Genetic architecture of winter hardiness and frost tolerance in triticale

Genome wide association study of frost tolerance in wheat

Winter wheat growing areas in the Northern hemisphere are regularly exposed to heavy frost. Due to the negative impact on yield, the identification of genetic factors controlling frost tolerance (FroT) and development of tools for breeding is of prime importance. Here, we detected QTL associated with FroT by genome wide association studies (GWAS) using a diverse panel of 276 winter wheat genotypes that was phenotyped at five locations in Germany and Russia in three years. The panel was genotyped using the 90 K iSelect array and SNPs in FroT candidate genes. In total, 17,566 SNPs were used for GWAS resulting in the identification of 53 markers significantly associated (LOD ≥ 4) to FroT, corresponding to 23 QTL regions located on 11 chromosomes (1A, 1B, 2A, 2B, 2D, 3A, 3D, 4A, 5A, 5B and 7D). The strongest QTL effect confirmed the importance of chromosome 5A for FroT. In addition, to our best knowledge, eight FroT QTLs were discovered for the first time in this study comprising one QTL on chromosomes 3A, 3D, 4A, 7D and two on chromosomes 1B and 2D. Identification of novel FroT candidate genes will help to better understand the FroT mechanism in wheat and to develop more effective combating strategies.

Gene Pyramiding for Sustainable Crop Improvement against Biotic and Abiotic Stresses

Sustainable agricultural production is endangered by several ecological factors, such as drought, extreme temperatures, excessive salts, parasitic ailments, and insect pest infestation. These challenging environmental factors may have adverse effects on future agriculture production in many countries. In modern agriculture, conventional crop-breeding techniques alone are inadequate for achieving the increasing population’s food demand on a sustainable basis. The advancement of molecular genetics and related technologies are promising tools for the selection of new crop species. Gene pyramiding through marker-assisted selection (MAS) and other techniques have accelerated the development of durable resistant/tolerant lines with high accuracy in the shortest period of time for agricultural sustainability. Gene stacking has not been fully utilized for biotic stress resistance development and quality improvement in most of the major cultivated crops. This review emphasizes on gene pyramiding techniques that are being successfully deployed in modern agriculture for improving crop tolerance to biotic and abiotic stresses for sustainable crop improvement.

Breeding approaches and genomics technologies to increase crop yield under low-temperature stress

Improved knowledge about plant cold stress tolerance offered by modern omics technologies will greatly inform future crop improvement strategies that aim to breed cultivars yielding substantially high under low-temperature conditions. Alarmingly rising temperature extremities present a substantial impediment to the projected target of 70% more food production by 2050. Low-temperature (LT) stress severely constrains crop production worldwide, thereby demanding an urgent yet sustainable solution. Considerable research progress has been achieved on this front. Here, we review the crucial cellular and metabolic alterations in plants that follow LT stress along with the signal transduction and the regulatory network describing the plant cold tolerance. The significance of plant genetic resources to expand the genetic base of breeding programmes with regard to cold tolerance is highlighted. Also, the genetic architecture of cold tolerance trait as elucidated by conventional QTL mapping and genome-wide association mapping is described. Further, global expression profiling techniques including RNA-Seq along with diverse omics platforms are briefly discussed to better understand the underlying mechanism and prioritize the candidate gene (s) for downstream applications. These latest additions to breeders' toolbox hold immense potential to support plant breeding schemes that seek development of LT-tolerant cultivars. High-yielding cultivars endowed with greater cold tolerance are urgently required to sustain the crop yield under conditions severely challenged by low-temperature.

Copy number variation of CBF-A14 at the Fr-A2 locus determines frost tolerance in winter durum wheat

Frost tolerance in durum wheat is mainly controlled by copy number variation of CBF - A14 at the Fr - A2 locus. Frost tolerance is a key trait for successful breeding of winter durum wheat (Triticum durum) which can increase the yield performance in regions favoring autumn-sown winter cereals. The aim of this study was to investigate the genetic architecture of frost tolerance in order to provide molecular support for the breeding of winter durum wheat. To this end, a diverse panel of 170 winter and 14 spring durum wheat genotypes of worldwide origin was evaluated for frost tolerance in the field, as well as in a semi-controlled test. A total of 30,611 polymorphic genome-wide markers obtained by a genotyping-by-sequencing approach and markers for candidate loci were used to assess marker-trait associations. One major QTL was detected on chromosome 5A, likely corresponding to Frost Resistance-A2 (Fr-A2). Further analyses strongly support the conclusion that copy number variation of CBF-A14 at the Fr-A2 locus is the causal polymorphism underlying this major QTL. It explains 91.6 % of the genotypic variance and a haploblock of two strongly associated markers in the QTL region also allowed to capture the variance of this QTL. In addition to this major QTL, a much smaller contribution of 4.2 % was observed for Fr-B2. We further investigated this major QTL and found that the copy number of CBF-A14 and the frequency of the frost tolerant haplotype mirrored the climatic conditions in the genotypes' country of origin, suggesting selection through breeding. Two functional KASP markers were developed which facilitate a high-throughput screening of the haploblock and thus a marker-based breeding of frost tolerance in winter durum wheat.

Population Structure, Genetic Variation, and Linkage Disequilibrium in Perennial Ryegrass Populations Divergently Selected for Freezing Tolerance

Low temperature is one of the abiotic stresses seriously affecting the growth of perennial ryegrass (Lolium perenne L.), and freezing tolerance is a complex trait of major agronomical importance in northern and central Europe. Understanding the genetic control of freezing tolerance would aid in the development of cultivars of perennial ryegrass with improved adaptation to frost. The plant material investigated in this study was an experimental synthetic population derived from pair-crosses among five European perennial ryegrass genotypes, representing adaptations to a range of climatic conditions across Europe. A total number of 80 individuals (24 of High frost [HF]; 29 of Low frost [LF], and 27 of Unselected [US]) from the second generation of the two divergently selected populations and an unselected (US) control population were genotyped using 278 genome-wide SNPs derived from perennial ryegrass transcriptome sequences. Our studies investigated the genetic diversity among the three experimental populations by analysis of molecular variance and population structure, and determined that the HF and LF populations are very divergent after selection for freezing tolerance, whereas the HF and US populations are more similar. Linkage disequilibrium (LD) decay varied across the seven chromosomes and the conspicuous pattern of LD between the HF and LF population confirmed their divergence in freezing tolerance. Furthermore, two F st outlier methods; finite island model (fdist) by LOSITAN and hierarchical structure model using ARLEQUIN, both detected six loci under directional selection. These outlier loci are most probably linked to genes involved in freezing tolerance, cold adaptation, and abiotic stress. These six candidate loci under directional selection for freezing tolerance might be potential marker resources for breeding perennial ryegrass cultivars with improved freezing tolerance.

Triticale biotic stresses--an overview

Triticale has been considered as resistant to diseases over a long time. Although, many authors perpetuate this opinion, it is no longer true. However, in comparison to wheat and rye triticale still may look as a healthy crop, but its healthiness has been steadily declining. It could be explained by steady expansion of the growing area and longer exposure to pathogens. On the other hand, triticale is a crop on which meet pathogens of wheat and rye, but there is evidence that on triticale embedded more so called "wheat pathogens", than rye ones. For such an notable example may serve races of Puccinia recondita. In the latter respect triticale also appears to be a bridge facilitating a direct contact between the pathogens, e.g. between physiological forms of the most important cereal rusts. Such contacts stimulate somatic hybridization on bridging triticale plant and may finally result in new hybrid pathotypes carrying virulence genes (factors) to all three hosts, i.e. triticale, wheat and rye. In addition to all triticale commercial and agronomical values, triticale still is and it will continue to be bridging transfers of resistance genes to various pathogens and pests mainly from rye to wheat. The paper will describe main diseases affecting triticale worldwide. The first disease which occurred on this cereal in epidemic proportions was stem rust (Pucinia graminis f. sp. tritici) in Australia. Leaf and stripe rusts (P. recondita f. sp. tritici and P. striiformis) are also have gained in importance everywhere triticale is grown. In recent years, at least in Poland, powdery mildew caused by Blumeria graminis occurred in epidemic proportions in quite a number of winter triticale cultivars. Similar phenomenon has been observed with quite a number of other diseases caused by facultative pathogens, such as the most damaging to triticale the Stagonospora spp. leaf and glume blotch disease complex and other pathogens like Cochliobolus sativus, Fusarium culmorum, and F. graminearum, Microdochium nivale, Bipolaris sorokiniana, Pseudocercosporella herpotrichoides, and Gaeumannomyces gramminis var. tritici inciting head, leaf and seedling blights and foot, crown and root rots. Diseases caused by bacteria, viruses, virus-like organisms and nematodes are also duly treated in this overview.