Flowering and true seed production in potato (Solanum tuberosum L.). 2. Effects of stem density and pruning of lateral stems

Summary Field experiments were carried out to evaluate the effect of stem density and pruning of lateral stems on flowering and true seed production in potato (Solanum tuberosum L.). Increasing stem density reduced flowering, berry and seed production from every inflorescence in all cultivars. Increasing density increased the proportion of primary flowers in the total number of flowers per plant and reduced the proportion of flowers on lateral stems, but its effect on the quality of the seed production was small. Differences in total seed production were principally determined by differences in flowering. There was an interaction between stem density and cultivars for the number of flowers produced and on the yield of true seed per m². Pruning lateral stems enhanced flowering of the main stem and decreased the total number of flowers per plant, but it did not affect berry and seed production from main-stem inflorescences.     

Evaluation of seed production potential in white clover (Trifolium repens L. varietal improvement programmes

The components of actual and potential seed yield were examined in field experiments on a wide range of varieties of white clover (Trifolium repens L.). The factors affecting seed yield under conditions typical of management regimes used in the production of commercial seed crops were assessed in two experiments. In the first, carried out on spaced plants, considerable diferences are shown between six varieties across the range of leaf sizes in the distribution and profuseness of inflorescence production through the flowering season. In the second, carried out in plots, typical on-farm criteria were used to choose a single harvest date. Significant variation was found between varieties, including representatives of different leaf size categories, for seed yield components that include number of inflorescences m^?2, number of florets per inflorescence and harvestable seed weight. Large-leaved varieties tended to produce more seeds per floret and higher seed weights per inflorescence, whereas small-leaved varieties gave the highest number of inflorescences ^?2. However, the small-leaved variety AderDale, selected for strong peduncles, was exceptional, giving high values for all seed yield components. The impact of weather conditions on many seed yield components (e.g. total number of inflorescences) was demonstrated by the differences between the 2 years of the experiment. However, other characterstics, e.g. number of florets per inflorescence and number of seeds per floret, did not vary between years. Deviations from potential seed yield were assessed fromthe perspective of commerical seed production. The implications of these results for the production of white clover varieties with increased seed yields under UK conditions are discussed.     

Variability and regulation of the number of ovules, seeds and pods according to assimilate availability in winter oilseed rape (Brassica napus L.)

The number of pods per plant and the number of seeds per pod are the most variable yield components in winter oilseed rape (WOSR). Both the number of ovules per pod and the potential for the ovule to develop into a mature seed may depend on pod position in the plant architecture and time of appearance. The complex developmental pattern of WOSR makes it difficult to analyse. The objectives of this study were to investigate the variability of the following yield components (a) ovules/pod, (b) seeds/pod, and (c) pods/axis in relation to two explanatory variables. These two variables include (1) flower and inflorescence position and (2) time of pod appearance, linked to the effect of assimilate availability.Field experiments were conducted with the variety Mendel. Different trophic states were created by clipping the main stem or ramifications. The number and position of flowers that bloomed within the inflorescence were recorded based on observations every two to three days throughout the flowering season.On the control plants, for the main stem we observed that the number of ovules per pod decreased for a few ranks and then tended to increase and again to decrease at the end. On ramification R1 and R4, the number of ovules increased at first, and then remained constant with the pod rank. Furthermore, the number of ovules per pod remained constant along the inflorescence on the other ramifications and increased with ramifications from top to bottom. The number of seeds per pod did not vary with the pod rank at the basal positions on inflorescences and decreased afterwards along the inflorescence. The clipping of the main stem or ramifications increased the number of ovules per pod, seeds per pod and pods per axis. The number of ovules and seeds per pod did not vary with the time of pod appearance for the pods located at normalised rank 0.01-0.1. However, the number of ovules and seeds per pod can be impacted by the time of pod appearance on the plant scale. Thus, our results indicate that the amount of available assimilates was the primary determinant of pod and seed production during the flowering period. The distribution of resources was significantly affected by both the positions of pods within an inflorescence and the position of inflorescences within a plant.     

The effect of time of harvest on seed production of three red clover cultivars

Small plots of red clover cv. Sabtoron, S123 (diploids) and Hungaropoly (tetraploid) were harvested for seed production at two-week intervals from 19 August to 17 October inclusive in 1981, inflorescence appearance rate, bee density and components of yield having been monitored throughout the summer. Inflorescence appearance rate reached a maximum at the end of July/early August for Hungaropoly and Sabtoron and during mid-August for S123. Bee density followed a similar pattern. Florets and seeds per inflorescence and 1000-seed weight decreased as flowering progressed except during the first three weeks in July. Potential seed yield was calculated from the components of yield for the harvests taken on 3 and 18 September. Losses in seed yield (difference between actual and potential) up to and during harvesting, threshing and cleaning were lower in the tetraploid cultivar (27–39%) than the diploid cultivars (35–l55%). Each cultivar had an optimum harvest time before which yield was affected by immature seeds and beyond which it was adversely affected by shedding of inflorescences and seeds and sprouting of seeds on the inflorescences. The optimum time to harvest Sabtoron was early September, Hungaropoly early to mid-September and the late flowering cultivar S123 mid-September when less than 4% of the inflorescences were still unripe. Seed yield and inflorescences per unit area were lower in the tetraploid cv, Hungaropoly (maximum 542 kg ha⁻¹) than diploid cv. Sabtoron and S123 (864 and 897 kg ha⁻¹ respectively) although the tetraptoid had heavier seeds. It is concluded that the optimum time to harvest red clover for seed production is about three or four weeks after the end of the period of rapid inflorescence production and that this coincides with the time when only a small proportion of unripe inflorescences remain.     

The effect of photoperiod on flowering and TPS production in the warm tropics

Summary Three similar field experiments with five cultivars were carried out to evaluate the effect of a 5-hour extension of the natural daylength and a 3-hour night break on flowering and TPS production in the warm tropics. Shoot length, number of inflorescence positions per plant and number of flowers per inflorescence varied considerably between the experiments. In each experiment, the supplementary photoperiods delayed cessation of shoot growth and thereby increased the orders of branching and the number of inflorescence positions per plant. The photoperiod treatments significantly increased the number of flowers at the last produced inflorescence positions, but not at other ones. Pollen production and quality, berry set, seed set and 100-seed weight were not affected by the photoperiod treatments. TPS production was characterized by variability in flowering and low and variable seed production per flower.     

Seed production in white clover (Trifolium repens L.). II. Effect of autumn defoliation on potential seed yield and seed yield components

A field experiment was conducted to assess the effect of autumn defoliation treatments on inflorescence production, potential seed yield and yield components of white clover cv Makibashiro. Between 10 July and 10 October 1992, white clover swards were subjected to one of three treatments: monthly cutting to 3–4 cm (4DEF), cutting to 3–4 cm on 10 August and 10 October (2DEF), and no cutting (control). The total numbers of inflorescences and the proportion of inflorescences in different development categories were counted throughout the period of seed crop development to determine the pattern of inflorescence development and optimum harvest date. There were consistent significant differences in inflorescence density between treatments. Plots which received the 2DEF treatment produced significantly more inflorescences than did the no-defoliation (control) and 4DEF-treatment plots. In this particular year the optimum harvest date (date at which the proportion of ripe inflorescences and potential seed yield was highest) was 26 July, approximately 30 d after peak flowering. Defoliation treatments had no effect on optimum harvest date. However, treatments differed in potential seed yield and ripe inflorescences on this date. The 2DEF treatment gave the highest potential seed yield because there were significantly more ripe inflorescences than either the contol or 4DEF plots. Control plots produced inflorescences with more florets than the other two defoliation treatments, but the differences were not always significant. Seed number per pod was higher in inflorescences obtained from previously defoliated plots than from control plots. The 1000-seed weight was significantly lower in inflorescences developed in 4DEF plots than those developed in 2DEF and control plots. The results are discussed in relation to the management of white clover seed crops and the importance of canopy structure and light intensity for seed production.     

Effect of seed crop management on potential seed yield of contrasting white clover varieties

An experiment is described in which the effects of different spring managements on the potential seed yield and seed yield components of three white clover cultivars of contrasting leaf types were assessed. Cv. S184, the small-leaved variety, produced more but smaller inflorescences than CVS Olwen, a large-leaved variety, or Menna, a medium-leaved variety. However, cv. Olwen, produced inflorescences with more florets, seeds per inflorescence and a higher seed yield per ten inflorescences than the other cultivars. Both potential seed yield and the individual yield components were influenced by management. Cv. Olwen produced more inflorescences and a higher potential seed yield under a cutting system than under grazing systems, which reduced the number and size of the inflorescences. Cvs S184 and Menna were less influenced by management system and performed similarly under cutting and grazing. The highly significant relationship between the number of ripe inflorescences and potential seed yield showed clearly that high seed yields are only achieved if the crop is harvested when the number of ripe inflorescences is at a maximum. The relatively short duration of the period of maximum ripe inflorescences emphasized the importance of determining the correct harvesting date, although weather conditions also play an important part in deciding when to harvest. Florets per inflorescence, seed set and 1000 seed weight remained relatively constant over the harvest period, and were not influenced by harvest date. The results are discussed in relation to the management of white clover seed crops and the importance of climatic conditions during seed production.     

Spring defoliation of white clover seed crops. 2. Potential harvestable seed yield and seed yield components of contrasting white clover cultivars

The effects of different spring defoliation managements on potential harvestable seed yield and seed yield components of three contrasting white clover cultivars were assessed. The small-leaved cv. S184 produced more but smaller inflorescences than the large-leaved cv. Olwen and Menna, a medium-leaved cultivar. Cultivar Olwen, however, produced more ripe and brown (nearly ripe) inflorescences with more florets, seeds per floret and a higher seed yield per ten inflorescences than the other cultivars. Potential harvestable seed yield and individual seed yield components were only influenced by defoliation after bud emergence, as defoliation before bud emergence had no effect on seed yield components. Defoliation after bud emergence had a similar effect on all cultivars: the number of ripe inflorescences was unaffected by defoliation but the number of brown and therefore harvestable (ripe + brown) inflorescences was highest following defoliation three weeks after bud emergence. Florets per inflorescence, seed per floret, 1000 seed weight, seed yield per ten inflorescences and potential harvestable seed yield were not influenced by defoliation after bud emergence. Season had a significant effect on seed yield components and influenced the effect of defoliation treatments, emphasizing the importance of climate in white clover seed production. The results are discussed in relation to the spring defoliation of white clover seed crops, harvesting techniques and the provision of guidelines for optimizing seed yield.     

Effect of plant density on the inflorescence production of stems and the distribution of flower production in potato

Summary A knowledge of the pattern of flowering and seed production is required for the development of large-scale field production of True Potato Seed (TPS). At the highland experimental station of the International Potato Center in Peru, data on flowering and seed production were collected from three cultivars planted at three densities. Main stems in which flowering was delayed ceased shoot growth at an earlier stage and produced fewer inflorescences. Inflorescences produced later had fewer flowers, a lower berry set and yielded less seed. Inflorescences flowering at the same time performed similarly, irrespective of their position on the plant. Increasing plant density resulted in cessation of shoot growth at an earlier stage and concentrated inflorescence and flower production at primary positions of early-flowering shoots. With cvs Renacimiento and Yungay a higher plant density increased the percentage of flowers produced in the first three weeks of the flowering period, but with cv. Atzimba the effect of plant density on the distribution of flower production was off-set by a slower stem development.     

The effects of nutrient supply on flowering and seed production in Poa annua

The effect of nutrient concentration on the reproductive development and seed yield of Poa annua was examined in a sand culture experiment. The nutrient concentration during the initial vegetative stage did not affect the time taken for double ridge formation by the main shoot but did influence the subsequent development of the inflorescence as did the post-initiation level of nutrients. At low nutrient levels flowering was inhibited in some individuals but at the higher concentrations inflorescence emergence was hastened, inflorescence size was increased and, in particular, the number of spikelets and hence the number of seeds per inflorescence was greatly increased. The mean weight of 100 seeds was unaffected by the nutrient concentration. The number of reproductive tillers per plant was increased by high nutrient supply but the proportion of dry weight allocated to root development was reduced.     

The male fertility of primary and further generation dihaploids ofSolanum tuberosum

Summary Male sterility in dihaploids ofSolanum tuberosum is often a barrier to their utilization in breeding and genetical studies. Although the male fertility of primary dihaploids (obtained directly from tetraploids) was generally low, a few were produced by the author which produced seed when used as pollen parents on female fertile dihaploids. The population of further generation dihaploids (from dihaploid intercrosses) produced from the showed a marked improvement in male fertility. Comparative data from measurements of different aspects of male fertility in dihaploids are presented. These showed that the weight of pollen per anther, the percentage of (iodine) stainable pollen and the number of seeds per berry were greater in further generation dihaploids than in primary dihaploids. It is suggested that interspecific crosses using dihaploids are not necessarily useful for increasing male fertility in diploid potatoes. The advantages of breeding at the diploid level withinS. tuberosum are discussed. Rare male-fertile dihaploids could be used to generate diploids with a high frequency of male fertility. These could then be used to cross with any other flowering dihaploids to combine characters at the diploid level, so exploiting the simpler genetic ratios associated with disomic inheritance.     

Potential seed yield of white clover varieties

Fifteen varieties of white clover were sown in order to assess the seed yielding ability of new and potential varieties and to examine those plant factors which affect seed yield. Counts were made on number of inflorescences m^-2, proportion of ripe inflorescences and other inflorescence and seed characters. The data were used to compute potential seed yields.
Average potential seed yields were 276 and 76 kg ha^-1 in the first and second year, respectively. The decrease in the second year seed yields underlines the overriding effect of adverse weather conditions during the critical June to August period. The major effect was a reduction in the number of inflorescences produced, the number of florets per inflorescence and seeds per floret.
Some of the new listed varieties have a significantly higher seed potential than SI00, e.g. Menna (+ 38%) and Olwen (+28%), and this should facilitate the production of adequate seed supplies of British bred varieties.     

Association of growth dynamics, yield components and seed quality in long-term trials covering rapeseed cultivation history at high latitudes

Brassica oilseed yield trend has declined in Finland by over 20% during the last 15 years. Improved genetic yield potential of turnip rape (B. rapa L.) and oilseed rape (B. napus L.) can be better realised with increased understanding of yield determining processes under northernmost growing conditions. This study aimed at (1) determining the genetic improvements in seed yield, yield components, quality traits and duration of the main growth phases and (2) comparing all these traits in turnip rape and oilseed rape. This work is based on the dataset from long-term Official Variety Trials (1976–2006), covering the entire historically relevant period of rapeseed cultivation in Finland. The results indicated that number of seeds per square metre dominated production of high yields, while single seed weight was not correlated with yield. Over the years, seed yields were produced with very different combinations of seed numbers and weights, differing markedly between the two crops. While high seed numbers were required for production of superior seed yields, single seed weights were not particularly high. Environmental variation markedly affected seed yield, seed number per square metre and duration of flowering compared with its effect on single seed weight. Duration of flowering was, however, negatively associated with seed number. Even though seed weight was largely determined by genotype, no marked plant breeding improvements were identified, contrary to those in number of seeds per square metre, seed yield, oil content and oil yield. For oilseed rape the increase in seed yield (41%) was far higher than for turnip rape (19%) without being associated with a longer seed-filling phase and later ripening, but rather the contrary.     

Effect of plant density on stolon growth and development of contrasting white clover (Trifolium repens) varieties and its influence on the components of seed yield

Plants of two contrasting white clover varieties (cv. Aberystwyth S184 and Olwen) were planted in the field in spring in each of 2 years at four densities (9, 25, 49 and 100 plants m⁻²) in 1-m² plots. The effect of plant density on stolon growth and development and the components of seed yield was subsequently measured.
Stolon growth and development was influenced by plant density, variety and year. At low plant densities both white clover varieties produced longer primary stolons than at higher densities. Plant density, however, had no significant effect on the number of inflorescences at harvest. At the high stolon densities there were significantly fewer reproductive nodes per primary stolon than at the lower plant densities. Plant density did not significantly affect any other seed yield components, but the number of inflorescences at harvest, florets per inflorescence, seed set per floret and 1000-seed weight were all significantly influenced by both variety and year.
The relationship between the vegetative and reproductive growth of white clover is discussed in relation to plant density, variety and climate and the possible role of defoliation managements on inflorescence development.     

去枝、疏花对甘蓝型杂交油菜苏优3号千粒重及产量的影响

以杂交油菜苏优3号为材料，研究去枝、疏花处理对千粒重及单株产量的影响，结果表明，去枝，蔬花后，主轴，一次分枝和二次分枝的千粒重显著增加，角果宽度和长度亦增加，去枝后单株千粒重增加16．61％，疏花后单株千粒重增加14．05％，均达极显著水平，去枝后单株产量下降，下降幅度最高为9．77％，达极显著水平，每个花序疏花5朵，单株产量增加0．38％，增产不显著，疏花10朵以上则单株产量逐渐下降。     

Berry and seed production using stored pollen of aSolanum phureja clone

Summary Pollen of theSolanum phureja clone IVP48 was stored with silica gel desiccant at −15°C for periods ranging from one month to five years. When used to pollinate anotherS. phureja clone there was a significant negative correlation of pollen age with the number of seeds produced per berry. The frequency of berry production and number of seeds per pollination, however, did not show significant negative correlations and berry production varied unpredictably with pollen of different ages. Each year of pollen storage reduced the average number of seeds produced per berry to about 60 per cent of the preceding year's.     

The effect of agronomic factors on seed and forage production in perennial legumes sainfoin (Onobrychis viciifolia Scop.) and French honeysuckle (Hedysarum coronarium L.)

Perennial legume varieties and ecotypes belonging to the species sainfoin ( Onobrychis viciifolia Scop.) and French honeysuckle ( Hedysarum coronarium L.) were investigated under different management treatments (two regimes of irrigation, cutting and seeding densities) at the Forage Crops Institute in Foggia, Italy (which has a typical Mediterranean environment) for two seasons, 1990 and 1991. Dry-matter production, seed production and seed yield components were affected more by harvest year and irrigation than by seeding density. Mean increases due to irrigation were 2·8% and 60·6% respectively for dry-matter and seed yield in sainfoin and 35·3% and 32·5% respectively in French honeysuckle. Under both cutting regimes, the higher seeding density was more suitable for sainfoin, increasing stems m⁻² with irrigation and seed yield without irrigation. In French honeysuckle the lower seeding density was more suitable for production of inflorescences per tiller and for seed weight without irrigation. Higher seeding density positively influenced seed yield under irrigation. The seed yield components most influenced by irrigation were: 1000-seed weight, seeds per inflorescence and inflorescence per stem. French honeysuckle genotypes were potentially more productive in dry matter and seed yield under both irrigation regimes than the sainfoin, which was more productive in seed yield when cut. The ecotypes of both legumes represent a genetic resource, particularly for seed yield after forage cutting, to be utilized in breeding programmes for developing varieties well adapted to Mediterranean environments.     

油菜结实特性与库源关系的研究

以4个油菜品种的结实特性研究表明，开花后20d内油菜角果体积和表面积急剧增长，角果和籽粒干重随成熟进程而增加，籽粒干重在开花25d后增重加热，40d左右超过果皮干重。具有生殖生长优势品种的单位角果皮面积的生产力（PPA）和单位角果皮表面积负担的籽粒数（SNPA）较高。果皮与种子的生理代谢进程不同，二者的全氮，叶绿素以及可溶性糖含量的动态变化与角果形态及干物质积累转化进程有明显的相关性。初花期去叶处理可使4个品种明显减产，去叶对分枝产量的影响大于主花序，主要减少分枝的每角粒数；去短叶的减产幅度大于去无柄叶。     

Seed production in grassland species: Morpho‐biological determinants in a species‐rich semi‐natural grassland

Studying the seed production of herbaceous species can help to conserve grassland habitats and re‐create new high‐value grassland surfaces. Studies on grassland seed production have focused mainly on individual species and traits, without characterizing their relative importance at the plant community level. The aim of this study was to investigate the entire seed production process of the main species in a temperate grassland. Fertile shoots (FS) of twenty‐nine grasses and forbs were collected over 4 years and analysed for sixteen traits that determine inflorescence size, seed production and seed quality. The per cent viability played a predominant role in determining the total production of viable seeds. Forbs showed a range of reproductive strategies, including variable distribution of flowers among growth periods, number of inflorescences per FS and relationship between seed size and FS density in the grassland. The flower production for grasses was concentrated in the first growth period, but this limitation was mitigated by a higher seed dormancy. The number of viable seeds per FS and seed size were important components of the reproductive strategy of forbs, with heavy‐seeded species being characterised by high individual densities in the community, but producing few seeds per FS. Light‐seeded species showed an opposite pattern. The results suggest that when using seeds from semi‐natural grasslands for ecological restoration, special attention should be paid to the seed amount, germinability and viability of forbs, as they seem to depend more on seed reproduction and have a lower ovule to seed transformation efficiency.     

Prevention of berry set and true seed production in six potato (Solanum tuberosum L.) cultivars by single foliar applications of MCPA

Summary True potato seed production may contribute to the spread of several diseases and pests. MCPA (500 or 750 g a.i. ha⁻¹) applied at early or full bud stage reduced berry number and seed number per berry, resulting in reduced true seed production. Effects on berry set differed between cultivars and were dependent on crop growth stage at application and true seed production was reduced most strongly in all cultivars with application at full bud stage. MCPA also slightly reduced yield and tuber size, but did not affect tuber dry matter content or fry colour.