Mean Number Of Seeds Research Articles

Factors influencing risk of acute urinary retention after TRUS-guided permanent prostate seed implantation

Purpose: To look for factors predictive of acute urinary retention (AUR) after permanent seed prostate brachytherapy. Methods and Materials: From March 1999 to February 2001, 150 permanent seed prostate implants were performed at Princess Margaret Hospital (Stage T1c, n = 113; T2a, n = 37; mean prostate-specific antigen level 5.9 ng/mL, prescription dose 145 Gy per Task Group No. 43). α-Blockers were used routinely after implantation. Dosimetry was based on the 1-month postimplant CT scan. The International Prostate Symptom Score (IPSS) and catheterization were recorded at 1 month and 3 months and then every 3 months. The following variables were examined: age, baseline IPSS, prior androgen ablation, prostate transrectal ultrasound volume, number of seeds, D 90, V 100, V 200, and urethral dose. Results: Twenty patients (13%) experienced AUR. No difference was seen in the mean D 90 (149 Gy vs. 152 Gy, p = 0.6), V 100 (90% vs. 91%, p = 0.6), V 200 (23% vs. 25% p = 0.4), IPSS (6.4 vs. 5.9, p = 0.8), or maximal urethral dose (204 Gy vs. 210 Gy, p = 0.5). The prostate volume was significantly larger in men with AUR (39.8 cm 3 vs. 34.3 cm 3, p = 0.003), and the mean number of seeds was higher (112 vs. 103, p = 0.006). Of the 20 patients experiencing AUR, 11 (55%) had received prior antiandrogen therapy to downsize their prostates vs. 35 (27%) of the 130 who did not have AUR ( p = 0.02). Multivariate analysis showed prostate volume and prior hormone use to be independent predictors of AUR. Conclusions: Implant quality as determined by D 90, V 100, V 200, and urethral dose did not predict AUR. Prostate size was the major determinant of AUR. For any given prostate size, prior androgen ablation increased the risk of AUR. Men with larger prostates should be aware of the increased risk when contemplating brachytherapy.

The Effect of Partial Self‐Incompatibility on the Breeding System ofCampanula rapunculoidesL. (Campanulaceae) under Conditions of Natural Pollination

The consequences of partial self‐incompatibility on the breeding system of Campanula rapunculoides is considered under conditions of natural pollination. We propagated two partially self‐incompatible genotypes of C. rapunculoides and established them in pollinator exclusion cages along with 18 donor plants that differed from the focal plants (recipients) in their genotype at the glucose‐1‐phosphate isomerase (GPI) locus. Cages of plants were opened for pollinator access for 1 h/d, 24 h every fourth day, or left continuously open (control treatment), and the experiment was carried out in two consecutive years (1997 and 1998). After flowering, recipient plants were scored for percentage fruit set and mean seed number per fruit, and then seeds were screened for paternity (self or outcross). ANOVA analyses showed that the mean number of seeds per flower was significantly greater in 1998 than in 1997 and that it was affected by the amount of pollinator access. ANOVA analyses further show that selfing rates were higher in the treatment in which pollinator access was open 24 h every fourth day, while the open‐1‐h/d treatment did not differ from control cages in any aspect of the breeding system. Selfing rates were higher overall in 1998 than in 1997. We also find a weak effect of the genotype of the recipient and the position of the flower on the selfing rate, although the first result is not unexpected because the genotypes used in the experiment showed similar levels of self‐fertility. Our data show that both between‐ and within‐years selfing rates can respond to environmental variation in pollinator availability in C. rapunculoides.

Geographic variation in seed‐setting by heather (Calluna vulgaris (L.) Hull) in the Scottish Highlands

AimTo assess the influence of oceanicity, altitude and latitude on spatial and temporal variations in the fecundity of heather (Calluna vulgaris (L.) Hull) in Scotland.LocationMountain study areas located throughout the Highlands of Scotland.MethodsSeed‐set was assessed as the number of seeds per heather capsule. At each mountain, the mean number of seeds per capsule was recorded at five sites spaced at 150 m height intervals up to heather’s upper altitudinal limit. Germinability was measured by incubating seeds at 20 °C after chilling at 2–3 °C for 6 weeks. Collateral cultivation of heather cuttings taken from sites below 450 m and above 900 m determined whether seed‐setting and germinability were under genetic or environmental control.ResultsNeither seed‐setting nor germinability was under genetic control. Seed‐setting generally declined with increasing site oceanicity and altitude but the effect of latitude was ill‐defined. Mean maximum temperature and total rainfall during August–September were the principal environmental controls. Germinability varied less widely but tended to be least towards heather’s upper altitudinal limit.Main conclusionsSeed‐setting by heather varied in both space and time, depending mainly on late summer warmth. It was always copious below about 600 m but was sparse or even failed altogether on higher ground, particularly in the hyperoceanic west Highlands.

Expression of the S receptor kinase in self-compatible Brassica napus cv. Westar leads to the allele-specific rejection of self-incompatible Brassica napus pollen.

Expression of an S receptor kinase (SRK910) transgene in the self-compatible Brassica napus cv. Westar conferred on the transgenic pistil the ability to reject pollen from the self-incompatible Brassica napus W1 line, which carries the S910 allele. In one of the SRK transgenic lines, 1C, virtually no seeds were produced when the transgenic pistils were pollinated with W1 pollen (Mean number of seeds per pod = 1.22). This response was specific to the W1 pollen since pollen from a different self-incompatible Brassica napus line (T2) and self-pollinations were fully compatible. Westar plants expressing an S locus glycoprotein transgene (SLG910) did not show any self-incompatibility response towards W1 pollen. Transgenic Westar plants resulting from crosses between the 1C SRK transgenic line and three SLG910 transgenic lines were also tested for rejection of W1 pollen. The additional expression of the SLG910 transgene in the SRK910 transgenic plants did not cause any significant further reduction in seed production (Mean seeds/pod = 1.04) or have any detectable effects on the number of pollen grains that adhered to the pistil. Thus, while the allele-specific SLG gene was previously reported to have an enhancing effect on the self-incompatibility response, no evidence for such a role was found in this study.

Distribution of Insect Attacks in Biological Control of Weeds: Infestation of Centaurea virgata Flowerheads by a Gall Fly

Abstract The success of biological control efforts to reduce weed density through release of insects may depend as much on the distribution of insect attacks among individual plants or plant parts as on the mean level of infestation. We used an index of dispersion to describe the distribution of Urophora quadrifasciata (Diptera: Tephritidae) galls among squarrose knapweed ( Centaurea virgata ) flowerheads at 18 west central Utah sites in the first 5 years following introduction of the biological control agent. Two thirds of the samples showed a significantly aggregated distribution of galls among flowerheads. Statistical analysis showed that site and year accounted for relatively small proportions of the variance in the index of dispersion. The degree of gall aggregation among flowerheads was positively correlated with the mean flowerhead quality (mean number of seeds per flowerhead; P = 0.013) and tended to be negatively correlated with the mean fly density per flowerhead at a site in a given year ( P = 0.097). Our data suggest that higher quality flowerheads, and possibly higher quality plants, are preferentially attacked by U. quadrifasciata and therefore are more heavily subject to reduced reproductive potential through biological control. However, an aggregated distribution of fly attacks may undercut the potential of the fly to reduce seed production by the weed population as a whole. Understanding both the distribution of insect attacks among individual plants and the behavioral mechanisms producing such distribution patterns is important to the biological control of weeds.

Contrasting growth and dry matter partitioning in winter and spring evening primrose crops ( Oenothera spp.)

Evening primrose ( Oenothera spp.) is a relatively new, high value oilseed crop for temperate regions. Despite a long growing season, seed yields are much lower than the average yields of the major arable seed crops and commercial spring crops can yield as much as winter ones. Biomass accumulation and partitioning and crop canopy development were compared between winter and spring crops of cv. Merlin in 2 years of field trials. A winter crop of cv. Peter was also studied in year 2. Although post-winter growth was slow to restart, the winter crops produced up to 1589 g biomass m −2. The harvest index was low (<14%) because the crops grew tall and approximately half of the assimilate was partitioned into stem. Biomass production of the spring crops was lower, but the harvest index was higher (up to 17%) and in year 1, the winter and spring crops produced similar seed yields. The evening primrose leaf canopy was planophile and the peak green area index was in the region of 3–4, except in the year 2 winter crops where it was 7–8. Population density after crop establishment varied substantially between treatments but crops compensated for low plant populations by the production of larger, more branched plants bearing more capsules. Following the start of seed growth, the cultivar Merlin partitioned a greater proportion of new biomass into seed than did cv. Peter. The mean number of seeds per capsule was higher in cv. Merlin, but the seeds were smaller. Machine harvesting resulted in the loss of 19 and 55% of the seed produced by the year 1 winter and spring crops. Improvements in harvest index in the winter crop, an earlier start to growth in the spring crop and an increase the proportion of seed recovered by combine harvesting would lead to substantial increases in the seed yield of evening primrose crops.

Evidence of apomixis in hemisexual dogroses, Rosa section Caninae

All members of Rosa section Caninae, dogroses are polyploid and characterized by their unbalanced meiosis, which in most cases leads to a pronounced morphological influence from the maternal parent. In a previous investigation on a pair of reciprocal crosses between two species in this section, Rosa dumalis and R. rubiginosa (2n=35), nine offspring plants (approximately 10%) did not receive any of the 21 RAPD markers present in the respective pollen parent. This was interpreted as a possible occurrence of apomixis. These nine plants have now been subjected to a further study with additional markers. Thirteen new RAPD markers showed the same result as in the previous investigation: none of the nine plants inherited any of the pollen donor markers. The reproducibility of the RAPD markers was checked by mixing DNA samples to obtain a series of artificial hybrids between the two parent plants. Twelve RAPD markers gave the expected result, whereas one marker appeared only 50% of the time. In addition, pollen viability, mean number of seeds per hip, mean seed weight, and mean weight of fruit flesh per hip have been studied on the four progeny groups: R. dumalis×R. rubiginosa plants which received pollen donor markers (PM plants), R. dumalis×R. rubiginosa plants which did not receive any pollen donor markers (NPM plants), R. rubiginosa×R. dumalis PM plants and R. rubiginosa×R. dumalis NPM plants. A canonical discriminant analysis based on these four reproductive characters separated the four progeny groups. There were significant differences between the two PM groups in all investigated characters, and also between the PM and the NPM groups in pollen viability. The result from the RAPD markers together with the differences in pollen viability between the PM and NPM progeny groups is taken as an indication that apomixis occurs within the Caninae section.

Spontaneous mutational effects on reproductive traits of arabidopsis thaliana.

A study of spontaneous mutation in Arabidopsis thaliana was initiated from a single inbred Columbia founder; 120 lines were established and advanced 17 generations by single-seed descent. Here, we report an assay of reproductive traits in a random set of 40 lines from generations 8 and 17, grown together at the same time with plants representing generation 0. For three reproductive traits, mean number of seeds per fruit, number of fruits, and dry mass of the infructescence, the means did not differ significantly among generations. Nevertheless, by generation 17, significant divergence among lines was detected for each trait, indicating accumulation of mutations in some lines. Standardized measures of mutational variance accord with those obtained for other organisms. These findings suggest that the distribution of mutational effects for these traits is approximately symmetric, in contrast to the usual assumption that mutations have predominantly negative effects on traits directly related to fitness. Because distinct generations were grown contemporaneously, each line was represented by three sublines, and seeds were equal in age, these estimates are free of potentially substantial sources of bias. The finding of an approximately symmetric distribution of mutational effects invalidates the standard approach for inferring properties of spontaneous mutation and necessitates further development of more general approaches that avoid restrictions on the distribution of mutational effects.

Patterns of fruit and seed set within inflorescences of Pancratium maritimum (Amaryllidaceae): nonuniform pollination, resource limitation, or architectural effects?

We investigated patterns of fruit and seed production on inflorescences of a population of Pancratium maritimum in northwest Spain over a 2-yr period. Initial findings showed that the earliest opening flowers on an inflorescence are more likely to set fruit and produce more seeds than later opening flowers and that this pattern is maintained throughout the flowering season. Supplementary pollination and flower-removal experiments were performed to investigate whether the observed pattern is attributable (a) to variation in pollen receipt, (b) to sequestration of resources by the earliest flowers on an inflorescence, and/or (c) to "architectural" limitations on the fruit/seed production of later flowers. Supplementary pollination did not improve fruit or seed production by late flowers in either of the 2 yr of study. In flower-removal experiments, the remaining flowers showed improved fruit set and mean number of seeds per flower, by comparison with flowers in the same position on control inflorescences. When all flowers except the latest third were removed, these showed fruit set and seed production similar to those of early flowers on control inflorescences. These results strongly suggest that the observed within-inflorescence patterns of fruit and seed production in P. maritimum are mainly attributable to competition for resources (i.e., explanation b), though other adaptive explanations cannot be ruled out.

Seed production in woodland and isolated trees of Eucalyptus melliodora (yellow box, Myrtaceae) in the South Western Slopes of New South Wales

Seed production in woodland and isolated Eucalyptus melliodora Cunn. ex Schauer trees was investigated. Measurement of physical parameters such as mean capsule weight, mean seed weight and mean ratio of the weight of the capsule contents to the weight of the empty capsule showed no significant differences between woodland and isolated trees. In contrast, reproductive output as measured by mean number of seeds per capsule, mean number of seeds per 10 g of capsule contents and mean seed weight as a percentage of the weight of the capsule contents, was significantly lower (45–48% less) in isolated trees than in woodland trees. Mean percentage seed germination was also significantly lower (14% less) in the isolated trees and the mean number of viable seeds per 10 g of capsule contents was only 38% of the woodland trees. These results indicate that E. melliodora, like many eucalypts, has a mixed mating breeding system with preferential outcrossing but is also capable of self pollination leading to a reduction in seed yield and viability. The woodland and isolated trees produced a mean of 4.6 and 2.1 seeds per capsule, respectively. It would be relatively easy to collect large numbers of seeds from isolated trees of E. melliodora and subsequently propagate potentially genetically inferior plants.

Effect of a substitution of a short chromosome segment carrying a histone H1 locus on expression of the homeotic gene Tl in heterozygote in the garden pea Pisum sativum L.

Mutation tlx was induced in pea by gamma-irradiation in the homeotic gene Tl, responsible for transformation of the upper leaflets into tendrils. Heterozygotes tlx/Tl+ possess ‘flat tendrils’ having narrow rudimentary leaf blades. By 15 generations of selfing the line Delta was established, in which closely linked loci Tl and His1 were maintained heterozygous, His1 encoding the most abundant histone H1 subtype. The heterozygous chromosome region was flanked by several recessive markers. The genotype of line Delta with respect to loci His1 and Tl was: tlxHis12/Tl+His11. There were derived two sublines, Delta-s and Delta-f, homozygous for each of the His1 alleles but heterozygous for the Tl and flanking markers. The three lines were compared for a number of quantitative traits, including parameters of flat tendrils reflecting the expression of the gene Tl in heterozygote, and for recombination rate within the heterozygous segment. The line Delta-s exceeded Delta-f in terms of the level of the first inflorescence, length of the internode 8–9, number of pods on the main stem and mean seed mass, but was inferior regarding the mean number of seeds per pod. The flat tendrils were wider in the Delta-s as compared with the Delta-f line ; the difference was highly significant and exceeded 15% at node 17. Recombination rate between the flanking markers also showed significant differences, being highest in the Delta-f and lowest in the Delta line. We do not exclude the possibility that the observed differences in the quantitative traits are caused by the substitution of alleles of the histone H1 gene. The effects of such substitution appeared to be especially strong for expression of the homeotic gene Tl.

Breeding system and temporal variation in fecundity of Pancratium maritimum L. (Amaryllidaceae): Reproductive ecology of Pancratium maritimum

Flowering phenology, breeding system and temporal variation in reproductive success were studied over two consecutive years in a population of Pancratium maritimum L. (Amaryllidaceae) on coastal sand-dunes in northwest Spain. The population flowering period was late June to early September, with the flowering peak in mid-July. Fruit set did not vary significantly between years. However, plants which flowered in July and August had higher fruit set than plants which flowered in June, though no such differences were observed in mean number of seeds per fruit or mean seed-to-ovule ratio. Pollen transfer experiments indicated that the plants of the study population are self-compatible and capable of spontaneous selfing: the value of the Schoen and Lloyd self-compatibility index was 0.91, indicating that the fertilization capacity of self pollen ist almost as high as that of nonself pollen. This contrasts with the results of a study of populations of P. maritimum in Israel, where plants were found to be self-incompatible; it thus seems possible that the breeding system of this species varies among populations.

Responses of faba bean (Vicia faba L.) to sowing rate in south-western Australia. I. Seed yield and economic optimum plant density

Sowing rate influences plant establishment, growth, seed yield, and the profitability of a crop. However, there is limited published information on the optimum sowing rate and plant density for faba bean in Australia. The response of the growth and seed yield of faba bean (cv. Fiord) to sowing rate (70-270 kg/ha) was examined in 19 field experiments conducted over 3 years in south-western Australia. The economic optimum plant density was estimated at each site by fitting an asymptotic model to the data and calculating the point where the cost of extra seed equalled the return from additional seed yield, allowing a 10% opportunity cost for the extra investment. On average across all sites and seasons, only 71% of the seeds sown emerged. Increasing sowing rate resulted in more dry matter production at first flower and at maturity, and at about half of the sites there was a small trend of reduced harvest index. In general, the mean number of seeds per pod (1·8-2·6) and mean seed weight (32-45 g/100 seeds) were unaffected by sowing rate. As sowing rate increased, the number of pods per plant (5-35) generally decreased, but this was compensated by the large plant population and more pods per unit area. The asymptotic models fitted to the seed yield data accounted for 15-81% of the variance. In 8 experiments, the models indicated that yield was continuing to increase substantially as sowing rate increased at the largest sowing rate treatment. The estimated optimum plant densities in these experiments were beyond the range of the data or had large standard errors and, hence, were excluded from any further consideration. Among the remaining 11 experiments, the estimated optimum plant densities varied from 31 to 63 plants/m2, with a mean of 45 plants/m2. This study demonstrates that targeting sowing rates greater than the current commercial practice for faba bean in southern Australia of 15-30 plants/m2 results in more yield and profit. Additional experiments are required with sowing rates in excess of 270 kg/ha to estimate accurately the optimum plant density for faba bean. Fungal diseases were either absent or controlled with fungicides in these experiments but the interactions between disease, time of sowing, and sowing rates also deserve further attention.

Effect of sowing date and plant density on yield and yield components in the faba bean

Faba bean cv. Fiord was sown at 3-week intervals between 24 April and 26 June at 6 densities varying from 20 to 56 plants/m2. Days to emergence, flowering, pod set, and maturity were determined. At harvest, the biomass, yield, pod number, seeds per pod, and weight per seed were evaluated per unit area and the distribution of the yield components was evaluated for each node of the main stem. Later sowing had little effect on the number of days to the appearance of the first pod but it progressively reduced the duration of the pod development period from 98 to 60 days. The biomass at maturity of the plants sown on 24 April was constant across all densities, at about 13·5 t/ha. Yield, however, decreased linearly with density from 6·7 to 5·2 t/ha. Harvest index, therefore, also fell with density. With later sowing, biomass and yield increased with density. The increase in yield was not as great; so again harvest index fell with density. Later sowing resulted in much lower yields and even at the highest density only reached 5·2 t/ha. Variation in yield was largely determined by variation in the number of pods per unit area. Seeds per pod was constant across the treatments but weight per seed decreased if sowing was delayed beyond 10 June. With later sowing, the number of pod-bearing nodes on the main stems declined from 27 to 15. Early-sown plants at high density had fewer pods per node at the lower nodes and more pods per node at the higher nodes than plants at low density. This interaction was not evident at the second sowing and the number of pods at each node was unaffected by density. For the sowings in June, all nodes of the low density plants bore more pods The number of seeds per pod was smaller at the lowest and highest nodes, but as there were so few pods at these nodes, this did not affect the mean number of seeds per pod when evaluated for all pods on a plant. Weight per seed was more uniform for the nodes of the early-sown plants than for those of the plants sown later, in which there was a marked decrease in weight per seed at the upper nodes

Physiological assessment of apetalous flowers and erectophile pods in oilseed rape (Brassica napus)

SUMMARYThe transmission of solar radiation within the crop canopies of oilseed rape is decreased both by the plant's yellow petals during flowering, and by the horizontal posture of the pods once they are formed. The significance of each of these morphologies was assessed, in the 1991/92 and 1992/93 growing seasons, by comparing the performances of an apetalous breeding line (N-o-112) and one with erectophile pods (N-5-130) with two conventional commercial genotypes (Falcon and Tapidor).The apetalous floral layer of line N-o-112 reflected and absorbed significantly less radiation than those of the conventional, petalled genotypes. This resulted in a greater transmission of photosynthetically active radiation (PAR) to the leaf and bract canopy situated below. At peak flowering, 70% more PAR was transmitted through the apetalous floral layer.The erectophile pods of line N-5-130 were angled 20–25° further from the horizontal than the conventional genotypes. The extinction coefficient (K) of its pod layer during late pod growth ranged from 0·35 to 0·44 as compared to 0·45 to 0·55 in the commercial varieties. Line N-5-130 carried a greater proportion of its total fertile pod number in the lower regions of the pod canopy compared to the two conventional genotypes. It also had a greater overall mean number of seeds per pod, and the number decreased proportionately less with depth in the canopy. The line was thus better able to maintain a higher photosynthetic area and to sustain pod and seed growth at the lower levels of the crop canopy than the conventional, commercial varieties. The potential physiological effects of apetalous flowers and erectophile pods are considered to be sufficiently beneficial for their introgression into near-isogenic lines to be pursued.

Spatial Variation in the Seed Ecology of a Woodland Herb (Primula vulgaris) in Relation to Light Environment

Patches of Primula vulgaris occur across a range of light conditions within forests. To understand how light affects the stages of the life cycle involved in reproduction and recruitment, several fecundity-related variables (flower and capsule production, seed set, seed germination and seedling establishment) were studied in eight populations across a range of light conditions. The mean number of seeds per plant varied greatly, from seven to 136, and the percentage of seedling establishment varied from 0.4 to 17.2%. These variables, as well as the number of flowers per plant and fecundity, were positively correlated with the light conditions. Primula vulgaris populations establish in newly opened gaps. How this species colonizes new clearings was investigated by looking at seed survival in the soil and seed removal by potential dispersers, in particular rodents and ants. After 14 months in the greenhouse, only three P. vulgaris seedlings were observed germinating from 200 soil samples taken from two populations. Germination of retrieved seeds from buried samples was generally lower than 10%. This suggests that only a small number of seeds remain viable in the soil for long periods of time. Seed removal was high in the populations studied (more than 70% in 10 days). Rodents harvested a greater proportion of seeds than ants. Seed dispersal by ants is known to occur within short distances but rodents may be long-distance dispersers, which may be important for the long-term persistence of P. vulgaris in a site because it allows seeds to reach newly opened gaps.

Characterisation of naturalised strains of Trifolium subterraneum var. brachycalycinum cv. Clare in northern New South Wales

Burrs were collected from paddocks on 3 properties in northern New South Wales where the age of the Trifolium subterraneum var. brachycalycinum cv. Clare swards varied from 19 to 28 years. At 1 site burrs were also sampled from swards sown 2 and 10 years previously. Twenty seedlings from these burrs and 20 plants of certified cv. Clare were grown as spaced plants in a nursery. These were assessed for vegetative and floral characters, flowering time, number of seeds per burr, seed weight, and percentage hardseed after storage at 25/25�C for 6 months and 25/45�C for a further 6 months. For most plants the mean number of days from sowing to first flower was similar to that of Clare. Compared with the naturalised strains, Clare had the lowest (P&lt;0.05) mean number of seeds per burr: about 25% below the mean of the strains (2.7 seeds per burr). While the lowest mean seed weights of the strains were not significantly different from those of Clare, the seed weights of plants from 3 sites were higher (P&lt;0.05) than those of Clare. After storage for either 6 or 12 months, hardseed levels were also lowest (P&lt;0.05) for Clare. Plants from the 2-year-old sward had the same median number of seeds per burr (2.0) as Clare. As sward age increased, the median number of seeds per burr increased to 2.8. Hardseed percentages were lowest for plants of Clare and for those from the 2-year-old sward after 6 months, and for Clare after 12 months. These studies indicated the presence of divergent strains in old swards of Clare in a summer rainfall environment. Natural selection among variability within Clare is the most likely reason for the development of these strains in an environment marginal for the long-term persistence of this softseeded cultivar. Although strains had the same vegetative and floral markings as Clare, differences in ecologically important characters such as number of seeds per burr, seed weight, and hardseededness may result in plants that are better adapted to the environment in which they evolved. From these studies 23 plants of T. subterraneum var. brachycalycinum were selected for further evaluation.

Quantitative analysis of pod formation, seed set and seed filling in winter oilseed rape ( Brassica napus L.) under field conditions

Pod formation, seed set and seed filling of winter oilseed rape ( Brassica napus L.) were studied in two field experiments with the variety Jet Neuf. Variations in total dry matter production (source size) and pod density (sink size) were established by varying seed rate, plant density, sowing date and the application of shading. od formation and seed set per pod were recorded on different branches, at various heights in the canopy and on pods initiated at different times during flowering. Pod density and seed density appear to be fully determined just after the end of flowering. The potential number of pods (i.e. the number of flower buds) did not appear to be a limiting factor, as at all positions in the canopy it was much higher than the number attained. Averaged over the whole canopy, pod set varied between 43 and 58%. Potential and actual pod density were linearly related to cumulative dry matter production of the crop until the onset of flowering and until the end of flowering, respectively, i.e. to total assimilate availability over that period. The number of seeds per pod did not vary with height in the canopy. Primary branch number and the time of pod initiation during flowering had some effect on the number of seeds per pod; however, this had little influence on the overall mean number of seeds per pod of the whole canopy and did not affect the differences among treatments. A linear relationship was found between seed density and dry matter production of the crop during flowering. Individual seed weight followed a sigmoid pattern when plotted against the temperature sum from the onset of flowering per flower bud until maturity. The pod hulls were the only competing sink during early seed fill and remobilization of reserve carbohydrates contributed at most 12% to final seed yield.

Evaluation of pasture legumes sown into a prepared seedbed at Tamworth, New South Wales. 2. Seed production and seed reserves

Plots sown in 1983 were used to examine the seed production and reserves (residual hardseeds) of 15 annual legumes over 5 years at Tamworth in northern New South Wales. Seed production characteristics were measured in 1983 for these annuals, and for 6 perennial legumes. After the annuals had set seed in 1983, an area of the plots was sprayed to prevent flowering in subsequent years, and the rates of decline in seed reserves were compared with those from areas that seeded annually. Seed yields of the perennials were often significantly lower than those of the annuals except Trifolium glomeratum. Seed yields of T. subterraneum var. subterraneum cvv. Seaton Park and Woogenellup were significantly higher than those of cv. Nungarin and T. subterrarzeum var. brachycalycinum cv. Clare. Seed numbers were lowest for Medicago scutellata cv. Sava among the annual medics, and for Nungarin among subterranean clovers. There was little relationship between the mean number of seeds produced from 1983-86 and maturity grading, and between seed numbers and relative dry matter yield. Seed reserves decreased over 5 years by more than 90% in the sprayed treatments of all species. This decrease was not continuous, with the largest declines occurring from December 1983 to August 1984. In the sprayed treatments of Seaton Park, Woogenellup, and Clare, and in both treatments of Astragalus hamosus cv. Ioman, Vicia dasycarpa var. villosa cv. Namoi, and T. hirtum cv. Hykon, none of the original 1983 seed was recovered in 1987. For the annual medics and Nungarin, the number of residual hardseeds in the sprayed treatments in 1987 was about 3-5% of the seed produced in 1983. From 1983 to 1987, seed numbers in the unsprayed treatments declined by 7040% for the annual medics and by 85-95% for Seaton Park, Woogenellup, and Clare. Long-term persistence of annual medics and Nungarin depended on seed production in most years and the maintenance of a high number of residual hardseeds in the soil. In contrast, the mid- and late-maturing subterranean clovers Woogenellup and Clare had low seed reserves and were dependent on seed production in most years for their continued regeneration.

Putrescine Increases Effective Pollination Period in Roses

Flowers of two cultivars of Rosa hybrida were treated or not with putrescine before being pollinated from 2 to 8 days after anther emasculation. On both cultivars the 10-3 M putrescine treatment extended the effective pollination period, as shown by the best hip formation rates and mean number of seeds per hip. On one cultivar, the 10-5 M putrescine treatment increased fertilization efficiency (more hips obtained). The effect of putrescine was proportionally more important on the cultivar characterized by the highest stigmatic exudate pH. Putrescine also influenced in vitro pollen germination by increasing the length of emitted pollen tubes (10-3 and 10-5 M-putrescine) and the quantity of germinated pollen grains (10-5 M putrescine).