同一基础材料的玉米双单倍体(DH)系配合力的分析

利用高频玉米单倍体诱导系,对选系材料M35/F35的F1代进行诱导获得大量单倍体籽粒,经自然加倍获得一批纯合双单倍体(DH)系,用测验系京24组配杂交组合分析DH系的配合力表现。结果表明,来源于同一基础材料的不同DH系之间,配合力差异较大,部分DH系的配合力比亲本增加,说明采用单倍体育种可以选育到高配合力的优良玉米自交系,组配出优良品种,从而加快育种进程,应用前景广阔。     

玉米单倍体加倍(DH)系籽粒性状表现的研究

玉米单倍体育种是快速选育纯合自交系的方法.研究利用单倍体诱导系,对来自BSSS杂种优势群的两个自交系BX08和BX19的杂交F1进行诱导获得单倍体,又经加倍获得33个加倍纯合系(DH),分析单倍体加倍纯合系与两个亲本及F1杂交种的果穗及籽粒性状表现.结果表明,单倍体加倍系的籽粒容积和质量比亲本籽粒都有所提高,子代的农艺性状获得显著改善,说明发生单倍体不是基因随机分离的结果,单倍体育种存在选择压力,有利于优良基因的累积,淘汰不良基因.     

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。     

东北早熟玉米育种方法改良的目标、必要性及主要内容

1改良目标围绕东北玉米种业发展对种质改良及技术需求,重点明确玉米产量及抗性性状基因的调控机制,创新高配合力多抗玉米自交系设计技术;规模化开发育种性状的功能分子标记,实现分子标记辅助育种技术实用化;开发高诱导率的单倍体诱导系和加倍技术,实现双单倍体（DR）育种技术的规模化应用;针对东北极早熟玉米区育种性状改良需求,引进多样性种质,通过表型和基因型评价,发掘优异基因资源,创建有效的种质改良与创新平台。     

玉米单倍体DH系特点及应用研究进展

利用单倍体诱导系选育技术能显著加快育种进程,高效单倍体诱导材料的培育及单倍体DH系应用是玉米单倍体育种的重要基础.本文就玉米单倍体DH系的特性及应用加以阐述,并对今后玉米单倍体DH系研究进行了展望.     

高效糯玉米单倍体加倍方法的研究

以DR 5为父本诱导5份糯玉米杂交种获得的单倍体籽粒为试验材料,探究处理方法、浓度、处理时间和温度对糯玉米单倍体的加倍效果.结果表明,浸芽法的加倍效果最好,加倍率均值达11.02％.秋水仙素浓度为0.8 mg/mL时,加倍率最高,均值达10.47％.处理时间以8h最好,加倍率均值达7.58％.处理温度为21℃时达到最佳,加倍率均值达10.96％.     

同一来源玉米DH系的性状分离分析

利用单倍体诱导系对遗传背景相近的玉米自交系MC1和MC2所组配的F1进行杂交诱导获得单倍体,经过自然加倍得181份纯系(DH系),分析DH系农艺性状的分离情况。结果表明:181个DH系株高、穗位高、穗长、秃尖长、穗行数、百粒重和单穗粒重等数量性状的次数分布符合正态分布;所得DH系各数量性状的变异类型丰富,且在产量性状上存在优于两亲本的分离;两亲本的21对SSR核心引物分子标记带谱在DH系中的分布都近似于1∶1比率,未出现偏分离。因此,通过遗传诱导的方法所得DH系类型多样,可以满足育种上的需要。单倍体育种是一种选育优良玉米纯系的有效方法。     

不同诱导系对不同基因型玉米材料的诱导率评价

玉米双单倍体（DH，Doubled haploid）技术是现代玉米育种的关键核心技术，能显著加快育种进程。为解决目前玉米单倍体育种普遍存在的诱导率低、杂株率高等问题，本研究利用 4 个单倍体诱导系和 12 个基础群体材料进行杂交，探讨不同诱导系及不同基因型材料对单倍体诱导率的影响。结果表明：（1）用 4 个诱导系诱导同一基础材料时 CS3 诱导系的平均诱导率最高，为 5.66%，稳定性也较好；不同基础材料与同一诱导系杂交时 D3 和 D4 的平均诱导率最高，分别达 7.44% 和 7.45%。 （2）用 4 个诱导系诱导同一基础材料时 CS3 诱导系的杂株率最小，为 16.95% ；不同基础材料与同一诱导系杂交时 HB4 的平均杂株率最小，为 10.93%。（3）诱导系 CS3 对 HB4 诱导时诱导率最高（11.9%），杂株率最低（0.81%）。研究结果可充实玉米单倍体育种理论研究，为玉米单倍体育种生产奠定理论基础。     

玉米单倍体鉴定方法研究进展

玉米单倍体鉴定是玉米单倍体育种三大关键技术(杂交诱导、单倍体鉴定、染色体加倍)之一,准确、高效的单倍体鉴定方法不仅可以提高玉米单倍体育种的效率,同时对筛选高诱导率的单倍体诱导系也十分重要。综述了国内外玉米单倍体鉴定方法的演变过程,旨在为玉米单倍体育种工作者把握鉴定方法发展的脉络提供帮助。     

几种糯玉米单倍体化学加倍方法的研究

以5份糯玉米杂交种为母本,以RH 20为父本进行杂交诱导获得的糯玉米单倍体籽粒为供试材料,比较不同化学加倍方法、处理浓度和处理时间对糯玉米单倍体的加倍效率.结果表明,滴心叶法的加倍效率最高,均值达11.14％;秋水仙素浓度为0.7 mg/mL时,加倍率最高,均值达11.00％;处理时间以10 h最好,加倍率均值达7.70％.     

Germplasm enhancement of maize: a look into haploid induction and chromosomal doubling of haploids from temperate‐adapted tropical sources

The allelic diversity (AD) project of the Germplasm Enhancement of Maize (GEM) programme utilized the double haploid (DH) breeding method to expedite development and release of lines derived from 300 exotic maize races. Using 18 races in this study, differential effects on haploid induction rates (HIRs) and doubling rates (DRs) by the recurrent parents PHB47 and PHZ51, the elevation that the race is traditionally grown at, and by the race itself were addressed in this study. Races from the AD project were grouped by elevation of their origin, high, middle or low altitude. Six races per elevation were randomly selected and backcrossed using both recurrent parents to generate 36 populations. Ten replications were randomized in a complete randomized design for two growing seasons. The recurrent parent effect was significant, with PHB47 having a higher HIR than PHZ51. Effect of elevation was significant with higher HIR associated with low‐elevation origin, and race also proved to be significant. Effects of elevation, recurrent parent and race were not significant for DR.     

Development of in vivo haploid inducers for tropical maize breeding programs

Lack of adapted haploid inducers currently impedes adoption of the doubled haploid technology in tropical maize breeding programs. Our objective was to generate inducers with improved adaptation to tropical conditions. We developed segregating generations from crosses between temperate inducers having haploid induction rates (HIR) of 8–10 % and tropical CIMMYT maize lines (CML; HIR = 0 %) and evaluated these for HIR and agronomic performance under tropical lowland field conditions. The applied pedigree breeding scheme comprising mass selection on individual F₂ plants for highly heritable and visually scorable traits, followed by family-based selection for HIR and other agronomic characteristics in advanced selfing and backcross (BC) generations seems highly suitable for breeding improved haploid inducers with adaptation to different agroecologies. The most advanced tropical inducer candidates (TIC) combine HIR of up to 10 % with improved pollen production, disease resistance, and plant vigor compared to temperate inducers under tropical conditions. Agronomic characteristics were significantly improved in the BC to CML compared to BC to inducers, while mean HIR of both populations were similar, indicating that backcrossing to the adapted parent was suitable to improve adaptation of new inducers without sacrificing high HIR. When screening random open-pollinated maize accessions, HIR of up to 3 % were observed, suggesting that novel genetic variation may be present in maize accessions that could be exploited to improve HIR in maize. In conclusion, tropical inducer development proceeds well, but evaluation of TIC in multi-environment trials needs to be completed before large-scale dissemination can commence.     

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.     

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.     

Review of doubled haploid production in durum and common wheat through wheat × maize hybridization

Production of doubled haploids (DHs) is an important methodology to speed the process of breeding and development of mapping populations in crops. The procedure for DH production includes two major steps: haploid induction and chromosome doubling. In recent years, wide hybridization between wheat and maize has become a main approach for haploid production in wheat. In this method, the maize chromosomes are completely eliminated during the early development of the hybrid seeds after wheat spikes were pollinated with maize pollen. Numerous wheat cultivars and mapping populations have been developed using wheat–maize hybridization. In this study, we review the procedures of DH production of durum and common wheat via wide hybridization with maize, the factors which affect the efficiency of DH production, and the mechanism of selective elimination of the maize genome during the early development of the hybrid embryos. We also report a highly efficient protocol for DH production in durum and common wheat, which was established based on the optimal conditions for each of the factors that affect the efficiency of DH production.     

Early spontaneous diploidization of maternal maize haploids generated by in vivo haploid induction

The production of doubled haploid (DH) lines has become a key technology in maize (Zea mays L.) research and breeding. However, most of the haploid plants are sterile and in many cases artificial chromosome doubling involves the use of costly and toxic chemicals. Here, we report a special kind of doubled haploid named the early doubled haploid (EH) that was generated directly by in vivo haploid induction. We found 83 EH plants induced from the hybrid Zhengdan958, 55 families of its F_2:3 population and the parental lines, all of which were confirmed to be homozygous diploids via flow cytometry and 104 SSR markers. The progeny of EH₀ (EH₁) behaved in the same manner and showed the same potentialities as the parents of Zheng58 and Chang7-2. EH plants were also detected in other genetic backgrounds at a frequency of 1–3.5 % based on the total number of haploid plants. Because the EH lines exhibited completely fertility and were obtained from induction directly in one step, they could be used in DH breeding as a new breeding strategy. According to our observations, it is likely that spontaneous doubling in EH occurred during embryo development when haploid induction. The possible mechanism of EH is also discussed.     

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.     

Effect of thidiazuron on microspore embryogenesis and plantlet regeneration in Chinese flowering cabbage (Brassica rapa. var. parachinenis)

Traditional breeding methods require more than 6 years to obtain homozygous inbred lines, while isolated microspore culture (IMC) is an effective way to cultivate double haploid homozygous lines in only 2 years. However, low embryogenesis induction frequency in Chinese flowering cabbage remains a key obstacle to the practical application of this technique. Thidiazuron was added at different concentrations to NLN‐13 medium to estimate its effects on microspore embryogenesis and plantlet regeneration. Results showed that three genotypes responded positively. Optimum thidiazuron concentrations produced embryo yields of up to 14.67 embryos per bud and increased microspore embryogenesis frequency with up to 100% survival. Plantlet regeneration rates were up to 81.67%, and the treatment groups showed lower callus formation. We obtained up to 552 diploid plants from the tested genotypes, and the percentage of doubled haploid at different TDZ concentrations showed slight differences, and doubled haploid rates in the three genotypes were above 70%. They showed a high uniformity and can be directly used for hybrid breeding. This method accelerates microspore application in Chinese flowering cabbage hybrid breeding.     

Early diagnosis of ploidy status in doubled haploid production of maize by stomata length and flow cytometry measurements

Reliable discrimination of haploid (H), doubled haploid (DH) and crossing (C) plants in early growth stages could streamline DH production in maize. By detecting in early growth stages undesirable sterile H plants and undesirable heterozygous C plants, a large proportion of resources required for DH production could be saved. The goal of this study was to evaluate the effectiveness of early classification of plants in growth stages V3‐V4 as H, DH or C in the context of DH production using flow cytometry and stomata length. As the reference classification, we used a field score based on plant phenotype commonly applied in DH production and research. Our results show that identification of misclassified C seeds is possible because the overlap in distributions of stomata length between H&DH and C plants is small and the association between flow cytometry and the reference field score is high. In contrast, overlap between H and DH distributions is substantial. Consequently, the main application we see for these classification methods in early growth stages is the identification of C seedlings.     

Classification approaches for sorting maize (Zea mays subsp. mays) haploids using single-kernel near-infrared spectroscopy

Doubled haploids (DHs) are an important breeding tool for creating maize inbred lines. One bottleneck in the DH process is the manual separation of haploids from among the much larger pool of hybrid siblings in a haploid induction cross. Here, we demonstrate the ability of single-kernel near-infrared reflectance spectroscopy (skNIR) to identify haploid kernels. The skNIR is a high-throughput device that acquires an NIR spectrum to predict individual kernel traits. We collected skNIR data from haploid and hybrid kernels in 15 haploid induction crosses and found significant differences in multiple traits such as percent oil, seed weight, or volume, within each cross. The two kernel classes were separated by their NIR profile using Partial Least Squares Linear Discriminant Analysis (PLS-LDA). A general classification model, in which all induction crosses were used in the discrimination model, and a specific model, in which only kernels within a specific induction cross, were compared. Specific models outperformed the general model and were able to enrich a haploid selection pool to above 50% haploids. Applications for the instrument are discussed.