Breeding of temperate forage grasses is aimed at improving the economic and environmental sustainability of production from cattle and sheep. The primary objective is to ensure that forage can be the main source of feed for ruminants. This requires consistent production of herbage with a high feeding value, usually under nitrogen-limiting conditions. The most important traits affecting the feeding value of herbage are in vitro dry matter digestibility (DMD), the ratios of crude protein, water-soluble carbohydrate and fibre, and the concentration of alkaloid toxins. Improvements in these primary quality traits must be combined with good plant persistency, adequate tolerance to a range of environmental stresses, adequate resistance to a large number of different pathogens and invertebrate pests, and adequate seed yield. Forage grasses also have considerable potential to produce material for refining, to provide protein extracts for feeding to monogastric animals and carbohydrate for fermentation into fuel or into feedstocks for other industries.

Progress in breeding perennial forage grasses for temperate agriculture

The first haploid angiosperm, a dwarf form of cotton with half the normal chromosome complement, was discovered in 1920, and in the ninety years since then such plants have been identified in many other species. They can occur either spontaneously or can be induced by modified pollination methods in vivo, or by in vitro culture of immature male or female gametophytes. Haploids represent an immediate, one-stage route to homozygous diploids and thence to F(1) hybrid production. The commercial exploitation of heterosis in such F(1) hybrids leads to the development of hybrid seed companies and subsequently to the GM revolution in agriculture. This review describes the range of techniques available for the isolation or induction of haploids and discusses their value in a range of areas, from fundamental research on mutant isolation and transformation, through to applied aspects of quantitative genetics and plant breeding. It will also focus on how molecular methods have been used recently to explore some of the underlying aspects of this fascinating developmental phenomenon.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1467-7652.2009.00498.x

Haploids in flowering plants: origins and exploitation.

Over the past 20 years, researchers investigating the mitochondria of plants have been astonished by the phenomenal variation these organelles display relative to their mammalian and fungal counterparts. Plant mitochondria have evolved distinct strategies for genome maintenance, genetic decoding,

Higher plant mitochondria

Summary It is generally assumed that mitochondrial genomes are uniparentally transmitted, homoplasmic and nonrecombining. However, these assumptions draw largely from early studies on animal mitochondrial DNA (mtDNA). In this review, we show that plants, animals and fungi are all characterized by episodes of biparental inheritance, recombination among genetically distinct partners, and selfish elements within the mitochondrial genome, but that the extent of these phenomena may vary substantially across taxa. We argue that occasional biparental mitochondrial transmission may allow organisms to achieve the best of both worlds by facilitating mutational clearance but continuing to restrict the spread of selfish genetic elements. We also show that methodological biases and disproportionately allocated study effort are likely to have influenced current estimates of the extent of biparental inheritance, heteroplasmy and recombination in mitochondrial genomes from different taxa. Despite these complications, there do seem to be discernible similarities and differences in transmission dynamics and likelihood of recombination of mtDNA in plant, animal and fungal taxa that should provide an excellent opportunity for comparative investigation of the evolution of mitochondrial genome dynamics.

/pdf/inheritance-and-recombination-of-mitochondrial-genomes-in-1tfaqvt6pb.pdf

Inheritance and recombination of mitochondrial genomes in plants, fungi and animals.

Association-mapping methods promise to overcome the limitations of linkage-mapping methods. The main objectives of this study were to (i) evaluate various methods for association mapping in the autogamous species wheat using an empirical data set, (ii) determine a marker-based kinship matrix using a restricted maximum-likelihood (REML) estimate of the probability of two alleles at the same locus being identical in state but not identical by descent, and (iii) compare the results of association-mapping approaches based on adjusted entry means (two-step approaches) with the results of approaches in which the phenotypic data analysis and the association analysis were performed in one step (one-step approaches). On the basis of the phenotypic and genotypic data of 303 soft winter wheat ( Triticum aestivum L.) inbreds, various association-mapping methods were evaluated. Spearman's rank correlation between P -values calculated on the basis of one- and two-stage association-mapping methods ranged from 0.63 to 0.93. The mixed-model association-mapping approaches using a kinship matrix estimated by REML are more appropriate for association mapping than the recently proposed QK method with respect to (i) the adherence to the nominal α-level and (ii) the adjusted power for detection of quantitative trait loci. Furthermore, we showed that our data set could be analyzed by using two-step approaches of the proposed association-mapping method without substantially increasing the empirical type I error rate in comparison to the corresponding one-step approaches.

https://www.genetics.org/content/genetics/178/3/1745.full.pdf

Comparison of mixed-model approaches for association mapping.

Knowledge of the genetic diversity of a species is important for the choice of crossing parents in line and hybrid breeding. Our objective was to investigate European winter triticale using simple sequence repeat (SSR) markers and the coancestry coefficient (f) with regard to genetic diversity and grouping of germplasm. Three to five primer pairs for each of the 42 chromosomes were selected to analyse 128 European winter triticale varieties and breeding lines. SSR analysis resulted in the identification of 657 alleles with an average of 6.8 alleles per primer pair. The average polymorphism information content (PIC) for polymorphic markers was 0.54. Correlation between f and genetic similarity (GS) estimates based on Rogers’ Distance was low (r
 f×GS(ABDR)=0.33). The analysis of molecular variance (AMOVA) revealed that 84.7% of the total variation was found within breeding companies, and 15.3% among them. In conclusion, SSR markers from wheat and rye provide a powerful tool for assessing genetic diversity in triticale. Even though no distinct groups within the European winter triticale pool could be detected by principal co-ordinate analysis, this study provides basic information about the genetic relationships for breeding purposes.

Genetic diversity in European winter triticale determined with SSR markers and coancestry coefficient

Triticale (×Triticosecale Wittmack) (genomes AABBRR, 2n = 6x = 42) hybrid breeding and heterosis have received increased attention in recent years, but a comprehensive study is lacking. We investigated (i) the level of heterosis, (ii) the relative importance of general combining ability (GCA) vs. specific combining ability (SCA), (iii) correlations between GCA and line per se performance, (iv) trait correlations in parents and hybrids, and (v) prospects for hybrid breeding. Two hundred nine F 1 hybrids of winter triticale, produced by a chemical hybridizing agent, together with their 57 female parents and five tester (male) lines were evaluated in six environments in Germany during the season 2001-2002. Midparent heterosis for grain yield averaged 10.3% and varied from -11.4 to 22.4%, whereas better-parent heterosis averaged 5.0% and varied from -16.8 to 17.4%. Midparent heterosis was also positive for 1000-kernel weight, number of kernels per spike, test weight, and plant height but negative for number of spikes per square meter, falling number, and protein concentration. GCA variance ( 2 GCA ) was more important than SCA variance ( 2 SCA ) for all traits except grain yield and protein concentration. For most traits, GCA X location and SCA x location interaction variances were small relative to 2 GCA and 2 SCA , respectively. Genetic correlations between midparent and hybrid performance and between GCA effects and line per se performance showed similar trends, being moderate for grain yield and protein concentration and higher for the other traits. We concluded that grain yield heterosis in winter triticale crosses from parents in the current European germplasm pool is adequate to justify continuing research on hybrid breeding. By selecting parents for combining ability and establishing genetically diverse heterotic groups, a midparent grain yield heterosis of 20% could presumably be surpassed. Further information is needed on F 1 seed production and the cytoplasmic male sterility system.

Prospects for Hybrid Breeding in Winter Triticale: I. Heterosis and Combining Ability for Agronomic Traits in European Elite Germplasm

Fusarium head blight (FHB) in wheat and triticale leads to contamination of the grain with the mycotoxin deoxynivalenol (DON) that is harmful to animal and man. A fast, low-cost, and reliable method for quantification of the DON content in the grain is essential for selection. We analysed 113 wheat and 55 triticale genotypes for their symptom development on spikes, Fusarium exoantigen (ExAg) and DON content in the grain after artificial inoculation with a highly aggressive isolate of F. culmorum in three (wheat) and six (triticale) location-by-year combinations. Additionally, in triticale the amount of Fusarium damaged kernels (FDK) was assessed. ExAg content was analysed by a newly developed Fusarium-specific plate-trapped antigen enzyme-linked immunosorbent assay (PTA-ELISA) and DON content by an immunoassay. A moderate disease severity resulted in an ExAg content of 0.87 optical density (OD) units in wheat and 1.02 OD in triticale. DON content ranged from 12.0 to 105.2 mg kg−1 in wheat and from 24.2 to 74.0 mg kg−1 in triticale. Genotypic and genotype-by-environment interaction variances were significant (P < 0.01). Coefficient of phenotypic correlation between DON content analysed by the immunoassay and ExAg content was r = 0.86 for wheat and r = 0.60 for triticale. The highest correlation between DON content and symptom rating was found by FHB rating in wheat (r = 0.77) and by FDK rating in triticale (r = 0.71). In conclusion, selection for reduced FHB symptoms should lead to a correlated selection response in low fungal biomass and low DON content in the grain.

Estimation of deoxynivalenol (DON) content by symptom rating and exoantigen content for resistance selection in wheat and triticale

Triticale, an intergeneric hybrid crop-plant, is generated when female wheat lines are fertilised with pollen from rye. We have investigated the mitochondrial DNA organisation and the expression of a total of 11 different triticale genotypes, varying in their nuclear and cytoplasmic backgrounds. In Southern hybridisations using probes homologous to the upstream flanking sequences, mtDNA fragments characteristic of both wheat and rye mtDNA can be detected in all triticale lines analysed. In addition, clones isolated fom a triticale lambda library exhibit either a maternal-like or paternal-like organisation of the orf25 gene region. By PCR cloning, four different orf25 gene copies were identified in triticale, three of which correspond to maternal (85%) or paternal (12%) orf25 sequences. Three percent of all clones represent a novel type, that might have arisen by homologous recombination. Although these data suggest biparental inheritance of mtDNA in wheat/rye crosses, paternal-like gene copies can also be detected in maternal wheat mitochondria. Their stoichiometry as assayed by competitive PCR is about 0.1% of total orf25 gene copies. The high abundance of paternal-like sequences in the F1 hybrid might therefore be due to either the transmission of rye mtDNA in the intergeneric cross and/or the amplification of sequences in triticale that persist in sub-stoichiometric amounts in wheat. These data suggest that amplification and recombination of sub-genomic mitochondrial molecules are affected by different nuclear genotypes. Interestingly, sequence analysis of triticale RT-PCR clones indicates a selective transcription of maternal-like orf25 gene copies in triticale. Mitochondrial gene expression may therefore possess mechanisms to compensate for the variation of mtDNA organisation.

Parental and novel copies of the mitochondrial orf25 gene in the hybrid crop-plant triticale: predominant transcriptional expression of the maternal gene copy.

Hybrid breeding is a widely discussed alternative for triticale. Heterosis as well as general (GCA) and specific combining ability (SCA) effects were estimated for eight agronomic traits. The experiment comprised 24 F1 hybrids, produced by a chemical hybridizing agent, together with their six female and four male parents, grown in drilled plots in two locations. In comparison with the mid-parent values, hybrids averaged a 6.4 dt/ha (10.1%) higher grain yield, 8.4% more kernels per spike, a 6.8% higher 1000-kernel weight, 9.7% lower falling number (FN) and 4.4% greater plant height. SCA effects for grain yield were significant and ranged from 4.5 to 6.9 dt/ha for grain yield. Together with GCA x location interactions, they explained most of the variation. For 1000-kernel weight, GCA effects were predominant. SCA and interactions with location accounted for most of the variation in FN, whereas interactions were negligible for plant height. Correlations between mid-parent and hybrid performance and between GCA and per se performance of parents were tight for all traits except grain yield, which allows for pre-selection of parental lines. Although the amount of heterosis in triticale at present is closer to wheat than to rye, by selecting parents for combining ability and identifying heterotic patterns, grain yield heterosis of up to 20% appears sufficiently encouraging to embark on hybrid breeding.

G. Oettler

Papers

Genetic diversity in European winter triticale determined with SSR markers and coancestry coefficient

Prospects for Hybrid Breeding in Winter Triticale: I. Heterosis and Combining Ability for Agronomic Traits in European Elite Germplasm

Estimation of deoxynivalenol (DON) content by symptom rating and exoantigen content for resistance selection in wheat and triticale

Parental and novel copies of the mitochondrial orf25 gene in the hybrid crop-plant triticale: predominant transcriptional expression of the maternal gene copy.

Heterosis and combining ability for grain yield and other agronomic traits in winter triticale