Genetic analysis of drought-adaptive traits at seedling stage in early-maturing maize inbred lines and field performance under stress conditions

Maize hybrids that are tolerant to drought at the seedling stage are needed to boost productivity in the rainforest agro-ecology of West Africa. Genetics of tolerance of maize seedling to drought stress is not well understood and is poorly documented. The objectives of this study were to screen early-maturing maize lines for seedling drought tolerance, determine the inheritance and the combining ability of selected inbred lines, and evaluate the performance of seedling drought-tolerant hybrids under field conditions. Forty-nine early maize lines were screened for drought tolerance at the seedling stage. Ten drought-tolerant and two susceptible inbred lines were selected and used in diallel crosses to generate 66 hybrids. The twelve inbred lines and their hybrids were evaluated under induced drought at seedling stage in the screen house and under marginal growing conditions on the field for two seasons. Data collected were subjected to analysis of variance using the DIALLEL-SAS program. Mean squares for both GCA and SCA were significant for most traits in all research environments, indicating that additive and non-additive gene actions are controlling seedling traits under stress conditions. However, for most traits, SCA was preponderant over GCA in all environments, indicating overdominating effect of non-additive gene action. Which in turn implied that the best improvement method for the traits is hybridization. Inbred TZEI 7 had the best GCA effect for seedling traits under screenhouse conditions and for grain yield and other agronomic traits under drought conditions in the field. Hybrids TZEI 357?×?TZEI 411 and TZEI 380?×?TZEI 410 showed superior SCA effects under screen house conditions. In conclusion, the study established wide genetic variability for drought tolerance at seedling stage among tropical early-maturing maize germplasm however, the non-additive gene action was more important for most seedling traits.     

Segregation of genetic markers among wheat doubled haploid lines derived from wheat x maize crosses

Summary Wheat doubled haploid (DH) lines were produced from the F₁ hybrid, Fukudo-komugi x Oligo Culm, through intergeneric crosses between wheat and maize. F₂ plants and 203 DH lines were analyzed for the segregation of the eight genetic markers, namely, grain proteins, grain esterases, GA-insensitivity and glume traits. The segregation in the F₂ plants fitted to the expected ratios. No deviation was observed among the DH lines, either, except for the glume pubescence. The result indicates the absence of correlation between the markers investigated and the efficiency of embryo formation in the DH lines.     

Doubled-haploid versus single-seed descent and S1-family variation for testcross performance in a maize population

Progress made in the in situ gynogenesis technique since 1990 now allows production of a high number of maize (Zea mays L.) doubled-haploid (DH) lines. The aim of the study was to compare DH lines versus selfing lines for testcross performance. DH and single-seed descent (SSD) lines were produced from random S₁ progenies of a broad-base population. For grain yield, kernel moisture, plant height, ear height and leaf length, the three population means were similar. Except for kernel moisture, the genetic variance of DH lines was nearly twice as high as the genetic variance of S₁ families, as expected. On the other hand, genetic variance among SSD lines was only 1.5 times higher than the genetic variance of S₁ families. This lower variance could be due to a selection bias in the method of production of SSD lines. However, for all traits, heritability of SSD or DH lines was higher than heritability of S₁ families. Epistasis effects in DH progenies were not significant. The consequence was a high correlation between S₁ testcross progenies and DH or SSD testcross progenies, meaning that the S₁ testcross value can be used to select the best families from which DH lines will be extracted. As a whole, the observed variation in DH lines appeared to be more in accordance with the observed variation among S₁ families than with the observed variation among SSD lines.     

玉米Reid种质DH系遗传分析

为探讨玉米Reid种质遗传改良效果,本研究以Reid类群重要种质J1491、J1492、J1493、J1495、J1498与PH6WC构建基础群体,通过DH技术育成DH系,经鉴定从中选取5个代表DH系6DH6、6DH7、6DH9、6DH10、6DH12作母本,以Non-Reid群5个优良自交系作父本,按NCII设计组配25个杂交组合,对DH系单株产量及其构成因素的杂种优势、配合力和相关方面进行了研究。结果表明,单株产量杂种优势以组合6DH7×J1628最高为180.22%,组合6DH12×J1673最低为54.94%;单株产量一般配合力效应值最高的有6DH7和6DH10,穗长、穗粗亦为正效应,因此认为6DH7和6DH10更具应用潜力;特殊配合力效应值最高的组合是6DH7×J1673。各产量性状中穗长、穗粗和秃尖长,狭义遗传率高,主要以基因加性效应为主。本研究为鉴定有潜在价值的DH系及杂交种提供选择,为玉米遗传改良提供参考。     

Variation in Doubled Haploid Plants of Wheat Obtained through Wheat (Triticum aestivum) × Maize (Zea mays) Crosses

Variation was investigated in 110 doubled haploid (DH) lines of wheat derived from wheat × maize crosses. Field observation revealed visible variations in 15 DH2 lines such as extreme dwarfism, low seed fertility, alteration of spike type and stripes. Six agronomic traits, i.e., heading date, spike number/ plant, culm length, spike length, seed fertility and grain weight were statistically analyzed in the DH2 and DH3 generations. Out of the 88 DH2 lines/DH3 groups, 26 %/64 % showed significant differences from the parental variety in the means of one or more traits. Ranges of the DH3 lines were larger than those of the DH2 lines, except for spike number/plant. Furthermore, analyses of variance within and between DH lines showed the presence of heterogeneity/heterozygosity in the DH2 lines/plants. These results indicated the occurrence of gametoclonal variation in the DH lines. It is considered that most of the variations detected were due to the colchicine treatment rather than to the 2,4-D treatment or in vitro culture.     

Mapping of QTL associated with waterlogging tolerance and drought resistance during the seedling stage in oilseed rape (Brassica napus)

Soil waterlogging and drought are major environmental stresses that suppress rapeseed (Brassica napus) growth and yield. To identify quantitative trait loci (QTL) associated with waterlogging tolerance and drought resistance at the rapeseed seedling stage, we generated a doubled haploid (DH) population consisting of 150 DH lines from a cross between two B. napus lines, namely, line No2127-17 × 275B F₄ (waterlogging-tolerant and drought-resistant) and line Huyou15 × 5900 F₄ (waterlogging-sensitive and drought-sensitive). A genetic linkage map was constructed using 183 simple sequence repeat and 157 amplified fragment length polymorphism markers for the DH population. Phenotypic data were collected under waterlogging, drought and control conditions, respectively, in two experiments. Five traits (plant height, root length, shoot dry weight, root dry weight and total dry weight) were investigated. QTL associated with the five traits, waterlogging tolerance coefficient (WTC) and drought resistance coefficient (DRC) of all the traits were identified via composite interval mapping, respectively. A total of 28 QTL were resolved for the five traits under control conditions, 26 QTL for the traits under waterlogging stresses and 31 QTL for the traits under drought conditions. Eleven QTL were detected by the WTC, and 19 QTL related to DRC were identified. The results suggest that the genetic bases of both waterlogging tolerance and drought resistance are complex. Some of the QTL for waterlogging tolerance-related traits overlapped with QTL for drought resistance-related traits, indicating that the genetic bases of waterlogging tolerance and drought resistance in the DH population were related in some degree.     

Mapping QTLs for seedling root traits in a doubled haploid wheat population under different water regimes

A deep and thick root system has a positive effect on wheat yield, particularly in drought environments. A doubled haploid (DH) population of 150 lines derived from the cross Hanxuan 10?×?Lumai 14 was used to map QTLs for seedling root characteristics. The DH lines were cultivated in an agarose gel-chamber under well-watered (WW) and water-stressed (WS) regimes. Water stress was simulated by adding mannitol to the agarose gel. The seminal root traits, including maximum root length (MRL), seminal root number, total root length, project root area, root surface area, and seminal root angle were measured after 6?days of seedling development. Grain yields (GY) were measured in a field experiment. A total of 29 QTLs were identified for seedlings cultured under WW regimes, and 23 QTLs under WS regimes. Individual QTL accounted for phenotypic variations ranging from 4.98 to 24.31?%. The QTLs were distributed on 17 chromosomes, except 1D, 4D, 6B and 6D. Seven consistently expressed QTLs were detected for all the traits tested except MRL under both water regimes. The QTLs for root traits were unevenly distributed among chromosomes, and clustered in eight loci on seven chromosomes, showing pleiotropic effects on target traits. One region in the interval Xgwm644.2?CP6901.2 on chromosome 3B contained 9 QTLs affecting most root traits. The present data provide an insight into the genetic basis of seedling root development under different water regimes and may benefit breeding programs using marker-assisted selection (MAS) for root traits.     

Agronomic performance of anther‐derived doubled haploid and single seed descent lines in crosses between primary and secondary winter triticale

Octoploid (8x) and hexaploid (6x) primary triticales (xTriticosecale Wittm.) can be used as crossing parents with secondary 6x triticales to enlarge the genetic basis of a breeding programme or introgress traits. Doubled haploid (DH) production permits to develop homozygous lines more rapidly from a segregating generation than other breeding methods such as single seed descent (SSD). Both anther‐derived DH and SSD lines were produced from reciprocal cross‐combinations between 8x and 6x primary and 6x secondary triticales. Field experiments of DH and SSD lines were conducted in three environments as two‐replicate lattices to measure seven agronomic traits. A tendency for higher grain yield, taller plants and a higher 1000‐kernel weight of SSD lines compared with DH lines was found. Significant genetic variation for all traits in both breeding methods was revealed, indicating their suitability to select superior genotypes. Hexaploid and even more so 8x primary triticales can profitably be included as crossing parents in a commercial breeding programme. In such crosses, the primary triticales should be used as the male parents if followed by DH method.     

Doubled haploids in tropical maize: <Emphasis Type="SmallCaps">II</Emphasis>. Quantitative genetic parameters for testcross performance

Single crosses (SC) of elite inbreds and open-pollinated populations (OP) are suitable source germplasm for doubled haploid (DH) line development in hybrid maize breeding, given that they combine a high population mean ([`(x)] \overline{x} ) for testcross performance with adequate response to selection ( \Updelta G \Updelta G ). This is the first study reporting testcross grain yield (TCGY) and dry matter content (TCDMC) evaluations of 131 DH lines developed from ten tropical source germplasm comprising five OP (OP1–OP5) and five SC (SC1–SC5). Gene diversity (d) and the average number of alleles (a <sub>r</sub> ) per locus was estimated for DH lines based on 24 simple sequence repeat markers. Analysis across three environments revealed no significant differences between [`(x)] \overline{x} of OP- and SC-derived DH lines for TCGY and TCDMC. Significant genetic variance for both traits was only detected among OP-derived DH lines which may be explained by a larger number of segregating quantitative trait loci (QTL) as suggested by higher d and a _r values than in SC-derived DH lines. The usefulness criterion ( U = [`(x)] + \Updelta G U = \overline{x} + \Updelta G ) was higher for OP-derived DH lines for TCDMC, but higher for SC-derived DH lines for TCGY. DH lines from OP1, OP2, and OP3 showed high TCGY, suggesting that they may be useful in tropical hybrid breeding. We conclude that tropical OP represent a valuable source of untapped genetic variation that can efficiently be exploited with DH technology for hybrid maize breeding.     

Quantitative trait loci mapping of forage stover quality traits in six mapping populations derived from European elite maize germplasm

Four forage maize stover quality traits were analysed including in vitro digestibility of organic matter (IVDOM), neutral detergent fibre (NDF), water‐soluble carbohydrates (WSC) and digestibility of NDF (DNDF). We mapped quantitative trait loci (QTL) in three DH (doubled haploid) populations (totally 250–720 DH lines): one RIL population (358 lines) and two testcross (TC) populations, based on field phenotyping at multiple locations and years for each. High phenotypic and genotypic correlations were found for all traits and significant (p < .01) at two locations, and NDF was negatively correlated with the other traits. QTL analyses were conducted by composite interval mapping. A total of 33, 23, 32 and 25 QTL were identified for IVDOM, NDF, WSC and DNDF, respectively, with three, four, five and two major QTL for each. Few consistent QTL for IVDOM, WSC and DNDF were detected in more than two populations. This study contributed to the identification of key QTL associated with forage maize digestibility traits and is beneficial for marker‐assisted breeding and fine mapping of candidate genes associated with forage maize quality.     

QTL mapping of three ear traits using a doubled haploid population of maize

Ear shape substantially correlates to grain yield, so understanding their genetic architecture is of great significance in maize breeding. Ear length (EL), ear diameter (ED), length of barren tip (LBT) and cob diameter (CD) were determined for 240 doubled haploid maize lines, and all four traits showed a relatively high broad sense heritability around 77%. Using this DH population consisting of 240 lines and a genetic map constructed from 964 SNPs, a total of five, four and three QTLs were identified for EL, ED and CD, respectively, in three various growing conditions. Among these, qEL1‐1, qED1 and qCD1 were consistently mapped at an overlapping location on Chr1, which contributed 15.7, 28.3 and 22.6% of the phenotypic variation in EL, ED and CD, respectively. All other QTLs exhibited minor effect with the phenotypic variation explained ranging from 4.7% to 7.8%. Because most of the QTLs were detected in at least two different planting environments, they appear to be potential loci for gene isolation and marker development in maize molecular breeding.     

Molecular and agronomic evaluation of wheat doubled haploid lines obtained through maize pollination and anther culture methods

Although maize pollination (MP) and anther culture (AC) are alternative techniques widely used for wheat doubled haploid (DH) production, there is only limited information on the attributes of the plant materials produced through both methods. This study was conducted to evaluate genetic fidelity, transmission of parental gametes, and to compare field performance of DH populations produced by the MP and AC methods from the F1s of two crosses between spring bread wheat cultivars. The DH populations were compared to single seed descent (SSD) lines created from the same crosses. In total, 76 MP and 122 AC lines of the cross between cultivars of divergent origin were subjected to RAPD and AFLP analysis. Only changes in AFLP banding patterns, at similarly low frequencies, 0.18% (MP) and 0.21% (AC), were detected. The frequency of the DH lines affected by the variation, 14.5% (MP) and 14.8% (AC), was similar in both populations. For most of the DH lines, variation in 1‐2 loci only, out of several hundreds scored, was observed. A total of 14.3% (MP) and 22.2% (AC) marker loci showed the significant segregation distortion from the expected 1 : 1 ratio, but in at least one polymorphic locus the within‐cultivar variation was responsible for the skewed segregation. The field performance of the corresponding MP and AC lines derived from two crosses confirmed the equivalency of both DH populations. In most of the traits analyzed, the MP and AC lines performed the same as the SSD populations created from the same crosses. No, or very small differences in means and ranges, were observed when the best 10% of the lines from all three methods were compared. Moreover, the best 10 % of the lines of the cross between Polish wheat cultivars adapted to the local environment performed significantly better for some traits than different groups of checks used in the study.     

Identification of quantitative trait loci for drought tolerance at seedling stage by screening a large number of introgression lines in maize

The maize genome hosts tremendous phenotypic and molecular diversity. Introgression lines (ILs), developed by continuous backcrossing to recurrent parents, could provide a unique genetic stock for quantitative trait locus (QTL) mapping. Using maize lines from six heterotic groups of different ecological zones, we developed >500 BC₂F₂ IL sets by crossing 11 inbred lines (as recurrent parents) with >200 local maize inbred lines (as donor parents). Of them, 34 IL sets were selected as a subset for drought tolerance screening and a total of 417 ILs survived under severe water stress at seedling stage. One set of 32 surviving ILs, derived from Chang7-2/DHuang212, was used for QTL mapping with simple sequence repeat markers covering the whole genome, with seven QTL detected. Furthermore, investigating all surviving ILs, we identified two common regions in bin 3.04, corresponding to marker intervals bnlg1904–umc1772 and umc1223–bnlg1957, respectively, which shared high genetic variation in three IL sets. Our results indicated that selective genotyping can be used to identify genetic loci for complex traits. The ILs, highly selected for drought tolerance in this study, provide a unique set of materials for both genomic studies and development of enhanced germplasm resources.     

QTL mapping of improving forage maize starch degradability in European elite maize germplasm

Improving maize starch content is of great importance for both forage and grain yield. In this study, 13 starch degradability traits were analysed including percentage of the seedling area, floury endosperm, hard endosperm of total grain area, percentage of the floury endosperm surface and vitreousness ratio surface hard: floury endosperm surface, etc. We mapped quantitative trait loci (QTL) in a biparental population of 309 doubled haploid lines based on field phenotyping at two locations. A genetic linkage map was constructed using 168 SSR (simple sequence repeat) markers, which covered 1508 cM of the maize genome, with an average distance of 9.0 cM. Close phenotypic and genotypic correlations were found for all traits, and were all statistically significant (p = 0.01) at two locations. Major QTL for more than two traits were detected, especially in two regions in bins 4.05–4.06 and 7.04–7.05, associated with 13 and 9 traits, respectively. This study contributes to marker‐assisted breeding and also to fine mapping candidate genes associated with maize starch degradability.     

Testcross performance and diversity analysis of white maize lines derived from backcrosses containing exotic germplasm

Introgression from exotic maize (Zea mays L.) into adapted breeding pools can broaden and diversify the genetic base of adapted germplasm. The first objective of this study was to determine the agronomic performance of white maize lines derived from adapted × exotic backcrosses in tropical environments. Six exotic white maize inbred lines were crossed to an adapted white line (1368) and the F₁s were backcrossed to 1368. Forty-one BC₁F₄ lines derived from these backcrosses and the recurrent parent were crossed with a common inbred tester (9071) and the progeny were evaluated at eight environments in Nigeria. The testcrosses × environment interaction mean square was not significant for all agronomic traits. The BC-derived lines containing exotic germplasm contributed significantly to the variation in testcross mean grain yields and other agronomic traits. Among the 41 testcrosses, only 5 yielded significantly less than 1368 × 9071, with the 7 best testcrosses producing between 304 and 867 kg ha⁻¹ more grain than 1368 × 9071. The second objective of this study was to assess the genetic divergence of the BC-derived white lines from their adapted recurrent parent. Thirty-nine BC-derived white lines along with 1368 and 9071 were genotyped with ten AFLP primer pairs that generated 506 polymorphic fragments. The average allelic diversity of the lines was 31 ± 0.07. The genetic distance (GD) estimates of each BC-derived line from 1368 varied from 0.76 to 0.84, with a mean of 0.80 ± 0.003. The average GD for all pairs of the BC-derived lines was 0.63 ± 0.005, varying from 0.31 to 0.89. The observed significant amount of variation among the BC-derived white lines suggests that they can contribute new alleles for expanding the genetic base of tropical maize and for developing high-yielding hybrids.     

不同来源玉米自交系植株性状特征分析

为了获得优良的玉米自交系，从而培育优良的玉米新品种，本研究通过统计分析和聚类分析对211 份不同来源的玉米自交系的11 个植株性状进行分析，并与玉米杂交种‘郑单958’和‘先玉335’的亲本自交系进行比较，从而筛选性状优良的玉米自交系。结果表明，自交系间除第一层气生根数呈显著差异外，其余均为极显著差异；各植株性状的变异系数均较大，其中雄穗分枝数的变异系数最大为27.99%，叶长的变异系数最小为6.04%；聚类分析将211 份自交系划分为9 个类群，G1~G4 类群包含192个自交系，占91%；与优良玉米杂交种‘郑单958’和‘先玉335’的亲本自交系进行比较，筛选出14 个植株性状优良的自交系。总之，本研究采用的211 份不同来源的玉米自交系材料之间遗传差异大，代表类型丰富，研究结果具有代表性。11 个植株性状之间均存在不同程度的相关性。聚类分析筛选出14 个植株性状优良的自交系，可为优良植株性状新品种选育提供参考。     

Phenotypic distribution of barley SSD lines and doubled haploids derived from F1 and F2 hybrids

Summary The doubled haploid (DH) system and the single seed descent (SSD) technique are frequently applied in breeding of self-pollinated crops to rapidly obtain homozygous lines from heterozygous hybrids. This study presents a comparison of populations of barley DH and SSD lines in terms of traits of stem structure. The SSD and DH lines derived from F₁ and F₂ hybrids Roland x Apex were examined in a field experiment. On the basis of a comparison of means, variances and correlations between traits in the F1DH, F2DH and SSD populations the occurrence/absence of linkage between genes responsible for the analysed traits was inferred. Independent inheritance was found for 1000-grain weight and the length of particular internodes, spike length and stem wall thickness. Moreover, no linkage was found for stem wall thickness and spike length, length of internodes I, II and thickness of stem walls, stem diameter and thickness of stem walls. The results obtained for the other pairs of traits indicate the presence of linkage.     

PEG模拟干旱胁迫下玉米胚芽鞘长与其抗旱性的关系分析

以6份抗旱性不同的玉米自交系为试材,用不同浓度的PEG-6000(polyethylene glycol,PEG)渗透溶液进行模拟干旱胁迫处理,分析玉米萌芽期中胚轴长、胚芽鞘长及苗长的变化,并将其与田间干旱胁迫处理下相应玉米自交系产量及产量相关性状的抗旱指数进行相关分析,以期揭示萌芽期玉米幼苗相关性状与其抗旱性的关系。结果表明:(1)萌芽期随着PEG浓度增加,玉米自交系胚芽鞘长、中胚轴长及苗长都呈下降趋势,其中苗长降低幅度最大,平均降幅为14%,中胚轴长次之,平均降幅为11%;(2)方差分析表明,不同玉米自交系幼苗的中胚轴长、胚芽鞘长在自交系间及PEG浓度间差异极显著,苗长在PEG浓度间差异极显著;(3)花期田间干旱胁迫下,各玉米自交系的千粒重、穗粒数及产量较正常灌溉明显下降,且其平均降幅分别为8%、14%、13%;(4)通过玉米田间产量及产量相关性状抗旱指数与萌芽期各性状相关性分析表明,中胚轴长与千粒重、穗粒数及产量的抗旱指数呈显著或极显著正相关。胚芽鞘长与千粒重、穗粒数及产量的抗旱指数呈极显著正相关,而在5%的PEG-6000渗透溶液模拟干旱胁迫下,胚芽鞘长与千粒重抗旱指数相关系数最高为0.832。因此,胚芽鞘较长的自交系其抗旱性较强,胚芽鞘长度可作为玉米早期抗旱性筛选的重要指标。     

甘蓝型油菜DH群体苗期抗旱性的评价

中国油菜主产区常常受到秋冬旱和春旱危害而影响产量及品质。本文通过盆栽试验,以株高(PH)、根长(RL)、地上部干重(SDW)、根干重(RDW)、根冠比(R/S)、总干重(TDW) 6个性状的抗旱系数作为抗旱性评价指标,对甘蓝型油菜DH(doubled haploid)群体的118个株系及其亲本进行苗期抗旱性评价,筛选极端抗旱DH系。结果表明,与对照相比,干旱严重抑制了甘蓝型油菜苗期的生长,6个评价指标均表现出显著差异,其中根干重的变异系数最大;在对照和干旱条件下,群体各株系各性状均表现出超亲连续分离,大部分呈正态分布,抗旱条件下的分离更为明显;相关性分析表明,地上部干重、根干重和总干重抗旱系数可作为甘蓝型油菜苗期抗旱性的主要评价指标;     

改良S1选择法对12个玉米群体改良效果的比较分析

为了对玉米群体进行合理有效的改良利用,通过改良S1选择法对12个玉米群体改良一轮后进行效果比较分析。结果表明,穗行数、行粒数和百粒重是构成产量的三因素,遗传增益最大的群体为蒙群2,其他依次为蒙群4、蒙群1等7个群体,蒙群3及3个国外引进群体遗传增益为负值;玉米群体在穗部、植株性状以及遗传变异中均存在一定的变化。试验研究得出,蒙群2、蒙群4、中综7号、蒙C群、蒙A群产量遗传增益均较大,并在其他农艺性状中改良效果显著,可直接选择优株自交进行选系,而其余7个群体遗传增益小,改良利用潜力不大。