Marker-Assisted Recurrent Selection for Pyramiding Leaf Rust and Coffee Berry Disease Resistance Alleles in Coffea arabica L.

In this study, marker-assisted recurrent selection was evaluated for pyramiding resistance gene alleles against coffee leaf rust (CLR) and coffee berry diseases (CBD) in Coffea arabica. A total of 144 genotypes corresponding to 12 hybrid populations from crosses between eight parent plants with desired morphological and agronomic traits were evaluated. Molecular data were used for cross-certification, diversity study and resistance allele marker-assisted selection (MAS) against the causal agent of coffee leaf rust (Hemileia vastatrix) and coffee berry disease (Colletotrichum kahawae). In addition, nine morphological and agronomic traits were evaluated to determine the components of variance, select superior hybrids, and estimate genetic gain. From the genotypes evaluated, 134 were confirmed as hybrids. The genetic diversity between and within populations was 75.5% and 24.5%, respectively, and the cluster analysis revealed three primary groups. Pyramiding of CLR and CBD resistance genes was conducted in 11 genotypes using MAS. A selection intensity of 30% resulted in a gain of over 50% compared to the original population. Selected hybrids with increased gain also showed greater genetic divergence in addition to the pyramided resistance alleles. The strategies used were, therefore, efficient to select superior coffee hybrids for recurrent selection programs and could be used as a source of resistance in various crosses.

Genomic prediction through machine learning and neural networks for traits with epistasis.

Genomic wide selection (GWS) is one contributions of molecular genetics to breeding. Machine learning (ML) and artificial neural networks (ANN) methods are non-parameterized and can develop more accurate and parsimonious models for GWS analysis. Multivariate Adaptive Regression Splines (MARS) is considered one of the most flexible ML methods, automatically modeling nonlinearities and interactions of the predictor variables. This study aimed to evaluate and compare methods based on ANN, ML, including MARS, and G-BLUP through GWS. An F2 population formed by 1000 individuals and genotyped for 4010 SNP markers and twelve traits from a model considering epistatic effect, with QTL numbers ranging from eight to 480 and heritability ( h 2 ) of 0.3, 0.5 or 0.8 were simulated. Variation in heritability and number of QTL impacts the performance of methods. About quantitative traits (40, 80, 120, 240, and 480 QTLs) was observed highest R2 to Radial Base Network (RBF) and G-BLUP, followed by Random Forest (RF), Bagging (BA), and Boosting (BO). RF and BA also showed better results for traits to h 2 of 0.3 with R 2 values 16.51% and 16.30%, respectively, while MARS methods showed better results for oligogenic traits with R 2 values ranging from 39,12 % to 43,20 % in h 2 of 0.5 and from 59.92% to 78,56% in h 2 of 0.8. Non-additive MARS methods also showed high R2 for traits with high heritability and 240 QTLs or more. ANN and ML methods are powerful tools to predict genetic values in traits with epistatic effect, for different degrees of heritability and QTL numbers.

Short-term changes related to autotetraploidy in essential oil composition of Eucalyptus benthamii Maiden & Cambage and its applications in different bioassays.

Some forest trees have been polyploidized to improve their traits and to supply new germplasms for breeding programs. As trees have a long juvenile stage, the early characterization of the chromosome set doubling effects is crucial for previous selection. Thus, we aimed to characterize the chemical variability of essential oils from diploid and autotetraploid germplasms (autotetraploid A and B) of Eucalyptus benthamii, as well as to evaluate their larvicidal and allelopathic effects. Autotetraploid A showed a higher essential oil yield than diploid and autotetraploid B, which did not differ quantitatively. Aromadendrene, viridiflorol and α-pinene were the major compounds in the diploid essential oil. In contrast, compounds were present in autotetraploids, such as 1,8-cineole, limonene, α-terpineol, and α-terpinyl-acetate. Essential oils from the diploid at 50-200 ppm were twice as larvicidal than those from autotetraploids against Aedes aegypti larvae. Considering the phytotoxicity bioassays using Lactuca sativa, essential oils from both ploidy levels affected root growth. Moreover, the essential oils inhibited shoot growth at all concentrations tested (187.5; 375; 750; 1500; and 3000 ppm). Autotetraploid A and B had the same effect on shoot growth as glyphosate. The essential oils had no cytogenotoxic effect on root meristematic cells of L. sativa, whereas phytotoxic potential was identified mainly in shoot growth. This work demonstrated a dramatic change in secondary metabolism (terpene composition) related to an increase in the ploidy level in Eucalyptus germplasms. In addition, we report the novelty of the chemical composition of essential oils among germplasms and their potential use as larvicidal and post-emergence weed control agents.

High Throughput Field Phenotyping for Plant Height Using UAV-Based RGB Imagery in Wheat Breeding Lines: Feasibility and Validation.

Plant height (PH) is an essential trait in the screening of most crops. While in crops such as wheat, medium stature helps reduce lodging, tall plants are preferred to increase total above-ground biomass. PH is an easy trait to measure manually, although it can be labor-intense depending on the number of plots. There is an increasing demand for alternative approaches to estimate PH in a higher throughput mode. Crop surface models (CSMs) derived from dense point clouds generated via aerial imagery could be used to estimate PH. This study evaluates PH estimation at different phenological stages using plot-level information from aerial imaging-derived 3D CSM in wheat inbred lines during two consecutive years. Multi-temporal and high spatial resolution images were collected by fixed-wing (P l a t F W ) and multi-rotor (P l a t M R ) unmanned aerial vehicle (UAV) platforms over two wheat populations (50 and 150 lines). The PH was measured and compared at four growth stages (GS) using ground-truth measurements (PHground) and UAV-based estimates (PHaerial). The CSMs generated from the aerial imagery were validated using ground control points (GCPs) as fixed reference targets at different heights. The results show that PH estimations using P l a t F W were consistent with those obtained from P l a t M R , showing some slight differences due to image processing settings. The GCPs heights derived from CSM showed a high correlation and low error compared to their actual heights (R 2 ≥ 0.90, RMSE ≤ 4 cm). The coefficient of determination (R 2) between PHground and PHaerial at different GS ranged from 0.35 to 0.88, and the root mean square error (RMSE) from 0.39 to 4.02 cm for both platforms. In general, similar and higher heritability was obtained using PHaerial across different GS and years and ranged according to the variability, and environmental error of the PHground observed (0.06-0.97). Finally, we also observed high Spearman rank correlations (0.47-0.91) and R 2 (0.63-0.95) of PHaerial adjusted and predicted values against PHground values. This study provides an example of the use of UAV-based high-resolution RGB imagery to obtain time-series estimates of PH, scalable to tens-of-thousands of plots, and thus suitable to be applied in plant wheat breeding trials.

Population structure analysis and identification of genomic regions under selection associated with low-nitrogen tolerance in tropical maize lines.

Increasing low nitrogen (N) tolerance in maize is an important goal for food security and agricultural sustainability. In order to analyze the population structure of tropical maize lines and identify genomic regions associated with low-N tolerance, a set of 64 inbred lines were evaluated under low-N and optimal-N conditions. The low-N Agronomic Efficiency index (LNAE) of each line was calculated. The maize lines were genotyped using 417,112 SNPs markers. The grouping based on the LNAE values classified the lines into two phenotypic groups, the first comprised by genotypes with high LNAE (named H_LNAE group), while the second one comprised genotypes with low LNAE (named L_LNAE group). The H_LNAE and L_LNAE groups had LNAE mean values of 3,304 and 1,644, respectively. The population structure analysis revealed a weak relationship between genetic and phenotypic diversity. Pairs of lines were identified, having at the same time high LNAE and high genetic distance from each other. A set of 29 SNPs markers exhibited a significant difference in allelic frequencies (Fst > 0.2) between H_LNAE and L_LNAE groups. The Pearson's correlation between LNAE and the favorable alleles in this set of SNPs was 0.69. These SNPs could be useful for marker-assisted selection for low-N tolerance in maize breeding programs. The results of this study could help maize breeders identify accessions to be used in the development of low-N tolerant cultivars.

Multi-trait multi-environment models in the genetic selection of segregating soybean progeny.

At present, single-trait best linear unbiased prediction (BLUP) is the standard method for genetic selection in soybean. However, when genetic selection is performed based on two or more genetically correlated traits and these are analyzed individually, selection bias may arise. Under these conditions, considering the correlation structure between the evaluated traits may provide more-accurate genetic estimates for the evaluated parameters, even under environmental influences. The present study was thus developed to examine the efficiency and applicability of multi-trait multi-environment (MTME) models by the residual maximum likelihood (REML/BLUP) and Bayesian approaches in the genetic selection of segregating soybean progeny. The study involved data pertaining to 203 soybean F2:4 progeny assessed in two environments for the following traits: number of days to maturity (DM), 100-seed weight (SW), and average seed yield per plot (SY). Variance components and genetic and non-genetic parameters were estimated via the REML/BLUP and Bayesian methods. The variance components estimated and the breeding values and genetic gains predicted with selection through the Bayesian procedure were similar to those obtained by REML/BLUP. The frequentist and Bayesian MTME models provided higher estimates of broad-sense heritability per plot (or heritability of total effects of progeny; [Formula: see text]) and mean accuracy of progeny than their respective single-trait versions. Bayesian analysis provided the credibility intervals for the estimates of [Formula: see text]. Therefore, MTME led to greater predicted gains from selection. On this basis, this procedure can be efficiently applied in the genetic selection of segregating soybean progeny.

Genetic diversity among accessions of sacha inchi (Plukenetia volubilis) by phenotypic characteristics analysis / Diversidade genética entre acessos de sacha inchi (Plukenetia volubilis) por análise de características fenotípicas

Sacha inchi (Plukenetia volubilis) is native to the Amazon region and has a high seed content of mono and polyunsaturated fatty acids, making it interesting for the pharmaceutical and cosmetic industry. The purpose of this study was to analyze sacha inchi genetic diversity and describe accessions based on phenotypic characteristics. Fruits and seeds of 25 accessions from the sacha inchi genebank of Embrapa Amazônia Ocidental in Manaus, Amazonas state, were sampled and biometrically measured. The data were subjected to analysis of variance, Mahalanobis distance, canonical correlation, and genetic diversity among and within accessions by analysis of molecular variance (AMOVA). There were significant differences among the means of the analyzed traits, but no significant canonical correlation for the groups of traits. According to AMOVA, approximately 60% of the observed variation was within accessions. The results showed variability among accessions, and that the variation within accessions should be explored to obtain best results in breeding programs.

Sacha inchi (Plukenetia volubilis) é nativa da região amazônica e suas sementes tem um alto teor de ácidos graxos mono e poliinsaturados, tornando-a interessante para a indústria farmacêutica e cosmética. O objetivo deste estudo foi analisar a diversidade genética de sacha inchi e caracterizar os acessos com base em características fenotípicas. Foi realizada coleta e biometria de frutos e sementes de 25 acessos do banco de germoplasma de sacha inchi da Embrapa Amazônia Ocidental em Manaus-AM. Os dados foram submetidos a análise de variância, distância de Mahalanobis, correlação canônica e diversidade genética por análise de variância molecular (AMOVA). Houve diferenças significativas entre as médias das variáveis analisadas, contudo, não houve correlação canônica significativa para os grupos de variáveis. De acordo com AMOVA, aproximadamente 60% da variação observada esteve dentro de acessos. Os resultados mostram variabilidade entre acessos, sendo importante explorar a variação intra-acessos para obter melhores resultados em programas de melhoramento.

Insights into soybean transcriptome reconfiguration under hypoxic stress: Functional, regulatory, structural, and compositional characterization.

Soybean (Glycine max) is one of the major crops worldwide and flooding stress affects the production and expansion of cultivated areas. Oxygen is essential for mitochondrial aerobic respiration to supply the energy demand of plant cells. Because oxygen diffusion in water is 10,000 times lower than in air, partial (hypoxic) or total (anoxic) oxygen deficiency is important component of flooding. Even when oxygen is externally available, oxygen deficiency frequently occurs in bulky, dense or metabolically active tissues such as phloem, meristems, seeds, and fruits. In this study, we analyzed conserved and divergent root transcriptional responses between flood-tolerant Embrapa 45 and flood-sensitive BR 4 soybean cultivars under hypoxic stress conditions with RNA-seq. To understand how soybean genes evolve and respond to hypoxia, stable and differentially expressed genes were characterized structurally and compositionally comparing its mechanistic relationship. Between cultivars, Embrapa 45 showed less up- and more down-regulated genes, and stronger induction of phosphoglucomutase (Glyma05g34790), unknown protein related to N-terminal protein myristoylation (Glyma06g03430), protein suppressor of phyA-105 (Glyma06g37080), and fibrillin (Glyma10g32620). RNA-seq and qRT-PCR analysis of non-symbiotic hemoglobin (Glyma11g12980) indicated divergence in gene structure between cultivars. Transcriptional changes for genes in amino acids and derivative metabolic process suggest involvement of amino acids metabolism in tRNA modifications, translation accuracy/efficiency, and endoplasmic reticulum stress in both cultivars under hypoxia. Gene groups differed in promoter TATA box, ABREs (ABA-responsive elements), and CRT/DREs (C-repeat/dehydration-responsive elements) frequency. Gene groups also differed in structure, composition, and codon usage, indicating biological significances. Additional data suggests that cis-acting ABRE elements can mediate gene expression independent of ABA in soybean roots under hypoxia.

Phenotypic correlation and path analysis in cultivars and strains of upland rice for drought tolerance / Correlação fenotípica e análise de trilha em cultivares e linhagens de arroz de sequeiro para tolerância à seca

The purpose of this study was to estimate the phenotypic correlations between 14 traits obtained in a thematic core collection of upland rice for drought tolerance and partition them into direct and indirect effects by path analysis. Two experiments were carried out (with and without water stress). One hundred samples were evaluated in a triple 10x10 lattice design. The plot was formed by four rows, 3.0 metres long, spaced at 0.35 m. The plot useful area was constituted by two central rows of 2.0 m in length, totalling 1.4 m2, where data from 14 traits were collected, five from the root system and nine from the aerial part of the plant. Of the evaluated traits, spikelet sterility was the main grain yield determinant, presenting relevant negative correlations of -0.77 and -0.59 in environments with and without drought stress, respectively. The partitioning of spikelet sterility correlations presented negative direct effects on grain yield in environments with (-0.60) and without (-0.62) water stress, corroborating the negative correlations between these traits. The obtained data confirmed that spikelet sterility is an important variable for the selection of rice strain submitted to water deficit. Partial correlation coefficients indicated that only 70.33% in the environment with stress and 50.30% in the environment without stress of grain yield variation were phenotypically explained by variables considered in path analysis, thereby showing the complexity of the selection for drought-tolerant rice.

O objetivo desse trabalho foi estimar as correlações fenotípicas entre 14 características obtidas em uma coleção nuclear temática de arroz de terras altas para tolerância à seca e desdobrá-las em seus efeitos diretos e indiretos por meio da análise de trilha. Foram conduzidos dois experimentos (com e sem estresse hídrico). Avaliou-se 100 materiais no delineamento experimental em látice triplo 10x10. A parcela foi formada por quatro linhas de 3,0 metros de comprimento espaçadas de 0,35 metros. A área útil da parcela foi constituída pelas duas linhas centrais de 2,0 metros de comprimento, perfazendo 1,4 m2 de onde foram coletados dados de 14 características sendo, cinco do sistema radicular e nove da parte aérea da planta. Das características avaliadas, esterilidade das espiguetas foi a principal determinante da produtividade de grãos apresentando correlação negativa de elevada magnitude de -0,78 e -0,59 nos ambientes com e sem estresse de seca, respectivamente. No desdobramento das correlações esterilidade das espiguetas apresentou efeitos diretos negativos na produtividade de grãos nos ambientes com (-0,60) e sem (-0,62) estresse hídrico, corroborando as correlações negativas entre estas características. Os dados obtidos enfatizaram que a esterilidade das espiguetas é uma variável importante para a seleção de linhagens de arroz submetidas à deficiência de água. Os coeficientes de determinações parciais indicaram que apenas 70,33% no ambiente com estresse e 50,30% no ambiente sem estresse da variação da produtividade de grãos foram explicados, fenotipicamente, pelas variáveis consideradas na análise de trilha evidenciando a complexidade da seleção para tolerância à seca em arroz.

Genetic Vulnerability and the Relationship of Commercial Germplasms of Maize in Brazil with the Nested Association Mapping Parents.

A few breeding companies dominate the maize (Zea mays L.) hybrid market in Brazil: Monsanto® (35%), DuPont Pioneer® (30%), Dow Agrosciences® (15%), Syngenta® (10%) and Helix Sementes (4%). Therefore, it is important to monitor the genetic diversity in commercial germplasms as breeding practices, registration and marketing of new cultivars can lead to a significant reduction of the genetic diversity. Reduced genetic variation may lead to crop vulnerabilities, food insecurity and limited genetic gains following selection. The aim of this study was to evaluate the genetic vulnerability risk by examining the relationship between the commercial Brazilian maize germplasms and the Nested Association Mapping (NAM) Parents. For this purpose, we used the commercial hybrids with the largest market share in Brazil and the NAM parents. The hybrids were genotyped for 768 single nucleotide polymorphisms (SNPs), using the Illumina Goldengate® platform. The NAM parent genomic data, comprising 1,536 SNPs for each line, were obtained from the Panzea data bank. The population structure, genetic diversity and the correlation between allele frequencies were analyzed. Based on the estimated effective population size and genetic variability, it was found that there is a low risk of genetic vulnerability in the commercial Brazilian maize germplasms. However, the genetic diversity is lower than those found in the NAM parents. Furthermore, the Brazilian germplasms presented no close relations with most NAM parents, except B73. This indicates that B73, or its heterotic group (Iowa Stiff Stalk Synthetic), contributed to the development of the commercial Brazilian germplasms.

Molecular mapping across three populations reveals a QTL hotspot region on chromosome 3 for secondary traits associated with drought tolerance in tropical maize.

Identifying quantitative trait loci (QTL) of sizeable effects that are expressed in diverse genetic backgrounds across contrasting water regimes particularly for secondary traits can significantly complement the conventional drought tolerance breeding efforts. We evaluated three tropical maize biparental populations under water-stressed and well-watered regimes for drought-related morpho-physiological traits, such as anthesis-silking interval (ASI), ears per plant (EPP), stay-green (SG) and plant-to-ear height ratio (PEH). In general, drought stress reduced the genetic variance of grain yield (GY), while that of morpho-physiological traits remained stable or even increased under drought conditions. We detected consistent genomic regions across different genetic backgrounds that could be target regions for marker-assisted introgression for drought tolerance in maize. A total of 203 QTL for ASI, EPP, SG and PEH were identified under both the water regimes. Meta-QTL analysis across the three populations identified six constitutive genomic regions with a minimum of two overlapping traits. Clusters of QTL were observed on chromosomes 1.06, 3.06, 4.09, 5.05, 7.03 and 10.04/06. Interestingly, a ~8-Mb region delimited in 3.06 harboured QTL for most of the morpho-physiological traits considered in the current study. This region contained two important candidate genes viz., zmm16 (MADS-domain transcription factor) and psbs1 (photosystem II unit) that are responsible for reproductive organ development and photosynthate accumulation, respectively. The genomic regions identified in this study partially explained the association of secondary traits with GY. Flanking single nucleotide polymorphism markers reported herein may be useful in marker-assisted introgression of drought tolerance in tropical maize.

Genetically engineered trees for plantation forests: key considerations for environmental risk assessment.

Forests are vital to the world's ecological, social, cultural and economic well-being yet sustainable provision of goods and services from forests is increasingly challenged by pressures such as growing demand for wood and other forest products, land conversion and degradation, and climate change. Intensively managed, highly productive forestry incorporating the most advanced methods for tree breeding, including the application of genetic engineering (GE), has tremendous potential for producing more wood on less land. However, the deployment of GE trees in plantation forests is a controversial topic and concerns have been particularly expressed about potential harms to the environment. This paper, prepared by an international group of experts in silviculture, forest tree breeding, forest biotechnology and environmental risk assessment (ERA) that met in April 2012, examines how the ERA paradigm used for GE crop plants may be applied to GE trees for use in plantation forests. It emphasizes the importance of differentiating between ERA for confined field trials of GE trees, and ERA for unconfined or commercial-scale releases. In the case of the latter, particular attention is paid to characteristics of forest trees that distinguish them from shorter-lived plant species, the temporal and spatial scale of forests, and the biodiversity of the plantation forest as a receiving environment.

QTL mapping in three tropical maize populations reveals a set of constitutive and adaptive genomic regions for drought tolerance.

Despite numerous published reports of quantitative trait loci (QTL) for drought-related traits, practical applications of such QTL in maize improvement are scarce. Identifying QTL of sizeable effects that express more or less uniformly in diverse genetic backgrounds across contrasting water regimes could significantly complement conventional breeding efforts to improve drought tolerance. We evaluated three tropical bi-parental populations under water-stress (WS) and well-watered (WW) regimes in Mexico, Kenya and Zimbabwe to identify genomic regions responsible for grain yield (GY) and anthesis-silking interval (ASI) across multiple environments and diverse genetic backgrounds. Across the three populations, on average, drought stress reduced GY by more than 50 % and increased ASI by 3.2 days. We identified a total of 83 and 62 QTL through individual environment analyses for GY and ASI, respectively. In each population, most QTL consistently showed up in each water regime. Across the three populations, the phenotypic variance explained by various individual QTL ranged from 2.6 to 17.8 % for GY and 1.7 to 17.8 % for ASI under WS environments and from 5 to 19.5 % for GY under WW environments. Meta-QTL (mQTL) analysis across the three populations and multiple environments identified seven genomic regions for GY and one for ASI, of which six mQTL on chr.1, 4, 5 and 10 for GY were constitutively expressed across WS and WW environments. One mQTL on chr.7 for GY and one on chr.3 for ASI were found to be 'adaptive' to WS conditions. High throughput assays were developed for SNPs that delimit the physical intervals of these mQTL. At most of the QTL, almost equal number of favorable alleles was donated by either of the parents within each cross, thereby demonstrating the potential of drought tolerant × drought tolerant crosses to identify QTL under contrasting water regimes.

An improved method for genomic DNA extraction from strawberry leaves / Otimização de um método para extração de DNA genômico a partir de folhas de morangueiro

Several extraction methods of genomic DNA for identification and characterization of genetic diversity in different plant species are routinely applied during molecular analysis. However, the presence of undesirable compounds such as polyphenols and polysaccharides is one of the biggest problems faced during the isolation and purification of high quality DNA in plants. Therefore, achievement of fast and accurate methods for DNA extraction is crucial in order to produce pure samples. Leaves of strawberry genotypes (Fragaria ananassa) have high contents of polysaccharides and polyphenols which increase the sample viscosity and decrease the DNA quality, interfering with the PCR performance. Thereby, in this study we evaluated the quality and amount of genomic DNA extracted from young leaves of strawberry after tissue lyophilization and maceration in presence of polivinilpirrolidone (PVP). The CTAB method was used as reference procedure and it was modified to improve the DNA extraction. The modifications consisted of tissue lyophilization overnight until it was completely freeze-dried and addition of PVP during the tissue maceration in liquid nitrogen. The results showed the efficiency and reliability of the modified method compared to the unmodified method, indicating that combination of lyophilization and PVP improve the quality and amount of the DNA extracted from strawberry leaves.

Vários métodos de extração de DNA genômico para a identificação e caracterização da diversidade genética em diferentes espécies de plantas são rotineiramente aplicados durante a análise molecular. Entretanto, a presença de compostos indesejáveis, tais como polifenóis e polissacarídeos, é um dos maiores problemas que ocorrem durante o isolamento e purificação de DNA de alta qualidade em plantas. Dessa forma, o sucesso no desenvolvimento de métodos de extração de DNA rápidos e acurados é crucial para produzir amostras puras. Folhas de genótipos de morangueiro (Fragaria ananassa) têm elevado conteúdo de polissacarídeos e polifenóis que aumentam a viscosidade da amostra e reduzem a qualidade do DNA, interferindo no desempenho da PCR. Neste estudo, avaliamos a qualidade e a quantidade de DNA genômico extraído de folhas jovens de morangueiro após a liofilização do tecido e a maceração na presença de polivinilpirrolidona (PVP). O método CTAB foi utilizado como procedimento de referência e foi modificado para melhorar a extração do DNA. As modificações consistiram na liofilização do tecido a baixa temperatura até que ele tivesse sido desidratado completamente, associada à adição de PVP durante a maceração do tecido no nitrogênio líquido. Os resultados demonstraram a eficiência e a confiabilidade do método modificado comparado ao método não modificado, indicando que a combinação da liofilização com PVP melhora a qualidade e quantidade do DNA extraído de folhas de morangueiro.

The relationship between population structure and aluminum tolerance in cultivated sorghum.

BACKGROUND: Acid soils comprise up to 50% of the world's arable lands and in these areas aluminum (Al) toxicity impairs root growth, strongly limiting crop yield. Food security is thereby compromised in many developing countries located in tropical and subtropical regions worldwide. In sorghum, SbMATE, an Al-activated citrate transporter, underlies the Alt(SB) locus on chromosome 3 and confers Al tolerance via Al-activated root citrate release. METHODOLOGY: Population structure was studied in 254 sorghum accessions representative of the diversity present in cultivated sorghums. Al tolerance was assessed as the degree of root growth inhibition in nutrient solution containing Al. A genetic analysis based on markers flanking Alt(SB) and SbMATE expression was undertaken to assess a possible role for Alt(SB) in Al tolerant accessions. In addition, the mode of gene action was estimated concerning the Al tolerance trait. Comparisons between models that include population structure were applied to assess the importance of each subpopulation to Al tolerance. CONCLUSION/SIGNIFICANCE: Six subpopulations were revealed featuring specific racial and geographic origins. Al tolerance was found to be rather rare and present primarily in guinea and to lesser extent in caudatum subpopulations. Alt(SB) was found to play a role in Al tolerance in most of the Al tolerant accessions. A striking variation was observed in the mode of gene action for the Al tolerance trait, which ranged from almost complete recessivity to near complete dominance, with a higher frequency of partially recessive sources of Al tolerance. A possible interpretation of our results concerning the origin and evolution of Al tolerance in cultivated sorghum is discussed. This study demonstrates the importance of deeply exploring the crop diversity reservoir both for a comprehensive view of the dynamics underlying the distribution and function of Al tolerance genes and to design efficient molecular breeding strategies aimed at enhancing Al tolerance.

Avaliação de três características fisiológicas em 4 ciclos de seleção no cultivar de milho BRS-4154 sob o solo encharcado / Evaluation of three physiologic characteristics in four cycles of selection in maize cultivar BRS-4154 under tolerance to waterlogging of the soil

Conduziu-se este trabalho, com o objetivo de avaliar plantas de milho (Zea mays L.) dos diferentes ciclos de seleção recorrentes da variedade de milho BRS 4154 - 'Saracura' quanto aos ganhos genéticos obtidos ao longo dos ciclos de seleção sob encharcamento do solo. Quatro ciclos de seleção da variedade de milho BRS 4154 foram plantados sob delineamento em blocos casualizados nos quais foram avaliados os ciclos 1, 5, 9 e 15, incluindo a variedade BR 107 e o híbrido simples BRS 1010 como testemunhas, por serem sensíveis ao encharcamento. Foram avaliados: fluorescência e teor de clorofila, área foliar e porosidade de raiz. O estresse causado pelo excesso de água no solo não influenciou a característica fluorescência da clorofila, demonstrando que essa não é uma boa característica para avaliação de tolerância ao encharcamento do solo. Houve uma significativa redução de área foliar do milho nas áreas de solo encharcado. Adicionalmente, a porosidade da raiz foi uma característica que apresentou significativa discrepância entre os dois ambientes de cultivo, tendo um aumento significativo em função do encharcamento.

This work aimed to evaluate plants of different cycles of recurrent selection of the maize (Zea mays L.) variety BRS 4154 - 'Saracura' for the genetic faced to the gains obtained along the selection cycles under waterlogging of the soil. Four cycles of selection of the maize variety BRS 4154 were planted in randomized block outline for evaluation of cycles 1, 5, 9 and 15, including the variety BR 107 and the simple hybrid BRS 1010 used as control, once they are sensitive to the waterlogging. One evaluated: chlorophylls fluorescence and content, leaf surface area and root porosity. The stress caused by the excess of water in the soil didn't influence the characteristic of chlorophyll fluorescence, demonstrating this is not a good characteristic to evaluate flooding tolerance. There was significant leaf surface area decrease of the corn in the areas of soaked soil. Additionally, the porosity of the root was a characteristic that presented significant discrepancy between the two cultivation environments, having a significant increase in function of waterlogging.

Plant breeding in the turn of the millennium

The transition from hunting and gathering to farming happened about 10,000 years ago, independently and diffusely in several places in the world. Plant breeders were responsible for genetic progress in a number of crop species. It included hybrids, the introgression of wild species genes and also the Green Revolution, which started in the 1960's with the cereals. The varieties developed by breeding, along with the use of new crop technology (fertilization, soil tillage, etc.) changed the status of some countries from importers to exporters of food. In the turn of the millennium,, plant breeding, faces new challenges in a globalized world, but it has new tools to deal with them. Notwithstanding the present contributions of plant breeding and crop management, its future contributions may be even greater. The partnership being developed between plant breeding and biotechnology will assure a more consistent and predictable genetic progress. Current contributions of biotechnology have arrived for many crops in different places of the world. Varieties developed by transformation are grown in large acreage in some countries. Some concerns have also arisen from the use of GMOs. For example, the introgression of a gene for insect resistance 4 into many different species could result in an undesirable endemic risk, here called interespecific biotechnological vulnerability. Another concern is that biotechnology race may create yield plateaus in programs using genes pyramiding for all new traits made available by biotechnology, resulting in what is called genetic gridlock. Nevertheless, the benefits of using biotechnology will substantially enhance the contributions of plant breeding to human life.

A transição da fase de coleta e caça para a agricultura ocorreu há cerca de dez mil anos independentemente e em vários locais no mundo. Naquela época iniciou-se a domesticação da maioria das espécies cultivadas, dando início às atividades agrícolas. Os melhoristas foram responsáveis pelo fenomenal progresso genético de um vasto número de espécies. Incluem-se os híbridos, a introgressão de genes de ancestrais silvestres e a própria Revolução Verde iniciada com os cereais na década de 60. As novas variedades desenvolvidas pelo melhoramento genético, associadas ao uso de tecnologia adequada (fertilizantes, preparo do solo etc.), permitiram que importadores de alimentos se tornassem exportadores. A despeito das contribuições do melhoramento genético e do ambiente, as perspectivas de contribuição no futuro são ainda maiores. Na virada do milênio o melhoramento no mundo globalizado enfrenta novos desafios, tendo a sua disposição novas tecnologias. Acredita-se que ele deva continuar evoluindo em direção a progressos genéticos mais previsíveis de forma gradativa, com o uso da biotecnologia. A parceira estabelecida entre melhoristas e biotecnologistas resultará em benefícios para a sociedade. Atualmente, variedades desenvolvidas via biotecnologia estão sendo cultivadas em grandes áreas em diversos países. Todavia, alguns possíveis impactos negativos da biotecnologia tem sido considerados, a exemplo da vulnerabilidade biotecnológica interespecífica, passível de ocorrer quando, por exemplo, um gene da resistência a uma praga fosse introduzido em várias espécies simultaneamente, resultando na possibilidade de uma suscetibilidade endêmica na eventualidade de quebra desta resistência. A corrida da biotecnologia certamente criará novas perspectivas para o melhorista mas, eventualmente, poderá estabelecer platôs de rendimentos com as restrições impostas pela piramidação de genes para as características criadas via biotecnologia, resultando no que se denomina de arresto gênico.