Congruence of conventional and molecular studies to locate genes that control flavone synthesis in maize silks

The presence of maysin, a flavone glycoside, and its analogues in the silks of corn is an important defence against invasion of the ear by corn earworm in the southeastern USA. Three dent maize inbreds with high silk‐maysin concentrations were evaluated for chromosomal location of major genes controlling synthesis of three antibiotic chemicals by crossing them to a series of waxy‐marked chromosome 9 reciprocal translocations. The data indicated that genes for maysin and its analogues are probably present on the short arms of chromosomes 1 and 10, and long arms of chromosomes 5 and 8 for inbred line GT114, the short arms of chromosome 1 and 6, and the long arms of chromosome 5 and 8 for inbred line GE37, and the short arms of chromosomes 1 and 10, and the long arm of chromosome 4 for inbred line SC102. These results are in general agreement with other translocation studies on corn earworm injury to sweet corn inbreds and gene and restriction fragment length polymorphism marker studies to locate quantitative trait loci (QTL) for maysin synthesis, with the exception that QTL on chromosome 9 have been found to be strongly associated with flavone synthesis. The most significant concordance between conventional and molecular techniques for locating chromosome regions influencing synthesis of antibiotic chemicals from silks of high silk antibiosis sources is found for the short arm of chromosome 1. This region is the most likely one on which to place emphasis during the initial stages of transferring high‐maysin silks to elite inbred lines. A chromosome 1 marker plus at least one more from any chosen high‐maysin inbred source should be sufficient to transfer high maysin silks to other lines. Other markers may be needed for transfer of specific traits when recovering recurrent parent genome types in a backcrossing procedure.     

Inheritance of Maysin Content in Silks of Maize Inbreds Resistant to the Corn Earworm

Genetic information is needed on maysin, a compound in maize, Zea mays L., silks that is antibiotic to corn earworm larvae, Helicoverpa (formerly Heliothis) zea (Boddie), to assist in the process of breeding for resistance to this pest. This study was initiated to elucidate the inheritance of maysin content in the silks of a cross between two maize inbreds (GT114 and GT119) having resistance to the corn earworm. Reversed phase high performance liquid chromatography (HPLC) procedures were used to quantify the maysin concentration of silks from individual plants in the parent, F₁, F₂, and first backcross generations of the cross GT114 × GT119. A model assuming dominance at a single locus for low maysin content which is expressed only when a dominant modifier is present was proposed to explain the segregation ratios obtained in the F₂ and first back-crosses of GT114 × GT119. This model also provided a fit for maysin data previously generated from a cross between inbreds F6 and F44. Observations of selfed families in the backcross of GT114 × GT119 to the low maysin parent confirmed the two-locus model (one factor with dominance for low maysin expressed only when a modifier gene is also present) as a plausible explanation for inheritance of silk maysin in the cross. The process of selection for high maysin will be complicated somewhat by the presence of a gene which modifies the expression of dominance unless a method of easily identifying the gene, independent of maysin content, can be developed.     

玉米须采收时期对其功能成分、可收集产量及玉米产量的影响

为研究玉米须的最佳采收时期,以黑龙江省主栽玉米品种‘京农科728’和‘德美亚3号’为试验材料,于2017年和2018年进行玉米须采收试验,比较不同采收时期对玉米须的功能成分、可收集产量及玉米产量的影响。结果表明,玉米须总黄酮含量随吐丝日数延长呈下降趋势,总多糖含量呈增加趋势,不同采收期的玉米须总黄酮含量的变幅大于多糖的变幅。以雌穗套袋方式延迟授粉能有效促进玉米须生长,但显著降低果穗结实率。‘京农科728’和‘德美亚3号’套袋6天的玉米须产量比自然授粉条件下的采收产量分别提高79.2%和65.5%,穗粒数分别下降了57.9%和88.2%;套袋12天玉米须产量分别提高107.6%和74.8%,穗粒数分别下降96.1%和96.0%;套袋3天果穗结实未受影响。不同品种玉米须生长量差异显著,玉米须产量变异范围界于0.443~1.003 g/穗之间,平均值为0.655 g/穗,变异系数24.78%。为兼顾玉米产量与玉米须品质及产量,吐丝3~5天为玉米须最佳采收期。     

Control of preharvest aflatoxin contamination in maize by pyramiding QTL involved in resistance to ear-feeding insects and invasion by Aspergillus spp.

Several resistance sources and resistance mechanisms to aflatoxin formation and corn earworm (Helicoverpa zea Boddie) damage to maize (Zea mays L.) have been identified. Based on this knowledge, experiments were initiated toward achievement of the following objectives: (1) to confirm earlier determinations on resistance traits of germplasm sources and to identify quantitative trait loci (QTL) associated with each of the traits, and (2) upon estimation of the degree of QTL effects on each trait, to generate a maize population, with chemical and physical resistance to Aspergillus spp. and ear-feeding insects, for inbred development. A 2-year field experiment to evaluate selected genotypes inoculated with A. flavus and infested with corn earworm revealed that significant variation exists among the genotypes for aflatoxin contamination and corn earworm damage. The protection of maize ears against aflatoxin contamination was primarily dependent on resistance to fungal infection and ear-feeding insects, and excellent husk coverage and tightness. A major QTL (p1) identified on chromosome 1S had effects of 54.0, 42.1, and 28.3% on the phenotypic variability for concentrations of silk maysin, 3′-methoxymaysin+apimaysin, and chlorogenic acid, respectively. Markers/QTLs for husk phenotypic traits and total aflatoxin concentrations have been determined, but more detailed mapping of these chromosomic regions will be necessary to locate precise markers/QTLs for husk traits and aflatoxin production. Realizing the complexity of the Aspergillus–aflatoxin-maize system and the factors affecting aflatoxin contamination, we are directing our program toward marker-assisted breeding to enhance or improve general genetic resistance to ear-feeding insects and invasion by Aspergillus spp.     

Antibiosis to Corn Earworm [Helicoverpa zea (Boddie)] by Vegetable Soybean Cultivars

Six cultivars of vegetable sovbean ( Glycine max [L.] Merr.) were evaluated in the laboratory for relative levels of antibiosis to corn earworm ( Helicoverpa zea [Boddie]). The cultivars evaluated were Fuji, Kim, Oakland, Peking, Sanga , and Toano. One plant introduction (PI 229.358) having known resistance to corn earworm and Essex , a commercial cultivar, were used as check plants. The biological data for antibiosis in a series of tests included larval weights. The results showed that cultivars Sanga, Peking , and Oakland were comparatively more susceptible while cultivars Fuji, Kim , and Toano exhibited a moderate level of leaf feeding resistance to corn earworm. The cultivars with moderate resistance can be useful in reducing corn earworm damage and cost of chemical control in vegetable soybean insect pest management systems.     

MS1与MS1-HS两种选择方法的比较研究Ⅱ.遗传方差、配合力及杂种优势

对ZZ4完成了4轮MS1-HS和MS1选择.结果表明,经4轮选择的群体,两种方法均有效地保留了各主要性状的遗传方差.MS1-HS选择的群体遗传方差下降速率更慢,C4群体的单株籽粒产量的遗传方差仅减少3.7%.穗长、穗粗、粒行数、行粒数、出籽率、百粒重的遗传方差的变化与单株籽粒产量一致,MS1C4的遗传方差减少了8%～15%,MS1-HSC4的遗传方差仅减少了4%～15%.株高、穗位高、抽丝期、植株保绿度、抗倒性等相关选择性状的遗传方差的变化与产量性状基本一致.MS1-HS法对改良玉米群体籽粒产量与测验种间的特殊配合力十分有效,呈逐轮上升的趋势;改良群体与测验种综系140间的杂交后代产量平均每轮提高6%,杂种优势平均每轮提高6.9%.两种方法在改良群体产量性状一般配合力方面,均得到了良好的效果.同时,穗部性状及株高、穗位、抽丝期、散粉期、抗性等田间农艺性状的一般配合力也获得了同步改良.通过ZZ4改良群体与6个测验种间杂交组合产量及杂种优势的比较研究,得出ZZ4与黄早四类种质为杂种优势模式对.     

MS1与MS1-HS两种选择方法在玉米群体ZZ4中的改良效果比较Ⅰ.主要农艺性状的变化

对中综4号（ZZ4）完成了4轮改良S1-半同胞联合家系选择（简称MS1-HS）和4轮改良S1后代选择（简称MS1）。结果表明：以籽粒产量为主要目标的MS1-HS选择，每轮群体自身产量获得3.6%的遗传增益，群体S1后代籽粒产量可获得6.6%的增益；MS1选择每轮群体则可获得4.0%的遗传增益，群体S1后代籽粒产量可获得7.3%的增益。单穗籽粒产量     

玉米“黄金”群体产量等性状轮回选择改良效果评价研究

利用群体改良方法,充分挖掘地方优异种质的遗传潜力是玉米种质改良与创新的一个重要途径。本研究以黄金群5个轮次改良群体为材料,通过1年2点产量比较试验,分析了混合选择和相互半姊妹轮回选择方法对黄金群产量及穗部性状的改良效果。结果表明,两种选择方法对群体产量改良是有效的,随着改良轮次的增加,黄金群的单株产量逐轮提高,平均每轮提高3.78%,其中,混合选择改良的3轮群体平均每轮提高4.27%,相互半姊妹轮回选择的改良群体提高2.07%;虽然群体产量的变异系数从15.43%下降到12.80%,但群体内仍有较丰富的变异。通过改良群体穗部性状比较发现,穗长和行粒数改良效果显著,分别提高14.71%和17.62%,说明它们的提高是群体单株产量提高的主要因素。     

中综3号玉米群体格子混合选择效果分析

用格子混合选择法完成了对中综3号玉米群体6轮混合选择, 并用5个测验种对C0、 C2、 C4和C6进行NCⅡ交配。 经过1995、 1996年对测交后代的2年3点鉴定, 结果表明： 中综3号与5个测验种的测交组合产量均逐轮提高。 经6轮选择后, 群体籽粒产量每公顷增加了1155(24.05%) kg, 平均每轮增加192(4.01%)kg。 产量的一般配合力从C0     

玉米花丝活力的遗传分析

花丝活力长短在一定程度上影响着玉米制种产量和杂交种产量,对玉米生产具有重要意义。为阐明玉米花丝活力的遗传机理,本研究利用来自优良玉米杂交种农大108的一套203个重组近交系群体,通过1年3点的田间试验对玉米花丝活力进行了遗传分析,结果发现同一基因型的花丝活力在不同环境中存在较大的差异。利用复合区间作图法定位了8个不同位点的QTL,分布在玉米第3、第5、第6、第7和第8染色体上,单个QTL可解释花丝活力表型变异的11.06%～20.82%,该研究为玉米花丝活力的选择提供了一定的理论依据。     

Temporal genetic structure patterns in tropical maize populations under reciprocal recurrent selection

In order to investigate the effect of long term recurrent selection on the pattern of gene diversity, thirty randomly-selected individuals from the progenitors (p) and four selection cycles (C0, C3, C6 and C11) were sampled for DNA analysis from the tropical maize (Zea mays L.) breeding populations, Atherton 1 (AT1) and Atherton 2 (AT2). Fifteen polymorphic Simple Sequence Repeat markers amplified a total of 284 and 257 alleles in AT1 and AT2 populations, respectively. Reductions in the number of alleles were observed at advanced selection cycles. About 11 and 12% of the alleles in AT1 and AT2 populations respectively, were near to fixation. However, a higher number of alleles (37% in AT1 and 33% in AT2) were close to extinction. Fisher’s exact test and analysis of molecular variance (AMOVA) showed significant population differentiations. Gene diversity estimates and AMOVA revealed increased genetic differentiations at the expense of loss of heterozygosity. Population differentiations were mainly due to fixation of complementary alleles at a locus in the two breeding populations. The estimates of effective population at an advanced selection cycle were close to the population size predicted by the breeding method.     

轮回选择对豫综5号玉米群体产量性状配合力的改良效果

玉米群体遗传基础广泛、遗传变异丰富,是培育优良玉米自交系的源泉。玉米群体的改良研究对玉米种质资源创新、优良自交系选育具有重要的指导意义。本研究采用NC II遗传交配设计,以豫综5号5个轮次改良群体为父本,以黄早四、丹340、中综5号、齐319、掖478、Mo17为测验种配制成30个测交组合,通过一年两点的产量性状及其配合力评价试验,研究轮回选择对豫综5号群体的改良效果。结果表明,轮回选择对群体单株产量的改良是有效的,群体与各测验种间的杂交后代产量平均每轮提高3.57%。半姊妹轮回选择和相互半姊妹轮回选择在改良群体产量一般配合力方面, 均得到显著提高,呈逐轮上升的趋势;采用半姊妹轮回选择对豫综5号群体3轮的选择后,C₃群体与C₀相比,一般配合力效应值从–11.63增长到5.57,差异极显著;经1轮相互半姊妹轮回选择后,群体的一般配合力效应值从C₃的5.57增加到C₄的9.75。豫综5号改良群体与黄早四的特殊配合力得到一定的提高,逐轮朝着Reid×唐四平头杂优模式水平提高的方向稳定发展。     

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.     

Selection for brown stripe downy mildew resistance in maize

Summary The maize (Zea mays L.) cultivar Makki Safed 1 (MS1) with susceptibility to brown stripe downy mildew (BSDM) caused by Sclerophthora rayssiae var. zeae Payak & Renfro, was subjected to two cycles of mass selection and one cycle of full-sib family selection. Selection was carried out primarily for BSDM resistance.The mass selection was practised under artificial epiphytotic conditions in a disease nursery. Full-sib progenies and performance trials on MS1 and its improved versions were grown in diseased and disease free environments.Mass selection resulted in a significant improvement for resistance to BSDM. A cycle of full-sib selection resulted in an additional improvement for resistance to the disease. The disease rating of the improved version was 1.5 against 4.5 for the original population (scale: 1, highly resistant to 5, highly susceptible). The yield of the improved populations of MS1 was significantly greater than that of MS1 in the disease nursery. In disease free experiments, the improved populations showed almost no yield advantage over MS1. There were also no significant differences between the original population and the improved population after three selection cycles for ear length, ear girth, number of kernel rows per ear, number of kernels per row, 1000-kernel weight, plant height, ear height and days to silk.     

Development of a recurrent apple breeding programme in New Zealand: a synthesis of results,and a proposed revised breeding strategy

This paper describes an apple breeding population that has been developed in New Zealand since 1990 to broaden the genetic base for cultivar breeding. The population is now in its third generation, with recurrent selection for general combining ability being the underlying approach. During the 20 years of the programme, nearly 1,000 trees have been progeny tested. An early focus on selection within open-pollinated tests has been replaced by selection within control-pollinated tests. Genetic evaluation methods along with estimates of genetic parameters (e.g. heritability, genetic correlations, and genotype-by-environment interactions), genetic gain, and genetic diversity are summarised in this paper. The third-generation crossing programme involving nearly 350 parents is almost completed and seedlings from these crosses are in the nursery. In the revised breeding strategy, three hierarchal populations are envisioned to better integrate this broad-based population with the more commercially focused cultivar breeding programme: main breeding population (MBP), elite breeding populations (EBP) and cultivar development populations (CDP). A two-subline structure and a minimum of two crosses per parent will be implemented in the MBP. EBP will focus on developing parents for breeding goals of the CDP. Forward-selected (based on estimated breeding values) candidates from the main- and elite populations will be used as parents of the CDP. Cloning of seedlings in elite populations and also in the first-stage of cultivar development, will be investigated as a tool for enhancing predictability and shortening the cycle for delivering genetic gain.     

控制双亲混合选择对不同玉米合成群体的改良效应

基于田间试验的统计分析和SSR分子标记的遗传参数评估,分析了3个玉米人工合成群体GP3、GP4和GP5经4轮控制双亲混合选择的改良效应。结果表明,多数性状在不同群体及不同轮回间存在真实的遗传差异,粒深遗传增益以GP4＞GP5＞GP3,穗行遗传增益以GP3＞GP5＞GP4,各个群体C4的粒深、穗行均值都显著或极显著大于C0,直接选择效应显著;株高和穗位高随选择周期增加呈明显增加趋势,且GP4的增幅显著大于GP3和GP5,单株产量及穗粗的遗传增益以GP4大于GP3和GP5,各群体多数产量性状的均值以C4显著大于C0,相关选择效应显著;除株高、穗位高外,其他性状GCA变异群体间差异达显著或极显著水平,GP5多数产量性状的GCA优于GP3和GP4,各群体多数产量性状的GCA效应值随改良进展呈增加趋势,对照优势大于8%的大部分测交组合均为各群体C4所配组合,间接选择效应显著;随改良世代进行,群体部分性状的表型变异系数虽有所减小,但变化幅度不大;基于SSR分子标记估算的群体内遗传相似系数,GP3和GP4改良后代呈略增趋势,GP5变化不大,对于群体基因型数,GP3和GP4随改良代数增加呈略减趋势,GP5呈略增趋势。上述结果说明,适度控制双亲混合选择在有效改良群体的同时,还能较好地保持群体的遗传多样性,但不同基础群体及不同性状间,其改良效应存在一定的差异。     

Response to Mass Selection for Plant Height and Grain Yield in Amaranth (Amaranthus spp.)

Two landrace accessions of amaranth, UCC 192 (Amaranthus cruentus) and UCH 213 (A. hypochondriacus), were used in a mass selection experiment; five per cent of the tallest and highest yielding plants in both populations were selected for three cycles. Selection gain was largest in the first cycle for both traits. Realized heritability estimates for plant height were C.22 in the UCC 192 population and 0.49 in UCH 213, and 0.09 in both populations for yield. The results supported earlier findings for the existence of genetic variability within amaranth landrace populations.     

Adaptation of tropical maize germplasm to temperate environments

Maize (Zea mays L.) is one of few crops that can offer significant genetic gains with the utilization of genetic diversity. Genetically broad-based germplasm has the potential to contribute useful and unique alleles to U.S. Corn Belt breeding programs not present in current U.S. genome sequences (e.g. B73, NAM, etc.). Our objectives were to determine if unique tropical genetic materials have been effectively adapted to temperate environments and how their agronomic performance was relative to adapted populations. An important long-term objective of the Iowa and North Dakota maize breeding programs has been, in addition to the typical elite by elite line pedigree selection cultivar development process, to adapt exotic and unique germplasm, maximize their genetic improvement, and develop unique products for breeding and commercial uses. Stratified mass selection methodology for earliness has been utilized for the adaptation of tropical and temperate populations to Iowa and North Dakota environments. This method has allowed screening of up to 25,000 genotypes per population cycle at a rate of one cycle per year. In addition, the estimated cost per year our programs had for the adaptation of each population was less than $2,000 which could successfully be applied in any breeding program across the globe. This cost has been less than 1 % of the total cost for finding minor genes on the same trait. Our results showed the successful adaptation of exotic populations was independent from genetic background. We can speculate there are a few major genes responsible for most of flowering date expression. We encourage the use of technology to target traits according to their genetic complexity. Stratified mass selection at the phenotypic level has been successful. Each of the populations with either 25 of 100 % tropical germplasm are available for anyone who may desire to expand the germplasm base of their breeding programs with tropical germplasm adapted to temperate mid- and short-season U.S. Corn Belt environments.     

半姊妹轮回选择对玉米群体改良效果研究

用半姊妹轮回选择法完成了对中综2号三轮改良,结果表明：该法对群体产量和配合力均有显著的改良效果。经三轮选择后平均每周期获得量为7.4;一般配合力从C0的-10 081增长到C3的15.924。二者每周期的获得量与选择轮数之间均呈显著的正相关。本研究第一轮的选择用遗传基础广泛的非亲缘综合种做测验种,二、三轮的选择用自交系     

对两个亚热带优质蛋白玉米群体的适应性混合选择研究——Ⅰ.开花期性状的直接选择响应

用混合选择法改良亚热带优质蛋白玉米(QPM)群体在我国北方长日照条件下的适应性。经过4轮选择,中群13和中群14两个群体在北京三年试验的平均抽丝日期分别从85.1和86.9天缩短为67.5和68.8天,平均每轮提早4.1和4.5天。散粉日期的变化幅度较小,平均每轮提早2.2和2.3天。由于这两个性状的选择响应有差异,使散粉至抽丝的间隔天数(PSSl)分别从11.2和12.2天缩短为2.4和2.5天,平均海轮缩短2.0和2.3天,大大改善了雌雄协调性。1991年在北京春播,三亚秋播和济南、武功、成都夏播所做的多点联合评价试验表现相同的趋势,两个群体的抽丝日期平均每轮提早2.0和1.6天,PSSI则平均每轮缩短1.11和0.97天。在北京长日照条件下积累的改良效果,在短日照和夏播条件下仍然表现极显著的选择响应。这表明,混合选择法是改良外来玉米种质适应性,提早开花和改善雌雄协调性的有效途径。