Coastal desert vegetation of the Arabian Peninsula is almost entirely dominated by halophytes. Natural populations provide a genetic resource for ecological remediation and may also have direct economic value. High intrapopulation variation of seed traits is presumed to increase population persistence in the unpredictable climatic conditions of this hyper-arid desert. We investigated whether intrapopulation variation of seed mass, dormancy and germinability of four species was attributable to maternal individuals. Arthrocnemum macrostachyum, Halothamnus iraquensis, Haloxylon salicornicum and Seidlitzia rosmarinus are commonly distributed Arabian halophytes with differing seed weight variation. All species exhibited a higher germination when exposed daily to 12 h light, compared to seeds in darkness. A higher germination was correlated with a shorter germination time. For H. iraquensis and S. rosmarinus, a shorter germination time was negatively correlated with germination synchrony. H. salicornicum showed the highest intrapopulation variation of seed traits, followed by A. macrostachyum, S. rosmarinus and H. iraqensis. We found that individuals within populations of all the studied species showed variability in germination but the extent of variation was species-specific. The variation in seed mass and germination among the individuals of the studied species may facilitate a temporal distribution of germination, which may reduce the risk of seed bank exhaustion. The results of this study could assist conservation and management by improving the efficiency of seed collection from wild populations of these species.

In order to gain an understanding of the genetic basis of traits of interest to breeders, the pea varieties Brutus, Enigma and Kahuna were selected, based on measures of their phenotypic and genotypic differences, for the construction of recombinant inbred populations. Reciprocal crosses were carried out for each of the three pairs, and over 200 F2 seeds from each cross advanced to F13. Bulked F7 seeds were used to generate F8–F11 bulks, which were grown in triplicated plots within randomized field trials and used to collect phenotypic data, including seed weight and yield traits, over a number of growing seasons. Genetic maps were constructed from the F6 generation to support the analysis of qualitative and quantitative traits and have led to the identification of four major genetic loci involved in seed weight determination and at least one major locus responsible for variation in yield. Three of the seed weight loci, at least one of which has not been described previously, were associated with the marrowfat seed phenotype. For some of the loci identified, candidate genes have been identified. The F13 single seed descent lines are available as a germplasm resource for the legume and pulse crop communities.

Greenhouse and field studies were conducted to examine the interaction of sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon for selective weed control in safflower. Under greenhouse conditions, the addition of chlorsulfuron to sethoxydim or fluazifop-P slightly improved the control of green foxtail above that achieved with either herbicide alone. Control of wild oat and wild mustard was similar with the tank mixes and each herbicide alone. In the field, control of wild oat with sethoxydim or fluazifop-P was not altered by adding chlorsulfuron or thiameturon in tank mixes. Similarly, control of common lambsquarters and wild mustard with chlorsulfuron or thiameturon was not affected by adding either sethoxydim or fluazifop-P in tank mixes. Plant height, date of flowering, seed yield, and quality data indicated that safflower tolerated these herbicides applied alone or in combination. Sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon provide a postemergent alternative for selective control of grass and broadleaf weeds in safflower.

Postemergence control of broadleaf weeds in canola with DPX A7881 was studied under controlled-environment and field conditions. DPX A7881 controlled weeds of the Cruciferae family such as wild mustard, field pennycress, and flixweed, which are not controlled with existing herbicides used for weed control in canola. Weed control was better when DPX A7881 was applied at the two-leaf than at the six-leaf stage of the weeds. At the two-leaf stage, control of flixweed was achieved with 15 g ai/ha of DPX A7881; 20 to 30 g ai/ha was required for control of wild mustard and field pennycress. Control of redroot pigweed required 30 g ai/ha. Common lambsquarters was not controlled in this study with DPX A7881 up to 60 g ai/ha. Control of weeds with DPX A7881 increased canola yields in this study without altering the important quality components: oil content, 1000-kernel weight, and green seed content. DPX A7881 provides a postemergence alternative to existing herbicides for broadleaf weed control in canola.

Electrophoretic analysis of storage protein accumulation in developing cowpea [Vigna unguiculata (L.) Walp. ‘Mississippi Purple’] seed indicated that a large increase in protein content per seed occurred between 10 and 11 days after flowering (DAF). Polypeptides with molecular weights of 54, 49, and 41 kilodaltons (kD) accumulated first, and one with a molecular weight of 59 kD appeared 2 days later at 13 DAF. Treatment of plants with glyphosate [N-(phosphonomethyl)glycine] when pods were 7 and 10 DAF prevented accumulation of the major storage protein polypeptides. The accumulation of these polypeptides was not inhibited as much when pods were 11, 12, or 13 DAF at the time of treatment with glyphosate. Pod length and seed fresh weight were inhibited by glyphosate treatment of plants bearing pods 7, 10, 11, and 12 DAF. Pod width, seed dry weight, and seed length were inhibited by glyphosate when plants bearing pods 7, 10, and 11 DAF were treated.

The response of Persian darnel, green foxtail, wild oat, and volunteer cereals to clethodim applied at two growth stages, and the effect of these treatments on flax yield and quality were determined in a series of field experiments in which each weed species was evaluated separately. Clethodim applied at 45 g/ha provided excellent control of Persian darnel, green foxtail, wild oat, and volunteer wheat and barley. Sethoxydim applied at 150 g/ha provided excellent control of Persian darnel, green foxtail, wild oat, and volunteer barley. Rax was tolerant at five times the recommended rate of application and was unaffected by plant growth stage at time of application. When applied at an early (2- to 3-leaf) stage, control of Persian darnel, green foxtail, wild oat, and volunteer wheat and barley was excellent at 20 g/ha. Except for Persian darnel, weed control as determined by reduction in plant dry weight, was negatively affected by growth stage at time of application. Although visible control and reduction in plant dry weight were somewhat less when clethodim was applied at the 4-to 5-leaf stage, control of each weed species was acceptable. When weight of water in plant tissue (fresh weight – dry weight) was used as a measure of living plant tissue, wild oat and volunteer barley control were unaffected by growth stage at time of application.

Field experiments were conducted to determine the growth, development, and seed yield response of scentless chamomile when planted at various dates throughout the growing season. Scentless chamomile emerged within 6 to 15 d of planting and required 75 to 131 growing degree days (GDD). Flowering occurred within 56 to 82 d of planting and required 584 to 845 GDD. Plants that emerged in mid-July and onward did not flower in that season but survived as winter annuals. Spring-planted scentless chamomile matured within 97 to 127 d and required 906 to 1,176 GDD. Plants that emerged in May and June attained more leaf area and biomass than plants that emerged in mid-summer. Plants that emerged early in the growing season produced three-to fourfold more seed than plants that emerged at later dates. Scentless chamomile seed production ranged from 71,000 to 256,000 plants−1 depending on planting date and existing environmental conditions. Results are discussed in terms of its potential to become an increasingly troublesome weed in crops of the Canadian prairies and possible management strategies for its control.

The influence of weed removal, cultivar, and row spacing on soybean [Glycine max (L.) Merr.] yields was determined for 3 yr at the western edge of the soybean production area in the Great Plains in order to establish the critical weed-control periods. Early weed removal aided soybean stand establishment, and there was an inverse relationship between soybean stand and production of weed top-growth. Soybean seed weight and numbers per plant both increased as weed growth decreased. The soybean variety ‘Amsoy 71’ was more competitive than ‘Beeson’ to both early and late emerging weeds. Soybeans weeded at 2 through 4 weeks after planting did not show significantly reduced soybean yields from later emerging weeds. Thus, weed control the first month after planting is the most critical in obtaining high soybean yields.

Soybeans [Glycine max (L.) Merr.] were planted in an untilled, stale seedbed and conventionally tilled seedbed of Sharkey clay (Vertic Haplaquept) at Stoneville, Mississippi, in 1979 and 1980 to determine the feasibility of the stale -seedbed approach for soybean production in the Mississippi River Delta. Chemical weed control included applications of preplant, preemergence, and postemergence herbicides. Prickly sida (Sida spinosa L.) was the dominant weed in all tillage and weed-control systems. Perennial species were observed at harvest mostly in the stale - seedbed plots. Preemergence herbicides reduced the total weight of weeds per plot. Conventional seedbed preparation caused delays in planting of 3 weeks or more. In the presence of adequate soil moisture, yields of ‘Bedford,’ ‘Tracy’, and ‘Bragg’ cultivars from the stale - seedbed planting and areas that had been treated preemergence were always equal to or greater than yields from the tilled - seedbed plantings and areas that had been treated postemergence. In 1980, the hot, dry conditions of the growing season apparently negated any effect from either earlier planting or preemergence vs. post-emergence weed control.

Growth and development of three wild-proso millet biotypes (Cambridge, LeSueur, and Morris) and one cultivated proso millet (‘Crown’) were compared under noncompetitive conditions in field studies. LeSueur and Cambridge were taller than Crown and Morris at maturity. All wild types had greater leaf area and dry weight at maturity than Crown. Crown headed earlier than the wild types, and among the wild types, Cambridge was slowest to mature. Seed production was 1.4 to 2 times greater for wild than cultivated proso millet, and averaged 48 000, 69 000, 83 000, and 94 000 seeds/plant for Crown, Cambridge, LeSueur, and Morris, respectively. Mean seed weight was 4.0 and 3.8 mg/seed for LeSueur and Morris, respectively, and 5.8 and 5.9 mg/seed for Crown and Cambridge, respectively. LeSueur and Morris seed shattered readily, but Cambridge seed shattered relatively little. Seed dormancy was greater in LeSueur and Morris than in Cambridge. Based on reproductive potential, shattering, and dormancy characteristics, LeSueur and Morris appeared to have more weedy characteristics than Cambridge.

The nitrogen (N) response of competing plants may be affected by photosynthetically active radiation (PAR) availability and maximum potential growth rate, which determine N requirements. The responses of two crop (corn and soybean) and six weed species (common lambsquarters, common waterhemp, giant foxtail, velvetleaf, wild mustard, and woolly cupgrass) in low and high (150 and 450 μmol m−2 s−1) PAR levels to daily fertilization with either low or high (0.2 or 7.5 mM) NH4NO3 levels were studied. Leaf area of all species responded positively to N by 8 d after emergence (DAE) when grown in high PAR; in low PAR, most species did not respond until 11 DAE. Dry weight and leaf area of all species at 18 DAE were greater with high than with low N. These responses to high N were also greater in high than in low PAR for all species. Dry weights with high N were up to 100% greater in low PAR and up to 700% greater in high PAR than dry weights with low N. These responses suggest that low PAR reduced the benefit of N to the plants. The regression of relative growth rate (RGR) with high N to RGR with low N had a slope that was less than unity (β = 0.79), indicating that species with a higher RGR with high N experienced greater decreases in RGR with low N. Similarly, the sensitivity (change in RGR) of plants grown with high and low N was positively related to RGR with high N. RGR differences among crop and weed species may be related to differences in N requirement that could be exploited for weed management. RGR and seed size were negatively correlated, which may explain previous observations that small-seeded weeds were more sensitive to environmental stress.

Experiments were conducted to determine the amount of time required for waterhemp to produce mature seeds after pollination. Female waterhemp plants were pollinated over a 24-h time period and then isolated from males. Two branches, each containing at least 500 flowers, were harvested from each female at the time of the initial pollination, designated as 0 d after pollination (DAP), as well as at multiple other times after pollination up to 62 DAP. One branch from each harvest was stored at 30 C for 48 h, while the other branch was stored at −20 C for 48 h. Branches were then stored at room temperature until all harvests were complete, at which time seeds from each branch at each time after pollination were collected, weighed, and stratified. Germination tests were then conducted to determine the time at which seeds become viable after pollination. Seeds that had not germinated by the end of the germination tests were subjected to tetrazolium testing for viability. Germination tests were also conducted on nonstratified seeds to investigate changes in seed dormancy that were expected to occur over the amount of time the seeds were allowed to remain on the plants. Seeds stored initially at 30 C postharvest became viable 7 to 9 DAP, whereas seeds stored initially at −20 C postharvest did not become mature until 11 DAP. Seed coat color was white soon after pollination and became dark brown to nearly black by 12 DAP, and seed weight increased until 12 DAP. Tetrazolium tests for seed viability correlated well with the germination tests. Germination tests on nonstratified seeds indicated that dormancy level was initially high in the population used, but began to decrease between 15 and 30 DAP. Results of this study have implications both for waterhemp management and research.

Early plant establishment through seed germination and seedling emergence is a crucial process that determines seedling number, emergence time distribution and the early growth of seedlings, all of which are affected by soil climate and soil structure. In the current context of climate change, in which increasing the diversity of cultivated species is considered desirable, and new tillage practices are considerably modifying top-soil surface characteristics, we need to improve our ability to model the effects of the environment on plant establishment. Using a trait-based and model-based framework, we aimed to identify general relationships between seed and seedling traits (e.g. seed mass and lipid content, seedling diameter, base temperature) and germination and emergence model parameters (e.g. time to mid-germination, shoot elongation rate) measured for 18 genotypes belonging to 14 species. Relationships were also investigated among model parameters or traits. Germination rates were faster for species with a high base temperature and for species with seed reserves located principally in the embryo (rather than the endosperm or perisperm). During heterotrophic growth, maximal shoot length and elongation rate increased with seed dry mass. The sensitivity of seedlings to soil obstacles was negatively related to shoot diameter. Thus apart from the known effects of seed mass on seedling establishment, we found that seed reserve location, seedling shoot diameter and shape affected germination rate and emergence success. Such generic rules linking plant traits to germination and emergence parameters enhance our understanding of the determinants of environmental effects on plant establishment success.

Chickpea (Cicer arietinum L.) is an important food legume crop grown mostly in Asia and Africa as well as in other parts of the world, and serves as an important source of protein in the diets of vegetarian people. Lot of variation in grain quality traits has been observed in cultivated chickpea in both desi and Kabuli types. It has often been observed that seeds with smaller size have more protein when compared with those with larger size. The joint dependence of these two traits on the same primary characteristics results in this negative relationship. This negative correlation coupled with breeding efforts aimed at increasing grain yield has hampered the progress of improving these two traits simultaneously. Therefore, a germplasm exhibiting wider variability for these quantitative traits is an important resource for the identification of novel alleles. Herein, we report the wide variation observed for five important quantitative traits including days to flowering, days to maturity, plant height, 100-seed weight and protein content, and also report the significant positive correlation observed between 100-seed weight and protein content in a diverse collection of chickpea germplasm comprising both desi and Kabuli types.

Dormancy and germination ecology of two Harpagophytum species (Pedaliaceae) from an open Acacia savanna in Botswana were investigated. The maintenance of dormancy is governed partly by the seed coat but mainly by the endosperm and the embryo itself, as demonstrated by removal of the endosperm. Dissemination of the seed from the fruit can be delayed for several years without affecting the viability of the embryo, due to very low respiration rates.

Germination can be enhanced slightly by high temperatures under natural conditions, and by gibberellic acid or removal of the endosperm under laboratory conditions. Relative growth rates for both Harpagophytum species are lower than for subtropical grasses and legumes, due to a strong investment in root and tuber biomass. Germination and seedling growth is discussed in relation to the drought avoidance syndrome and the animal disperser syndrome.

This is the first report on the SEed Ecological Database (SEED) being developed under the co-ordination of the author. In its first version the database will cover physical characteristics of seeds, such as: slenderness (length/width), flatness (thickness/width) and thousand-seed weight. The list of species encompasses all seed plants (gymnosperms and angiosperms) native or naturalized in Hungary (about 2450 species). Two examples to demonstrate the power of SEED are included. The significantly lower slenderness values of Hungarian C4 grasses (compared with C3 types), shown in the first example, is a new contribution to understanding the ecology of C4 grasses. In the second example heavier seed weights of shade plants are statistically demonstrated, compared to their heliophilous congeners with the same life forms. The 113 congeneric species pairs considered are derived from a wide range of plant families.

Changes in tomato (Lycopersicon esculentum Mill.) seed quality were monitored during seed development and maturation in glasshouse experiments in 2 years. The end of the seedfilling period (mass maturity) occurred 35–41 d after anthesis (differing among trusses) in 1989 and 42 d after anthesis in 1990. Seed moisture contents at this developmental stage were 53–72% (wet basis), while the onset of ability to germinate (during 21-d tests at 20°/30°C) and the onset of tolerance to rapid enforced desiccation occurred just before (1990) or just after (1989) mass maturity. In 1989, seed quality was assessed primarily by seedling size in a glasshouse experiment; maximum mean seedling dry weight 25 d after sowing was not achieved until 24–40 d after mass maturity. In 1990, seed quality was assessed primarily by germination following storage; maximum normal germination after 35 d in storage at 40 °C with 14 ± 0.5% moisture content was attained 23 d after mass maturity, but with little difference among seed lots harvested 10 d earlier or up to 30 d later. The results contradict the hypothesis that maximum seed quality is attained at the end of the seed-filling period and that seed viability and vigour begin to decline immediately thereafter.

Marrow (Cucurbita pepo L.) seed quality was monitored during seed development and maturation in 2 years. Mass maturity (end of the seed-filling phase) was attained 61–63 d and 54 d after anthesis in 1989 and 1990, respectively, when seed moisture contents had declined to 40–48% (wet basis). Considerable dormancy was encountered during standard germination tests, but was overcome by decoating the seeds. The ability of dried, decoated seeds to germinate normally in standard tests reached near maximal values shortly after mass maturity; these values were more or less maintained in seeds from subsequent harvests. Maximum seed longevity in air-dry storage was detected in seeds harvested 24 d (1989) and 26–31 d (1990) after mass maturity. Seedling dry weights 15 d after sowing were greatest for seeds harvested 2–22 d (basal fruits) or 14 d (apical fruits) after mass maturity in 1989, and were positively correlated (P<0.01) with times from seedling emergence to seedling harvest. Consequently in the subsequent year the hypothesis that these differences in seedling dry weight were solely due to differences in times from sowing to emergence was tested (and confirmed). Seedling relative growth rates did not differ with seed harvest date (P>0.25) in 1990, but absolute seedling size did (P<0.005); seeds harvested 21–31 d after mass maturity had the greatest seedling weight and also growth rate (in absolute terms) at any one time after sowing. Decline in seed quality (when assessed by both potential seed longevity and seedling growth) was not detected until the final harvest interval in 1990 (85–90 d after anthesis, 31–36 d after mass maturity). These results for marrow contradict both aspects of the general hypothesis that seed quality is maximal at the end of the seed-filling phase and that viability and vigour begin to decline thereafter.

The field emergence ability of a total of 88 seed lots of spring barley (Hordeum vulgare L.) harvested serially during development in 2 years was compared, as was the size of the resultant seedlings. For seedsproduced in each year, field emergence and the mean dry weight of emerged seedlings were significantly greater for seed lots harvested some timeafter physiological maturity (end of the seed-filling period) than for those harvested at or before this developmental stage. This is compatiblewith results for the potential longevity of these lots. It is concluded that barley seed quality continues to increase after physiological maturity, and that the developing seeds attain maximum quality (however this is assessed) close to when the seed crop can be combine harvested. Positive correlations were detected between seedling emergence and seed dry weight (P<0.05) and between the mean dry weight of emerged seedlings and seed dry weight (P<0.005) among seed lots harvested close to when maximum quality was attained in four seed production environments.

Seed mass distribution in grassland communities of slopes of contrasting aspect was analysed in dolomite regions of the Pannonian Basin. Species frequencies were obtained for four pairs of data sets, which originated from corresponding south- and north-facing dolomite grasslands, thus forming four independent case studies. The data sets comprised 5–15 sample plots and 51–114 (average 85) species. The species were classified using an eight-class system reflecting their mean seed mass (MSM) records (class 1 being the lowest, MSM ≤ 0.2 mg; class 8 being the highest, MSM > 50 mg). Seed mass class distributions derived from slopes of contrasting aspect showed strong significant differences in chi-square tests for trend for all the four case studies. Small-seeded species (classes 1 and 2) showed a positive balance for the south-facing slopes, whereas large-seeded species (classes 5, 6, 7 and 8) were more frequent on north-facing slopes. Species with intermediate seed mass (classes 3 and 4) were not distinctive between the slopes. These results represent strong evidence of increased seed mass in the vegetation of north-facing grasslands, when compared to their south-facing counterparts. Among the phenomena potentially responsible for the new findings, we discuss the roles of microclimatic effects (especially drought stress and light regime), grass litter, interspecific competition and seed predation.