Reciprocal recurrent selection applied to Coffea canephora Pierre

Summary Genetic parameters were estimated in trials planted in connection with a reciprocal recurrent selection programme applied to Coffea canephora in Côte d'Ivoire. Narrow sense heritability values, estimated from a breakdown of the analysis of variance, were high for architectural characters (0.22 to 0.78) and medium for tree vigour (0.13 to 0.40) and for bean weight (0.15 to 0.28). Calculated heritability values for the first two harvests were high (h²>0.7), but much lower for the following harvests (less than 0.2). Heritability estimates by parent-offspring regressions gave variable results, though they were often similar to those obtained by variance analysis, especially for bean weight. Phenotypic and genetic correlations between tree vigour traits and productivity were high. Bean weight was not correlated with vigour or production. Canopy diameter of 4 year-old trees was closely correlated with cumulated productivity from 2 to 5 years in the absence of development competition between trees, but the correlation was low if trees were in competition with each other. The consequences of the results for the choice of characters to be selected among intergroup hybrids or the parents of both populations are discussed.     

Causal relationships between inbreeding, seed characteristics and plant performance in leek (Allium porrum L.)

Leek (Allium porrum L.) is an important outdoor vegetable in West Europe, where it is cultivated on about 30,000 ha. Most commercial cultivars of leek are open pollinated. One of the major problems with the crop is poor uniformity. Leek is an outbreeding species with up to 20% self-fertilisation. Much of the variation of open pollinated cultivars is explained by the strong sensitivity to in breeding depression after selfing. In this study we attempt to analyse in a systematic way the relationship between degree of selfing and agricultural performance in leek. The results obtained confirm a negative correlation between selfing and somea gricultural aspects important for vigour such as seedling emergence, plant growth and plant fresh yield. Also negative correlations between degree of selfing and seed individual weight and between selfing and seed individual size were found. The negative relationship between inbreeding and plant weight at harvest is further confirmed in an experiment in which the origin (cross-pollination orself-pollination) of each individual offspring plant analysed was determined using AFLP-markers. Finally, the correlation between chlorophyll deficiency genes and the loss of vigour that follows selfing was investigated. The results obtained demonstrate a significant decrease of pigment content in two generations of selfing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic interpretations of the effects of bulk breeding on four populations of beans (Phaseolus vulgaris L.)

Summary The effects of bulk breeding on yield and its components in two high-yeilding and two low-yielding bean populations when grown at crop densities are interpreted in terms of gene action and selection. There was considerable additive variation in the crosses, dominance effects were variable but tended to be negative. The results were compared with results obtained at low density by another worker with the same populations, and this showed that interpretations of gene action in hybrid vigour depend on the test environment used. The interpretations were also compared with plant breeding interpretations made on the same material (Hamblin, 1977), and it was found that a single pattern of response to natural selection, in plant breeding terms, may be explained by more than one genetic interpretation and, conversely, a single genetic interpretation may result in different patterns of response in plant breeding terms. The value of composite crosses in plant breeding are discussed and it is concluded that there is a greater chance of producing improved lines from a large number of simple crosses than from a smaller number of composite crosses.     

A comparison of apple and pear seedlings with reference to the juvenile period I. Seedling growth and yield

Summary Several thousand apple and pear seedlings of many progenies were studied in connection with their juvenile period (J.P.). The initially significant inverse relation between the vigour (stem diameter) and the J.P. of the seedlings became insignificant as the trees grew older, due to a retardation of growth occurring when the seedlings become generative. This relation can be used effectively in pre-selecting for vigour in the nursery. Cumulative yields were higher when the J.P. was shorter, but there was no evident link between the J.P. and annual yield in full bearing, that is to say, precocity and preductivity are not directly connected. Better growing conditions and pre-selection have shortened the mean progeny J.P. of either crop by three years since the 1950's. Generally, the pear seedlings appear to grow faster, to become generative slower and to yield lower than comparable apple seedlings. The mean J.P. of apple and pear progenies averaged 4.2 and 6.0 years respectively. The difference between apple and pear may be attributable to a greater selection pressure on both precocity and productivity with apple than with pear.This possibly also led to a smaller tree in the productive phase on the assumption that tree size at first flowering-small at a short, large at a long J.P.-expresses reproductive efficiency and as such is reflected in the size of the adult tree.Also presented at the Juvenility Symposium held at West-Berlin, November 1976.     

Vigour evaluation for genetics and breeding in rose

Breeding of cut and pot rose cultivars for efficient production under low-energy conditions in greenhouses will be facilitated by understanding the inheritance of vigour. To get insight into the genetic variation of vigour-related traits, a diploid rose population was employed for an evaluation study in greenhouses in The Netherlands and Denmark. For all the traits investigated the population showed a continuous quantitative variation as well as a considerable transgression. For most of the traits, the genetic variation found among the tested entries was highly significant and tended to be large in comparison to the effects of genotype by environment interaction. The heritability based on means of the traits was high and ranged from 68 to 92%. Strong simple correlations (r = 0.65 to 0.95) were found among the traits shoot length, leaf area, leaf dry weight, stem dry weight, total dry weight and growth rate. The total dry weight and leaf area are suggested to be good parameters for early selection of rose genotypes with vigorous growth under suboptimal growth conditions.     

Inheritance of conditional dormancy in over-summering buds of Phalaris aquatica L.

Summary The relative ability of the underground buds of a Mediterranean perennial grass species to break dormancy in response to summer rain was compared between individual plants and between half-sib families in two experiments with broadly-based breeding populations under different environmental conditions. Significant genetic variation was found in summer regrowth activity in both experiments. The narrow-sense heritability of the ratio of new to old, dead tillers after summer rain under spaced plant conditions at a relatively cool site was 0.40±0.16. Under sward conditions at a warm site, the narrow-sense heritability of an index of summer regrowth potential on a half-sib family mean basis was 0.36±0.08. Summer regrowth activity was negatively but weakly correlated with flowering time (r_g=–0.22), and strongly positively correlated with early autumn herbage yield (r_g=0.79). Summer regrowth activity was not genetically correlated with seedling size or herbage yield in the second or third growing seasons. These correlations are different in sign or magnitude from those observed in collections of Mediterranean ecotypes from which the breeding populations were derived by crossing to Australian cultivars and recurrent selection for vigour and persistence. The correlations in Mediterranean populations therefore are not due to pleiotropic effects; they can be altered by recombination. Phenotypic variance relative to the population mean was considerable in both experiments, and hence the level of the responsiveness of dormant buds to summer rainfall should be manipulable readily by selection. The possible effects of altered responsiveness on long term survival and productivity in several different environments are discussed.     

尾叶桉(Eucalyptus urophylla)杂种家系遗传测定及抗风选择

中国华南沿海地区台风影响频发,为选育桉树抗风和速生品种,本研究估算广东鹤山9年和11.5年生56个尾叶桉家系(含母本和对照)生长、抗风等性状的杂种优势、育种值及配合力。结果表明:两个不同年度各性状在杂种家系间存在极显著差异。以单株蓄积为指标筛选优良杂交组合,两个年度均排名前3的是37号和40号,分别是家系128号9年生平均0.207 9 m^3和11.5年生0.336 9 m^3的1.33和1.79倍以及1.28和1.52倍,11.5年生超过128号的家系共6个,6个家系平均超亲优势达到15.99%;两个年度单株蓄积育种值均超过0.05且抗风性育种值为正的仅4个家系;以11.5年生调查数据和最优56号家系为选择标准,超过其平均单株蓄积0.345 7 m^3和抗风等级值4.33的杂种单株有173株。本研究发现,2号、15号、21号、22号、和64号是具有较高母本一般配合力的亲本,而2号、21号、22号、29号和56号这5个父本的一般配合力较高,通过优化组合可获得具有优良性状的子代;生长结合抗风指标选择到的3个特殊配合力高的杂交家系和173株优株,是今后高世代育种重点利用对象,也可为台风区人工林建设提供更多资源产品。     

Analysis of competitive ability among genotypes of perennial ryegrass. II. Effect upon dry matter production

Summary An analysis of the effects of competition upon the dry matter production per plant (after square root transformation) revealed no significant differences between the two genotypes of perennial ryegrass (Lolium perenne) used as regards the pressures which they exerted upon each other. Their response to these pressures differed significantly however. Using these estimates of the pressure and response parameters it was shown that the impact of intra-genotypic competition upon these two genotypes was considerably greater than that of inter-genotypic competition. In general this will be true whenever the pressure and response parameters take the same sign. Intensity of competition increased linearly with vigour of growth in both cutting regimes, though changes in vigour had a significantly greater effect upon the intensity of competition under frequent cutting.     

Morphology and vigour of monohaploid potato clones,their corresponding homozygous diploids and tetraploids and their heterozygous diploid parent

Summary To study the joint effects of homozygotization and polyploidization in potato, the performance has been examined of five potato genotypes at three (x, 2x, 4x) and two genotypes at two (x, 2x) ploidy levels. Six out of the seven genotypes studied were compared with their heterozygous diploid parental clone. In this way comparisons could be made between i) the heterozygous diploid and its monohaploid derivatives, ii) three or two ploidy levels per genotye and iii) homozygous di- and tetreploids and their heterozygous diploid source.Large variation could be detected between monohaploids obtained from one diploid source. A striking increase in vigour was observed with somatic chromosome doubling from x to 2x, but less clearly from 2x to 4x. The relatively vigorous diploids showed a weaker response to tetraploidization than the less vigorous ones. The heterozygous diploid exceeded all homozygous di- and tetraploid derivatives in performance. The results of this study suggest positive gene dosage effects for tuber production more than for leaf area and plant height. The observations on plant vigour in homo- and heterozygotes suggest that dominance effects are stronger than additive gene effects. Owing to sterility problems, homozygous potato clones will presumably be of little importance for practical breeding.     

Selection for adaptation in multipurpose trees and shrubs for production and function in agroforestry systems

Summary With the greater uniformity in site conditions in cultivated fields and higher levels of inputs (soil amendments and labour) for modern agroforestry systems, selection and breeding for optimal tree adaptation to site conditions and management practices call for strategies radically different from those for plantation forestry. Furthermore, specific requirements for the most efficient growth resource sharing arrangements between the tree and its companion crop call for evaluation both above-ground and below-ground tree growth characteristics in much greater details than has been the case for forestry practice.Specific adaptations in tree-soil relations are highlighted. Tree ideotype profiles are defined for a valuable fodder species (Calliandra calothyrsus) and a valuable timber species (Grevillea robusta). Results from half-sib progeny testing experiment on C. calothyrsus in alley farming system indicate differential adaptedness to frequent cutting for fodder production among the families after 6 cutting cycles (over a period of 2 years). If this differential response to frequent cutting among genotypes is confirmed, phyllomorphs which are more tolerant to this management practice could be selected for further improvement research.Excavation of 2 trees per family within G. robusta half-sib progeny testing experiments at two locations in Kenya provided the base for studying (a) variations in root growth patterns and (b) correlations between stem and root growth patterns in the background of efficient soil resource sharing strategies and of potentials for indirect selection for root growth characteristics. Analyses based on 7 categories of root growth and 7 categories of stem growth patterns involving 94 families selected in Australia and 60 families selected from landraces in Kenya indicate (a) insignificant variation among families in root growth patterns and (b) non existent or weak correlations between stem and root growth pattenrs.     

成龄苹果树丰产优质栽培技术研究

1976—1986年试验结果,明确了稀植成龄苹果树冠光照分布及其与产量、质量的关系,为树形改造提供了理论依据,并认为“双层延迟开心形”是改造苹果稀植树冠的较好树形.提出了大、中型果的合理留果指标,并把一个小枝组作为疏花疏果的单位,使操作者易于掌握.明确亩产2500—3000公斤的丰产园所要达到的施肥水平和土壤肥力水平.为节约劳力、减少伤根和促进根系生长,提出以一面轮替沟施取代生产上普遍采用的环状沟施基肥的方法.还根据树势提出了相应的修剪措施.     

Assessment of the reproductive system of Isatis tinctoria L.

Isatis tinctoria L. (woad) is a dye plant whose cultivation is increasing because of its adaptability to marginal conditions and increasing demand for natural products. Suitable breeding schemes need to be set up in order to obtain woad varieties for each proposed environment. Presently, no data about the reproductive system are available. The effects of selfing and crossing on setting and progeny vigour were assessed. Results showed the existence of an outcrossing system in I. tinctoria. Obligate self-pollinated plants produced fewer siliques (7.1 g per plant) with lower weight (6.0 mg) and lower seed germinability (8.2%) than outcrossing plants (44.1 g, 8.0 mg and 46.0% for each character, respectively). Self-pollinated progenies also generally showed lower vigour than outcrossing progenies.     

侧柏母树大小对种子特性和幼苗生长的影响

阐明母树大小对种子质量的影响有助于揭示侧柏林的幼苗建立机制。采集泰山普照寺周边60年生侧柏人工林内不同胸径等级母树的种子,通过盆栽试验研究母树大小对种子萌发和幼苗生长的影响。结果表明:种子的千粒重、种子最大长和最大宽在不同径级之间差异不显著。在种子萌发上,发芽率和发芽指数随径级增加逐渐增加,而平均发芽时间逐渐降低。在幼苗生长上,母树胸径9.2~11.8cm的比胸径18.8~21.2cm的有着低的生物量、地径和相对苗高生长速率,但有着高的根冠比。随母树径级的增加,侧柏种子的质量和幼苗生长能力显著提升。因此,母树大小是侧柏人工林幼苗建立的重要影响因素。     

Quantitative evaluation of the degree of sprout leaf bending of rice cultivars using P-type Fourier descriptors and principal component analysis

For decades, seedling peaches have been used as the standard rootstock in California almond orchards. Vigorous, deep rooted trees are needed in almond orchards for maximum yields and to withstand the annual tree-shaking at harvest. Currently, researchers are actively evaluating rootstocks for almonds in field trials and in various screening protocols. In this study, seedling rootstocks, obtained from male-sterile advanced generation peach-almond (PEAL) hybrid mother trees, were compared with ‘Nemaguard’ peach seedlings for emergence in the nursery row, trunk caliper at propagation time, and end of season dormant above ground tree weight. Seedling emergence was affected significantly (P ≤ 0.05) by seed source, as was trunk caliper and end of season dormant above ground tree weight. Trunk caliper and dormant above ground tree weight were also affected significantly (P ≤ 0.05) by planting year. Results obtained in this study demonstrate the enhanced first year growth from seedlings of advanced generation PEAL hybrids, as compared to ‘Nemaguard’ seedlings. Seedling emergence in the rootstock bed was not affected significantly by planting year. Advanced generation PEAL hybrid seedlings were ready for June-budding at an earlier date compared to ‘Nemaguard’ seedlings, providing the potential for larger-sized finished nursery stock by the end of the growing season. Due to the male-sterile status of the advanced generation PEAL mother trees, bloom periods of several root-knot nematode resistant rootstock cultivars were examined for their degree of synchronicity with the mother trees. The examined rootstocks and mother trees varied in both chill hour and post-chill heat requirements necessary to effect bloom. ‘Flordaguard’ peach rootstock began bloom in advance of the male-sterile mother trees, whereas the bloom period of ‘Tsukuba No. 4’ occurred well after, suggesting they would not be effective synchronous pollenizers for consistent hybrid seed production. Based on more limited flowering period data, better bloom synchronicity was achieved with a Tsukuba No. 4 X Flordaguard hybrid.     

Heat stress during seed development affects forage brassica (Brassica napus L.) seed quality

In two consecutive seasons, forage rape (Brassica napus L.) plants were exposed to short periods (240°C hr) of heat stress (30°C day/25°C night) during seed filling (80% seed moisture content = S1), at physiological maturity (50% seed moisture content = S2) and at both S1 plus S2 (=S3) in a Biotron before being returned to the field until seed harvest. Seeds were hand harvested at 14% seed moisture content and their quality assessed by measuring germination, seed vigour (using the accelerated ageing and conductivity tests) and seed mass (as determined by thousand seed weight). Heat stress at both S1 and S2 caused a small (<10%) but significant reduction in germination in both seasons. There was a significant heat stress timing interaction in the first but not the second season. Reductions in germination were a result of increased abnormal seedling production not seed death. All three heat stress treatments significantly reduced seed vigour, with S3>S2>S1. Seed mass was reduced by heat stress at S1 but not at S2. Variable seed vigour in high‐germinating New Zealand‐produced forage rapeseed lots is most likely explained by short periods of heat stress during seed development.     

Genetic variation in bitter pit and fruit calcium concentrations within a diverse apple germplasm collection

Summary Genetic variability in the apple [Malus] fruit disorder bitter pit and fruit calcium concentrations ([Ca]) was determined in 25 seedling families at each of two sites from 1999 to 2000 and again for one site, in 2001. Most trees were free of pit or had low pit incidence, which could be approximated by an over-dispersed binomial distribution. A genetic component to external and internal pit incidence was found across both sites and all years. This effect was irrespective of the use of several cropping factors, average fruit weight or fruit mineral concentrations as covariates in the analyses. Year and/or site always had substantial effects on pit incidence. Interactions of genetic effects with site or year were also detected with large differences in mean pit incidence between sites or years for some families but not others. No relationship was found between mean family pit incidence and mean family [Ca] or mean family harvest date. However fruit [Ca] and harvest date were usually important predictors of within-family variation in pit incidence. For any one seedling, family had the largest effect on bitter pit incidence followed by site and [Ca] and the smallest effect was that of harvest date. [Ca] showed a strong genetic component and estimated family means of [Ca] were consistent at different sites and years. These results suggest that susceptibility of apple genotypes to bitter pit in breeding programmes may be best assessed through screening across multiple sites and seasons. Fruit [Ca] might be useful as an indirect selection index for bitter pit within, but not among families.     

Effects of inbreeding on growth and yield of oil palm

The effects of inbreeding were studied in three oil palm (Elaeis guineensis Jacq.) trials in the Democratic Republic of Congo (Congo). In selfings, marked inbreeding depression was observed for yield of fruit bunches, mean bunch weight and bunch number, but there was little effect on bunch composition. Most vegetative measurements were significantly affected by selfing, but leaf production rate and leaf area ratio were unaffected. Sib-crossing had less depressive effect than selfing, and in some families sib-crosses were superior to outcrosses. Where selection needs to be done within inbred families, our study suggests that leaf area ratio and bunch composition would be useful criteria.     

Bayesian threshold analysis of breeding values,genetic correlation and heritability of flowering intensity in <Emphasis Type="Italic">Eucalyptus cladocalyx</Emphasis> under arid conditions

In the dry regions of Chile, prolific flowering from forest plantation is particularly advantageous for honey production, in order to supplement the erratic flowering in native plants. Eucalyptus cladocalyx is a species suitable for areas with low water availability and their flowers provide a reliable source for the production of honey. The aim of this study was to examine the heritability of flowering intensity in 49 open-pollinated families of E. cladocalyx in southern Atacama Desert, Chile, with the view to the selection for prolific flowering, but with minimal impact on precocious flowering. The Bayesian variance component estimation model was assumed using the Gibbs sampling algorithm. Threshold models were fitted to flowering data (bi-character model). Flowering intensity was found to be highly heritable (posterior mean: h ² = 0.48; and credible interval: 0.41–0.56). The posterior mean of the genetic correlation between flowering precocity and intensity was positive (r = 0.45) and according to the credible interval (0.341–0.542), it was significantly different from zero, indicating that selection on breeding values of early flowering at age three, would have significant and positive impact on flowering intensity 5 years later (or in 8-year-old trees). These results are important for the start of a small-scale breeding program for the species in southern Atacama Desert. The genetic variability found in these breeding populations may be used for breeding purposes in regions where arid environmental conditions are limiting to the establishment of eucalypts trees.     

Developmental Dynamics and Early Growth Vigour in Rice 2. Modelling Genetic Diversity Using Ecomeristem

Early vigour is an important objective in rice breeding. A previous study reported strong positive effects of development rate (DR, 1/phyllochron) on early growth vigour in two rice panels. This study provided a model‐based analysis of DR effects on rice early vigour and underlying source–sink processes during exponential growth, using Ecomeristem model. Relevant model parameters were fitted to panel observations, and their effect on early vigour was quantified. A sensitivity analysis was performed to quantify the impact of model parameters on simulation outputs. The simulated behaviour of a population of virtual genotypes defined by the combination of model parameter values was compared with that of diversity panel. Finally, a simulation experiment was conducted to analyse source–sink adjustments constituting early vigour across a range of DR. Parameters governing structural development, particularly DR, had greater impact on vigour than parameters for resource acquisition. High DR was associated with rapid dry weight accumulation and low transitory carbohydrate reserves in both real and virtual populations. Genotypic DR is thus a major driver of early vigour in rice under stress‐free conditions. To evaluate traits contributing to vigour, the capacity of crop models to simulate interactions between structural development and resource acquisition must be improved.     

A cassava clonal evaluation trial based on a new cassava breeding scheme

Cassava (Manihot esculenta) breeding at the earlier stages so far has been mainly based on a mass phenotypic recurrent selection, as little data is taken. This has resulted in a long breeding cycle and lack of organised information on the breeding values of parental lines used in the breeding programmes. The International Institute of Tropical Agriculture (CIAT) recently initiated a scheme to try and correct this, by introduction of replication and blocking in the clonal evaluation trial (CET) and collection of data on all genotypes at early stages of breeding. The aim of the study was to evaluate a CET using the new breeding scheme. Replicating and blocking of clones improved the accuracy of the data obtained. High broad-sense heritability values, comparable to those at advanced selection stages, were obtained, as environmental effects were minimised. The highest was for harvest index (HI) (0.80), followed by cassava frogskin disease (CFSD) (0.79), dry matter content (DMC) (0.75) fresh and dry root yields (DRY) (0.73), root weight (RtWt) (0.61), number of commercial roots (0.60) and roots per plant (RtPlt) (0.43). DMC, HI and RtWt were identified as important variables in selection and determination of economic yield at early stages of selection.