rate was 50% and 90% in 2000 and 2003 respectively, with a 42% of immature seeds in 2000 harvest that was associated to high precipitations and high temperatures during flowering and ripping of fruits. The incidence of pathogens was low and did not have association to germination.     

Persistence of seeds from crops of conventional and herbicide tolerant oilseed rape (Brassica napus)

A series of rotation experiments at five sites over four years has explored the environmental and agronomic implications of growing herbicide tolerant oilseed rape and sugar beet. This paper reports on the population dynamics of volunteer rape (Brassica napus). The experiments compared four winter oilseed rape (WOSR) cultivars: a conventional cultivar (Apex) and three developmental cultivars either genetically modified (GM) to be tolerant to glyphosate or glufosinate, or conventionally bred to be tolerant to herbicides of the imidazolinone group. Seed losses at harvest averaged 3575 seeds m(-2) but ranged from less than 2000 up to more than 10000 seeds m(-2). There was a rapid decline in seed numbers during the first few months after harvest, resulting in a mean loss of seeds of 60%. In subsequent seasons, the seedbank declined much more slowly at four of the five sites (ca 20% per year) and the models predicted 95% seed loss after approximately 9 years. Seed decline was much faster at the fifth site. There were no clear differences between the four cultivars in either the numbers of seeds shed at harvest or in their subsequent persistence. The importance of the persistence of GM rape seeds, in the context of the coexistence of GM and non-GM crops and the role of good management practices that minimize seed persistence, are discussed.     

Maternal phenotypic effects due to soil nutrient levels and sink removal in Arabidopsis thaliana (Brassicaceae)

Three levels of soil nutrients and systematic removal of racemes and siliques, intended to reduce reproductive sink size, induced maternal effects in a genetically uniform, inbred accession of Arabidopsis thaliana ecotype Col-0. Soil nutrient levels but not trimming treatments caused significant differences in maternal plant weight and number of seeds per silique. Trimming and increased soil nutrient level resulted in larger seeds. Germination rates were significantly affected only by the trimming main effect, while there were no significant effects on germination percentage. At 14 and 19 d harvest dates, soil nutrient level treatments resulted in significant differences in offspring aerial biomass, but this effect was nonsignificant at 24, 29, and 34 d harvest dates. The effect of trimming on offspring aerial biomass was significant at all harvest dates. No significant soil nutrient level × trimming interaction was observed on any harvest date. Phenotypic correlations among aerial biomass at each harvest date and seed weight of the six offspring classes were highly significant. Analyses of variance for germination and biomass data adjusted for seed weight showed no significant differences due to soil nutrient level, trimming, or their interaction, indicating that maternal effects influencing these variables were determined by seed weight. Relative growth rates were estimated from changes in biomass over time. The negative correlation between initial relative growth rate and rate of change of the relative growth rate was highly significant (R = -0.99; P < 0.01).     

Fungi that infect cottonseeds before harvest

As a part of an investigation of aflatoxins and other mycotoxins in cottonseeds at harvest, samples of seeds collected from the 1971 crop at locations across the U.S. Cotton Belt were examined to determine the kinds of microorganisms causing internal or seed-coat infection in the field. Aspergillus flavus infection was absent from all seeds examined from most areas but was present in some samples from Arizona, California, and Texas. Fusarium spp., Alternaria sp., and A. niger caused internal infection at many locations; Colletotrichum gossypii and Rhizopus stolonifer were present in seeds from some areas but were generally much less common. Many of the infections with A. niger were in the seed coat. Bacterial infections were fairly frequent. In a series of commerical samples from Arizona. A. flavus infection was found in 61% of seeds, with fiber showing the bright, greenish-yellow (BGY) fluorescence that is diagnostic for A. flavus boll rot. Aflatoxin contamination was also concentration in the same seeds. The above findings agree with previous data showing that aflatoxin contamination of cottonseeds before harvest occurs rarely, if at all, in most parts of the U.S. Cotton Belt and that when such contamination does occur, it tends to be concentrated in seeds with the BGY fluorescence in their fiber and seed fuzz.     

Changes in RNA and Protein Metabolism Associated with Alterations in the Germination Efficiency of Sunflower Seeds

Precise knowledge of seed quality after harvest and during storageis of particular importance for seed producers. We analyseddifferent sunflower seed lots (Helianthus annuusL.) characterizedby extremes of germination ability. We used RNA analysis tostudy possible changes in gene expression in seeds unable togerminate. Total RNA content was very small in dry seeds showinga low germination ability. Capacity for total RNA synthesisat the onset of imbibition was also reduced in these seeds.In addition, correlations were found between these parametersand germination ability at 19 °C. We demonstrated a highcorrelation between the amount of total RNA in the dry seed,the capacity of RNA synthesis at the onset of imbibition andthe seed moisture content at the time of the harvest. The abilityof dry seed mRNAs to be translatedin vitrowas also reduced andseven polypeptides, from stored mRNAs, were characteristic ofthe cotyledons from high germinability seeds. Germination canthus be affected at several levels including membrane, enzymaticand nucleic acid deteriorations. Gene expression; germination ability; Helianthus annuusL.; marker; protein; RNA; seed; sunflower     

The influence of seed quality and pregermination treatment on cauliflower and cabbage transplant production and field growth

Seedling emergence and subsequent growth from untreated seeds and selected-germinated seeds which had been dried before sowing (low-moisture-content germinated (LMCG) seeds) were compared in cellular trays in a glasshouse and in the field following transplanting. Three seed lots of different quality of the same cultivar were used for cabbage and cauliflower. In all cases, seedling emergence was greater, earlier and more uniform from LMCG seed than that from untreated seeds. LMCG seed effectively eliminated the differences due to seed quality shown by untreated seeds at emergence suggesting an improvement in seed vigour as well as viability from the selection treatment. Higher quality seed and LMCG cauliflower seed led to larger curd weights and therefore an increase in marketable yield at harvest compared to that from lower quality seeds. However, differences in transplant uniformity due to seed quality and seed treatment had little impact of agronomic significance following transplanting.     

Grassland composition affects season shifts in seed preference by Pogonomyrmex barbatus (Hymenoptera: Myrmicinae) in the Edwards Plateau, Texas

The effects of season and community composition as generated by livestock herbivory of differing intensity on seed species preference by Pogonomyrmex barbatus (F. Smith) were studied in a semiarid savanna on the Edward's Plateau, TX. Seasonal differences in nutrient requirements of the colony could lead to differential preferences for seeds harvested in spring and fall. Field cafeteria studies were conducted to test the hypothesis that late successional species, with their high nutrient content, would be chosen regardless of grazing intensity or season. Commercial seeds of known nutrient content were used to test the hypothesis that high protein levels would be chosen in spring and high carbohydrate levels in the fall. Naturally occurring seeds were differentially harvested and some were preferred regardless of relative availability. Total seed harvest in cafeteria experiments was higher in spring than in fall. Commercial seeds were harvested equally among treatments within a season; thus, nutrient selection was indistinguishable. Preference for native species was significantly different in both seasons but was influenced by a significant interaction with grazing treatments. Bouteloua curtipendula, a late successional mid-grass, was harvested significantly more in the spring than the fall and at higher rates in the heavily grazed treatment, rejecting the hypothesis that they would be chosen regardless of treatment or season. Seed preference for late successional grasses within heavily grazed communities may slow succession after grazing. During disturbance recovery, late successional species may be reduced by forager preference and rates of spring harvest.     

Effects of body size,seed density,and soil characteristics on rates of seed harvest by heteromyid rodents

Summary Although it is well established that coexisting heteromyid rodent species forage in different microhabitats, we do not yet know the basis for divergent microhabitat choice. One possibility is that seed harvest rates differ among microhabitats, and each species forages where it can extract seeds most efficiently. Microhabitats vary in several factors that could affect heteromyid foraging efficiency, including seed density, soil organic content and particle size distribution. We have explored the effect of each of these variables on harvest rates of several species feeding from petri dishes containing known densities of millet seeds embedded in soil of known particle size and density. Results indicate that the number of seeds harvested per second increases uniformly with seed density and soil density and decreases with soil particle size. Body size affects these relationships: larger animals have higher harvest rates for a given set of conditions and experience a greater relative change in harvest rate for a give change in conditions. This implies that heteromyids can be expected to exhibit species-specific microhabitat preferences while foraging in nature.     

Alteration of selection regime resulting from harvest of American ginseng, <Emphasis Type="Italic">Panax quinquefolius</Emphasis>

Replicate harvest simulations were conducted in a large natural population of Panax quinquefolius L.␣(Araliaceae) to determine the selective effects of harvest. We investigated how minimum size requirements and the influence of size on apparency to human harvesters could result in preferential removal of large plants. To determine which plants were encountered in the large population, harvesters were tracked using GPS as they searched for every legally harvestable, adult plant they could find. Plants were assigned stage-specific fitness measures based on their contributions to population growth rate (λ) under three demographically based harvest regimes: no harvest, harvest and harvest removing seeds. Plant size was codified into a size-index equal to the product of total leaf area and stem height. Heterogeneity of slopes was tested to determine if the selection gradients (β) describing the relationship between fitness and size varied among the three harvest regimes. Harvest differentially reduced the fitness of larger plants in one of four individual harvest simulations. The combined harvest simulation significantly altered the selection regime for size in the population of juvenile and adult (harvestable) plants. Seed removal by harvesters intensified fitness declines for larger plants. Because larger plants contribute most to population growth, the selective effects of harvest could result in a shift in the evolutionary dynamics of this species with significant conservation implications.     

Anatomical and biochemical studies in persisting and shedding seeds during the development of peach fruits

ABSTRACT

Peach fruits were collected in the period between anthesis and harvest. The relationship between histological structure, free abscisic acid (ABA) and carbohydrate content was investigated in control seeds (class A) and in the seeds of fruit that were affected by fruit-drop and that were not yet abscised from the plant (class B). The results of the histological analysis showed that seeds from class A generally showed a normal embryogenesis, whereas we did not detect any embryo and endosperm in seeds of class B because they were undergoing degeneration. The ABA level reached a positive peak during the first 75 days after anthesis in seeds of class A, whereas the seeds of class B showed a negative peak in the same period. Carbohydrate content followed a similar trend to that of ABA. Results are discussed in relation to the development of the fruits.