人工老化对老芒麦醇溶蛋白遗传完整性的影响

以4份老芒麦种质为试验材料,对其人工加速老化后种子活力及其醇溶蛋白的遗传完整性进行了分析。结果表明,随着老化时间的延长,老芒麦种子的发芽率、发芽势、发芽指数和活力指数逐渐降低,其中供试材料的发芽势、活力指数均随发芽率的下降与对照呈极显著差异。与未老化的种子相比,人工老化后种子醇溶蛋白的遗传完整性发生了明显变化。在发芽率降低为55%及以下,育成品种川草1号、农牧由最初的2、3种谱带类型减少为仅表现1种谱带类型,而2份野生材料较对照分别丢失了2~3种谱带类型。老芒麦醇溶蛋白谱带的遗传多样性指数分析结果也显示,当发芽率低于55%时,4份材料的等位基因数均与对照间呈显著差异。因此,建议60%~70%作为老芒麦繁殖更新的参考发芽率标准,最低临界值为55%。     

干旱锻炼对B73自交后代当代干旱胁迫记忆基因表达及其启动子区DNA甲基化的影响

植物可能会记住已有的逆境刺激,且这种记忆可以跨代遗传。为研究G₀代干旱锻炼对玉米B73 G₁代当代干旱胁迫记忆基因表达的影响及其启动子区DNA甲基化的影响,实验用20%PEG-6000模拟干旱条件,选取在玉米和拟南芥已知的当代均具有干旱胁迫记忆特性的6个基因为研究对象,利用qRT-PCR技术分析这些基因的表达水平变化,并进一步利用重亚硫酸盐测序PCR技术分析在2个世代中表达差异最显著基因启动子区的DNA甲基化率变化规律。结果表明:干旱胁迫上调了6个当代胁迫记忆基因的表达水平,均呈+/+模式,同当代多次干旱胁迫时表达水平变化趋势一致,且G₁代表达水平显著高于G₀代;干旱胁迫降低了GRMZM2G₀88396基因启动子区的甲基化水平,检测区1两个世代DNA甲基化率的降低主要由CHG和CHH甲基化水平降低造成,检测区2 DNA甲基化率的降低主要是由CG和CHH甲基化水平降低造成,G₁代2个检测区总胞嘧啶甲基化率均显著低于G₀代,说明G₀代干旱锻炼使G₁代GRMZM2G₀88396基因启动子区的DNA甲基化修饰产生了可遗传的变异,它可能直接参与GRMZM2G₀88396基因的表达。     

干旱锻炼对B73自交后代当代干旱胁迫记忆基因表达及其启动子区DNA甲基化的影响

植物可能会记住已有的逆境刺激,且这种记忆可以跨代遗传。为研究G₀代干旱锻炼对玉米B73 G₁代当代干旱胁迫记忆基因表达的影响及其启动子区DNA甲基化的影响,实验用20%PEG-6000模拟干旱条件,选取在玉米和拟南芥已知的当代均具有干旱胁迫记忆特性的6个基因为研究对象,利用qRT-PCR技术分析这些基因的表达水平变化,并进一步利用重亚硫酸盐测序PCR技术分析在2个世代中表达差异最显著基因启动子区的DNA甲基化率变化规律。结果表明:干旱胁迫上调了6个当代胁迫记忆基因的表达水平,均呈+/+模式,同当代多次干旱胁迫时表达水平变化趋势一致,且G₁代表达水平显著高于G₀代;干旱胁迫降低了GRMZM2G₀88396基因启动子区的甲基化水平,检测区1两个世代DNA甲基化率的降低主要由CHG和CHH甲基化水平降低造成,检测区2 DNA甲基化率的降低主要是由CG和CHH甲基化水平降低造成,G₁代2个检测区总胞嘧啶甲基化率均显著低于G₀代,说明G₀代干旱锻炼使G₁代GRMZM2G₀88396基因启动子区的DNA甲基化修饰产生了可遗传的变异,它可能直接参与GRMZM2G₀88396基因的表达。     

大龙虎泡野生日本沼虾遗传多样性分析

为了深入了解本地日本沼虾的遗传特性,为育种选育提供理论支撑,利用微卫星分子标记技术,对大龙虎泡日本沼虾进行遗传多样性比较分析。结果显示,12个微卫星位点均属于高多态性位点(PIC>0.5);太湖2号养殖群体的等位基因数为4～11,有效等位基因为3.686 4～7.480 5,观测杂合度为0.318 2～0.833 3,期望杂合度为0.744 9～0.884 8;各位点的多态性为0.691 9～0.851 7,属于高遗传多样性的群体。大龙虎泡野生群体等位基因数为1～2,有效等位基因为1.00 0 0～2.000 0,观测杂合度为0.000 0～1.000 0,期望杂合度为0.000 0～0.517 2,各位点的多态性为0.000 0～0.375 0,属于遗传多样性较低的群体。2个群体均有7个位点显著偏离Hardy-Weinberg平衡,大龙虎泡野生群体另出现3个位点无法进行Hardy-Weinberg平衡检验。太湖2号养殖群体的7个位点表现出来的是杂合子缺失,大龙虎泡野生群体的7个表现的是杂合子过剩。分子方差分析显示,有36.15%(P<0.01)的遗传变异来源于群体间,而6...     

高粱微卫星分析中遗传完整性样本量的确定

采用微卫星分析高粱不同样本量对遗传多样性指数的影响,从而确定最佳样本量,为遗传完整性研究奠定基础。试验设置了10个样本量梯度,对群体的等位基因数目、有效等位基因数目、香农指数、观察杂合度、预期杂合度、多态位点百分数和稀有等位基因频率的变化趋势进行了分析。结果表明,10～40个样本量范围内,等位基因数目、有效等位基因数目、香农指数、多态位点百分数随着样本量的增大而增大;在40个样本量时,等位基因数目、有效等位基因数目和香农指数达到较高值,分别代表了100个群体98.5%的等位基因数、99.1%的有效等位基因数和98.5%的香农指数,之后样本量继续增加,各指标变化不显著。稀有等位基因频率在40个样本量以上,随着样本量的增加数值变化很小。以稀有等位基因频率、等位基因数、有效等位基因数和香农指数为多样性指标,在高粱遗传完整性研究中样本量大小的确定上达到一致性。因此,建议在用SSR技术对高粱进行遗传完整性分析时,样本量要选择40个单株以上。     

对热带玉米种质群体控制双亲混合选择适应性的评价

为评价控制双亲混合选择对1份非洲玉米种质合成基础群体AC₀主要性状适应性改良效果,利用联合方差分析和变异系数分析群体间性状变异程度。结果表明,改良群体AC₁和AC₂的株高分别比AC₀提高了8.60%和11.60%,差异达到极显著水平;穗位分别比AC₀提高了11.34%和16.18%,差异达到极显著水平;改良群体AC₁和AC₂的穗长与AC₀相比分别降低2.60%和提高1.57%,AC₁与AC₂间达到极显著水平;与AC₀相比,AC₁和AC₂穗行数分别提高了2.44%和1.12%,均未达到显著水平;与AC₀相比,AC₁和AC₂的秃尖长分别提高了0.75%和13.12%,均未达到显著水平。由以上可知,虽然控制双亲混合选择对热带种质产量性状早期改良进展较小,但随着改良的进行,群体多数性状的表型变异系数有所下降,但也有部分性状变异系数的变化幅度较小或有所增大,但控制双亲混合选择较好地保持了群体的遗传多样性。     

基于EST-SSR标记的天山云杉天然群体遗传多样性分析

本研究采用7对引物对新疆26个天山云杉群体中的945个样本进行了EST-SSR标记分析,揭示其遗传多样性。研究发现,新源和阜康等17个地区群体的基因多样性指数介于0.374~0.520之间;在新源和阜康的种群中发现的位点等位基因数表明海拔和等位基因多样性存在一定正相关关系。根据Hardy-weinberg平衡定律,基于EST-SSR标记的天山云杉天然群体的稀有等位基因频率没有出现偏离(Fis=-0.018),其中92.84%的遗传变异出现于群体内部。通过与其他云杉物种对比分析,表明天山云杉具有中度的遗传多样性水平;在新源、阜康地区发现了7个独有的等位基因。通过天山云杉群体的遗传多样性分析,为天山云杉种质资源的保护和遗传改良提供了实践参考。     

云南野生大蜜蜂(Apis dorsata)群体遗传多样性的微卫星分析

为了阐明大蜜蜂的群体遗传特征,评价云南地区大蜜蜂的遗传多样性,本研究利用14对微卫星引物对采自云南省的35群野生大蜜蜂进行了群体遗传变异检测和遗传多样性分析。在大蜜蜂群体中共检测到51个等位基因,平均等位基因数为3.642 9,平均有效等位基因数2.809 2,平均期望杂合度为0.573 0,平均多态信息含量为0.524 3。根据Nei’s遗传距离用UPGMA方法对35群大蜜蜂进行亲缘关系分析,结果聚为A,B,C,D共4个支系。结果表明云南大蜜蜂群体遗传多样性相对贫乏,分化程度较低。     

基于SSR标记的钱塘江中下游三角鲂4个放流苗种群体遗传多样性和遗传结构检测

为检测钱塘江中下游三角鲂放流苗种群体遗传多样性和遗传结构,采用毛细管电泳基因分型技术,基于9对荧光标记SSR引物对来自4个放流苗种群体的192尾样本进行扩增和基因分型测序。结果表明,各群体单个位点检测到的等位基因数Na均值为(20±2)～(24±2),有效等位基因数Ne均值为(10.76±1.51)～(13.66±1.33),其中余杭群体等位基因数Na和有效等位基因数Ne最大,建德和桐庐群体的这2项指标大体相当;4个群体Shannon’s信息指数I均值为(2.55±0.13)～(2.83±0.09);4个群体观测杂合度Ho均值为(0.83±0.08)～(0.94±0.03),期望杂合度He均值为(0.88±0.02)～(0.92±0.01),绝大多数位点表现出杂合子过剩;余杭、建德、桐庐、富阳各群体的私有等位基因数依次为54、9、15、17个;4个放流三角鲂苗种群体遗传多样性处于较高水平,部分群体出现了杂合子过剩和等位基因丢失现象。分子方差分析显示,98.7%的遗传变异来自群体内的个体间,1.3%遗传变异来自群体间,4个放流群体间遗传分化指数为0.013～0.017,遗传分化很小(0&...     

“神舟八号”搭载‘航恢173’种子的当代生物效应及SSR分析

水稻空间诱变的当代效应与地面其他常用的理化诱变方法存在较大差别,并且不同航天器的诱变效应往往也不尽一致。为了探明搭载“神舟八号”飞船的当代效应及其特征,以籼稻‘航恢173’种子经“神舟八号”搭载诱变当代(SP₁)为材料,考察其发芽率、苗高、成熟期株高、剑叶长和宽、主穗长和结实率等7个性状,探讨“神舟八号”搭载的当代效应,并与250 Gy ⁶⁰Co-γ射线辐照当代(G₁)和1% EMS诱变处理当代(E₁)进行对比;进一步利用位于水稻12条染色体的24个SSR标记对100个混合SP₁样品（300个单株）进行变异检测,以期从分子水平了解“神舟八号”搭载的诱变效应。结果表明,与对照相比,SP₁的发芽率、主穗结实率分别显著和极显著下降,而其余5个性状差异不显著;对比分析表明,与“神舟八号”搭载对植株后期生长无明显影响不同的是,G₁和E₁的植株其后期生长受到促进,导致G₁、E₁和SP₁在株高、剑叶长和宽上均存在显著或极显著差异。SSR座位的扩增结果表明,仅SSR标记RM267在1个样品中检测到明显的变异条带,变异频率约为0.014%。     

Comparison of random bulk population and single-seed-descent methods for lentil breeding

Summary Three lentil (Lens culinaris Medic.) populations were advanced from the F₂ to the F₄ generation by singleseed-descent (SSD) and bulk-population (BP) breeding methods and used to compare the relative efficiency of the methods for maintaining genetic variation and selection opportunities.SSD maintained more genetic variation (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaaiaacaqabeaadaqaaqaaaOqaaiqbeo8aZzaaja% Waa0baaSqaaiaadEgaaeaacaaIYaaaaaaa!3B04!\[\hat \sigma _g^2 \]) in 15 of 21 comparisons of characters that were made. Genetic variances were significantly higher with SSD for plant height, days to maturity and yield in population 1; height of lowest pod in population 2; and days to blooming, height of lowest pod, plant type, and yield in population 3. SSD-derived populations had 10, 9, and 13% more erect lines in the three populations, respectively, when compared to the same populations advanced by BP. The BP method maintained 14, 2, and 4% more taller types in the three populations, respectively, and 16 and 33% more segregants that carried their pods higher from the ground. This indicated a reduced frequency of short plants with low flowers as a result of natural selection operating within BP against less competitive short types. The SSD method is an efficient cost-saving method of advancing lentil populations and is recommended for lentil breeding.Scientific Paper No. 5478.     

Genetic analysis of low-temperature tolerance during germination in tomato, Lycopersicon esculentum Mill.

The genetic basis of low-temperature tolerance during germination of tomato seed was investigated using two approaches. First, a cold-tolerant (PI 120256) and a cold-sensitive tomato cultivar (UCT5) and their reciprocal F₂, F₃ and BC₁ progeny (total of 10 generations) were evaluated for germination at a low (11 ± 0.5°C) and a high (control) temperature 20 ±0.5° C) Weighted least-square regression analysis indicated that in the low-temperature treatment most of the variation resulted from additive genetic effects, and dominance and epistatic interactions were nonsignificant. Partitioning of the total genetic variance into those attributable to the effects of embryo, endosperm, testa and the cytoplasm indicated that additive effects of endosperm and embryo could individually account for 80% and 77% of the total variance, respectively. In the control treatment, greater than 60% of the variation could be explained by individual additive effects of endosperm or embryo and ? 27% of the variation could be explained by embryo dominance effects. Across generations, there was a positive correlation (r = 0.78, P < 0.01) between germination in the control and low-temperature treatments and there were no significant genotype × temperature interactions. The results indicate the presence of similar or identical genes with predominantly additive effects on germination under both low and high temperatures. In the second approach, the effectiveness of directional phenotypic selection to improve tomato cold tolerance during germination was evaluated by selecting (in an F₂ population of the same cross) the fastest germinating seeds under low temperature and comparing the germination of the selected F₃ progeny with germination of an unselected F₃ population. The results indicated that selection was highly effective and significantly improved germination performance of the progeny; a realized heritability of 0.74 was obtained for low-temperature tolerance during germination. It is concluded that in these tomato lines germination under low temperature is genetically controlled, with additivity being the major genetic component, and thus the trait can be improved by phenotypic selection.     

Recurrent Mass Selection for Reduced Seed Dormancy in Cuphea lanceolata and Cuphea laminuligera

Seed dormancy is a domestication barrier in certain Cuphea species. Between and within species variation has been observed for seed dormancy in agronomically promising Cuphea species, e.g., C. laminuligera Koehne and C lanceolata Ait. In tins note, we report on progress made in reducing seed dormancy through recurrent mass selection in the C. lanceolata population LN43 and LN78. The germination percentages of unselected LA12 and LN43 populations increased from 0.0 % to greater than 95.0 % following an after-ripening period of 20 weeks. We observed no germination percentage differences between unselected and selected LN43 populations following two cycles of selection. In contrast, there were highly significant differences between the unselected and selected populations of LA12 following two cycles of selection. The germination percentages of cycle zero (C₀) and cycle two (C₂) populations after-ripened 10 weeks were 10.7 and 92.7 %, respectively. After one cycle of selection in the C. Lanceolata population LN78, the germination percentage of seed after-ripened 10 weeks had increased from 1.3 % for the C_o population to 28.7 % for the C₀ population. In summary, mass selection greatly reduced seed dormancy in LA12 and LN78, but had no effect in LN43.     

Effects of high- vs. low-yield environments on selection for increased biomass yield in switchgrass

No information is available on the effects of different biomass yield environments on selection efficiency in switchgrass (Panicum virgatum L.) breeding improvement. This study was conducted to assess the effects of high- and low-biomass yield environments (HYE and LYE, respectively) on recurrent selection for general combining ability (RSGCA) in a lowland population of switchgrass (NL-94). The top 14 of 65 NL-94 C₀ parent plants were selected based on biomass yield of half-sib (HS) progeny tested for one post-establishment year under HYE and LYE conditions. Nine of the 14 C₀ parent plants were the same based on HS performance under HYE and LYE. Selected plants were intercrossed to produce NL-94 HYE and NL-94 LYE C₁ populations. One hundred and twenty-five HS C₁ progeny families (60 NL-94 HYE and 65 NL-94 LYE) were evaluated for biomass yield for 3 years (2002–2004) under HYE and LYE conditions. The HYE produced about 2.5 times higher biomass yields than the LYE in both C₀ and C₁ HS progeny tests. Estimated additive genetic variance and predicted gains from selection (ΔG) were high in the C₁ populations indicating that RSGCA should achieve higher biomass yields. Mean biomass yields of C₁ HS families originating from the LYE protocol were significantly higher than those of families originating from the HYE protocol in both HYE and LYE performance tests, suggesting greater selection response under LYE in the C₀ population. The estimates of narrow-sense heritability ( ) and ΔG from the C₁ populations indicate that positive response to selection for biomass yield is possible in subsequent cycles of selection under either HYE or LYE, with a possible small advantage for HYE.     

利用海岛棉染色体片段导入系定位衣分和籽指QTL

以染色体片段导入系IL-15-5和IL-15-5-1构建的F2和F2:3分离群体,利用SSR标记对数量性状衣分和籽指QTL进行了定位。应用复合区间作图法分析两个组合的774个F2单株和F2:3家系衣分和籽指,检测到2个衣分的QTL,1个籽指的QTL。衣分QTLqLP-15-1在两世代中都被检测到,位于相同的分子标记置信区间JESPR152～NAU3040,置信的遗传距离分别为5.40cM和3.20cM;qLP-15-2只在F2:3中被检测到,位于分子标记NAU5302～NAU2901之间,置信的遗传距离为0.08cM。籽指QTLqSI-15-1在F2和F2:3中都被检测到,分别位于分子标记NAU2814～NAU3040和JESPR152～NAU3040,置信的遗传距离分别为6.70cM和5.70cM。利用染色体片段导入系能准确地定位产量组分的QTL,为棉花产量的分子设计育种奠定基础。     

Recurrent selection for yield in Glycine max using genetic male-sterility

Summary Recurrent selection, using genetic male sterility to facilitate intermating in Glycine max, was evaluated when selecting among individual space-planted S₀ soybean plants for three yield-related traits: 1) seed yield per se (YLD), 2) apparent harvest index (AHI), and 3) a selection index in which seed yield was regressed on maturity (REG). The original intermating population was a combination of the cultivar Century and two F₂ populations segregating for male sterility. The selection intensity through three cycles of selection was 20%. The YLD population increased in mean yield by 2.8±2.2 g plant^-1 cycle^-1 buf shifted significantly toward late maturity by 3.9±0.6 days cycle^-1. The AHI population decreased in yield by 4.4±2.6 g cycle^-1 while maturity shifted slightly earlier; there was very little change in AHI. The REG population increased in yield by 5.7±2.4 g plant^-1 cycle^-1 while shifting toward later maturity by only 0.8±0.5 day cycle^-1. We concluded that selection among S₀ plants in these populations, using the selection index of yield regressed on maturity, was affective in increasing single plant yields without causing a significant shift in maturity. Selecting for yield per se caused an unacceptable shift toward late maturity and selection for AHI was ineffective for increasing yield or AHI.     

Research on the inheritance of seed dormancy in lettuce (Lactuca sativa L.) and selection for non-dormancy

Summary Inheritance of dormancy and the results of selection of non-dormant genotypes in segregating populations of lettuce were investigated. Diallel crosses were therefore carried out between two dormant (DOR) and two non-dormant (NDOR) cultivars. F₁, F₂ and F₃ populations were analysed.Environmental variation for dormancy usually was large. The mean germination time (GT) of F₁ seeds from the NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses was often intermediate to the GT of the NDOR and DOR parent. The mean GT of F₁ seeds from DOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses equalled the mean GT of the parents; the same applies for the NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]NDOR crosses. No differences between reciprocals were observed and neither were such differences found for F₂ populations. F₂ populations from DOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses showed no significant segregation of rapidly germinating seeds and in F₂ populations from NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses no accumulation of genes for long GT occurred. In F₂ populations from NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses usually 40–60% of the seeds germinated as rapidly as the seeds of the NDOR parents. Only one gene (D) could be responsible for the difference in dormancy behaviour of the DOR and NDOR cultivars. The behaviour of the F₃ lines from various NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses supports this hypothesis. A regression of F₃ means on the value of F₂ seeds for GT of various NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses showed that h²-narrow usually was rather high for most crosses implying that selection for non-dormancy can be carried out in F₂ populations.     

Comparison of QTLs for seed germination under non-stress, cold stress and salt stress in tomato

The purpose of this study was to examine whether rate of tomato seed germination under non-stress, cold-stress and salt-stress conditions was under similar genetic control by identifying and comparing quantitative trait loci (QTLs) which affect germination rate under these conditions. A fast-germinating accession (LA722) of the wild tomato species Lycopersicon pimpinellifolium Jusl. and a slow-germinating cultivar (NC84173, maternal and recurrent parent) of tomato (Lycopersicon esculentum Mill.) were hybridized and BC₁ and BC₁S₁ progeny produced. The BC₁ population was used to construct a linkage map with 151 restriction fragment length polymorphism (RFLP) markers. The BC₁S₁ population (consisting of 119 BC₁S₁ families) was evaluated for germination under non-stress (control), cold-stress and salt-stress conditions and the mean time to 50% germination (T50) in each treatment was determined. Germination analyses indicated the presence of significant (P < 0.01) phenotypic correlations between T50 under control and cold stress (r = 0.71), control and salt stress (r = 0.58) and cold stress and salt stress (r = 0.67). The QTL analysis indicated the presence of genetic relationships between germination under these three conditions: a few QTLs were identified which commonly affected germination under both stress- (cold-, salt- or both) and non-stress conditions, and thus were called stress-nonspecific QTLs. A few QTLs were also identified which affected germination only under cold or salt stress and thus were called stress-specific QTLs. However, the stress-nonspecific QTLs generally exhibited larger individual effects and together accounted for a greater portion of the total phenotypic variation under each condition than the stress-specific QTLs. Whether the effects of stress-nonspecific QTLs were due to pleiotropic effects of the same genes, physical linkage of different genes, or a combination of both could not be determined in this study. The results, however, indicate that the rate of tomato seed germination under different stress and nonstress conditions is partly under the same genetic control.     

Genetic relationships among cold, salt and drought tolerance during seed germination in an interspecific cross of tomato

Seed of BC₁ progeny of an interspecific cross between a slow germinating Lycopersicon esculentum breeding line(NC84173; maternal and recurrent parent) and a fast germinating L.pimpinellifolium accession (LA722) were evaluated for germination under cold stress, salt stress and drought stress, and in each treatment the most rapidly germinating seeds (first 2%) were selected. Selected individuals were grown to maturity and self-pollinated to produce BC₁S₁ progeny families. The selected BC₁S₁ progeny from each experiment were evaluated for germination rate in each of a non stress (control),cold-, salt- and drought-stress treatment, and their performances were compared with those of a non selected BC₁S₁population in the same treatments. Results indicated that selection for rapid seed germination in each of the three stress treatments was effective and significantly improved progeny germination rate under all three stress conditions. The results support the suggestion that same genes might control the rate of seed germination under cold, salt and drought stress. Furthermore, selection in each of the three stress treatments resulted in improved progeny seed germination rate under nonstress conditions, suggesting that genetic mechanisms that facilitate rapid seed germination under stress conditions might also contribute to rapid germination under nonstress conditions. In practice, therefore, selection for rapid seed germination under a single stress environment may result in progeny with improved seed germination under a wide range of environmental conditions. Furthermore, to improve germination rate under nonstress conditions, it might be more efficient to make selections under stress conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic structure of putative heterotic populations of alfalfa

Semi‐hybrids between genetically distant alfalfa (Medicago sativa subsp. sativa) populations may display heterosis whose extent is affected by the structure of genetic diversity across populations. This study aimed to assess the genetic diversity across three putative heterotic populations, one Italian, one Egyptian and one of semi‐erect germplasm from Eastern Europe, Canada and Spanish Mielga (EECM population). Each population was bred from ten parents after various selection cycles. Fifteen genotypes per population were characterized by 20 polymorphic SSR markers. The among‐population variance was over eightfold smaller than the average within‐population variance (2.05 vs. 17.24) and accounted for 10.6% of the total variation. G’_ST = .090 across markers indicated modest population differentiation. Various diversity measures, multidimensional scaling, and cluster analysis of the genetic structure indicated that the Italian population was more distant from the EECM population than the Egyptian one. The EECM and Egyptian populations were the most distant geographically and genetically. EECM displayed widest intrapopulation variation, accordingly to its constitutive geographical diversity. In conclusion, this study indicates modest genetic differentiation between alfalfa populations even for geographically distant germplasm.