Estimating heritability of wool shedding in a cross‐bred ewe population

Low wool prices and high production costs in sheep systems have resulted in the introduction of genotypes that shed wool into flocks to reduce shearing costs. Wool shedding occurs naturally in a few breeds and can be incorporated by cross‐breeding. The opportunity to enhance shedding through selection depends on the extent of genetic variability present. Genetic and environmental parameters for wool shedding for ewes from a three‐breed composite population were estimated using Bayesian inference. Data on 2025 cross‐bred ewes, including 3345 wool shedding scores (WS) and 1647 breeding weight (BW) records, were analysed using bivariate and, for WS, univariate animal repeatability models. Breeding weight was included to account for possible selection bias. Breeding weight was moderately heritable and highly repeatable with means of 0.317 and 0.724, respectively. Under both models, WS was found to be moderately heritable and repeatable with means of 0.256 and 0.399, respectively. Based on a cumulative link model and contingency table analysis, age and reproductive activity influenced the extent of WS (p < 0.05). Given that WS is moderately heritable, selective gain in WS can be achieved.     

Breeding for drought tolerance: Direct selection for yield, response to selection and use of drought-tolerant donors in upland and lowland-adapted populations

Drought is the most important constraint reducing rice yield in rainfed areas. Earlier efforts to improve rice yield under drought mainly focused on improving secondary traits because the broad-sense heritability (H) of grain yield under drought stress was assumed to be low, however gains in yield by selecting for secondary traits have not been clearly demonstrated in rice. In present study, the effectiveness of direct selection for grain yield was assessed under lowland reproductive stage stress at Raipur in eastern India and under upland reproductive stage drought stress at IRRI. The selection under severe stress (in both upland and lowland trials) resulted in greater gains under similar stress levels (yield reduction of 65% or greater under stress) in evaluation experiments than did selection under non-stress conditions, with no yield reduction under non-stress conditions. We observed similar H of grain yield under stress and non-stress conditions, indicating direct selection for yield under drought will be effective under both lowland and upland drought stresses. None of the secondary traits (panicle exsertion, harvest index, leaf rolling, leaf drying) included in our study showed a higher estimate for H than grain yield under stress. Secondary traits as well as indirect selection for grain yield under non-stress situation were predicted to be less effective in improving yield under drought in both lowland and upland ecosystem than direct selection for grain yield under the respective stress situations. The low, but positive values observed for genetic correlation (r_G) between yield under stress and non-stress indicated that it is possible to combine drought tolerance with high-yield potential but low values also indicated that selection for grain yield needs to be carried under stress environments. The study also indicated that under lowland drought stress, the use of highly drought-tolerant donors, as parents in crosses to high yielding but susceptible varieties resulted in a much higher frequency of genotypes combining high-yield potential with tolerance than did crosses among elite lines with high-yield potential but poor tolerance. Breeding strategies that use drought-tolerant donors and that combine screening for yield under managed drought stress with screening for yield potential are likely to result in the development of improved cultivars for drought-prone rainfed rice producing areas.     

Stand establishment and early field vigour variation in a tropicalised shrunken-2 maize population

Low field emergence and early field vigour are major problems in shrunken-2 maize (sh-2). The genetic variability for stand-ability and early field vigour in a shrunken-2 maize population previously improved for adaptability to a tropical environment was investigated using a Design I mating system in which 40 randomly sampled males were crossed to four randomly sampled plants that served as females. Plants of the 160 crosses, representing full- and half-sib relationships, were evaluated in four sets, each composed of 40 crosses derived from 10 males during two growing seasons. Experimental design was randomized complete block with three replications. Difference in Emergence Index (EI) was not significant between the two seasons. Emergence Percentage (E%), Emergence Rate Index (ERI), and early field vigour traits viz. vigour score and seedling height determined at 28 days after planting (DAP) were, however, significantly (P < 0.05–P < 0.01) better in the first growing season. For all traits, the ‘female/male’ item was significant (P < 0.01) while ‘male’ was mostly non-significant. ‘Season × female/male’ interaction was significant for stand establishment traits but not for early field vigour traits. Averaged over all traits, dominance variance was 8.2 times higher than additive variance. Genetic variation for stand establishment and early field vigour in the tropicalised shrunken-2 maize population would be best exploited through the development of inbred lines, hybrids and synthetics. Broad-sense heritability was 53.0% for E%, 36.0% for EI, 33.0% for ERI, 71.5% for vigour score and 90.0% for seedling height. One hundred-seed weight ranged between 82.0 and 182.0 mg but correlation coefficients between seed weight on one hand, and E%, EI, ERI, vigour score and plant height on the other hand, were low (mostly <0.30) and, in general, non-significant. Emergence percentage had the highest average genotypic correlation value with the other traits studied (Mean Absolute Value = 0.71 in the first season and 0.45 in the second season). Emergence percentage, determined 10 days after planting, thus has potential for use as a selection index for stand establishment and early field vigour.     

极大似然法探测主基因的效能

采用Monte Carlo模拟数据和极大似然法探测F2群体主基因(MG). 研究了遗传力、显性比和样本容量三因素对探测F2群体MG的影响. 结果表明: 1) 在主基因的被发现率上, 三因素的影响力为: 遗传力>样本容量>显性比. 当遗传力较小时, 如0.3, 即使样本容量高达1000, 其发现能力也仅有51.63%; 当遗传力大于0.5时, 样本容量大于300, MG     

野牛草叶片枯黄程度及叶片颜色的遗传参数测定

选用8个性状稳定的野牛草材料,采用不完全双列杂交试验设计,配制了16个杂交组合,分析了叶片枯黄程度、枯黄过程中叶片颜色遗传力及配合力.结果表明:0号和62号材料的叶片颜色的一般配合力较高,利用它们作亲本较易选出枯黄过程中叶片颜色较好的野牛草材料;叶片枯黄程度的一般配合力较小,但其特殊配合力较高;叶片颜色的遗传力为72.89%.     

杉木无性系生长的遗传控制和早期选择初探

对两片包括１８个和１７个无性系试验林历年树高和胸径作了测量,分析了树高和胸径历年位次,表型和遗传相关,遗传力、遗传和环境方差随年龄增高的时间趋势,历年树高和胸径与最后一年测量中所计算的单株材积的表型和遗传相关等。看到无论树高还量胸径,早－晚龄的表型和遗传相关都是极显著的,但少数生长型和生长动态模式偏离常态的无性系影响着这些在树龄间的稳定性。认为杉木的适宜早期选择年龄在４￣６ａ生时,但最好从３ａ后开     

奥帕克-2背景下玉米蛋白质含量的配合力分析

本文对奥帕克 - 2背景下玉米蛋白质含量的配合力和遗传参数进行了研究 ,研究表明 ,①一般配合力对杂交种蛋白质含量的作用比特殊配合力更重要 ,培育高蛋白高赖氨酸玉米杂交种 ,应重点选择一般配合力高的自交系作亲本 ②蛋白质含量的遗传力较高 ,加性方差明显大于非加性方差 ,这说明玉米蛋白质含量和玉米蛋白质含量的杂种优势主要受加性基因影响 ,可在早代进行选择     

甘蓝型油菜芥酸含量的基因分析

【目的】芥酸含量是油菜非常重要的品质性状,研究芥酸含量的遗传模式为低芥酸和高芥酸育种提供指导。【方法】应用多世代联合分析数量性状主基因和多基因混合遗传的统计方法,分析了甘蓝型油菜组合1141B×垦C1的5个世代——亲本P1,P2,F1,F2和F2﹕3家系材料芥酸含量的遗传效应。【结果】分离世代F2及F2﹕3家系芥酸含量次数分布均呈混合的正态分布,符合主基因＋多基因的遗传特征;E-1模型为芥酸含量的最适合性模型,即芥酸含量遗传是由2对加-显-上位性主基因+加-显多基因控制的。2对主基因加性效应值da、db分别为-16.26和-2.83,表明亲本1141B中主基因位点上的等位基因降低芥酸含量,而亲本垦C1中的等位基因增加芥酸含量。显性效应值ha、hb分别为10.93和-4.71,第一对主基因加性效应值和显性效应绝对值均高于第二对主基因显性效应值。因此,2对主基因控制芥酸含量,第一对主基因控制的芥酸含量高于第二对主基因。该组合2对主基因间互作效应明显,加性与加性效应互作值（i）为-1.21,显性与显性互作值（l）为-3.27。第一对主基因的加性效应与第二对主基因的显性效应互作值（jab）为5.70,第二对主基因的加性效应与第一对主基因的显性效应互作值（jba）为-7.25。其芥酸含量还受多基因控制,多基因加性效应（[a]）值为-0.08,多基因显性效应（[d]）值为2.32;F2的主基因遗传力和多基因遗传力分别为50.00%和16.62%;F2﹕3的主基因遗传力和多基因遗传力分别为89.70%和6.01%。【结论】芥酸含量是由2对加-显-上位性主基因+加-显多基因控制的,第一对主基因控制的芥酸含量高于第二对主基因。低芥酸和高芥酸育种中在F2﹕3家系进行选择效率较高。     

中国南瓜主要性状配合力与遗传力分析

以12个中国南瓜高世代自交系为试验材料，采用NCⅡ设计配制36个杂交组合，分析了12个数量性状的遗传力、配合力。结果表明：在一般配合力上，6个母本的优劣顺序为Q1〉Q3〉Q4〉Q6〉Q2〉Q5，6个父本的优劣顺序为B1〉B3〉B5〉B4〉B2〉B6；亲本的一般配合力与其在杂交组合中的特殊配合力之间无必然联系；主蔓长度、可溶性固形物含量、干物质含量的狭义遗传力较高，早代选择效果较好；节间长度、单果质量、多糖含量、β-胡萝h素含量、维生素C含量、果实纵径、果实横径的狭义遗传力较低，活合存中高代讲行进择.