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Introduction: Fungal foliar diseases can severely affect the productivity of the peanut crop worldwide. Late leaf spot is the most frequent disease and a major problem of the crop in Brazil and many other tropical countries. Only partial resistance to fungal diseases has been found in cultivated peanut, but high resistances have been described on the secondary gene pool. Methods: To overcome the known compatibility barriers for the use of wild species in peanut breeding programs, we used an induced allotetraploid (Arachis stenosperma × A. magna)4x, as a donor parent, in a successive backcrossing scheme with the high-yielding Brazilian cultivar IAC OL 4. We used microsatellite markers associated with late leaf spot and rust resistance for foreground selection and high-throughput SNP genotyping for background selection. Results: With these tools, we developed agronomically adapted lines with high cultivated genome recovery, high-yield potential, and wild chromosome segments from both A. stenosperma and A. magna conferring high resistance to late leaf spot and rust. These segments include the four previously identified as having QTLs (quantitative trait loci) for resistance to both diseases, which could be confirmed here, and at least four additional QTLs identified by using mapping populations on four generations. Discussion: The introgression germplasm developed here will extend the useful genetic diversity of the primary gene pool by providing novel wild resistance genes against these two destructive peanut diseases.

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Climate change has led to the search for strategies to acclimatize plants to various abiotic stressors to ensure the production and quality of crops of commercial interest. Sorghum is the fifth most important cereal crop, providing several uses including human food, animal feed, bioenergy, or industrial applications. The crop has an excellent adaptation potential to different types of abiotic stresses, such as drought, high salinity, and high temperatures. However, it is susceptible to low temperatures compared with other monocotyledonous species. Here, we have reviewed and discussed some of the research results and advances that focused on the physiological, metabolic, and molecular mechanisms that determine sorghum cold tolerance to improve our understanding of the nature of such trait. Questions and opportunities for a comprehensive approach to clarify sorghum cold tolerance or susceptibility are also discussed.

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The rajado seeded Andean bean (Phaseolus vulgaris L.) cultivar BRSMG Realce (striped seed coat) developed by Embrapa expressed a high level of anthracnose resistance, caused by Colletotrichum lindemuthianum, in field and greenhouse screenings. The main goal of this study was to evaluate the inheritance of anthracnose resistance in BRSMG Realce, map the resistance locus or major gene cluster previously named as Co-Realce, identify resistance-related positional genes, and analyze potential markers linked to the resistance allele. F2 plants derived from the cross BRSMG Realce × BRS FC104 (Mesoamerican) and from the cross BRSMG Realce × BRS Notável (Mesoamerican) were inoculated with the C. lindemuthianum races 475 and 81, respectively. The BRSMG Realce × BRS FC104 F2 population was also genotyped using the DArTseq technology. Crosses between BRSMG Realce and BAT 93 (Mesoamerican) were also conducted and resulting F2 plants were inoculated with the C. lindemuthianum races 65 and 1609, individually. The results shown that anthracnose resistance in BRSMG Realce is controlled by a single locus with complete dominance. A genetic map including 1,118 SNP markers was built and shown 78% of the markers mapped at a distances less than 5.0 cM, with a total genetic length of 4,473.4 cM. A major locus (Co-Realce) explaining 54.6% of the phenotypic variation of symptoms caused by the race 475 was identified in Pv04, flanked by the markers snp1327 and snp12782 and 4.48 cM apart each other. These SNPs are useful for marker-assisted selection, due to an estimated selection efficiency of 99.2%. The identified resistance allele segregates independently of the resistance allele Co-33 (Pv04) present in BAT 93. The mapped genomic region with 704,867 bp comprising 63 putative genes, 44 of which were related to the pathogen-host interaction. Based on all these results and evidence, anthracnose resistance in BRSMG Realce should be considered as monogenic, useful for breeding purpose. It is proposed that locus Co-Realce is unique and be provisionally designated as CoPv04R until be officially nominated in accordance with the rules established by the Bean Improvement Cooperative Genetics Committee.

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Pastures based on perennial monocotyledonous plants are the principal source of nutrition for ruminant livestock in tropical and subtropical areas across the globe. The Urochloa genus comprises important species used in pastures, and these mainly include Urochloa brizantha, Urochloa decumbens, Urochloa humidicola, and Urochloa ruziziensis. Despite their economic relevance, there is an absence of genomic-level information for these species, and this lack is mainly due to genomic complexity, including polyploidy, high heterozygosity, and genomes with a high repeat content, which hinders advances in molecular approaches to genetic improvement. Next-generation sequencing techniques have enabled the recent release of reference genomes, genetic linkage maps, and transcriptome sequences, and this information helps improve our understanding of the genetic architecture and molecular mechanisms involved in relevant traits, such as the apomictic reproductive mode. However, more concerted research efforts are still needed to characterize germplasm resources and identify molecular markers and genes associated with target traits. In addition, the implementation of genomic selection and gene editing is needed to reduce the breeding time and expenditure. In this review, we highlight the importance and characteristics of the four main species of Urochloa used in pastures and discuss the current findings from genetic and genomic studies and research gaps that should be addressed in future research.

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Fusarium wilt (Fusarium oxysporum f. sp. phaseoli, Fop) is one of the main fungal soil diseases in common bean. The aim of the present study was to identify genomic regions associated with Fop resistance through genome-wide association studies (GWAS) in a Mesoamerican Diversity Panel (MDP) and to identify potential common bean sources of Fop's resistance. The MDP was genotyped with BARCBean6K_3BeadChip and evaluated for Fop resistance with two different monosporic strains using the root-dip method. Disease severity rating (DSR) and the area under the disease progress curve (AUDPC), at 21 days after inoculation (DAI), were used for GWAS performed with FarmCPU model. The p-value of each SNP was determined by resampling method and Bonferroni test. For UFV01 strain, two significant single nucleotide polymorphisms (SNPs) were mapped on the Pv05 and Pv11 for AUDPC, and the same SNP (ss715648096) on Pv11 was associated with AUDPC and DSR. Another SNP, mapped on Pv03, showed significance for DSR. Regarding IAC18001 strain, significant SNPs on Pv03, Pv04, Pv05, Pv07 and on Pv01, Pv05, and Pv10 were observed. Putative candidate genes related to nucleotide-binding sites and carboxy-terminal leucine-rich repeats were identified. The markers may be important future tools for genomic selection to Fop disease resistance in beans.

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BACKGROUND: Transmembrane protein 95 (TMEM95) plays a role in male fertility. Previous studies showed that genes with a significant impact on reproductive traits can also affect the growth traits of livestock. Thus, we speculated that the genetic variation of TMEM95 gene may have effects on growth traits of cattle. RESULTS: Two SNPs were genotyped. The rs136174626 and rs41904693 were in the intron 4 and 30 -untranslated region, respectively. The linkage disequilibrium analysis illustrated that these two loci were not linked. The rs136174626 was associated with six growth traits of Nanyang cattle, four traits of Luxi cattle, and three traits of Ji'an cattle. For rs41904693 locus, the GG individuals had greater body height and abdominal girth in Ji' an cattle than TT and TG individuals. In Jinnan cattle, GG and TT individuals had greater body height, height at hip cross, body length, and heart girth than TG individuals. The potential splice site prediction results suggest that the rs136174626 may influence the splicing efficiency of TMEM95, and the miRNA binding site prediction results showed that the rs41904693 may influence the expression of TMEM95 by affecting the binding efficiency of Bta-miR-1584 and TMEM95 30 -UTR. CONCLUSIONS: The findings of the study suggested that the two SNPs in TMEM95 could be a reliable basis for molecular breeding in cattle.

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BACKGROUND: Apomixis, an asexual mode of plant reproduction, is a genetically heritable trait evolutionarily related to sexuality, which enables the fixation of heterozygous genetic combinations through the development of maternal seeds. Recently, reference floral transcriptomes were generated from sexual and apomictic biotypes of Paspalum notatum, one of the most well-known plant models for the study of apomixis. However, the transcriptome dynamics, the occurrence of apomixis vs. sexual expression heterochronicity across consecutive developmental steps and the orientation of transcription (sense/antisense) remain unexplored. RESULTS: We produced 24 Illumina TruSeq®/ Hiseq 1500 sense/antisense floral transcriptome libraries covering four developmental stages (premeiosis, meiosis, postmeiosis, and anthesis) in biological triplicates, from an obligate apomictic and a full sexual genotype. De novo assemblies with Trinity yielded 103,699 and 100,114 transcripts for the apomictic and sexual samples respectively. A global comparative analysis involving reads from all developmental stages revealed 19,352 differentially expressed sense transcripts, of which 13,205 (68%) and 6147 (32%) were up- and down-regulated in apomictic samples with respect to the sexual ones. Interestingly, 100 differentially expressed antisense transcripts were detected, 55 (55%) of them up- and 45 (45%) down-regulated in apomictic libraries. A stage-by-stage comparative analysis showed a higher number of differentially expressed candidates due to heterochronicity discrimination: the highest number of differential sense transcripts was detected at premeiosis (23,651), followed by meiosis (22,830), postmeiosis (19,100), and anthesis (17,962), while the highest number of differential antisense transcripts were detected at anthesis (495), followed by postmeiosis (164), meiosis (120) and premeiosis (115). Members of the AP2, ARF, MYB and WRKY transcription factor families, as well as the auxin, jasmonate and cytokinin plant hormone families appeared broadly deregulated. Moreover, the chronological expression profile of several well-characterized apomixis controllers was examined in detail. CONCLUSIONS: This work provides a quantitative sense/antisense gene expression catalogue covering several subsequent reproductive developmental stages from premeiosis to anthesis for apomictic and sexual P. notatum, with potential to reveal heterochronic expression between reproductive types and discover sense/antisense mediated regulation. We detected a contrasting transcriptional and hormonal control in apomixis and sexuality as well as specific sense/antisense modulation occurring at the onset of parthenogenesis.

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Circular RNAs (circRNAs) are a widespread class of endogenous noncoding RNAs and they have been studied in the past few years, implying important biological functions in all kingdoms of life. Recently, circRNAs have been identified in many plant species, including cereal crops, showing differential expression during stress response and developmental programs, which suggests their role in these process. In the following years, it is expected that insights into the functional roles of circRNAs can be used by cereal scientists and molecular breeders with the aim to develop new strategies for crop improvement. Here, we briefly outline the current knowledge about circRNAs in plants and we also outline available computational resources for their validation and analysis in cereal species.

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BACKGROUND: Wheat is one of the most important crops cultivated all over the world. New high-yielding cultivars that are more resistant to fungal diseases have been permanently developed. The present study aimed at the possibility of accelerating the process of breeding new cultivars, resistant to eyespot, by using doubled haploids (DH) system supported by marker-assisted selection. RESULTS: Two highly resistant breeding lines (KBP 0916 and KBH 4942/05) carrying Pch1 gene were crossed with the elite wheat genotypes. Hybrid plants of early generations were analyzed using endopeptidase EpD1 and two SSR markers linked to the Pch1 locus. Selected homozygous and heterozygous genotypes for the Pch1-linked EpD1b allele were used to produce haploid plants. Molecular analyses were performed on haploids to identify plants possessing Pch1 gene. Chromosome doubling was performed only on haploid plants with Pch1 gene. Finally, 65 DH lines carrying eyespot resistance gene Pch1 and 30 lines without this gene were chosen for the eyespot resistance phenotyping in a field experiment. CONCLUSIONS: Results of the experiment confirmed higher resistance to eyespot of the genotypes with Pch1 in comparison to those without this gene. This indicates the efficiency of selection at the haploid level.

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MAIN CONCLUSION: In spite of the limited investment in orphan crops, access to new technologies such as bioinformatics and low-cost genotyping opens new doors to modernise their breeding effectively. Innovation in plant breeding is imperative to meet the world's growing demand for staple food and feed crops, and orphan crops can play a significant role in increasing productivity and quality, especially in developing countries. The short breeding history of most orphan crops implies that genetic gain should be achievable through easy-to-implement approaches such as forward breeding for simple traits or introgression of elite alleles at key target trait loci. However, limited financial support and access to sufficient, relevant and reliable phenotypic data continue to pose major challenges in terms of resources and capabilities. Digitalisation of orphan-crop breeding programmes can help not only to improve data quality and management, but also to mitigate data scarcity by allowing data to be accumulated and analysed over time and across teams. Bioinformatics tools and access to technologies such as molecular markers, some of them provided as services via specific platforms, allow breeders to implement modern strategies to improve breeding efficiency. In orphan crops, more marker-trait associations relevant to breeding germplasm are generally needed, but implementing digitalization, marker-based quality control or simple trait screening and introgression will help modernising breeding. Finally, the development of local capacities-of both people and infrastructure-remains a necessity to ensure the sustainable adoption of modern breeding approaches.

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Young breeding programs in developing countries, like the Chibas sorghum breeding program in Haiti, face the challenge of increasing genetic gain with limited resources. Implementing genomic selection (GS) could increase genetic gain, but optimization of GS is needed to account for these programs' unique challenges and advantages. Here, we used simulations to identify conditions under which genomic-assisted recurrent selection (GARS) would be more effective than phenotypic recurrent selection (PRS) in small new breeding programs. We compared genetic gain, cost per unit gain, genetic variance, and prediction accuracy of GARS (two or three cycles per year) vs. PRS (one cycle per year) assuming various breeding population sizes and trait genetic architectures. For oligogenic architecture, the maximum relative genetic gain advantage of GARS over PRS was 12-88%, which was observed only during the first few cycles. For the polygenic architecture, GARS provided maximum relative genetic gain advantage of 26-165%, and was always superior to PRS. Average prediction accuracy declines substantially after several cycles of selection, suggesting the prediction models should be updated regularly. Updating prediction models every year increased the genetic gain by up to 33-39% compared to no-update scenarios. For small populations and oligogenic traits, cost per unit gain was lower in PRS than GARS. However, with larger populations and polygenic traits cost per unit gain was up to 67% lower in GARS than PRS. Collectively, the simulations suggest that GARS could increase the genetic gain in small young breeding programs by accelerating the breeding cycles and enabling evaluation of larger populations.

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Several of the over 200 known species of Agave L. are currently used for production of distilled beverages and biopolymers. The plants live in a wide range of stressful environments as a result of their resistance to abiotic stress (drought, salinity, and extreme temperature) and pathogens, which gives the genus potential for germplasm conservation and biotechnological applications that may minimize economic losses as a result of the global climate change. However, the limited knowledge in the genus of genome structure and organization hampers development of potential improved biotechnological applications by means of genetic manipulation and biocatalysis. We reviewed Agave and plant sequences in the GenBank NCBI database for identifying genes with biotechnological potential for fermentation, bioenergy, fiber improvement, and in vivo plant biopolymer production. Three-dimensional modeling of enzyme structures in plant accessions revealed structural differences in sucrose 1-fructosyltransferase, fructan 1-fructosyltransferase, fructan exohydrolase (1-FEH), cellulose synthase (CES), and glucanases (EGases) with possible effects in fructan, sugar, and biopolymer production. Although the coding genes of FEH and enzymes involved in biopolymer production (CES, sucrose synthase, and EGases) remain unidentified in Agave L., our results could aid isolation of such genes in Agave. By comparing nucleotide and amino acid sequences in accessions of Agave and other plants, knowledge may be gained about transcriptional regulation and enzymatic activity factors. Future study is needed of biotechnological application of Agave genes for crop breeding aided by genetic engineering and biocatalysis. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1314-1334, 2018.

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Background: Cultivated peanut (Arachis hypogaea L.) is a major oilseed crop worldwide. Fatty acid composition of peanut oil may affect the flavor and shelf life of the resulting food products. Oleic acid and linoleic acid are the major fatty acids of peanut oil. The conversion from oleic acid to linoleic acid is controlled by theΔ12 fatty acid desaturase (FAD) encoded byAhFAD2AandAhFAD2B, two homoeologous genes from A and B subgenomes, respectively. One nucleotide substitution (G:C→A:T) ofAhFAD2Aand an "A" insertion ofAhFAD2Bresulted in high-oleic acid phenotype. Detection ofAhFAD2mutation had been achieved by cleaved amplified polymorphic sequence (CAPS), real-time polymerase chain reaction (qRT-PCR) and allele-specific PCR (AS-PCR). However, a low cost, high throughput and high specific method is still required to detectAhFAD2genotype of large number of seeds. Kompetitive allele specific PCR (KASP) can detect both alleles in a single reaction. The aim of this work is to develop KASP for detectionAhFAD2genotype of large number of breeding materials. Results: Here, we developed a KASP method to detect the genotypes of progenies between high oleic acid peanut and common peanut. Validation was carried out by CAPS analysis. The results from KASP assay and CAPS analysis were consistent. The genotype of 18 out of 179 BC4F2seeds was aabb. Conclusions: Due to high accuracy, time saving, high throughput feature and low cost, KASP is more suitable fordeterminingAhFAD2genotype than other methods.

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Rust resistance in the sunflower line P386 is controlled by Pu 6 , a gene which was reported to segregate independently from other rust resistant genes, such as R 4 . The objectives of this work were to map Pu 6 , to provide and validate molecular tools for its identification, and to determine the linkage relationship of Pu 6 and R 4 . Genetic mapping of Pu 6 with six markers covered 24.8 cM of genetic distance on the lower end of linkage Group 13 of the sunflower consensus map. The marker most closely linked to Pu 6 was ORS316 at 2.5 cM in the distal position. ORS316 presented five alleles when was assayed with a representative set of resistant and susceptible lines. Allelism test between Pu 6 and R 4 indicated that both genes are linked at a genetic distance of 6.25 cM. This is the first confirmation based on an allelism test that at least two members of the R adv /R 4 /R 11 / R 13a /R 13b /Pu 6 cluster of genes are at different loci. A fine elucidation of the architecture of this complex locus will allow designing and constructing completely new genomic regions combining genes from different resistant sources and the elimination of the linkage drag around each resistant gene.

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Rice hoja blanca (white leaf) disease can cause severe yield losses in rice in the Americas. The disease is caused by the rice hoja blanca virus (RHBV), which is transmitted by the planthopper vector Tagosodes orizicolus. Because classical breeding schemes for this disease rely on expensive, time-consuming screenings, there is a need for alternatives such as marker-aided selection. The varieties Fedearroz 2000 and Fedearroz 50, which are resistant to RHBV and to the feeding damage caused by T. orizicolus, were crossed with the susceptible line WC366 to produce segregating F2:3 populations. The F3 families were scored for their resistance level to RHBV and T. orizicolus. The F2:3 lines of both crosses were genotyped using microsatellite markers. One major QTL on the short arm of chromosome 4 was identified for resistance to RHBV in the two populations. Two major QTL on chromosomes 5 and 7 were identified for resistance to T. orizicolus in the Fd2000 × WC366 and Fd50 × WC366 crosses, respectively. This comparative study using two distinct rice populations allowed for a better understanding of how the resistance to RHBV and its vector are controlled genetically. Simple marker-aided breeding schemes based on QTL information can be designed to improve rice germplasm to reduce losses caused by this important disease.

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Sunflower rust, caused by Puccinia helianthi Schw., can result in significant yield losses in cultivated sunflower (Helianthus annuus L. var. macrocarpus Ckll.). HAR6 is a germplasm population resistant to most predominant rust races. The objectives of this study were to map the resistance factor present in HAR6 (R HAR6 ), and to provide and validate molecular tools for the identification of this gene for marker assisted selection purposes. Virulence reaction of seedlings for the F2 population and F2:3 families suggested that a single dominant gene confers rust resistance in HAR6-1, a selected rust resistance line from the original population. Genetic mapping with eight markers covered 97.4 cM of genetic distance on linkage group 13 of the sunflower consensus map. A co-dominant marker ZVG61 is the closest marker distal to R HAR6 at a genetic distance of 0.7 cM, while ORS581, a dominant marker linked in the coupling phase, is proximal to R HAR6 at a genetic distance of 1.5 cM. Validation of these markers was assessed by converting a susceptible line into a rust resistant isoline by means of marker assisted backcrossing. The application of these results to assist the breeding process and to design new strategies for rust control in sunflower is discussed.

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A pecuária de corte brasileira tem sofrido grande pressão devido às questões ambientais, às exigências dos mercados consumidores por carne de qualidade e rígidos padrões sanitários. Esses fatores aumentam a importância da melhoria da eficiência produtiva da pecuária de corte. A proposta do presente trabalho foi avaliar o efeito da inclusão dos valores genéticos moleculares, de um painel de marcadores genéticos comerciais (Perfil IGENITY® Nelore V3) na seleção de animais da raça Nelore. Foram utilizados dados de 9.749 animais da raça Nelore mensurados para área de olho de lombo, espessura de gordura subcutânea e espessura de gordura na picanha e 39.687 animais na matriz de parentesco. Dois modelos de análise foram utilizados. O modelo de análise uni-característica em que apenas os parâmetros genéticos do fenótipo foram estimados e o modelo bi-característica em que os valores genéticos moleculares de 3.033 animais foram incluídos como característica correlacionada. A inclusão dos valores genéticos moleculares no modelo aumentou as acurácias das estimativas dos valores genéticos preditos dos animais genotipados, principalmente dos machos jovens. As analises dos conflitos de seleção demonstraram maiores divergências nos touros e machos jovens que tiveram seus genótipos definidos. A taxa de ganho genético anual com a inclusão dos valores genéticos moleculares no modelo foi aumentada em 2,4% para área de olho de lombo, 0,9% para espessura de gordura subcutânea e 1,9% para espessura de gordura na picanha. Esses resultados demonstram que a utilização dos valores genéticos moleculares , mesmo quando oriundos de painéis de marcadores de DNA de baixa densidade, pode contribuir na seleção de animais superior mérito genético e, além de promover aumento nos ganhos genéticos dos programas de melhoramento genético da raça Nelore

The Brazilian beef cattle chain is suffering a huge pressure due to environmental issues, the demand of consumer markets for meat quality and strict sanitary standards of the international market. These factors increase the importance of improving productive efficiency of beef cattle. The proposal of this study was to evaluate the effect of inclusion of the molecular breeding values of a commercial panel of genetic markers (Nellore Profile IGENITY® V3) in the genetic selection of Nellore cattle. Data of 9,749 animals measured for ribeye area, fat thickness and rump fat thickness were used in this study, with a relationship matrix compound of 39,687 animals. Two models of analysis were performed. Single trait model was performed only for each observed phenotypes and two-trait model was performed phenotypes and molecular breeding values of 3,033 animals as a correlated trait. The inclusion of molecular information in genetic evaluation provided increases on the accuracies of predicted breeding values of genotyped animals and, mainly, for replacement young bulls. The divergences of selection for 20% best animals classified by 1-trait breeding values and 2-trait breeding values demonstrated highest divergence for sires and replacement young bulls. The genetic change rate on the 2-trait model increased 2,4% for ribeye area, 0,9 for fat thickness and 1,9% for rump fat thickness. These results demonstrated that the inclusion of molecular breeding values, even when estimated from low density genetic markers panels, on animal breeding evaluations can contribute on the selection of best genetic merit animals and increase of genetic change rate on animal breeding programs for Nellore cattle

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La yuca (Manihot esculenta) constituye la base de la alimentación para más de 1.000 millones de personas en el mundo, consolidándose como el cuarto cultivo más importante en el mundo después del arroz, el maíz y el trigo. La yuca es considerada como un cultivo relativamente tolerante a condiciones de estrés abiótico y biótico; sin embargo estas características se encuentran principalmente en variedades no comerciales. Las estrategias de mejoramiento genético convencional o mediadas por transformación genética representan una alternativa para introducir las características deseadas dentro de las variedades comerciales. Un paso fundamental con miras a acelerar los procesos de mejoramiento genético en yuca requiere el descubrimiento de los respectivos genes relacionados con las características buscadas, para lo cual los ESTs (del inglés Expressed Sequence Tags) son una vía rápida para este fin. En este estudio se realizó un análisis de la colección completa de ESTs disponibles en yuca, representada por 80.459 secuencias, los cuales fueron ensamblados en un conjunto de 29.231 genes únicos (unigen), representado por 10.945 contigs y 18.286 singletones. Estos 29.231 genes únicos pueden representar cerca del 80% de los genes del genoma de yuca. Entre el 5 y 10% de los unigenes de yuca no presentaron similitud con las secuencias presentes en las bases de datos de NCBI y pueden constituir genes específicos de yuca. A un grupo de secuencias del set unigen (29%) fue posible asignarles una categoría funcional de acuerdo al vocabulario Gene Ontology. El componente función molecular es el mejor representado con 43% de las secuencias, seguido por el componente proceso biológico (38%) y finalmente el componente celular (19%). Dentro de la colección de ESTs de yuca se identificaron 3.709 microsatélites que podrán ser empleados como marcadores moleculares. Este estudio representa una contribución importante al conocimiento de la estructura genómica funcional de la yuca y se constituye en una herramienta para la identificación de genes asociados a características de interés agrícola para posteriores programas de mejoramiento genético.

Cassava (Manihot esculenta) is the main source of calories for more than 1,000 millions of people around the world and has been consolidated as the fourth most important crop after rice, corn and wheat. Cassava is considered tolerant to abiotic and biotic stress conditions; nevertheless these characteristics are mainly present in non-commercial varieties. Genetic breeding strategies represent an alternative to introduce the desirable characteristics into commercial varieties. A fundamental step for accelerating the genetic breeding process in cassava requires the identification of genes associated to these characteristics. One rapid strategy for the identification of genes is the possibility to have a large collection of ESTs (Expressed Sequence Tag). In this study, a complete analysis of cassava ESTs was done. The cassava ESTs represent 80,459 sequences which were assembled in a set of 29,231 unique genes (unigen), comprising 10,945 contigs and 18,286 singletones. These 29,231 unique genes represent about 80% of the genes of the cassava’s genome. Between 5% and 10% of the unigenes of cassava not show similarity to any sequences present in the NCBI database and could be consider as cassava specific genes. A functional category was assigned to a group of sequences of the unigen set (29%) following the Gene Ontology vocabulary. The molecular function component was the best represented with 43% of the sequences, followed by the biological process component (38%) and finally the cellular component with 19%. In the cassava ESTs collection, 3,709 microsatellites were identified and they could be use as molecular markers. This study represents an important contribution to the knowledge of the functional genomic structure of cassava and constitutes an important tool for the identification of genes associated to agricultural characteristics of interest that could be employed in cassava breeding programs.

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Most traits of interest in plant breeding show quantitative inheritance, which complicate the breeding process since phenotypic performances only partially reflects the genetic values of individuals. The genetic variation of a quantitative trait is assumed to be controlled by the collective effects of quantitative trait loci (QTLs), epistasis (interaction between QTLs), the environment, and interaction between QTL and environment. Exploiting molecular markers in breeding involve finding a subset of markers associated with one or more QTLs that regulate the expression of complex traits. Many QTL mapping studies conducted in the last two decades identified QTLs that generally explained a significant proportion of the phenotypic variance, and therefore, gave rise to an optimistic assessment of the prospects of markers assisted selection. Linkage analysis and association mapping are the two most commonly used methods for QTL mapping. This review provides an overview of the two QTL mapping methods, including mapping population type and size, phenotypic evaluation of the population, molecular profiling of either the entire or a subset of the population, marker-trait association analysis using different statistical methods and software as well as the future prospects of using markers in crop improvement.

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