Addition of rye chromosome 4R to wheat increases anther length and pollen grain number

Rice Big Grain1 improves grain yield in ectopically expressing rice and heterologously expressing tobacco plants

Functional genomics through transgenesis has provided faster and more reliable methods for identifying, characterizing, and utilizing genes or quantitative trait loci linked to agronomic traits to target yield. The present study explored the role of Big Grain1 (BG1) gene of rice (Oryza sativa L.) in yield improvement of crop plants. We aimed to identify the genetic variation of OsBG1 in various indica rice cultivars by studying the allelic polymorphism of the gene, while also investigating the gene's potential to increase crop yield through the transgenic approach. Our study reports the presence of an extra 393 bp sequence having two 6 bp enhancer elements in the 3' regulatory sequence of OsBG1 in the large-grain cultivar IR64 but not in the small-grain cultivar Badshahbhog. A single copy of the OsBG1 gene in both the cultivars and a 4.1-fold higher expression of OsBG1 in IR64 than in Badshahbhog imply that the grain size is positively correlated with the level of OsBG1 expression in rice. The ectopic expression of OsBG1 under the endosperm-specific glutelin C promoter in Badshahbhog enhanced the flag leaf length, panicle weight, and panicle length by an average of 33.2%, 33.7%, and 30.5%, respectively. The length of anthers, spikelet fertility, and grain yield per plant increased in transgenic rice lines by an average of 27.5%, 8.3%, and 54.4%, respectively. Heterologous expression of OsBG1 under the constitutive 2xCaMV35S promoter improved the number of seed pods per plant and seed yield per plant in transgenic tobacco lines by an average of 2.2-fold and 2.6-fold, respectively. Improving crop yield is crucial to ensure food security and socio-economic stability, and identifying suitable genetic factor is the essential step towards this endeavor. Our findings suggest that the OsBG1 gene is a promising candidate for improving the grain yield of monocot and dicot plant systems by molecular breeding and genetic engineering.

Green Revolution dwarfing Rht genes negatively affected wheat floral traits related to cross-pollination efficiency

Hybrid breeding is a promising strategy to quickly improve wheat yield and stability. Due to the usefulness of the Rht 'Green Revolution' dwarfing alleles, it is important to gain a better understanding of their impact on traits related to hybrid development. Traits associated with cross-pollination efficiency were studied using Near Isogenic Lines carrying the different sets of alleles in Rht genes: Rht1 (semi-dwarf), Rht2 (semi-dwarf), Rht1 + 2 (dwarf), Rht3 (extreme dwarf), Rht2 + 3 (extreme dwarf), and rht (tall) during four growing seasons. Results showed that the extreme dwarfing alleles Rht2 + 3, Rht3, and Rht1 + 2 presented the greatest effects in all the traits analyzed. Plant height showed reductions up to 64% (Rht2 + 3) compared to rht. Decreases up to 20.2% in anther length and 33% in filament length (Rht2 + 3) were observed. Anthers extrusion decreased from 40% (rht) to 20% (Rht1 and Rht2), 11% (Rht3), 8.3% (Rht1 + 2), and 6.5% (Rht2 + 3). Positive correlations were detected between plant height and anther extrusion, anther, and anther filament lengths, suggesting the negative effect of dwarfing alleles. Moreover, the magnitude of these negative impacts depends on the combination of the alleles: Rht2 + 3 > Rht3/Rht1 + 2 > Rht2/Rht1 > rht (tall). Reductions were consistent across genotypes and environments with interactions due to magnitude effects. Our results indicate that Rht alleles are involved in multiple traits of interest for hybrid wheat production and the need to select alternative sources for reduced height/lodging resistance for hybrid breeding programs.

Identification and DNA Marker Development for a Wheat-Leymus mollis 2Ns (2D) Disomic Chromosome Substitution

Leymus mollis (2n = 4x = 28, NsNsXmXm), a wild relative of common wheat (Triticum aestivum L.), carries numerous loci which could potentially be used in wheat improvement. In this study, line 17DM48 was isolated from the progeny of a wheat and L. mollis hybrid. This line has 42 chromosomes forming 21 bivalents at meiotic metaphase I. Genomic in situ hybridization (GISH) demonstrated the presence of a pair chromosomes from the Ns genome of L. mollis. This pair substituted for wheat chromosome 2D, as shown by fluorescence in situ hybridization (FISH), DNA marker analysis, and hybridization to wheat 55K SNP array. Therefore, 17DM48 is a wheat-L. mollis 2Ns (2D) disomic substitution line. It shows longer spike and a high level of stripe rust resistance. Using specific-locus amplified fragment sequencing (SLAF-seq), 13 DNA markers were developed to identify and trace chromosome 2Ns of L. mollis in wheat background. This line provides a potential bridge germplasm for genetic improvement of wheat stripe rust resistance.

Pollen Production of Selected Grass Species in Russia and India at the Levels of Anther, Flower and Inflorescence

Grasses produce large amounts of pollen and are among the main causes of pollen allergy worldwide. Quantification of the roles of individual grass species in airborne pollen is an important task, because morphologically indistinguishable pollen grains of different species may differ in allergenicity. This requires knowledge of the pollen production of individual grass species; however, accumulated data are insufficient in this respect. Attempting to fill this gap, we studied pollen production per inflorescence in 29 grass species which are widespread in Middle Russia and India. Pollen production per inflorescence is determined by the number of grains per anther, the number of flowers in a spikelet and the number of spikelets per inflorescence, with the latter parameter being the most variable. We support the hypothesis that pollen production per inflorescence differs significantly between annual and perennial grasses. The greater pollen production of perennials can be interpreted as a tendency to guarantee cross-fertilization of species with self-incompatibility. The inferred pollen/ovule (P/O) ratios suggest the occurrence of facultative xenogamy in all annuals and obligate xenogamy in most perennials in the present dataset, though some self-incompatible annuals exist outside our sampling. Earlier data indicated that the P/O ratio of the annual cereal crop rye (Secale cereale) is higher than in any annual or perennial species sampled here. A ratio of pollen production to seed set (P/S ratio) is suggested to be another efficient parameter in reproductive biology of grasses. We highlight a need for detailed studies of reproductive biology in grasses that include both pollen and seed production. We found a correlation between pollen production per anther and anther length. A rough approximation of c. 1000 pollen grains per 1 mm of the length of an anther provides an instrument for estimates of pollen production in plant communities.

Wheat Escapes Low Light Stress by Altering Pollination Types

Although low light stress seriously affects florets fertility and grain number during the reproductive period, crops can be fertilized by heterologous pollen to alleviate the reduction of grain number. However, wheat is strongly autogamous, how to change to outcross after low light remains unclear. To understand the mechanisms of this change process, an approach combined morphological, physiological, and transcriptomic analyses was performed under low light stress imposed at the young microspore stage the booting stage from tetrad to uni-nucleate microspores stage. The results showed that low light stress caused pollen abortion, and the unfertilized ovary is fertilized by heterologous pollen after floret opening. Compared to control, the opening angle of lemma and glume were increased by 11.6-48.6 and 48.4-78.5%, respectively. The outcross of stressed wheat compensated for the 2.1-18.0% of grain number loss. During this process, phytohormones played an important role. Jasmonic acid (JA) and methyl jasmonate (MeJA) levels in spikelets were increased. Meanwhile, lignin and cellulose content decreased, and genes associated with cell wall related GO terms were enriched. Among the differentially expressed genes (DEGs), were identified 88-710 transcription factors genes, of which some homologs in Arabidopsis are proposed to function in lignin and cellulose, influencing the glume and lemma opening. Our finding can provide new insight into a survival mechanism to set seeds through pollination way alteration in the absence of self-fertilization after the stress of adversity.

Potential of Impedance Flow Cytometry to Assess the Viability and Quantity of Cannabis sativa L. Pollen

Over the last decade, efforts to breed new Cannabis sativa L. cultivars with high Cannabidiol (CBD) and other non-psychoactive cannabinoids with low tetrahydrocannabinol (THC) levels have increased. In this context, the identification of the viability and quantity of pollen, which represents the fitness of male gametophytes, to accomplish successful pollination is of high importance. The present study aims to evaluate the potential of impedance flow cytometry (IFC) for the assessment of pollen viability (PV) and total number of pollen cells (TPC) in two phytocannabinoid-rich cannabis genotypes, KANADA (KAN) and A4 treated with two different chemical solutions, silver thiosulfate solution (STS) and gibberellic acid (GA3). Pollen was collected over a period of 8 to 24 days after flowering (DAF) in a greenhouse experiment. Impedance flow cytometry (IFC) technology was used with Cannabis sativa to assess the viability and quantity of pollen. The results showed that the number of flowers per plant was highest at 24 DAF for both genotypes, A4 (317.78) and KAN (189.74). TPC induced by STS was significantly higher compared to GA3 over the collection period of 8 to 24 DAF with the highest mean TPC of 1.54 × 105 at 14 DAF. STS showed significantly higher viability of pollen compared to GA3 in genotype KAN, with the highest PV of 78.18% 11 DAF. Genotype A4 also showed significantly higher PV with STS at 8 (45.66%), 14 (77.88%), 18 (79.37%), and 24 (51.92%) DAF compared to GA3. Furthermore, counting the numbers of flowers did not provide insights into the quality and quantity of pollen; the results showed that PV was highest at 18 DAF with A4; however, the number of flowers per plant was 150.33 at 18 DAF and was thus not the maximum of produced flowers within the experiment. IFC technology successfully estimated the TPC and differentiated between viable and non-viable cells over a period of 8 to 24 DAF in tested genotypes of Cannabis sativa. IFC seems to be an efficient and reliable method to estimate PV, opening new chances for plant breeding and plant production processes in cannabis.

Genome-Wide Association and Prediction of Male and Female Floral Hybrid Potential Traits in Elite Spring Bread Wheat Genotypes

Hybrid wheat breeding is one of the most promising technologies for further sustainable yield increases. However, the cleistogamous nature of wheat displays a major bottleneck for a successful hybrid breeding program. Thus, an optimized breeding strategy by developing appropriate parental lines with favorable floral trait combinations is the best way to enhance the outcrossing ability. This study, therefore, aimed to dissect the genetic basis of various floral traits using genome-wide association study (GWAS) and to assess the potential of genome-wide prediction (GP) for anther extrusion (AE), visual anther extrusion (VAE), pollen mass (PM), pollen shedding (PSH), pollen viability (PV), anther length (AL), openness of the flower (OPF), duration of floret opening (DFO) and stigma length. To this end, we employed 196 ICARDA spring bread wheat lines evaluated for three years and genotyped with 10,477 polymorphic SNP. In total, 70 significant markers were identified associated to the various assessed traits at FDR ≤ 0.05 contributing a minor to large proportion of the phenotypic variance (8–26.9%), affecting the traits either positively or negatively. GWAS revealed multi-marker-based associations among AE, VAE, PM, OPF and DFO, most likely linked markers, suggesting a potential genomic region controlling the genetic association of these complex traits. Of these markers, Kukri_rep_c103359_233 and wsnp_Ex_rep_c107911_91350930 deserve particular attention. The consistently significant markers with large effect could be useful for marker-assisted selection. Genomic selection revealed medium to high prediction accuracy ranging between 52% and 92% for the assessed traits with the least and maximum value observed for stigma length and visual anther extrusion, respectively. This indicates the feasibility to implement genomic selection to predict the performance of hybrid floral traits with high reliability.

Factors Affecting the Number of Pollen Grains per Male Strobilus in Japanese Cedar (Cryptomeria japonica)

Japanese cedar (Cryptomeria japonica) is the most important timber species in Japan; however, its pollen is the primary cause of pollinosis in Japan. The total number of pollen grains produced by a single tree is determined by the number of male strobili (male flowers) and the number of pollen grains per male strobilus. While the number of male strobili is a visible and well-investigated trait, little is known about the number of pollen grains per male strobilus. We hypothesized that genetic and environmental factors affect the pollen number per male strobilus and explored the factors that affect pollen production and genetic variation among clones. We counted pollen numbers of 523 male strobili from 26 clones using a cell counter method that we recently developed. Piecewise Structural Equation Modeling (pSEM) revealed that the pollen number is mostly affected by genetic variation, male strobilus weight, and pollen size. Although we collected samples from locations with different environmental conditions, statistical modeling succeeded in predicting pollen numbers for different clones sampled from branches facing different directions. Comparison of predicted pollen numbers revealed that they varied >3-fold among the 26 clones. The determination of the factors affecting pollen number and a precise evaluation of genetic variation will contribute to breeding strategies to counter pollinosis. Furthermore, the combination of our efficient counting method and statistical modeling will provide a powerful tool not only for Japanese cedar but also for other plant species.

Genetic factors associated with favourable pollinator traits in the wheat cultivar Piko

Hybrid breeding in wheat has the potential to boost yields. An efficient hybrid seed production system requires elite pollinators; however, such germplasm is limited among modern cultivars. Piko, a winter wheat (Triticum aestivum L.) cultivar, has been identified as a superior pollinator and has been used in Europe. Piko has favourable pollinator traits for anther extrusion, anther length, pollen mass and hybrid seed set. However, the genetic factors responsible for Piko's favourable traits are largely unknown. Here, we report on the genetic analysis of a Piko-derived F2 mapping population. We confirmed that Piko's Rht-D1a allele for tall stature is associated with large anthers and high anther extrusion. However, Rht-D1 was not found to be associated with anther filament length, confirmed by near isogenic lines. Piko's photoperiod sensitive Ppd-B1b allele shows an association with increased spike length, more spikelets and spike architecture traits, while the insensitive Ppd-B1a allele is linked with high anther extrusion and larger anthers. We identified an anther extrusion quantitative trait locus (QTL) on chromosome 6A that showed significantly biased transmission of the favourable Piko allele amongst F2 progenies. The Piko allele is completely absent in the distal 6AS region and the central 6A region revealed a significantly lower ratio (<8%) of F2 with homozygous Piko alleles. Our study provided further evidence for the effects of Rht-D1 and Ppd-B1 loci on multiple pollinator traits and a novel anther extrusion QTL that exhibits segregation distortion.

Towards a new understanding of the division of labour in heterantherous flowers: the case of Pterolepis glomerata (Melastomataceae)

Pollen-flowers with heteromorphic stamens have been shown to promote an intrafloral division of labour as a solution to fitness costs arising from pollen consumption by bees, known as the pollen dilemma. Usually, the division is based on morphological differences in anther and pollen traits that correlate with stamen function: pollinating anthers are larger and contain more and higher-quality pollen grains than feeding anthers. Here, we present a new strategy based on a high investment in reward production and thus attraction, in the heterantherous Pterolepis glomerata, to overcome short flower longevity and maintain reproductive success. In P. glomerata small feeding anthers not only produced more pollen grains and more grains with cytoplasmic content, but also released more pollen than pollinating anthers after a single visit. This pattern was consistent until the end of floral anthesis, showing the existence of pollen-dosing mechanisms. Bees equally visited flowers with yellow feeding anthers and pollinating anthers with yellow connective appendages, indicating a visual similarity, as predicted by bee vision modelling. Our results demonstrate that the division of labour might have different outcomes. Instead of the classical expectation of more investment in reproductive pollen in pollinating stamens, P. glomerata invested more in attraction and reward in feeding stamens.

Diverse Wheat-Alien Introgression Lines as a Basis for Durable Resistance and Quality Characteristics in Bread Wheat

Wheat productivity has been significantly improved worldwide through the incorporation of novel genes from various gene pools, not least from wild relatives of wheat, into the commonly cultivated bread and durum wheat. Here, we present and summarize results obtained from a diverse set of wheat-alien introgression lines with mainly introgressions of rye, but also of Leymus spp. and Thinopyrum junceiforme into bread-wheat (Triticum aestivum L.). From this material, lines carrying 2RL were found with good agronomic performance and multiple resistance not least towards several races of powdery mildew. A novel resistance gene, one of few showing resistance towards all today identified stem rust races, designated Sr59, was also found originating from 2RL. Lines with multiple introgressions from 4R, 5R, and 6R were found resistant towards the majority of the stripe rust races known today. Due to lack of agricultural adaptation in these lines, transfer of useful genes into more adapted wheat material is a necessity, work which is also in progress through crosses with the CSph1b mutant, to be able to only transfer small chromosome segments that carry the target gene. Furthermore, resistance towards Russian wheat aphid was found in lines having a substitution of 1R (1D) and translocations of 3DL.3RS and 5AL.5RS. The rye chromosomes 1R, 2R, and 6R were found responsible for resistance towards the Syrian Hessian fly. High levels of especially zinc was found in several lines obtained from crosses with Leymus racemosus and Leymus mollis, while also some lines with 1R, 2R, or 5R showed increased levels of minerals and in particular of iron and zinc. Moreover, lines with 1R, 2R, 3R, and Leymus spp. introgressions were also found to have a combination of high iron and zinc and low cadmium concentrations. High variation was found both in grain protein concentration and gluten strength, measured as %UPP, within the lines, indicating large variation in bread-making quality. Thus, our study emphasizes the impact that wheat-alien introgression lines can contribute to current wheat lines and shows large opportunities both to improve production, resistance, and quality. To obtain such improvements, novel plant breeding tools, as discussed in this paper, opens unique opportunities, to transfer suitable genes into the modern and adapted wheat cultivars.

Hybrid breeding in wheat: how shaping floral biology can offer new perspectives

Hybrid breeding in wheat (Triticum aestivum L.) has the potential to deliver major yield increases. This is a requisite to guarantee food security for increasing population demands and to counterbalance the effects of extreme environmental conditions. Successful hybrid breeding in wheat relies on forced outcrossing while preventing self-pollination. To achieve this, research has been directed towards identifying and improving fertility control systems. To maximise cross-pollination and seed set, however, fertility control systems need to be complemented by breeding phenotypically distinct male and female lines. This review summarises existing and novel male sterility systems for wheat hybridisation. We also consider the genetic resources that can be used to alter wheat's floral development and spike morphology, with a focus on the genetic variation already available. Exploiting these resources can lead to enhanced outcrossing, a key requirement in the progress towards hybrid wheat breeding.

Effects of Rht-B1 and Ppd-D1 loci on pollinator traits in wheat

Elite wheat pollinators are critical for successful hybrid breeding. We identified Rht-B1 and Ppd-D1 loci affecting multiple pollinator traits and therefore represent major targets for improving hybrid seed production. Hybrid breeding has a great potential to significantly boost wheat yields. Ideal male pollinators would be taller in stature, contain many spikelets well-spaced along the spike and exhibit high extrusion of large anthers. Most importantly, flowering time would match with that of the female parent. Available genetic resources for developing an elite wheat pollinator are limited, and the genetic basis for many of these traits is largely unknown. Here, we report on the genetic analysis of pollinator traits using biparental mapping populations. We identified two anther extrusion QTLs of medium effect, one on chromosome 1BL and the other on 4BS coinciding with the semi-dwarfing Rht-B1 locus. The effect of Rht-B1 alleles on anther extrusion is genotype dependent, while tall plant Rht-B1a allele is consistently associated with large anthers. Multiple QTLs were identified at the Ppd-D1 locus for anther length, spikelet number and spike length, with the photoperiod-sensitive Ppd-D1b allele associated with favourable pollinator traits in the populations studied. We also demonstrated that homeoloci, Rht-D1 and Ppd-B1, influence anther length among other traits. These results suggest that combinations of Rht-B1 and Ppd-D1 alleles control multiple pollinator traits and should be major targets of hybrid wheat breeding programs.

Yielding to the image: How phenotyping reproductive growth can assist crop improvement and production

Reproductive organs are the main reason we grow and harvest most plant species as crops, yet they receive less attention from phenotyping due to their complexity and inaccessibility for analysis. This review highlights recent progress towards the quantitative high-throughput phenotyping of reproductive development, focusing on three impactful areas that are pivotal for plant breeding and crop production. First, we look at phenotyping phenology, summarizing the indirect and direct approaches that are available. This is essential for analysis of genotype by environment, and to enable effective management interpretation and agronomy and physiological interventions. Second, we look at pollen development and production, in addition to anther characteristics, these are critical points of vulnerability for yield loss when stress occurs before and during flowering, and are of particular interest for hybrid technology development. Third, we elaborate on phenotyping yield components, indirectly or directly during the season, with a numerical or growth related approach and post-harvest processing. Finally, we summarise the opportunities and challenges ahead for phenotyping reproductive growth and their feasibility and impact, with emphasis on plant breeding applications and targeted yield increases.

Development and molecular cytogenetic identification of a new wheat-rye 4R chromosome disomic addition line with resistances to powdery mildew, stripe rust and sharp eyespot

A wheat-rye 4R chromosome disomic addition line with resistances to powdery mildew, stripe rust, sharp eyespot and high kernel number per spike was developed and characterized by molecular cytogenetic method as novel resistant germplasm. Rye (Secale cereale L.), a close relative of common wheat, is an important and valuable gene donor with multiple disease resistance for wheat improvement. However, resistance genes derived from rye have successively lost resistance to pathogens due to the coevolution of pathogen virulence and host resistance. Development and identification of new effective resistance gene sources from rye therefore are of special importance and urgency. In the present study, a wheat-rye line WR35 was produced through distant hybridization, embryo rescue culture, chromosome doubling and backcrossing. WR35 was then proven to be a new wheat-rye 4R disomic addition line using sequential GISH (genomic in situ hybridization), mc-FISH (multicolor fluorescence in situ hybridization) and ND-FISH (non-denaturing FISH) with multiple probes, mc-GISH (multicolor GISH), rye chromosome arm-specific marker analysis and SLAF-seq (specific-locus amplified fragment sequencing) analysis. At the adult stage, WR35 exhibited high levels of resistance to the powdery mildew (Blumeria graminis f. sp. tritici, Bgt) and stripe rust (Puccinia striiformis f. sp. tritici, Pst) pathogens prevalent in China, and a highly virulent isolate of Rhizoctonia cerealis, the cause of wheat sharp eyespot. At the seedling stage, it was highly resistant to 22 of 23 Bgt isolates and four Pst races. Based on its disease responses to different pathogen isolates, WR35 may possess resistance gene(s) for powdery mildew, stripe rust and sharp eyespot, which differed from the known resistance genes from rye. In addition, WR35 was cytologically stable and produced high kernel number per spike. Therefore, WR35 with multi-disease resistances and desirable agronomic traits should serve as a promising bridging parent for wheat chromosome engineering breeding.

Variable Patterning of Chromatin Remodeling, Telomere Positioning, Synapsis, and Chiasma Formation of Individual Rye Chromosomes in Meiosis of Wheat-Rye Additions

Meiosis, the type of cell division that halves the chromosome number, shows a considerable degree of diversity among species. Unraveling molecular mechanisms of the meiotic machinery has been mainly based on meiotic mutants, where the effects of a change were assessed on chromosomes of the particular species. An alternative approach is to study the meiotic behavior of the chromosomes introgressed into different genetic backgrounds. As an allohexaploid, common wheat tolerates introgression of chromosomes from related species, such as rye. The behavior of individual pairs of rye homologues added to wheat has been monitored in meiotic prophase I and metaphase I. Chromosome 4R increased its length in early prophase I much more than other chromosomes studied, implying chromosome specific patterns of chromatin organization. Chromosome conformation affected clustering of telomeres but not their dispersion. Telomeres of the short arm of submetacentric chromosomes 4R, 5R, and 6R failed more often to be included in the telomere cluster either than the telomeres of the long arms or telomeres of metacentrics such as 2R, 3R, and 7R. The disturbed migration of the telomeres of 5RS and 6RS was associated with failure of synapsis and chiasma formation. However, despite the failed convergence of its telomere, the 4RS arm developed normal synapsis, perhaps because the strong increase of its length in early prophase I facilitated homologous encounters in intercalary regions. Surprisingly, chiasma frequencies in both arms of 4R were reduced. Similarly, the short arm of metacentric chromosome 2R often failed to form chiasmata despite normal synapsis. Chromosomes 1R, 3R, and 7R showed a regular meiotic behavior. These observations are discussed in the context of the behavior that these chromosomes show in rye itself.

Simultaneous Transfer of Leaf Rust and Powdery Mildew Resistance Genes from Hexaploid Triticale Cultivar Sorento into Bread Wheat

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, and wheat leaf rust, caused by Puccinia triticina Eriks, are two important diseases that severely threaten wheat production. Sorento, a hexaploid triticale cultivar from Poland, shows high resistance to the wheat powdery mildew isolate E09 and the leaf rust isolate PHT in Beijing, China. To introduce resistance genes into common wheat, Sorento was crossed with wheat line Xuezao, which is susceptible to both diseases, and the F1 hybrids were then backcrossed with Xuezao as the recurrent male parent. By marker analysis, we demonstrate that the long arm of the 2R (2RL) chromosome confers resistance to both the leaf rust and powdery mildew isolates at adult-plant and seedling stages, while the long arm of 4R (4RL) confers resistance only to powdery mildew at both stages. The chromosomal composition of BC2F3 plants containing 2R or 2RL and 4R or 4RL in the form of substitution and translocation were confirmed by GISH (genomic in situ hybridization) and FISH (fluorescence in situ hybridization). Monosomic and disomic substitutions of a wheat chromosome with chromosome 2R or 4R, as well as one 4RS-4DL/4DS-4RL reciprocal translocation homozigote and one 2RL-1DL translocation hemizigote, were recovered. Such germplasms are of great value in wheat improvement.

Unfertilized ovary pushes wheat flower open for cross-pollination

Bread wheat is strongly autogamous; however, an opportunity for outcrossing occurs when self-pollination fails and florets open. The first phase of floret opening at anthesis is short and induced by lodicule turgidity. Some wheat florets re-open post-anthesis for several days, known as the 'second opening', for which the underlying mechanisms are largely unknown. We performed detailed physiological, anatomical, and histological investigations to understand the biological basis of the flower opening process. Wheat florets were observed open when the ovary was unfertilized. Unfertilized ovaries significantly increased in radial size post-anthesis, pushing the lemma and palea apart to open the florets. The absence of fertile pollen was not directly linked to this, but anther filament elongation coincided with initiation of ovary swelling. The pericarp of unfertilized ovaries did not undergo degeneration as normally seen in developing grains, instead pericarp cells remained intact and enlarged, leading to increased ovary radial size. This is a novel role for the ovary pericarp in wheat flower opening, and the knowledge is useful for facilitating cross-pollination in hybrid breeding. Ovary swelling may represent a survival mechanism in autogamous cereals such as wheat and barley, ensuring seed set in the absence of self-fertilization and increasing genetic diversity through cross-pollination.

Mapping quantitative trait loci for heat tolerance of reproductive traits in tomato (Solanum lycopersicum)

Global warming has become a worldwide concern due to its adverse effects on agricultural output. In particular, long-term mildly high temperatures interfere with sexual reproduction and thus fruit and seed set. To uncover the genetic basis of observed variation in tolerance against heat, a bi-parental F2 mapping population from two contrasting cultivars, i.e. Nagcarlang and NCHS-1, was generated and phenotyped under continuous mild heat conditions for a number of traits underlying reproductive success, i.e. pollen viability, pollen number, style length, anther length, style protrusion, female fertility and flowering characteristics, i.e. inflorescence number and flowers per inflorescence. Quantitative trait loci (QTLs) were identified for most of these traits, including a single, highly significant one for pollen viability, which accounted for 36% of phenotypic variation in the population and modified pollen viability under high temperature with around 20%. QTLs for some traits colocalised, indicating trait dependency or pleiotropic-effect loci. We conclude that a limited set of major genes determines differences in performance of reproductive traits under continuous mild heat in tomato. The results contribute to our fundamental understanding of pollen thermotolerance and may support development of more heat-tolerant tomato varieties.

Physical Location of New PCR-Based Markers and Powdery Mildew Resistance Gene(s) on Rye (Secale cereale L.) Chromosome 4 Using 4R Dissection Lines

Rye (Secale cereale L.) 4R chromosome contains elite genes that are applicable for wheat (Triticum aestivum L.) cultivar improvement. PCR-based 4R-specific markers can benefit the detection of elite genes on 4R in wheat backgrounds. In this study, a new fluorescence in situ hybridization (FISH) map of the 4R^Ku chromosome of rye Kustro has been constructed. A set of 4R^Ku dissection lines was obtained and 301 new 4R^Ku-specific markers were developed using specific length amplified fragment sequencing (SLAF-seq) technology. These markers were combined with the 99 4R^Ku-specific markers previously developed, and were physically mapped to 4R^Ku chromosome using the new FISH map and the 4R^Ku dissection lines. A total of 338 of the 400 markers have been successfully mapped to six regions of 4R^Ku chromosome. Additionally, the powdery mildew resistance gene(s) on the 4RL^Ku arm was located to the segment between L.4 and L.8, the same region where 115 4RL^Ku-specific markers were mapped. The markers developed in this study can be used to identify a specific segment of 4R chromatin in wheat backgrounds, help construct a high-density physical map of 4R chromosome, and facilitate the utilization of elite genes on 4R chromosome in wheat breeding programs.

Chromosomal Localization of Genes Conferring Desirable Agronomic Traits from Wheat-Agropyron cristatum Disomic Addition Line 5113

Creation of wheat-alien disomic addition lines and localization of desirable genes on alien chromosomes are important for utilization of these genes in genetic improvement of common wheat. In this study, wheat-Agropyron cristatum derivative line 5113 was characterized by genomic in situ hybridization (GISH) and specific-locus amplified fragment sequencing (SLAF-seq), and was demonstrated to be a novel wheat-A. cristatum disomic 6P addition line. Compared with its parent Fukuhokomugi (Fukuho), 5113 displayed multiple elite agronomic traits, including higher uppermost internode/plant height ratio, larger flag leaf, longer spike length, elevated grain number per spike and spikelet number per spike, more kernel number in the middle spikelet, more fertile tiller number per plant, and enhanced resistance to powdery mildew and leaf rust. Genes conferring these elite traits were localized on the A. cristatum 6P chromosome by using SLAF-seq markers and biparental populations (F1, BC1F1 and BC1F2 populations) produced from the crosses between Fukuho and 5113. Taken together, chromosomal localization of these desirable genes will facilitate transferring of high-yield and high-resistance genes from A. cristatum into common wheat, and serve as the foundation for the utilization of 5113 in wheat breeding.

A unified framework for hybrid breeding and the establishment of heterotic groups in wheat

Global wheat genetic diversity can be used in a unified framework to support and accelerate hybrid breeding and the development of heterotic groups in wheat. Hybrid wheat breeding has great potential to increase the global wheat grain yield level particularly in view of the increasing abiotic and biotic stress challenges as well as variable climatic conditions. For the long-term success of hybrid wheat breeding and the maximum exploitation of heterosis, high-yielding heterotic patterns must be established. Here, we propose a unified framework for hybrid breeding and the establishment of heterotic groups in autogamous crops and exemplify it for hybrid wheat breeding in Germany. A key component is the establishment of genetic distance between heterotic groups and in this context, we assessed genetic diversity in a global collection of 1110 winter wheat varieties released during the past decades in 35 countries but with a focus on European origin. Our analyses revealed the absence of major population structure but nevertheless suggest genetically distinct subgroups with potential for hybrid wheat breeding. Taking our molecular results and additional phenotypic data together, we propose how global genetic diversity can be used to accelerate and support reciprocal recurrent selection for the development of genetically distinct heterotic groups in hybrid wheat breeding.

Cytogenetic Behavior of Trigeneric Hybrid Progeny Involving Wheat, Rye and Psathyrostachys huashanica

Trigeneric hybrids are commonly used as bridges to transfer genes from some wild species to cultivated wheat and to measure the genomic interaction between donor species. We previously reported that trigeneric germplasms were produced by crossing wheat-Psathyrostachys huashanica amphiploids (PHW-SA, 2n = 8x = 56, AABBDDNsNs) with hexaploid triticale (Zhongsi 828, 2n = 6x = 42, AABBRR). In the present study, chromosome pairing behavior and the genome constitution of the F4 progenies of wheat-rye-P. huashanica trigeneric hybrids were studied. Cytological analysis showed that the chromosome number of F4 progenies ranged from 39 to 46, and 57.5% of them had 42 chromosomes. The mean meiotic configuration of F4 lines was 1.71 univalents, 20.26 bivalents, 0.04 trivalents, and 0.001 quadrivalents per pollen mother cell. Among the lines with 2n = 42, the average pairing configuration was 1.21 univalents, 16.22 ring bivalents, 4.16 rod bivalents, and 0.01 trivalents. This result indicated that these lines were cytologically stable. Other lines with 2n = 39, 40, 41, 43, 44, 45, and 46, bearing a high number of univalents or multivalents, showed abnormal meiotic behavior. Genomic in situ hybridization (GISH) revealed that all F4 lines had 11-14 rye chromosomes, but no P. huashanica chromosomes. The complete set of 14 rye chromosomes was found in 19 lines. At meiosis, GISH detected 1-6 univalents with hybridization signals of rye in 13 lines. Bivalents with fluorescence signals were identified in each line, ranging from 3 to 7. A quadrivalent with hybridization signals was observed in only 1 line, K13-714-8. Lagging chromosomes, chromosome bridges, micronuclei, and chromosome fragments hybridizing with the probe were not discovered in any of the lines. These results inferred that the behavior of rye chromosomes was normal during meiosis. In addition, 21 lines of 2n = 42 (91.3%) with 12 or 14 rye chromosomes, always contained 6 or 7 bivalents bearing fluorescence signals. This suggested that the rye chromosomes exhibiting complete pairing in these lines were cytologically stable during meiosis and may therefore be considered as new hexaploid triticales. Thus, these lines might be potential materials for further hexaploid triticale improvement.