Genomic Selection for Crop Improvement: New Molecular Breeding Strategies for Crop Improvement

Genomic Selection for Crop Improvement serves as handbook for users by providing basic as well as advanced understandings of genomic selection. This useful review explains germplasm use, phenotyping evaluation, marker genotyping methods, and statistical models involved in genomic selection. It also includes examples of ongoing activities of genomic selection for crop improvement and efforts initiated to deploy the genomic selection in some important crops. In order to understand the potential of GS breeding, it is high time to bring complete information in the form of a book that can serve as a ready reference for geneticist and plant breeders

Recent publications from the Alzheimer's Disease Neuroimaging Initiative: Reviewing progress toward improved AD clinical trials

INTRODUCTION: The Alzheimer's Disease Neuroimaging Initiative (ADNI) has continued development and standardization of methodologies for biomarkers and has provided an increased depth and breadth of data available to qualified researchers. This review summarizes the over 400 publications using ADNI data during 2014 and 2015. METHODS: We used standard searches to find publications using ADNI data. RESULTS: (1) Structural and functional changes, including subtle changes to hippocampal shape and texture, atrophy in areas outside of hippocampus, and disruption to functional networks, are detectable in presymptomatic subjects before hippocampal atrophy; (2) In subjects with abnormal β-amyloid deposition (Aβ+), biomarkers become abnormal in the order predicted by the amyloid cascade hypothesis; (3) Cognitive decline is more closely linked to tau than Aβ deposition; (4) Cerebrovascular risk factors may interact with Aβ to increase white-matter (WM) abnormalities which may accelerate Alzheimer's disease (AD) progression in conjunction with tau abnormalities; (5) Different patterns of atrophy are associated with impairment of memory and executive function and may underlie psychiatric symptoms; (6) Structural, functional, and metabolic network connectivities are disrupted as AD progresses. Models of prion-like spreading of Aβ pathology along WM tracts predict known patterns of cortical Aβ deposition and declines in glucose metabolism; (7) New AD risk and protective gene loci have been identified using biologically informed approaches; (8) Cognitively normal and mild cognitive impairment (MCI) subjects are heterogeneous and include groups typified not only by "classic" AD pathology but also by normal biomarkers, accelerated decline, and suspected non-Alzheimer's pathology; (9) Selection of subjects at risk of imminent decline on the basis of one or more pathologies improves the power of clinical trials; (10) Sensitivity of cognitive outcome measures to early changes in cognition has been improved and surrogate outcome measures using longitudinal structural magnetic resonance imaging may further reduce clinical trial cost and duration; (11) Advances in machine learning techniques such as neural networks have improved diagnostic and prognostic accuracy especially in challenges involving MCI subjects; and (12) Network connectivity measures and genetic variants show promise in multimodal classification and some classifiers using single modalities are rivaling multimodal classifiers. DISCUSSION: Taken together, these studies fundamentally deepen our understanding of AD progression and its underlying genetic basis, which in turn informs and improves clinical trial desig

Identifying Quantitative Trait Loci for Resistance Against Stripe Rust and Septoria tritici blotch in Soft White Winter Wheat

Stripe rust (Puccinia striiformis f. sp. tritici) and Septoria tritici blotch (Zymoseptoria tritici) are a constant and significant threat to wheat production, significantly reducing wheat quality and yield. Wheat is responsible for 20% of the world’s human calorie intake, and wheat production must increase to supply the demand of the world’s growing population. Both stripe rust and Septoria tritici blotch (STB) are critical foliar diseases of wheat in the Pacific Northwest (PNW). Increasing stripe rust and STB resistance through plant breeding is the most cost-effective, sustainable, and environmentally friendly approach to manage these diseases. A recombinant inbred line population was developed from a cross between ‘Madsen’ and ‘Foote’ soft white winter wheat cultivars to study stripe rust and STB resistance. Foote (PI 599663) was initially resistant to stripe rust but is now considered susceptible to new, virulent strains of the pathogen. However, Foote has maintained moderate resistance to STB in the PNW. Madsen (PI 511673) has provided effective resistance to stripe rust, but it is considered moderately susceptible to STB. The recombinant inbred line (RIL) population, consisting of 217 lines, was phenotyped across multiple environments for stripe rust and STB response and genotyped using Illumina HiSeq 3000 Sequencing. The 217 lines were also phenotyped for seedling resistance for stripe rust in growth chambers against a bulk population of spores collected from the field in 2012 and a single isolate of race Pstv-37. Pstv-37 has been the most abundant race in the PNW in the last six years. The STACKS and Bfctools programs were used for calling genotype variation. The best linear unbiased prediction (BLUP) was calculated across environments and used to detect QTL resistance. Results of quantitative trait locus (QTL) analysis indicated minor alleles for adult plant resistance to STB in wheat chromosomes 4B, 5A, 6B, 6D and 7DS. Stacking these genes is the best strategy to develop durable resistance to STB. For wheat stripe rust in the field, major alleles for resistance were identified in wheat chromosome 2AS, which is likely the known stripe rust resistance gene Yr17, and in 1AS. Two minor QTL were found in 2AS/2DS and 4DL. For the growth chamber study, four QTL were found in 1B, 2B, 6B, and 7B, with the identified QTL dependent on the stripe rust race used for screening. Combining Yr17, 1AS, and the other QTLs will lead to developing durable resistance to individual cultivars. The QTL identified in this thesis could help to develop breeder-friendly molecular markers for use in genotypic selection for improved STB and stripe rust resistance in whea

Unravelling the genetic base of the meiotic recombination landscapes in two varieties of the button mushroom, Agaricus bisporus

The button mushroom, Agaricus bisporus var. bisporus, is one of the most cultivated mushrooms worldwide. Even though wild isolates of this variety have a broad genetic variation, the traditional and present-day hybrids only have a very narrow genetic base. The button mushroom has a typical meiotic recombination landscape (MRL) in which crossover (CO) events are predominantly restricted to the extreme ends of the chromosomes. This has been one of the main obstacles for mushroom breeders in improving or generating new mushroom hybrids due to a considerable linkage drag. A wild variety of A. bisporus, i.e., burnettii appeared to have CO spread more evenly across the genome. The existence of two extremely different MRLs in two compatible A. bisporus varieties offers an excellent opportunity to study the genetic basis for positioning CO in meiosis. The main objective of the research presented in this thesis initially was to examine meiosis of the var. burnettii in more detail and subsequently to identify genomic regions revealing the difference in MRL of the two A. bisporus varieties. The availability of genome sequences in the bisporus variety has produced many more informative markers such as SNP. We aimed to de novo sequence one of the haplotypes of a heterokaryotic strain of the burnettii variety using the PacBio sequencing technique and resequencing the other haplotype using Illumina HiSeq. In parallel to this, we used Genotyping by Sequencing (GBS) to construct the first linkage map of the burnettii variety, showing a more or less even distribution of COs across the genome. The constructed linkage map has also proved to be a useful tool for de novo assembly of the burnettii variety genome sequence. In addition, we performed comparative genome sequence studies between the burnettii variety and the previously sequenced genomes of two of the bisporus variety homokaryons, indicating high levels of collinearity between all three genomes. The only chromosomal rearrangement to be found was on chromosome 10, where an inversion of ~ 800 kb in the burnettii variety was detected compared to the var. bisporus genomes. As a starting point for unravelling the genetic basis underlying MRL in the A. bisporus, we performed quantitative trait loci (QTL) analysis using bisporus and burnettii varieties. An inter-varietal population was developed from a cross between a constituent nucleus of the bisporus and the burnettii variety. This population contains 178 haploid progenies which were genotyped by 210 SNP markers to construct a genetic linkage map, which proves to be a solid foundation for exploring the genetic control of MRL of A. bisporus. In addition, we performed a comparative genetic mapping study using the genetic maps of the bisporus variety Horst U1, the burnettii variety Bisp119/9 and the inter-varietal hybrid by selecting markers having similar positions in these three maps. In contrast to the bisporus variety where CO events are mainly restricted to chromosome ends, the burnettii variety shows a more or less equal distribution of CO events across the entire genome. The recombination landscape of the inter-varietal hybrid shows an intermediate pattern to that of both varieties. The MRL trait is expressed as a CO event in the offspring of each individual of the inter-varietal mapping population. For this reason, the individuals of the inter-varietal mapping population were intercrossed and outcrossed to generate three types of second generation hybrids. Two compatible tester homokaryons derived from the bisporus and burnettii varieties were used for outcrossing. Subsequently, the haploid progenies from each type of second generation hybrids were isolated to generate three types of segregating populations. The haploid progenies from segregating populations were genotyped with SNP markers covering the whole length of all the chromosomes. Recombination frequencies were determined at distal ends and elsewhere on the chromosomes and used to compare recombination frequencies between chromosomes within each population as well as between segregating populations across all chromosomes. A prerequisite for successful QTL mapping the MRL is to select segregating populations in which the segregation of MRL is clear. We observed that segregating populations outcrossed with the bisporus tester homokaryon were the most useful populations to generate haploid offspring in which COs are assessed for further QTL study of MRL at the time when this research was carried out. To map genomic regions involved in the different MRLs of A. bisporus, 71 homokaryotic offspring of the inter-varietal hybrid were outcrossed with an unrelated tester homokaryon of the bisporus variety. Subsequently, the haploid progenies were isolated from each hybrid and genotyped with SNP markers. Marker pairs were generated for the end regions of chromosomes to assess CO there or anywhere else on the chromosomes for each segregating population. QTL mapping analysis revealed two QTLs located on chromosome l and three others located on chromosomes IV, VI and VII. The QTLs identified span large parts of their respective chromosomes; therefore further strategies are needed for a more precise assessment and localisation of MRL.</p