Maize Pollination Research Articles

Study of Pollen Traits, Production, and Artificial Pollination Methods in Zea mays L.

The optimization of artificial pollination is crucial in breeding programs for allogamous plants. In maize, achieving a balance between the labor-intensive nature of controlled pollinations and the need for large-scale production of hybrid seeds, along with considerations of germinability and pollen production, determines the success of genetic improvement programs. Breeding programs in maize have resulted in a reduction in the number of tassel branches to increase light interception and plant density in production fields. However, despite this genetic improvement, the decreased pollen production per plant has raised critical concerns regarding pollination and subsequent ear filling, especially under adverse environmental conditions. The aim of this work was the analysis of factors that can contribute to increasing the efficiency of controlled pollination in maize. The data obtained showed that pollen diameter, flavonoid, and phenolic acid content do not influence the percentage of germination and therefore the efficiency of pollination. The quantity of pollen is a central factor in ensuring the efficiency of controlled pollinations, and the data obtained by comparing traditional varieties with modern hybrids of maize showed that an increase in pollen production is determined by the increase in branching of the male inflorescence. Furthermore, we propose the use of a “smart” pollination method to make this step in maize breeding programs easier and faster.

Heat stress and sexual reproduction in maize: unveiling the most pivotal factors and the greatest opportunities.

The escalation in the intensity, frequency, and duration of high-temperature (HT) stress is currently unparalleled, which aggravates the challenges for crop production. Yet, the stage-dependent responses of reproductive organs to HT stress at the morphological, physiological, and molecular levels remain inadequately explored in pivotal staple crops. This review synthesized current knowledge regarding the mechanisms by which HT stress induces abnormalities and aberrations in reproductive growth and development, as well as by which it alters the morphology and function of florets, flowering patterns, and the processes of pollination and fertilization in maize (Zea mays L.). We identified the stage-specific sensitivities to HT stress and accurately defined the sensitive period from a time scale of days to hours. The microspore tetrad phase of pollen development and anthesis (especially shortly after pollination) are most sensitive to HT stress, and even brief temperature spikes during these stages can lead to significant kernel loss. The impetuses behind the heat-induced impairments in seed set are closely related to carbon, reactive oxygen species, phytohormone signals, ion (e.g. Ca2+) homeostasis, plasma membrane structure and function, and others. Recent advances in understanding the genetic mechanisms underlying HT stress responses during maize sexual reproduction have been systematically summarized.

Ca and Mg stimulate protein synthesis in maize kernel through the action of endogenous hormones and defense enzymes

Soil calcium (Ca) and magnesium (Mg) mineral states in rain-fed arid regions of Northwest China are inefficient, and their levels of substitution and water-soluble states are far below the lowest threshold required for maize growth, resulting in frequent physiological diseases, restricting synthesis of kernel protein (CRP). Our study set up different levels of foliar spraying of Ca and Mg fertilizers before maize pollination to examine the response characteristics of physiological and biochemical indicators in kernel, and the driving process of CRP synthesis. The main findings were: (1) Ca and Mg significantly increased the levels of CRP and endogenous hormones, and the activities of defense enzymes and CRP synthesis enzymes, which decreased significantly and stabilized at the maturity stage of maize. (2) The synthesis and accumulation of CRP were synergistically regulated by endogenous hormones, defense enzymes, and CRP synthase enzymes, with the degree of regulation varying with the level of Ca and Mg supplementation. Indole-3-acetic acid (IAA), gibberellin (GA), zeatin riboside (ZR), catalase (CAT), malondialdehyde (MDA), and glutamate dehydrogenase (GDH) were the primary physiological driving indicators of CRP synthesis, with CRP having a significant synergistic relationship with CAT and a remarkable trade-off with other driving indicators. (3) The dominant driving pathway of CRP synthesis was “Ca, Mg-IAA or GA or ZR-CAT-GDH-CRP”. Ca and Mg positively affected IAA and GA levels, and IAA and GA positively regulated CAT activity. However, CAT negatively regulated GDH levels, causing GDH to negatively influence the synthesis and accumulation of CRP and its components. The findings provide theoretical support for further study of inter-root endogenous hormones and soil microbe-driven processes in the regulation of maize quality by Ca and Mg.

Production of Haploids in Ancient, Local and Modern Wheat by Anther Culture and Maize Pollination

Production of Haploids in Ancient, Local and Modern Wheat by Anther Culture and Maize Pollination

Characterization of Source–Sink Traits and Carbon Translocation in Maize Hybrids under High Plant Density

Both compact planting and selecting superior maize (Zea mays L.) hybrids can greatly optimize the source–sink relationship and enhance maize productivity. However, the underlying physiological mechanism for regulating carbon (C) assimilate transport and influencing grain yield between maize cultivars has remained unclear under contrasting plant densities. A two-year field experiment was conducted to investigate grain yield, vascular bundle character, grain filling, C allocation in grains and other tissues, and hormone level and enzyme activity in grains under 60,000 (ND) and 90,000 plants ha−1 (HD) densities using Xianyu 335 (XY335) and Zhengdan958 (ZD958) hybrids. Compared to the ZD958, XY335 increased grain yield, kernel number per plant (KNP), and sink capacity by 11.4%, 15.7%, and 7.4%, respectively. Moreover, XY335 performed higher net photosynthetic rate and sucrose synthase activities in grains than those in ZD958, and higher levels of sucrose phosphate synthase and soluble acid invertase activity were mainly exhibited in the middle of the grain filling stage, which contributed to increasing the proportion of grain in total dry matter, grain C content and leaf C transport efficiency by 4.3%, 12.2%, and 52.9%, respectively, under HD conditions. Additionally, a greater area and number of small vascular bundle in ear of XY335 resulted in 21.3% higher matter transport efficiency and 4.8% higher maximum grain filling rate than ZD958 under HD conditions. In addition, grains of XY335 exhibited generally higher levels of indole acetic acid (IAA) and abscisic acid (ABA), as well as ABA/GA3 ratio after maize pollination relative to those from ZD958, conducive to regulating C translocation from leaves to grains. Overall, our study illustrates that stronger source activity, sink characteristics, and matter transport channels for maize hybrids are significant for C assimilate transport to grain for achieving high grain yield under higher plant density.

Reduction in seed set upon exposure to high night temperature during flowering in maize.

High temperature reduces crop production; however, little is known about the effects of high night temperature (HNT) on the development of male and female reproductive organs, pollination, kernel formation and grain yield in maize (Zea mays L.). Therefore, a temperature-controlled experiment was carried out using heat-sensitive maize hybrid and including three temperature treatments of 32/22°C (day/night; control), 32/26°C and 32/30°C during 14 consecutive days encompassing the flowering stage. When exposed to 30°C night temperature, grain yield and kernel number reduced by 23.8 and 25.1%, respectively, compared with the control. The decrease in grain yield was mainly because of the lower kernel number rather than change in kernel weight under HNT exposure around flowering. No significant differences in grain yield and kernel number were found between 22 and 26°C night temperatures. HNT had no significant effects on the onset of flowering time and anthesis-silking interval but significantly reduced time period of pollen shedding duration and pollen viability, and increased leaf night respiration. Different from high daytime temperature, HNT had no lasting effects on daytime leaf photosynthesis, biomass production and assimilate transportation. From the perspective of source-flow-sink relationship, the unchanged source and flow capacities during daytime are supposed to alleviate the adverse effects on sink strength caused by HNT compared with daytime heat stress. These new findings commendably filled the knowledge gaps concerning heat stress in maize.

Bulk pollen pollination in maize for efficient construction of introgression populations with high genome coverage

AbstractIntrogression populations consist of a set of introgression lines or families, constructed by continuous backcrossing to the recurrent parent, while carrying a limited number of chromosome segments from a donor parent in their genomes. Increasing the genome coverage is an important aim when constructing introgression population. In this study, we proposed bulk pollen pollination (BPP) method and used it to increase the genome coverage of a maize introgression population. The results showed that the genome coverage of the introgression population constructed using BPP method reached 100% at BC3 generation, which accorded with the simulation result. The BPP‐based BC3F1:2 population could identify most quantitative trait loci (QTL) detected using the F2:3 population, especially major QTL. Simulation analysis showed that the genome coverage of introgression population increased with the increase of population size and the number of bulked plants, and decreased with the increase of backcross generation. Our results proved the reliability of the BPP‐based introgression population in increasing genome coverage and detecting QTL, and provided references for constructing high‐coverage introgression populations.

Association of phytic acid towards the yield attributing traits in maize (Zea Mays. L)

The current investigation was done to understand the role of phytic acid and its contribution to yield and yield attributing traits in maize. Phytic acid is an anti-nutritional factor involved in chelating phosphorus and other micronutrients in food. On contrary, it is a major regulator of the metabolic pathways in plants. This study involved the correlation and path analysis of nineteen morphological and two biochemical traits with phytic acid as the dependent factor. A significant positive correlation of seed girth, seed thickness, hundred seed weight, cob weight, starch content and single plant yield with phytic acid were observed. This elaborated the essentiality of phytic acid in seed set and pollination in maize. Consequently, this study also ensured the increase in free inorganic phosphorous content in reduced phytic acid lines through their negative association and revealed its chelating ability in foods. Further the path analysis established highest positive direct effect of single plant yield, seed girth, cob placement height, cob weight, days to 50 percent silking and cob girth towards the phytic acid content in maize. This reinforces the direct contribution of phytic acid in crop development. The correlation also encompasses the role of phytic acid in starch accumulation and seed thickness in maize by means of their positive association. Therefore, from this study it could be concluded that phytic acid has a functional relationship with the major yield contributing traits in maize. Hence proper selection criteria have to be followed for producing elite lines with low phytic acid in maize.

Limits to maize productivity in the North China Plain: A comparison analysis for spring and summer maize

Assessing the constraints to maize productivity and narrowing the yield gap between yield potential and actual farmers’ yield in intensive maize production are essential to meeting future food demand with finite resources. A 6-year experiment that compared spring and summer maize was conducted to illuminate the limiting factors to maize productivity in the North China Plain (NCP). Drought stress in 2015 and overcast and rainy stress at the critical stage (15 d pre-silking to 15 d post-silking) in 2009, 2010 and 2016 reduced the kernel number in spring maize, and the overcast and rainy stress around silking in 2009, 2010, 2013 and 2016 led to poor pollination and low kernel number in summer maize, i.e., environmental stress at the key stage bracketing silking severely restricted the kernel number of spring and summer maize. The main limits to spring maize weight were that there was a low filling rate during the early stage and that the abundant solar and thermal resources after silking were not efficiently utilized due to heat stress; the limiting factor for summer maize weight was that the filling rate declined rapidly during the late stage because low temperature and solar radiation at late September reduced the filling rate.

Comparative proteomic analysis of the maize responses to early leaf senescence induced by preventing pollination

The aim of this study was to explore the molecular mechanisms of induced leaf senescence by preventing pollination in maize using a proteomic method combined with other physiological methods. An elite maize inbred line Yu816 was selected for evaluation of its senescence mechanism. Phenotypic and chlorophyll content analysis revealed that the onset of leaf senescence occurred earlier in non-pollinated (NONPOL) leaves than pollinated (POL) leaves. Leaf protein species of NONPOL and POL leaves were separately extracted and their proteomes were assessed using isobaric tags for relative and absolute quantitation (iTRAQ) analysis. A total of 4371 protein species were identified, of which 809 exhibited differentially altered abundance (P < 0.05). The identified protein species were related to diverse functions including photosystems, plant hormones, cell death, oxidative degradation, and protein metabolism, suggesting a potential signaling cascade for ear leaf senescence induced by pollination prevention. In addition, leaf total soluble sugar and leaf starch contents were remarkably higher in NONPOL plants than in POL plants. These findings suggest that induced leaf senescence might be associated with nutrient remobilization. Our results reveal a network of molecular mechanisms at the protein level and provide some insights into the early senescence mechanism in higher plants.Biological significance: The coordination between growth and timing for senescence is critical for maize production. However, the molecular mechanism of induced leaf senescence by preventing pollination in maize remains to be further elucidated at the proteomic level. Herein, we revealed some new protein species that are involved in hormone signaling, glycometabolism, oxidation-reduction, protein degradation and photosystem breakdown, and other biological processes that were not previously known to be associated with leaf senescence. This is the first large-scale proteomics study to examine induced leaf senescence in maize by preventing pollination.

Delayed pollination and low availability of assimilates are major factors causing maize kernel abortion.

Selective seed abortion is a survival strategy adopted by many species that sacrifices some seeds to allow the remaining ones to set. While in evolutionary terms this is a successful approach, it causes huge losses to crop yields. A pollination time gap (PTG) has been suggested to be associated with position-related grain abortion. To test this hypothesis, we developed a novel approach to alter the natural pattern of maize (Zea mays L.) pollination and to examine the impact of PTGs on kernel growth and the underlying physiological basis. When apical and basal kernels were synchronously pollinated, the basal kernels set and matured but the apical kernels were aborted at an early stage. Delaying pollination to the basal ovaries suppressed their development and reduced invertase activity and sugar levels, which allowed the apical kernels to set and grow normally. In situ localization revealed normal cell wall invertase activity in apical and basal kernels under synchronous pollination but reduced activity in the delayed-pollinated kernels independent of their position. Starch, which was abundant in basal kernel areas, was absent in the apical kernel regions under synchronous pollination but apparent with delayed pollination. Our analyses identified PTG-related sink strength and a low level of local assimilates as the main causes of grain abortion.

Backcross-breeding and doubled-haploid facilitated introgression of stripe rust resistance in bread wheat

Stripe rust caused by the fungus Puccinia striiformis f. sp. tritici (Pst) may decrease wheat yield significantly in severe outbreaks. The most cost-effective and environmentally friendly approach to reduce yield losses due to rust diseases is deployment of effective resistant genes in wheat cultivars. The causal agents evolve and may break existing resistant sources as well. Therefore, long-term conventional breeding strategies and the ongoing evolution of pathogen populations in the region would put the success of breeding programmes at risk so that there is always a need for speeding up the process of germplasm enhancement through production of doubled-haploid breeding materials. In this study, we aimed at introgression of stripe rust resistance trait from three genotypes (Flanders, Martonvasar-17 (MV17) and Bersee) into a widely adapted cultivar “Ghods”. Positively selected F2BC2 progenies of three backcrossing schemas, i.e. (i) Flanders/3*Ghods; (ii) Ghods*3/MV17; and (iii) Hybride-de-bersee/3*Ghods, were used to produce three small-size doubled-haploid populations via wheat × Maize pollination methodology. The doubled-haploid populations were examined against two predominantly isolates of P. striiformis f. sp. tritici (Pst) i.e. 6E134A+ and 6E2A+Yr27+ and the screening revealed that 44 and 52 of the progenies are resistant to the above-mentioned isolates, respectively. Field data have shown that the stripe rust resistance doubled-haploid germplasm are comparable to local check cultivars in yield and earliness.

Transcriptional and Metabolic Analysis of Senescence Induced by Preventing Pollination in Maize

Transcriptional and metabolic changes were evaluated during senescence induced by preventing pollination in the B73 genotype of maize (Zea mays). Accumulation of free glucose and starch and loss of chlorophyll in leaf was manifested early at 12 d after anthesis (DAA), while global transcriptional and phenotypic changes were evident only at 24 DAA. Internodes exhibited major transcriptomic changes only at 30 DAA. Overlaying expression data onto metabolic pathways revealed involvement of many novel pathways, including those involved in cell wall biosynthesis. To investigate the overlap between induced and natural senescence, transcriptional data from induced senescence in maize was compared with that reported for Arabidopsis (Arabidopsis thaliana) undergoing natural and sugar-induced senescence. Notable similarities with natural senescence in Arabidopsis included up-regulation of senescence-associated genes (SAGs), ethylene and jasmonic acid biosynthetic genes, APETALA2, ethylene-responsive element binding protein, and no apical meristem transcription factors. However, differences from natural senescence were highlighted by unaltered expression of a subset of the SAGs, and cytokinin, abscisic acid, and salicylic acid biosynthesis genes. Key genes up-regulated during sugar-induced senescence in Arabidopsis, including a cysteine protease (SAG12) and three flavonoid biosynthesis genes (PRODUCTION OF ANTHOCYANIN PIGMENT1 (PAP1), PAP2, and LEUCOANTHOCYANIDIN DIOXYGENASE), were also induced, suggesting similarities in senescence induced by pollination prevention and sugar application. Coexpression analysis revealed networks involving known senescence-related genes and novel candidates; 82 of these were shared between leaf and internode networks, highlighting similarities in induced senescence in these tissues. Insights from this study will be valuable in systems biology of senescence in maize and other grasses.

Effects of temperature changes on maize production in Mozambique

We examined intraseasonal changes in maize phenology and heat stress exposure over the 1979-2008 period, using Mozambique meteorological station data and maize growth require- ments in a growing degree-day model. Identifying historical effects of warming on maize growth is particularly important in Mozambique because national food security is highly dependent on domes- tic food production, most of which is grown in already warm to hot environments. Warming temper- atures speed plant development, shortening the length of growth periods necessary for optimum plant and grain size. This faster phenological development also alters the timing of maximum plant water demand. In hot growing environments, temperature increases during maize pollination threaten to make midseason crop failure the norm. In addition to creating a harsher thermal environ- ment, we find that early season temperature increases have caused the maize reproductive period to start earlier, increasing the risk of heat and water stress. Declines in time to maize maturation suggest that, independent of effects to water availability, yield potential is becoming increasingly limited by warming itself. Regional variations in effects are a function of the timing and magnitude of tempera- ture increases and growing season characteristics. Continuation of current climatic trends could induce substantial yield losses in some locations. Farmers could avoid some losses through simple changes to planting dates and maize varietal types.

Different recombination frequencies in wheat doubled haploid populations obtained through maize pollination and anther culture

This study compared the meiotic recombination frequency between wheat doubled haploid (DH) populations obtained through two different methods, maize pollination (MP♀) and anther culture (AC♂). The comparison was based on a genetic linkage analysis, performed with DNA markers. Thirty-five polymorphic markers (15 SSR, 15 AFLP, 5 RAPD) were screened in MP♀ and AC♂ doubled haploids populations, derived from the same hybrid genotype (F1 of ‘Eta’ × ‘Darkhan 15’). Nine linkage groups, comprising 35 loci (the MP♀ lines) and 31 loci (the AC♂ lines), were constructed. The linkage groups in both DH populations showed identical orders of markers, except for one group mapping to chromosome 6B. The MP♀ and AC♂ linkage maps differed significantly in recombination frequencies for corresponding intervals. In total, the AC♂ linkage map (495.5 cM) was 40.5% longer than the MP♀ map (352.8 cM), indicating a significantly higher meiotic recombination rate in pollen mother cells. The enhancement in recombination was visible in five of nine linkage groups, and in 7 intervals between individual loci out of 19 compared. Moreover, for 6 other intervals a lack of linkage was observed in the AC♂ population, as compared to the MP♀ map.

Ethylene Synthesis and Auxin Augmentation in Pistil Tissues are Important for Egg Cell Differentiation after Pollination in Maize

The role of ethylene and auxin in stigma-to-ovule signalling was investigated in maize (Zea mays L.). Maturation of the egg cells in an ear was stimulated before actual fertilization by the application of fresh pollen grains or quartz sand to fully receptive stigmas. Ethylene emission by maize ears increased in response to those treatments. Silks and ovaries were involved in ethylene synthesis after pollen or sand was shed over the silks. The content of ethylene precursor [1-aminocyclopropane-1-carboxylic acid (ACC)] increased in both pistil parts soon after pollination. ACC rise was delayed by 4 h in the ovaries, and by 8 h in the silks after mock-pollination with sand. The auxin level increased rapidly in the silks and ovaries after pollination, and it was very high in the pollinated silks due to the high indole-3-acetic acid (IAA) content of pollen grains. IAA rise also appeared in the silks and ovaries after treatment with sand but it was delayed by 8 h. Application of ACC (10 microM) or IAA (6 microM) solutions to non-pollinated silks stimulated maturation of the egg cells. Moreover, the response of the egg cells to pollination was cancelled by l-alpha-(2-aminoethoxyvinyl)-glycine, alpha-aminoisobutyric acid or 2,3,5-triiodobenzoic acid applied to the silks before pollination. Thus ethylene synthesis and polar auxin transport in the silks pollinated with fresh pollen were necessary to evoke accelerated differentiation of the egg cells in maize ovules. Differences in pistil responses found between true- and mock-pollination suggest that signalling pathways are at least partially different for the reception of pollen grains and sand crystals on maize stigma.

Genetic analysis of adult-plant resistance to leaf rust in a double haploid wheat (Triticum aestivum L. em Thell) population

A genetic analysis of adult plant resistance to leaf rust (Puccinia triticina) was performed in in vitro obtained double haploid progenies from a cross between the Brazilian wheat cultivar Trigo BR 35, which, under the high inoculum pressure of the southern region, has been resistant to leaf rust for more than 12 years, and the susceptible cultivar IAC 13-Lorena. Haplodiploidization via in vitro gimnogenesis was done by somatic elimination of the pollen donor genome after maize pollination of the F1 plants. The advantages and usefulness of double haploids (DH) for genetic analysis of complex inherited traits like durable adult-plant resistance to wheat leaf rust were evident: it was possible to analyze inheritance patterns in this cross by using only the 35 DH homozygous segregant lines obtained by in vitro embryo culture of F1 flowers pollinated by maize, this number being equivalent to 1,225 conventional F2 lines because of lack of heterozygosity. After being infected with MCG and LPG races, the results indicated that Trigo BR 35 has two resistance genes. One of the genes expressed resistance only after the intermediate stage of plant development (5-6 leaves).

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

AbstractAlthough 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.

Effect of zearalenone treatment on the production of wheat haploids via the maize pollination system.

The ability of zearalenone (ZEN) to stimulate the growth of haploid wheat embryos formed following the pollination of wheat spikes with maize pollen was tested. The maize pollination system was used as a model to compare the activity of ZEN with that of auxin analogues. Three solutions, each with a different concentration of ZEN (6.0, 3.0 or 1.5 microM), and a solution of 2,4-dichlorophenoxyacetic acid (control) were tested for their effect on ovary swelling, frequency of embryo formation and the ability to regenerate plants. In total, 3,105 florets of 282 spikes from five different cultivars of hexaploid winter wheat ( Triticum aestivum L.) were pollinated with maize ( Zea mays L. cv. Gama) pollen and treated with the ZEN solutions. The highest concentration of ZEN (6.0 microM) was the most effective in inducing ovary swelling (84 swollen ovaries/100 pollinated florets) and increasing the frequency of embryo induction (18.9 embryos/100 pollinated florets), but these embryos were severely deformed. They had low capability to germinate in vitro, while callus was easily formed and indirect regeneration of plants was possible. The lowest ZEN concentration (1.5 micrroM) induced ovary swelling in 42.8/100 pollinated florets and embryo growth in 3.3 out of 100 pollinated florets. The embryos were regular in shape, and almost half of them germinated in vitro while callus induction from them failed. The concentration of 3 microM ZEN had an intermediate effect. The type of response of the various wheat genotypes was similar, while frequencies were different, with cv. Izolda being the most responsive. The results show that ZEN has some of the properties of an auxin analogue, while other effects of its action are unique. It can be used in the maize pollination system of doubled haploid production to replace auxin analogues when indirect regeneration of plants via callus tissue is planned.

The effects of parthenogenesis on wheat embryo formation and haploid production with and without maize pollination

Doubled haploid (DH) lines are important in wheat (Triticum aestivum L.) breeding, and haploids produced via maize pollination precede DH line development. Although maize pollination has proven reliable and broadly applicable to wheat, its success is determined by the wheat and maize genotypes employed. A wheat genotype consisting of nuclear and cytoplasm components predisposing it to parthenogenesis was compared with three other genotypes, each possessing only one or neither component necessary for parthenogenesis. In a glasshouse experiment, each genotype was pollinated with maize and subsequently treated with a2,4-Dichlorophenoxyacetic Acid (2,4-D) solution to determine if parthenogenesis affected embryo formation frequency (EFF)and haploid formation efficiency (HFE). Wheat genotypes were also treated with the2,4-D solution alone to determine if embryos and haploid plants could be produced in vivo without maize pollination. ‘Salmon(K)’, a parthenogenetic genotype consisting of a Salmon 1BL.1RS nucleus in a Ae. kotschyii cytoplasm, had a mean EFF of 32%; whereas, the non-parthenogenetic genotypes had mean EFF calculations ranging from 7 to 21%. Mean HFE for Salmon(K) was not significantly different than the mean HFE for non-parthenogenetic Salmon; however, EFF and HFE calculations for Salmon(K) and Salmon, each with a 1BL.1RS translocation, were generally higher than calculations for genotypes without the translocation. Salmon(K) was the only genotype to produce a 3% or higher EFF and HFE after treatment with 2,4-D alone. Parthenogenesis significantly affected the frequency at which embryos were produced after pollination with maize and the frequency at which embryos and haploid plants were produced after treatment with 2,4-D alone.