Accelerating crop improvement in sorghum, a staple food for people in semiarid regions across the developing world, is key to ensuring global food security in the context of climate change. To facilitate gene discovery and molecular breeding in sorghum, we have characterized ∼265,000 single nucleotide polymorphisms (SNPs) in 971 worldwide accessions that have adapted to diverse agroclimatic conditions. Using this genome-wide SNP map, we have characterized population structure with respect to geographic origin and morphological type and identified patterns of ancient crop diffusion to diverse agroclimatic regions across Africa and Asia. To better understand the genomic patterns of diversification in sorghum, we quantified variation in nucleotide diversity, linkage disequilibrium, and recombination rates across the genome. Analyzing nucleotide diversity in landraces, we find evidence of selective sweeps around starch metabolism genes, whereas in landrace-derived introgression lines, we find introgressions around known height and maturity loci. To identify additional loci underlying variation in major agroclimatic traits, we performed genome-wide association studies (GWAS) on plant height components and inflorescence architecture. GWAS maps several classical loci for plant height, candidate genes for inflorescence architecture. Finally, we trace the independent spread of multiple haplotypes carrying alleles for short stature or long inflorescence branches. This genome-wide map of SNP variation in sorghum provides a basis for crop improvement through marker-assisted breeding and genomic selection.Sorghum bicolor | quantitative trait locus | adaptation

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Recombinant inbred lines of the International Triticeae Mapping Initiative (ITMI) mapping population were used to localize genetic loci that affect traits related to the free-threshing habit (percent threshability, glume tenacity, and spike fragility) and to spike morphology (spike length, spikelet number, and spike compactness) of wheat ( Triticum aestivum L.). The ITMI population was planted in three environments during 1999 and 2000, and phenotypic and genotypic data were used for composite interval mapping. Two quantitative trait loci (QTL) that consistently affected threshability-associated traits were localized on chromosomes 2D and 5A. Coincident QTL on the short arm of 2D explained 44% of the variation in threshability, 17% of the variation in glume tenacity, and 42% of the variation in rachis fragility. QTL on chromosomes 2D probably represent the effect of Tg, a gene for tenacious glumes. Coincident QTL on the long arm of 5A explained 21% and 10% of the variation in glume tenacity and rachis fragility, respectively. QTL on 5A are believed to represent the effect of Q. Overall, free-threshing-related characteristics were predominantly affected by Tg and to a lesser extent by Q. Other QTL that were significantly associated with threshability-related traits in at least one environment were localized on chromosomes 2A, 2B, 6A, 6D, and 7B. Four QTL on chromosomes 1B, 4A, 6A, and 7A consistently affected spike characteristics. Coincident QTL on the short arm of chromosome 1B explained 18% and 7% of the variation in spike length and spike compactness, respectively. QTL on the long arm of 4A explained 11%, 14%, and 12% of the variation in spike length, spike compactness, and spikelet number, respectively. A QTL on the short arm of 6A explained 27% of the phenotypic variance for spike compactness, while a QTL on the long arm of 7A explained 18% of the variation in spikelet number. QTL on chromosomes 1B and 6A appear to affect spike dimensions by modulating rachis internode length, while QTL on chromosomes 4A and 7A do so by affecting the formation of spikelets. Other QTL that were significantly associated with spike morphology-related traits, in at least one environment, were localized on chromosomes 2B, 3A, 3D, 4D, and 5A.

All 10 chromosomes of maize (Zea mays, 2n ϭ 2x ϭ 20) were recovered as single additions to the haploid complement of oat (Avena sativa, 2n ϭ 6x ϭ 42) among F 1 plants generated from crosses involving three different lines of maize to eight different lines of oat. In vitro rescue culture of more than 4,300 immature F 1 embryos resulted in a germination frequency of 11% with recovery of 379 F 1 plantlets (8.7%) of moderately vigorous growth. Some F 1 plants were sectored with distinct chromosome constitutions among tillers of the same plant and also between root and shoot cells. Meiotic restitution facilitated development of un-reduced gametes in the F 1. Self-pollination of these partially fertile F 1 plants resulted in disomic additions (2n ϭ 6x ϩ 2 ϭ 44) for maize chromosomes 1, 2, 3, 4, 6, 7, and 9. Maize chromosome 8 was recovered as a monosomic addition (2n ϭ 6x ϩ 1 ϭ 43). Monosomic additions for maize chromosomes 5 and 10 to a haploid complement of oat (n ϭ 3x ϩ 1 ϭ 22) were recovered several times among the F 1 plants. Although partially fertile, these chromosome 5 and 10 addition plants have not yet transmitted the added maize chromosome to F 2 offspring. We discuss the development and general utility of this set of oat-maize addition lines as a novel tool for maize genomics and genetics.

BackgroundPearl millet [Pennisetum glaucum (L.) R. Br.] is a widely cultivated drought- and high-temperature tolerant C4 cereal grown under dryland, rainfed and irrigated conditions in drought-prone regions of the tropics and sub-tropics of Africa, South Asia and the Americas. It is considered an orphan crop with relatively few genomic and genetic resources. This study was undertaken to increase the EST-based microsatellite marker and genetic resources for this crop to facilitate marker-assisted breeding.ResultsNewly developed EST-SSR markers (99), along with previously mapped EST-SSR (17), genomic SSR (53) and STS (2) markers, were used to construct linkage maps of four F7 recombinant inbred populations (RIP) based on crosses ICMB 841-P3 × 863B-P2 (RIP A), H 77/833-2 × PRLT 2/89-33 (RIP B), 81B-P6 × ICMP 451-P8 (RIP C) and PT 732B-P2 × P1449-2-P1 (RIP D). Mapped loci numbers were greatest for RIP A (104), followed by RIP B (78), RIP C (64) and RIP D (59). Total map lengths (Haldane) were 615 cM, 690 cM, 428 cM and 276 cM, respectively. A total of 176 loci detected by 171 primer pairs were mapped among the four crosses. A consensus map of 174 loci (899 cM) detected by 169 primer pairs was constructed using MergeMap to integrate the individual linkage maps. Locus order in the consensus map was well conserved for nearly all linkage groups. Eighty-nine EST-SSR marker loci from this consensus map had significant BLAST hits (top hits with e-value ≤ 1E-10) on the genome sequences of rice, foxtail millet, sorghum, maize and Brachypodium with 35, 88, 58, 48 and 38 loci, respectively.ConclusionThe consensus map developed in the present study contains the largest set of mapped SSRs reported to date for pearl millet, and represents a major consolidation of existing pearl millet genetic mapping information. This study increased numbers of mapped pearl millet SSR markers by >50%, filling important gaps in previously published SSR-based linkage maps for this species and will greatly facilitate SSR-based QTL mapping and applied marker-assisted selection programs.