Quantitative trait loci for early maturity and their potential in breeding for earliness in Brassica juncea

A doubled haploid population of Brassica juncea, developed from a cross between two parental lines differing for days to maturity, was used to study the efficiency of indirect selection for a primary trait through selection of secondary trait(s) over direct selection for the primary trait when quantitative trait loci information is available for both primary and secondary traits, and applied. Days to maturity was considered as primary trait, while days to first flowering, days to end of flowering, flowering period and plant height were considered as secondary traits. An RFLP linkage map was employed for QTL analysis of maturity and maturity-determinant traits, and a stable QTL B6 simultaneously affecting these two types of traits was identified. This linked QTL explained 11.7% phenotypic variation for days to maturity, 20.7% variation for days to first flowering, 24.3% variation for days to end of flowering and 14.4% variation for plant height. Phenotypic evaluation of maturity and/or maturity-determinant traits, viz. days to first flowering, days to end of flowering and plant height revealed that limited genetic advance for early maturity can be achieved through phenotypic selection of the primary and/or the secondary trait(s). However, the estimates of genetic advance for early maturity based on combined phenotypic evaluation and linked QTL data was found to be, at least, three times higher compared to genetic advance based on phenotypic evaluation only, demonstrating the potential of marker-assisted selection in breeding for early maturity in B. juncea.     

Effects of divergent selection on correlations between morphological traits in white clover (Trifolium repens L.)

The effects of two generations of divergent selection for stolon diameter and stolon amount on the pattern of phenotypic correlations between important agronomic traits in white clover (Trifolium repens L.) were studied. The effects of selection were: the proportions of the variances of traits under direct selection were considerably lower within selection lines than overall and this was associated with a loss of correlation between traits. Unselected traits showed higher proportions of variances remaining within the selection lines and shifts from non-significant to significant correlations from the plants overall to selection lines. The significance of these results and their relevance to strategies of germplasm improvement is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

克氏原螯虾形态与体重的通径分析

[目的]确定影响克氏原螯虾体重的主要形态性状,以期为克氏原螯虾的亲本选育、形态辅助育种提供理论基础。[方法]选取了350尾雌性克氏原螯虾和302尾雄性克氏原螯虾,分别测量其体重(Y)、全长(X1)、头胸甲长(X2)、头胸甲宽(X3)、腹节总长(X4)、第一腹节长(X5)和第一腹节宽(X6)。采用相关分析、多元回归分析和通径分析,以体重为因变量形态性状为自变量,计算了雌雄克氏原螯虾各性状间的相关系数,通径系数和决定系数。[结果]相关分析结果显示,雌雄克氏原螯虾各性状间相关性皆达到了极显著水平(P<0.01)；多元回归分析中,雌雄克氏原螯虾剔除了与体重性状不显著的形态性状,建立的多元回归方程分别为Y雌=－34.689+10.629X2+6.479X3+0.803X1,Y雄=－33.413+5.727X2+6.770X3+2.043X1+3.045X6 ；通径分析结果表明,头胸甲长在雌性克氏原螯虾中对体重的直接作用最大,其次是全长和头胸甲宽,全长和头胸甲宽通过头胸甲长对体重的间接作用较大。在雄性中,也是头胸甲长的直接作用最大,其次是全长和头胸甲宽以及第一腹节宽,第一腹节宽通过头胸甲长、宽和全长对体重的间接作用最大。[结论]以上结果可为克氏原螯虾的选育奠定基础。     

Correlated responses of fatty acid composition, grain quality, and agronomic traits to nine cycles of recurrent selection for increased oil content in oat

Increases in the groat-oil content of oat (Avena sativa L.) increase the energy value of the grain and improve the feasibility of extracting oat oil for use as a vegetable oil. Nine cycles of recurrent selection for greater groat-oil content conducted in a genetically broad-based oat population resulted in dramatic increases in groat-oil content. Our objectives were todetermine if selection for greater groat-oil content affected fatty acid composition, grain quality traits (test weight and seed weight), or agronomic traits (straw yield, biomass, harvest index, heading date, and height). We evaluated 100 random lines from the base (C0) population and each of the nine selection cycle populations in three environments in order to estimate means, genetic variances, heritabilities, and genotypic and phenotypic correlations of grain quality and agronomic traits. We also evaluated 20 random lines from each population to estimate changes in fatty acid contents. Oleate and stearate contents increased over cycles of selection, as did the ratio of unsaturated to saturated fatty acids. Palmitate, linoleate, and linolenate contents and all grain quality and agronomic traits except harvest index decreased over cycles of selection. There was no evidence for reduced genetic variance or heritability in C9 for any trait, but the genotypic and phenotypic correlations between agronomic traits and oil content fluctuated over cycles. Selection for increased groat-oil content improved oil quality but reduced grain quality and agronomic performance of the population. This revised version was published online in August 2006 with corrections to the Cover Date.     

不同性别中国蛤蜊数量性状的相关与通径分析

为了查明中国蛤蜊各数量性状间的相关性及影响产量的因素组成。随机选取大连庄河野生群体中国蛤蜊二龄个体115个,测量其壳长、壳宽、壳高、活体重和软体重,并显微鉴定其性别,采用相关与通径分析方法分析不同性别中国蛤蜊表型性状对软体重的作用效果,为中国蛤蜊人工繁育和品系选育提供理论依据和测度指标。结果表明：不同性别中国蛤蜊的形态学指标无显著差异(P>0.05);两者各数量性状之间的相关关系均达到极显著水平(P<0.01);决定系数分析表明：不同性别中国蛤蜊影响软体重的主要表型性状并不相同;雌性中国蛤蜊,壳高对软体重的直接作用最大,是影响软体重的主要因素,壳高通过壳长的间接作用是影响软体重的次要因素;雄性蛤蜊的壳高对软体部重的直接作用大于活体重对软体重的直接作用,壳高通过活体重对软体重的间接作用是影响软体重的次要因素。剔除通径系数检验不显著的自变量,利用逐步回归的方法,建立了不同性别中国蛤蜊估计软体重的最优回归方程： ; ,回归方程分析表明回归关系均达到极显著水平(P<0.01)。     

Maize participatory breeding in Portugal: Comparison of farmer's and breeder's on‐farm selection

“VASO” is a Portuguese participatory maize breeding project (1984), where several maize landraces such as “Pigarro” have been selected both by a farmer's (phenotypic recurrent selection) and a breeder's approach (S2 lines recurrent selection). The objectives of this study were to determine the phenotypic and genotypic responses to participatory selection using these two different approaches, to clarify to which extent both selection methods preserve genetic diversity, and conclude what is the preferred method to apply in sustainable farming systems. The results, obtained via ANOVA, regression analyses and molecular markers, indicate that for both selection methods, genetic diversity was not significantly reduced, even with the most intensive breeder's selection. Although there were some common outputs, such as the determinated versus indeterminated ears, cob and ear weight ratio per ear and rachis 2, specific phenotypic traits evolved in opposite directions between the two selection approaches. Yield increase was only detected during farmer selection, indicating its interest on PPB. Candidate genes were identified for a few of the traits under selection as potential functional markers in participatory plant breeding.     

A comprehensive multisite recurrent selection strategy in perennial ryegrass

Summary As the seed market for forage grasses in France is rather limited, proposed varieties should have a broad adaptation to a range of different environment. Therefore a comprehensive strategy of multisite recurrent selection has been devised for perennial reyegrass. It is based on an experimental cooperative network between National Institute for Agronomic Research (INRA) and private companies. A pragmatic approach has been retained that gives a compromise between theoretical and practical considerations. The method is illustrated by results from a breeding population consisting of 33 half-sib families derived from a local germplasm. Family selection with an intensity of 30% was applied to yield and persistence data from sward plot trials. The strategy was based on a multisite index where trait x location combinations are considered as different traits and given equal economic weights. Improvements of 10–15% were expected for summer-autumn production and persistence. For spaced plant nursery traits, a subset of locations was chosen according to a multiplicative model decomposition of G x E interaction, where a 10% mass selection was practised. This leads to interesting progress on crown rust tolerance, growth scores, leafiness and persistence. Moreover, the expected indirect responses from selection on spaced plant traits to sward traits and vice-versa are almost all favourable. As significant improvements are expected for most traits in all locations, this programme should allow to increase the general adaptation of ryegrass varieties for France.     

Comments on the Calculation of Mean Harvest Indices

The harvest index Z is defined, for example for cereals, as the ratio between grain yield X and total yield Y: Z = X/Y. For individual measurements x_i of X and y_i of Y the individual harvest index is calculated by z_i= x_i/y_i. These individual measurements i are based on N different experimental units (single plants, random samples from plots or total plots).
Mean harvest indices are commonly calculated either by     or by     where the means of X, Y and Z are denoted by , and respectively.
Both approaches     are, in general, different. But, in this paper it is shown that for most situations which may occur in the field of practical applications in agronomy and plant breeding both procedures will lead to nearly identical results. Only in some special situations the two results differ significantly. These conditions are investigated and explicitly given.
Some explicit formulae (approximations) for the calculation of mean harvest indices are derived and discussed.
Finally, all the theoretical investigations and results are demonstrated and applied to a numerical example of winter-rapeseed data.     

Root characteristic system improves drought tolerance in orchardgrass

Plant genotypes with higher drought tolerance through improved root characteristics are poorly studied in orchardgrass. In the current research, 30 orchardgrass genotypes were polycrossed and the resulting half‐sib families evaluated under both normal and water stress environments. Under water stress conditions, values for most root traits decreased at 0–30 cm soil depth, while at 30–60 cm depths, the root length (RL), root area (RA), root volume, percentage of root dry weight (RDW) and the ratio of root to shoot were increased. We identified drought‐tolerant genotypes with a high combining ability for root characteristics and a high yield potential. High estimates of heritability as well as genetic variation for root traits indicated that phenotypic selection would be successful in order to achieve genetic progress. Indirect selection to improve dry matter yield was most efficient when selecting for RL and RDW under water stress conditions. Significant associations between a drought tolerance index and RL, RA and root volume confirmed the importance of these traits in conferring drought tolerance of orchardgrass.     

Recurrent selection for seed quality traits in an opaque-2 maize population

Summary The aim of this research was to evaluate the response to phenotypic recurrent selection for four seed quality traits, i.e. protein content, dye binding capacity, tryptophan content, and specific weight, in a modified opaque-2 population of maize (Zea mays L.). Changes in other agronomic traits were also studied. Four selection cycles, using as selection criterion an index constructed from the four seed quality traits, were completed on an individual plant basis. The material from each cycle and from testerosses of each cycle with a homozygous opaque-2 tester was grown for two consecutive years to evaluate the progress due to selection. The results showed that four cycles of recurrent selection induced sizeable variations among cycles for all selected traits. The rate of progress for the four seed quality traits was nearly linear. Further-more, theldata show that improvement in seed-protein related traits had no negative effects on grain yield and kernel weight, when evaluated as the mean performance of testerosses. There was also no appreciable alteration in the other agronomic traits caused by selection for seed quality traits.     

表型轮回选择和混合选择改良小麦群体效应的研究

在吴兆苏等(1984)创建的小麦基础群体中,采用不同的选择方案,对不育株和可育株分别进行两轮选择。结果表明两轮选择显著地降低了可育株和不育株群体的株高。可育株群体株高的下降速率大于不育株群体。单株产量和单株穗数没有得到显著的改良。相关性状穗长、千粒重等出现负向间接选择效应。轮回选择通过选株间的互交,维持了不     

Quantitative genetic analysis of flowering time in the Davis Population of gerbera

Summary Phenotypic and genetic correlations of flowering time (FT) with cut-flower yield (Y) were estimated from six generations of the Davis Population of gerbera (Gerbera hybrida, Compositae). The phenotypic correlation was –0.34; the genetic correlation was –0.47 when estimated from ANOVA of a NCII design and –0.72 when estimated from parent-offspring analysis. An indirect selection model was constructed to assess the efficiency of indirect selection for Y using FT as a marker. This model includes population size and generation time as variables because they differ for FT and Y. The results indicate that indirect selection will be more efficient than direct selection.Correlations of FT with flower quality traits, including scape length (SL), flower diameter (FD), scape dry weight (SDW) and flower dry weight (FDW), were also estimated. FT was phenotypically independent of these traits. However, statistically significant estimates of genetic correlation indicate that FT may be correlated with flower quality traits. Thus, indirect selection on FT to increase Y may result in undesirable correlated responses for flower quality.     

On the Variability of Harvest Indices

The harvest index Z is defined, for example for cereals, as the ratio between grain yield X and biological yield Y: Z = X/Y. For many purposes the variance of Z is of major interest. In this paper several approximations for this variance are derived and their accuracy was investigated. These explicit formulae depend on some characteristics (means, variances or coefficients of variation, covariances or correlations) of the component variables grain yield X and biological yield Y. It is shown that for most practical applications the approximation v²z = v²x + v²y - 2rv_xv_y provides a sufficient accuracy for numerical calculations (v_x v_y and v_z are the coefficients of variation for grain yield X, biological yield Y and harvest index Z and r denotes the correlation coefficient between X and Y). Some conclusions on the relations between v_x, v_y and v_z are derived.
Finally, all the theoretical investigations and results are demonstrated and applied to a numerical example of winter-rapeseed data.     

基于表型性状构建中国花生地方品种骨干种质

中国花生地方品种遗传多样性丰富,是花生新品种选育的重要亲本来源。本研究以种质库保存的2741份地方种质为材料,基于种植区划和植物学类型分组,平方根法确定取样量,组内按13个表型数据进行UPGMA聚类分析,类内随机取样,构建骨干种质。利用t检验、F测验、卡方测验、极差、表型保留比例、表型相关性等对骨干种质代表性进行检验和评价;并利用主成分分析和直方图对骨干种质进行确认。结果表明,构建了包含259份种质的中国花生地方品种骨干种质,占全部种质的9.4%,包括多粒型14份、珍珠豆型85份、龙生型42份、普通型103份、中间型15份。在P 0.05概率条件下,骨干种质13个性状的均值、方差、变异系数、香农指数与全部种质无显著差异,且保留了全部种质的分布范围、表型保留比例和表型相关性;二者的植物学类型组成和生态分布是一致的,具有相似的遗传结构和分布频率。建立的骨干种质很好地代表了全部种质的遗传变异和群体结构,可为花生种质创新和优异等位基因发掘奠定良好的基础。     

利用回交导入系定位干旱环境下水稻植株水分状况相关QTL

日益严重的水资源危机使水稻的耐旱育种尤为迫切, 干旱环境下较高的植株水分含量有助于提高或维持作物产量的稳定性, 挖掘与耐旱性密切相关的分子标记有助于提高耐旱品种的选育效率。从供体Lemont (粳稻)导入到特青(籼稻)背景的254个高代回交导入系中筛选出覆盖供体全基因组的55个回交导入系, 采用PVC管栽培, 分析了干旱(胁迫)条件下水稻植株水分状况相关性状与籽粒产量、生物量的相关性并定位了相关QTL。研究表明, 植株水分相关性状(相对含水量、叶片水势、渗透势、卷叶度)均与籽粒产量显著相关。检测到7个相对含水量QTL, 7个叶片水势QTL, 5个渗透势QTL及5个卷叶QTL; 另检测到5个产量QTL, 7个生物量QTL。分析发现, 不仅QLwp5、QLr5、QRwc5和QY5同时分布在RM509~RM163区域, 且该区域还分布有对水分环境表现稳定的产量QTL(QGy5), 效应方向一致, 从遗传学角度解释了籽粒产量与水分相关性状之间的显著相关性。另外, QLr5、QRwc5、QY5、QLr2、QLr7、QLr8、QLr9、QRwc3、QRwc4a、QRwc12及QY7 等11个QTL曾在不同遗传背景群体中被检测到, 它们控制相同目标性状。研究认为RM509~RM163区域及QLr2、QLr7、QLr8、QLr9、QRwc3、QRwc4a、QRwc12和QY7所分布的染色体区域对水分环境或者遗传背景相对稳定, 在水稻分子标记辅助选择(MAS)耐旱育种实践中有较重要利用价值。     

Responses in Agronomic Traits Associated with Three Recurrent Selection Regimes for Groat-Oil Content in Oat*

Crop strains with high values for the selected trait but unacceptable agronomic characteristics are not useful as varieties. In this study, we determined whether selection for groat-oil content in oat (Avena sativa L.) via three recurrent selection regimes caused associated changes in 10 agronomic traits. Random lines of each cycle of selection of each regime were evaluated in a replicated field experiment at two locations. Biomass, grain yield, groat yield, and test weight decreased in all three regimes. Seed weight and plant height decreased in two regimes, and groat fraction in one. Oil yield increased in two regimes and decreased in the other. Plants headed earlier in one and later in another regime over cycles of selection. No changes in harvest index occurred. Heritabilities and genetic variances were relatively high for all traits in each regime. Factor analysis of the phenotypic correlation matrices indicated that simultaneous increases in grain yield and in groat-oil content are possible, that continuous selection for groat-oil content decreases groat fraction and test weight, and that seed weight is strongly and negatively associated with groat-oil content. A new recurrent selection regime for increasing groat-oil content of oat that may overcome the negative responses of agronomic traits was proposed.     

Use of genomic and phenotypic selection in lines for prediction of testcrosses in maize II: grain yield and plant traits

Plant breeders have been trying to predict the performance of hybrids based on their parental performance. One application of molecular markers is its use in selection. The objectives were to map quantitative trait loci (QTL) and verify its congruence in maize lines and in their testcrosses and verify the possibility to select testcrosses from the predicted means of the lines by using information from markers. Two-hundred and fifty six lines and the testcrosses of these lines with two testers were evaluated in six environments, considering grain yield, plant lodging, days to anthesis and silking, anthesis-silking interval, plant and ear height and ear placement. QTL were mapped in the lines and in testcrosses and the predicted means of the lines were computed based on QTL effects and in all markers of the genome. The congruence of QTL detected in the lines and testcrosses were small for all traits. The correlations between the predicted means of the lines and the phenotypic means of the testcrosses ranged from low for grain yield to moderate for cycle and stature traits. The highest coincidences of the lines and selected testcrosses were observed for cycle and stature traits and the lowest for grain yield. Even by using molecular markers information, it is only possible to predict the testcrosses performance from the lines information to less complex traits and with reduced dominance effect. For complex traits and with pronounced dominance effect, information of markers must be obtained directly in the testcrosses, so they can be used for selection.     

彭泽鲫生长性状的遗传参数估计

为深入了解彭泽鲫(Carassius auratus var. pengzesis)生长性状的遗传变化规律,并以此为基础制定彭泽鲫合理的育种方案。以九江市水产研究所培育的彭泽鲫23个全同胞家系的个体为实验材料,测量这些家系中1冬龄个体的生长性状（总长、体长、体高、体厚、体重）,并用动物模型对数据进行遗传分析。结果表明：彭泽鲫1冬龄总长、体长、体高、体厚、体重5个性状的遗传力分别为0.64±0.17、0.51±0.16、0.79±0.18、0.57±0.16、0.65±0.17,均属于高水平遗传力。这5个性状之间表型相关(0.79~0.94)和遗传相关(0.95~1.00)均较高。采用个体选育或者个体选育与家系选择法相结合的方法对彭泽鲫进行遗传改良都能获得较好的遗传进展,且对某一生长性状进行选育时,其他性状也会得到间接改良。     

Marker-assisted selection for complex trait in common bean (Phaseolus vulgaris L.) using QTL-based index

A procedure was developed for marker-assisted selection of complex traits for common bean (Phaseolus vulgarisL.) using an index based on QTL-linked markers and ultrametric genetic distances between lines and a target parent. A comparison of the mean seed yields of the top five lines selected by different schemes demonstrated that the highest yielding group was selected on the basis of a combination of phenotypic performance and a high QTL-based index,followed by groups identified by a high QTL-based-index, conventional selection,and a low QTL-based-index. This study demonstrated a simple way to use information obtained from QTL studies to make selection decisions. The study also showed that the use of the QTL-based-index in conjunction with the ultrametric genetic distance to the target parent would enablea plant breeder to select lines that retain important QTL in a desirable genetic background. Therefore, this type of MAS would be expected to be superior to the phenotypic selection. This revised version was published online in August 2006 with corrections to the Cover Date.     

在干旱和正常水分条件下玉米穗部性状QTL分析

穗部性状与产量密切相关,因此对其进行遗传剖析可为玉米高产育种提供理论基础,尤其是对干旱胁迫下的稳产有重要意义。本研究以玉米骨干亲本黄早四分别与自交系掖478和齐319进行杂交,构建了两套F_2:3群体(分别记为Y/H和Q/H)。在正常水分灌溉和干旱胁迫下对穗长、穗粗、轴粗、穗行数、行粒数、穗粒重和穗重等7个穗部性状进行了表型鉴定,采用基于混合线性模型的单环境分析和相同处理水平的联合分析方法进行了QTL分析。结果表明,在干旱胁迫下,2个群体的亲本及F_2:3家系的各性状值均低于正常水分条件,且穗粒重与穗长、穗重、穗粗呈正相关。在干旱胁迫下和正常水分条件下,通过两种检测方法共定位到75个玉米穗部性状QTL,其中Y/H群体共定位了20个QTL,分布在第1、第2、6、第5、第7、第10染色体上;Q/H群体共定位了55个QTL,分布在第2、第3、第4、第5、第6、第7、第9、第10染色体上;但是在干旱条件下两群体分别只检测到4个和19个QTL,明显低于正常水分条件下检测到的QTL数目。通过联合分析只检测到3个QTL与环境发生显著互作和6对QTL存在上位性互作效应,说明玉米穗部性状的遗传基础较为复杂。同时还发现,Y/H群体在正常灌溉与干旱条件下检测到2个一致性的QTL,分别是qKRE1-5-1和qKRE1-7-1,对表型变异解释的变化范围是6.15%~19.48%;Q/H群体检测到3个一致性QTL,分别是qKRE2-5-1、qGW2-10-1和qKRE2-3-1,对表型变异解释的变化范围是7.14%~16.65%,说明这些QTL受环境影响较小,能够稳定遗传,可以作为分子标记辅助选择的候选区间应用于玉米穗部性状抗旱性改良。