Recurrent selection of tropical tree crops

The recurrent selection schemes recommended by CIRAD for 6 tropical tree crops are presented and compared. Breeding programmes are carried out under cooperation between CIRAD and its partners in regions where the crops are grown. The crops are cacao, coffee, rubber tree, oil palm, coconut and eucalyptus. After a short look at the background, the reasons behind the options chosen are given and the main characteristics of the schemes are described and illustrated. The state of progress and some major results are discussed. Over and above the differences linked to plant biology, the genetic diversity available and the type of varietal output, common characteristics are emphasized. The time taken for each generation means simplifying the intercrossing phases between successive breeding cycles, and thus, the parents tested are heterozygous: whenever possible, a clonal varietal output is an additional source of progress. The use of biotechnologies to study diversity is a valuable asset, and their application for early selection (QTL) is also promising. The preponderance of combining ability coexists with marked heterosis, which poses the problem of the latter's origin. As a result, all of the schemes described, but one, are reciprocal recurrent selection schemes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Efficiency of Recurrent Selection Methods to Improve the Line Value of a Population

Five breedings methods have been studied for their efficiency in improving the line value of a population, i.e. the value of all lines that can be derived from the population. These methods are: half-sib family recurrent selection (HSF-RS), full-sib family recurrent selection (FSF-RS), half-sib progeny recurrent selection (HSP-RS), recurrent selection (S₁-RS) and the single-doubled-haploid descent recurrent selection (SDH-RS). All breeding methods are compared on the basis of the genetic advance per unit of time, with the constraint of the same effective size after the first cycle of selection. Two modalities of SDH-RS are considered for an annual plant without an off-season generation: one with a cycle in four years (SDH₁-RS) and the other with a cycle in five years (SDH₂-RS). For all methods the possibility of one off-season generation for intercrossing is considered. Fields of efficiency of the best methods are determined considering five main parameters, the heritability, the importance of additive variance, the correlation QL between the additive effect for line value and the additive effect for the per se value, the length of the cycle for SDH-RS and the selection intensities. SDH-RS is the best method when the heritability is low, with a low proportion of additive variance and with a relatively low correlation QL between additive effects for per se and line values. Without off-season generation, S₁-RS is the best method among the remaining realistic situations; with one off-season generation for intercrossing it is FSF-RS. The use of an off-season generation reduces the domain of efficiency of SDH-RS while an increase in the selection intensity increases this domain. With a selection intensity for SDH-RS equal to that for S₁-RS, SDH-RS is the best in a large range of realistic situations except for SDH₂ with one offseason generation and medium to high correlation QL.     

Feasibility of breeding male-sterile populations for use in developing interpopulation hybrids of pearl millet

Inter‐population hybrids of pearl millet, Pennisetum glaucum (L.) R. Br., have a substantial grain yield advantage over open‐pollinated varieties that makes them an appropriate and economically viable proposition for many African agricultural situations, provided that stable male‐sterile populations can be developed for use as seed parents. The objective of this research was to examine the feasibility of breeding stable male‐sterile populations, using the d₂ dwarf version of Nigerian Composite NCD₂ and the A₄ cytoplasmic‐nuclear male sterility system as a test case. Results showed that two cycles of recurrent selection for sterility maintenance ability led to the development of a fully effective maintainer version of NCD₂. There was no significant difference between the original C₀ cycle bulk and the C₃ cycle bulk (developed from the third and final cycle of recurrent selection) for grain yield and other agronomic traits. The male‐sterile population at the third backcross stage, developed from the maintainer version of NCD₂, had as high a level of stable male sterility as the A¹ system commercial inbred male‐sterile line 841A₁. Thus, it is concluded that with the use of the A₄ cytoplasmic male‐sterile system, it would be possible rapidly to develop a maintainer version of any population without detrimental effects on grain yield and agronomic traits. Male sterility of populations developed from these maintainers will be highly stable, paving the way for their effective utilization as seed parents in breeding inter‐population hybrids.     

Hybrid reconstruction in maize

Summary The production of seed of the maize single cross hybrid F68^*NE2 is uneconomic because of the low grain yield of the maternal line. Therefore the aim was to produce it from newly developed inbred lines obtained by reshuffling the genes in the hybrid, accompanied by selection. Thus in open pollinating generations derived from this hybrid, i.e. in C0, C1, C2, C3 and C4, honeycomb selection for grain yield improvement was applied. Selfing of one ear and open pollination of another ear of selected prolific C4 plants yielded 20 pairs of S1/half sib progenies. Plants grown from remnant S1 seed corresponding to superior progeny pairs were selfed. In each S2-line a single plant was selected and selfed. The S3-lines were evaluated for yield. Two S3-lines, i.e. 6D and 2B, attracted attention because they yielded two and a half times as much as the best commercial inbred line B73.The S1-and S2-lines were tested for combining ability with the related inbred lines NE2 and F68 by means of honeycomb design experiments and for combining ability with unrelated, freely available inbred lines by means of randomized complete block designs. Two S2-lines, i.e. 5C and 6E, were selected for their good combining ability. The six single cross hybrids produced by crossing the four S3-lines 6D, 2B, 5C, and 6E were compared with the original hybrid F68^*NE2 in a honeycomb design at two sites. The grain yields of the single cross hybrids 6D^*6E and 5C^*6E were similar to that of F68^*NE2. However, these two reconstructed hybrids can be produced in a cheaper way because the new maternal inbred lines yield as good as B73 (line 5C) or much better (line 6D).     

水稻QTL定位在杂种优势理论和杂交稻育种中的应用现状

水稻多数重要农艺性状属于数量性状,因此,数量性状的遗传效应研究对水稻育种具有十分重要的意义。本文就水稻QTL定位在杂种优势基础理论研究中的现状进行了回顾与探讨,同时就定位结果在杂交稻育种中的应用现状展开论述,最后就这些领域的研究进展提出了科学的展望,以期为今后开展杂种优势基础理论研究方式以及杂交育种思路提供一定的帮助和借鉴。     

运用半同胞轮回选择法对‘运轮1号’相关性状的改良效果分析

为获取高配合力优良育种群体,对‘运轮1号’群体开展半同胞轮回选择改良。选择‘运轮1号’C4群体中优良单株自交,以‘昌7-2’为测验种配制对应的测交种,鉴定筛选20个优良单株,等量种子经混合授粉形成C5群体。结果显示：C5群体的株高、穗位、茎腐病率较C4分别下降4cm、2cm和3.5%。群体内单株间产量配合力差异达极显著水平,预计C5群体测交种产量增益为7.7%;与选择前相比,中选测交种穗位和茎腐病下降0.7 cm、6.3%,穗长、行粒数、出籽率、持绿度分别增加0.1 cm、0.6粒、0.4%、0.3级,但株高、籽粒含水量各增加0.3 cm、0.2%,穗粗、穗行数、百粒重保持不变;除含水量和百粒重外,其余性状的变异系数呈下降趋势,且多数性状的变异系数仍然在10%以下。进一步改良需扩大群体,增加测验种数量,并加入新的种质;单株选择应严格控制株高、穗位及生育期。     

栽培稻籼,粳交F1杂种优势与同功酶表达

水稻杂种优势的表现,前人已作过部分研究,初步的结论是:水稻的杂种优势具有遗传多样性。那么,灿、粳交F_1代杂种优势有哪些特点呢?本文拟讨论这个问题。 1 材料和方法 1984年组成珍汕97×城堡_2、桂朝_2×城堡_2、珍汕97×密阳_(23)桂朝_2×密阳_(23)桂朝_(13)×密阳_(23)、川新糯×密阳_(23)等6个杂交组合。密阳_(23)是南朝鲜用籼梗交育成的偏籼型品种,城堡_2是日本用籼粳交育成的偏粳型品种。杂交时     

Population improvement in pyrethrum (Chrysanthemum cinerariaefolium Vis.)

Summary A population improvement programme in pyrethrum had progressively increased the mean pyrethrins content from 1.33 percent in the unselected base population to 1.97 percent in the population developed after one cycle of each of mass and recurrent selections. The selection had also increased the range of variation and the relative frequency of desirable plants.     

中国超级杂交稻育种研究的进展与策略探讨

介绍了中国超级杂交稻育种的目标,技术路线和育种理论,综述了中国超级杂交稻育种研究的概况,以及在亲本选育,品种选育和分子育种技术等方面取得的进展,阐述了通过加强水稻种质资源的创新与利用,扩大亲本遗传差异,提高水稻生物学产量,改善水稻生理机能等技术策略,选育出综合性状优良的超级杂交稻新组合,进一步提高中国超级杂交稻产量水平     

论“株系循环双向选优法”

“株系循环双向选优法”是将新品种选育与原种繁殖相结合的新方法。该方法在遵循“纯中选优”原则生产原种的同时,根据育种目标,按照“优中选优”的原则选育新品种。该方法既区别于单纯生产原种的“株系循环法”,也区别于选育新品种的纯系育种法。     

提高棉花抗盐性的途径

棉花比较耐盐碱,在滨海与内陆盐碱地得到广泛种植,因而提高棉花的抗盐性很有意义。本文简要概括了提高棉花抗盐性的４条主要途径：（１）培育抗盐的棉花品种;（２）通过组织培养筛选抗盐品系;（３）进行种子处理;（４）合理施肥。     

CHA杂种小麦灌浆优势规律研究

以4个CHA杂种及其亲本和CK为材料, 采用数学模型分析、 相关分析、 通 径分析等方法, 研究了CHA杂种灌浆优势及其动态规律和与气象因子的关系, 结果表明 , (1) 4个CHA 杂种籽粒干物质积累动态过程均存在杂种优势, 最终干物质积累均存在 超亲优势, 最终干物质超亲优势形成过程有灌浆全期形成、 灌浆中后期形成和灌浆后期