Effect of source germplasm and season on the in vivo haploid induction rate in tropical maize

For in vivo production of doubled haploid (DH) lines in maize, the rate of haploid induction is of crucial importance. Maternal haploid induction depends primarily on the inducer used as a pollinator. However, the source germplasm used as a maternal parent and the environmental conditions for induction may also influence haploid induction and these aspects have not been examined in tropical maize so far. The objectives of our study were to (i) monitor the variation for haploid induction rate (HIR) among diverse source germplasm in tropical maize, (ii) determine the relative importance of general (GCA) and specific (SCA) combining abilities for HIR, and (iii) investigate the influence of summer and winter seasons and genotype × season interactions on this trait. Ten inbreds were mated in a half diallel design. The resulting 45 F₁ single crosses were pollinated with the haploid inducer hybrid RWS × UH400 during the summer 2008 and winter 2009 seasons in a lowland tropical environment in Mexico. HIR of the single crosses averaged over seasons ranged from 2.90 to 9.66% with an overall mean of 6.74%. Mean HIR was significantly (P < 0.01) higher during the winter (7.37%) than summer season (6.11%). Significant (P < 0.01) variation was observed due to GCA effects of parental inbreds of single crosses but not for SCA, GCA × season and SCA × season interactions. Our study underpins that a higher HIR in tropical maize can be obtained by selecting appropriate source germplasm and undertaking pollination under favorable environmental conditions.     

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.     

我国玉米地方种质的单倍体诱导和加倍特性研究

双单倍体(doubled haploid,DH)育种技术具有加速育种进程的突出优势,已成为玉米育种关键性核心技术并在国外广泛应用.本试验选用47份玉米地方种质,进行单倍体诱导和单倍体加倍特性研究.结果表明,47份玉米地方种质材料之间杂交诱导的拟单倍体率有显著差异,介于1.64％～14.50％之间,平均为5.95％.种植12份玉米地方种质的拟单倍体籽粒进行田间鉴定,标记鉴定准确率介于40.2％～82.3％之间,校正单倍体诱导率介于2.33％～6.45％之间,表明玉米遗传背景影响到籽粒标记的表达,单倍体诱导率有明显差异.将15份玉米地方种质拟单倍体于冬季在海南田间种植,加倍授粉株率介于2.7％～27.2％之间,加倍结实株率介于0.7％～8.9％.说明我国玉米地方种质的遗传多样性丰富,单倍体诱导率和加倍率具有明显差异,利用DH育种技术可以拓宽和加强我国玉米地方种质在玉米育种中的利用.     

Molecular identification of Pm12-carrying introgression lines in wheat using genomic and EST-SSR markers

The traditional process of obtaining maize hybrids involves the generation of inbred lines through successive generations of selfing and subsequent testcrosses in order to identify the best combining ability by allelic complementation. A fast alternative to obtain inbred lines is to induce the formation of haploids followed by chromosome doubling. However, even with the aid of haploid-inducing genetic sources, this strategy has not been widely used in maize breeding programs, partly due to difficulties inherent to haploid generation and identification. In order to evaluate the possibility of using dihaploids to generate homozygous maize tropical lines, we used the androgenetic haploid inducer line W23 as a female parent in crosses with the tropical single-cross hybrid BRS1010. Within the progeny of these crosses, 462 seeds were phenotypically selected as putative haploids by the purple-colored endosperm and colorless embryo conditioned by the R1-nj gene. Among these, only four individuals were confirmed as being haploids using SSR markers, chromosome counting and flow cytometry, showing that the phenotypic marker was not efficient in detecting haploids in the tropical maize genotype used. All four haploids as well as some diploid plants presented reduced size, corroborating the difficulties for haploid identification by phenotypic evaluation. Genetic diversity analysis revealed by SSR markers divided the haploids in two groups represented by flint and dent maize inbred lines, which could be helpful in identifying complementary dihaploid lines. The present article demonstrates that a combination of haploid production and SSR fingerprinting is a feasible strategy for maize hybrid development in tropical germplasm.     

Inducer line generated double haploid seeds for combined waxy and opaque 2 grain quality in subtropical maize (<Emphasis Type="Italic">Zea mays.</Emphasis> L.)

The implementation of modern inducer lines in maize breeding can substantially decrease the time required to create elite inbred lines. In industrialized countries, this method has already largely replaced conventional backcross methods. However, the application of in vivo gynogenesis for inducing doubled haploids is still limited to European and US maize germplasms and has still to be adapted for exotic plant material. The reliability of three modern European inducer lines from the University of Hohenheim (Germany) was investigated for the production of haploid progenies from subtropical specialty maize. Three Chinese hybrids heterozygous for waxy maize and opaque 2 were used as maternal donor material, as maize double recessive for waxy and opaque 2 may improve the nutrition of ethnic minorities in Southeast Asia. However, many false positives were detected by flow cytometry among putative haploid seeds based on anthocyanin pigmentation because the color expression was inhibited in almost 50% of the induced seeds from this maternal plant material. Based on flow cytometry, the haploid induction rates were high with 10.2–12.3%, and the chromosome doubling rates were around 50%; therefore the principal potential of producing DH was confirmed for subtropical maize. However inducer lines for the precise and fast recognition of truly induced haploid seeds still need to be developed.     

Utilization of exotic germplasm in Nordic barley breeding and its consequences for adaptation

Summary Utilization of exotic germplasm is one way to broaden genetic variation in breeding populations. This approach has recently been adopted in Sweden and Finland, where experimental barley populations has been established for research and pre-breeding purposes. The aim of the project is threefold: (1) to increase overall genetic diversity of Nordic barley breeding material; (2) to develop breeding material which possesses a high level of resistance for various barley diseases; and (3) to study effects of exotic germplasm on adaptation and agronomic performance. Both the Finnish and the Swedish barley populations include the same exotic material i.e. unadapted landraces from different parts of Asia and wild barley (Hordeum vulgare ssp. spontaneum) accessions. Locally adapted high-yielding barley lines were included in the populations. The establishment of these populations involved six crossing generations in order to promote recombination and enhance the break-up of linkage blocks. The paper discusses the third aim of the project. Studies on agronomic performance and adaptation showed that (1) agronomically valuable genotypes can be constructed through recombination using exotic germplasm for Nordic conditions, (2) that incorporation of exotic material is most successful when made in a local genetic base and (3) that exotic germplasm has an effect on adaptation.     

利用玉米黄绿苗标记单倍体诱导系选育早期加倍双单系（EDH）的研究

介绍了一种新型玉米单倍体诱导系,该诱导系兼具籽粒标记、幼苗标记和成株标记,可在幼苗期通过黄绿苗性状鉴别出杂合二倍体植株,可在早期加倍（EDH）、高自然加倍、单倍体回交和单倍体轮回选等技术方面应用,有明显的技术优势与应用前景。     

Comparison of QTLs mapped in RILs and their test-cross progenies of tropical maize for insect resistance and agronomic traits

Quantitative trait loci (QTL) affecting resistance to south-western corn borer Diatraea grandiosella (SWCB) and sugarcane borer Diatraea saccharalis (SCB) have been identified previously in F_2:3 lines and recombinant inbred lines (RILs) of tropical maize using restriction fragment length polymorphism (RFLP) analyses. Our objective was to determine whether QTLs identified in these generations are also expressed in test crosses (TC) of RILs. A population of 166 TC progenies was developed by crossing RILs from the cross CML131 (susceptible) × CML67 (resistant) with the unrelated, susceptible tester line CML216. Resistance to first-generation SWCB, measured as leaf-feeding damage (LFD) under artificial infestation, and other agronomic traits were evaluated in two environments for the TC progenies and three environments for 183 RILs. The correlation between line per se and TC performance was low for LFD and intermediate for most agronomic traits. Estimates of the genotypic variance and heritabilities were smaller in the TC progenies than in the RILs for all traits. Quantitative trait loci were identified using an RFLP linkage map with 136 loci. For LFD, four QTLs were detected in the TC progenies, of which two were in common with nine QTLs previously mapped in the RILs. Few QTLs for agronomic traits were common to the two types of progeny, because of the low consistency of QTL positions for all traits in RIL and TC progenies, the use of TC progenies should be considered in QTL mapping studies as the first step for marker-assisted selection in hybrid breeding.     

Discrimination of haploid and diploid maize kernels via multispectral imaging

The use of doubled haploids (DHs) in maize has become ubiquitous in maize breeding programmes as it allows breeders to go from cross to evaluation in as little as 2 years. Two important aspects of the in vivo DH system used in maize are as follows: (i) the identification of haploid progeny and (ii) doubling of the haploid genome to produce fertile inbred lines. This study is focused on the first step. Currently, identification of maize haploid progeny is performed manually using the R1‐nj seed colour marker. This is a labour‐intensive and time‐consuming process; a method for automated sorting of haploids would increase the efficiency of DH line development. In this study, six inbred lines were crossed with the maternal haploid inducer ‘RWS/RWK‐76’ and a sample of seed was sorted manually for each line. Using the VideometerLab 3 system, spectral imaging techniques were applied to discriminate between haploids and hybrids. Using DNA markers to confirm the haploid/diploid state of the tested seed, for the majority of genotypes haploid identification was possible with over 50% accuracy.     

玉米生物诱导孤雌生殖单倍体影响因素研究进展

玉米单倍体育种技术能显著缩短育种周期,提高育种效率,在现代商业化育种中占有重要的地位。规模化高效单倍体的产生是单倍体育种技术应用的前提条件。总结了父本诱导系、母本的遗传背景、诱导的环境、授粉方式等影响玉米生物诱导孤雌生殖单倍体产生的因素,通过文献综合分析得出了获得大量的孤雌生殖单倍体除了选择合适的高频率孤雌生殖诱导系外,同时要考虑其他诱导因素的影响。并就高效生产孤雌生殖单倍体的未来研究及发展方向进行了讨论,以期促进单倍育种技术的规模化应用。

     

玉米生物诱导孤雌生殖单倍体影响因素研究进展

玉米单倍体育种技术能显著缩短育种周期,提高育种效率,在现代商业化育种中占有重要的地位。规模化高效单倍体的产生是单倍体育种技术应用的前提条件。总结了父本诱导系、母本的遗传背景、诱导的环境、授粉方式等影响玉米生物诱导孤雌生殖单倍体产生的因素,通过文献综合分析得出了获得大量的孤雌生殖单倍体除了选择合适的高频率孤雌生殖诱导系外,同时要考虑其他诱导因素的影响。并就高效生产孤雌生殖单倍体的未来研究及发展方向进行了讨论,以期促进单倍育种技术的规模化应用。     

诱变育种在改良热带亚热带玉米种质资源中的 应用及前景展望

近10年中国玉米单产几乎没有什么实质性的突破。种质资源狭窄是造成这种现象的一个重要原因。引进热带亚热带种质资源是拓宽温带玉米种质的一个重要途径。但是热带亚热带种质资源引进到温带以后会出现成熟期延迟、营养生长优于生殖生长等现象。针对热带亚热带玉米种质这些特点，诱变可以发挥重要的作用。主要对目前经常应用的几种诱变方法在改良热带亚热带玉米种质资源上的应用前景进行了比较。对将来大规模地运用诱变方法改良外来种质进行了预测。     

陆海BC4F3和BC4F4代主要农艺性状的相关和通径分析

为了更有效地对棉花农艺性状进行选择,缩短选择育种的年限,通过采用相关、偏相关、通径以及回归分析的方法,研究了陆海高代回交自交后代BC4F3和BC4F4群体的6个农艺性状间的关系。结果表明：铃重、衣分、铃数、果枝数、株高与单株皮棉产量呈极显著正相关,其中铃数是决定单株皮棉产量最主要的因素,在BC4F3和BC4F4代对单株皮棉产量的直接通径系数分别为0.6650、0.6689,其次是铃重和衣分,两者的贡献大小相当;果枝数和株高可以通过铃数对单株皮棉产量起较大的正向促进作用;最优回归方程显示,铃重、衣分、铃数和株高对单株皮棉产量有显著的正向影响。本研究明确了棉花产量育种的主攻方向,为提高棉花选择育种效率和实现高产提供理论指导。     

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.     

Inheritance of anther-culture response in perennial ryegrass (Lolium perenne L.)

Genetic control of the capacity to respond to anther culture in perennial ryegrass was studied in F₁ offspring from crosses between 11 clones selected for anther-culture response (‘inducers’) and 10 clones selected from breeding material on the basis of good agronomic performance. Large differences in anther-culture response were observed between the two types of parent, with inducer clones producing an average of 10.7 green plants per 100 anthers, compared with only 0.3 for breeding clones. Hybrid populations produced an average of 2.2 green plants per 100 plated anthers, which is 7.3 times the response of the breeding material. This improvement was mainly due to a 9.4-fold increase in the percentage of green plants regenerated from hybrid populations to 4.7% compared to an average of 0.5% from breeding clones. Most of the GCA (general combining ability) in the experiment was contributed by the breeding material, constituting 55.8, 100.0 and 36.7% of genetic variation among hybrids for embryo formation, regeneration and green plant percentage, respectively. Any remaining genetic variation among hybrids was predominantly due to SCA (specific combining ability) effects, with percentages of 44.2 and 63.3%, respectively, for embryo and green plant formation. These results are discussed with respect to the possible exploitation of genes controlling anther-culture response for haploid production in breeding programmes of perennial ryegrass.     

玉米Iodent种质在Suwan材料改良利用中的有效性分析

种质资源狭窄和杂种优势单一,是制约我国玉米产业发展的重要因素之一。拓宽玉米种质基础,培育突破性育种新材料是选育优良玉米杂交种的基础与前提。热带、亚热带种质已经被证明具有较温带种质丰富的遗传多样性,其引入、改良和应用对丰富我国玉米种质多样性具有十分重要的意义。本研究以28份温热玉米自交系、4份Suwan群体来源自交系(QR 273、ZHL 908、T 32和QB 48)作母本,来自Iodent、Reid、PB、Lancaster和塘四平头类群的8个温带玉米自交系作父本的杂交后代为材料,2015年分别在河南郑州和河南华县对28份自交系和32个杂交组合进行农艺性状评价。结果显示,Suwan×Iodent杂交组合的株型、生育期、感光性等与温带地区杂交种相近;而Suwan自交系与其他类群自交系的杂交组合则表现出植株繁茂、抗倒性差、感光性强和生育期太晚等问题。利用Iodent种质早熟、马齿的特性能够有效改良Suwan种质生育期晚、光周期敏感的不足,获得较高的配合力。     

Genetic dissection of haploid male fertility in maize (Zea mays L.)

Haploid genome doubling is a key limiting step of haploid breeding in maize. Spontaneous restoration of haploid male fertility (HMF) provides a more promising method than the artificial doubling process. To reveal the genetic basis of HMF, haploids were obtained from the offspring of 285 F_2:3 families, derived from the cross Zheng58 × K22. The F_2:3 families were used as the female donor and Yu high inducer No. 1 (YHI‐1) as the male inducer line. The rates of HMF from each family line were evaluated at two field sites over two planting seasons. HMF displayed incomplete dominance. Transgressive segregation of haploids from F_2:3 families was observed relative to haploids derived from the two parents of the mapping population. A total of nine quantitative trait loci (QTL) were detected, which were distributed on chromosomes 1, 3, 4, 7 and 8. Three major QTL, qHMF3b, qHMF7a and qHMF7b were detected in both locations, respectively. These QTL could be useful to predict the ability of spontaneous haploid genome doubling, and to accelerate the haploid breeding process by introgression or aggregation of those QTL.     

Genetic architecture of plant height in maize phenotype‐selected introgression families

This study aimed at developing, characterizing and evaluating two maize phenotypic‐selected introgression libraries for a collection of dominant plant height (PHT)‐increasing alleles by introgressing donor chromosome segments (DCS) from Germplasm Enhancement of Maize (GEM) accessions into elite inbred lines: PHB47 and PHZ51. Different backcross generations (BC₁‐BC₄) were developed and the tallest 23 phenotype‐selected introgression families (PIFs) from each introgression library (PHB47 or PHZ51) were selected for single nucleotide polymorphism genotyping to localize DCS underlying PHT. The result shows that most PIFs carrying DCS were significantly (α = 0.01) taller than the respective recurrent parent. In addition, they contained larger donor genome proportions than expected in the absence of selection or random mating across all BC generations. The DCS were distributed over the whole genome, indicating a complex genetic nature underlying PHT. We conclude that our PIFs are enriched for favourable PHT‐increasing alleles. These two libraries offer opportunities for future PHT gene isolation and allele characterization and for breeding purposes, such as novel cultivars for biofuel production.     

水稻核心种质资源的苗期耐冷性鉴定与评价

苗期冷害是一种影响水稻群体建成和生长发育的延迟性冷害,最终导致水稻减产。筛选苗期耐冷性强的种质资源可以为水稻耐冷育种提供亲本资源。本研究采用3000份全球水稻核心种质资源中的1542份在人工气候箱进行苗期耐冷鉴定及评价,以存活率为评价指标。发现种质资源苗期耐冷性变异非常丰富,筛选出存活率80%以上的苗期耐冷资源材料73份,其中籼稻9份,温带粳稻47份,热带粳稻4份,粳稻混合型8份,籼粳中间型和香稻类型各1份,籼粳混合型3份,XI-B、XI-2和亚热带粳稻中未筛选到苗期耐冷材料。耐冷材料主要集中在温带粳稻中,但亦有部分籼稻材料表现出较强的耐冷性。多数苗期耐冷资源材料的综合农艺性状较差,结合株高、生育期性状等筛选出14份半矮秆和生育期适中的强耐冷性材料,可作为水稻苗期耐冷育种亲本应用。对利用种质资源开展苗期耐冷基因挖掘和选育全生育期耐冷品种进行了讨论。本研究初步阐明了水稻耐冷种质资源的分布,为水稻耐冷育种提供了优异的供体亲本材料。     

Relative efficiency of maize and Imperata cylindrica for haploid induction in Triticum durum following chromosome elimination‐mediated approach of doubled haploid breeding

Intergeneric hybridization in seven diverse durum wheat genotypes was carried out using two composite varieties of Himalayan maize, viz., Bajaura Makka and Early Composite, and a wild grass, Imperata cylindrica, as pollen sources. Observations related to various haploid induction parameters put forth I. cylindrica as significantly better pollen source for haploid induction in durum wheat over maize in terms of pseudoseed formation (46.93%), embryo formation (38.06%), haploid regeneration (40.42%) and haploid formation efficiency (7.44%). The line x tester analysis revealed that both male and female genotypes had significant effects on all haploid induction parameters except haploid formation frequency in later. Among the pollen sources, I. cylindrica emerged as best combiner based on GCA values when compared with the two Himalayan maize composites. Durum wheat genotype, A‐9‐30‐1 was recognized as the best general combiner followed by PDW 314. The present investigation proposed durum wheat × I. cylindrica as a superior technique over maize‐mediated system, and its large‐scale use can open a new horizon in the sphere of durum wheat doubled haploidy breeding programme.