Biometric analysis and mapping of QTLS for drought tolerance in maize

Um dos grandes objetivos do melhoramento de culturas é o aumento da produtividade agrícola associado à melhoria para o consumo humano ou animal. Esses objetivos podem ser alcançados por meio de melhorias nas condições ambientais ou por melhoria no potencial genético das populações. Nos últimos tempos, muito tem sido discutido a respeito do aquecimento global, mudanças climáticas, sobre o cenário agrícola frente a estas alterações e a contribuição do melhoramento genético na atenuação dos problemas advindo do aquecimento global. A seca é um dos maiores estresses ambientais que limitam o crescimento de plantas e, consequentemente, o rendimento das culturas. As plantas respondem ao déficit hídrico e se adaptam às condições de seca por meio de várias alterações fisiológicas e bioquímicas, incluindo modificações fenológicas. Entretanto, no milho, as perdas na produção de grãos são severas quando a cultura está sob condição de estresse hídrico, sendo este um dos principais fatores limitantes. O milho é particularmente sensível ao estresse hídrico na fase reprodutiva. Os programas de melhoramento de milho, nacionais e internacionais, têm considerado o estudo simultâneo de (i) análises biométricas de caracteres relacionados à seca e correlacionados à produção de grãos e (ii) ao uso da tecnologia de marcadores moleculares para detecção de QTLs, que são a identificação de regiões genômicas responsáveis por induzir a tolerância à seca. Ambos os estudos possibilitam aosgeneticistas o entendimento da herança do caráter tolerância à seca. As investigações genéticas indicam que a maioria dos caracteres relacionados ao estresse abiótico é de herança complexa, controlados por vários genes e altamente influenciados pela variação ambiental. O presente trabalho teve como objetivos abordar estes dois tipos de análises para o estudo de uma população F2:3 de milho desenvolvida pela Embrapa/Milho e sorgo. Os experimentos instalados nos anos de 2006 e 2007 permitiram realizar inferências precisas para fins de melhoramento e para o mapeamento de QTLs. Ambos apresentaram variabilidade genética para as características de interesse, predizendo o sucesso de futuros estudos e uma possível utilização em programas de melhoramento. A interação genótipos x ambientes foi, predominantemente, complexa, mostrou a necessidade da condução e avaliação das populações segregantes nos diferentes anos da cultura do milho, bem como no ambiente com estresse hídrico. Os maiores ganhos com a seleção indireta para produção de grãos é através da característica prolificidade. Entretanto, os maiores ganhos diretos para produção de grãos, no ambiente de seca são realizados com base no desempenho médio dos genótipos. Da análise de detecção de QTLs, foi gerado um mapa de ligação com 82 marcadores microssatélites, cobrindo 825,03 cM do genoma do milho, com um marcador em média a cada 20 cM. Foram mapeados 45 QTLs pela metodologia de intervalo simples: seis para intervalo entre florescimentos, treze para altura de plantas, seis para produção de grãos, dez para folhas mortas, cinco para prolificidade e cinco para produção relativa.One of the major goals of crop improvement is the increase in agricultural productivity associated with the improvement for the consumption in human or animal feeding. These goals can be achieved through improvements in environmental conditions or by improving the genetic potential of populations. Recently, much has been discussed about global warming, climate change on the agricultural scenario in the face of these changes and the contribution of genetic improvement in mitigating the problems arising from global warming. Drought is a major environmental stresses that limit plant growth and consequently crop yields. Plants respond to water deficit and adapt to drought conditions through a variety of physiological and biochemical changes, including phenological changes. However, the losses in grain production in maize are severe when the crop is under water stress condition, which is one of the main limiting factors. Maize is particularly sensitive to water stress during the reproductive phase. National and international maize breeding programs, have considered the simultaneous study of (i) biometric analysis of traits related to drought and their correlation with grain yield and (ii) the use of molecular markers technology for detection of QTLs, which are the identification of genomic regions responsible for inducing tolerance to drought. Both studies make it possible for geneticists understand the inheritance of the tolerance to drought. The genetic investigations indicate that most of the traits related to abiotic stress have complex inheritance, controlled by several genes and highly influenced by environmental variation. This study aimed to address these two types of analysis for the study of an F2:3 maize population developed by Embrapa / Maize and Sorghum. The experiments conducted during 2006 and 2007 allowed us to estimate accurate inferences for both improvement and QTL mapping. Both approaches showed genetic variability for characteristics of interest, predicting the success of future studies and possible use in breeding programs. The genotype x environment interaction was predominantly complex, showed the need for the conduct and evaluation of segregating populations in different maize seasons (years) and in the water stress environment. The major gains with indirect selection for grain production are achieved in the prolificacy trait. However, the largest direct gains for grain production, in the water stress environment, are achieved based on the average performance of the genotypes. The QTL detection analysis allowed the generation of a linkage map with 82 microsatellite markers, covering 825.03 cM of the maize genome, with an average of one marker every 20 cM. Forty and five QTLs were mapped by the simple interval methodology: anthesis silking interval (six), plant height (thirteen), yield (six), leaf senescence (ten), prolificacy (five), and relative production (five).Fundação de Amparo a Pesquisa do Estado de Minas Gerai

Hierarchical genetic clusters for phenotypic analysis

ABSTRACT Methods to obtain phenotypic information were evaluated to help breeders choosing the best methodology for analysis of genetic diversity in backcross populations. Phenotypes were simulated for 13 characteristics generated in 10 populations with 100 individuals each. Genotypic information was generated from 100 loci of which 20 were taken at random to determine the characteristics expressing two alleles. Dissimilarity measures were calculated, and genetic diversity was analyzed through hierarchical clustering and graphic projection of the distances. A backcross was performed from the two most divergent populations. A set of characteristics with variable heritability was taken into account. The environmental effect was simulated assuming x~N(0, σ2). For hierarchical clusters, the following methods were used: Gower Method, average linkage within the cluster, average linkage among clusters, the furthest neighbor method, the nearest neighbor method, Ward's method, and the median method. The environmental effect and heritability of the analyzed variables had an influence on the pattern of hierarchical clustering populations according to the backcrossed generations. The nearest neighbor method was the most efficient in reconstructing the system of backcrossing, and it presented the highest cophenetic correlation. The efficiency of the nearest neighbor method was the highest when the analysis involved characteristics of high heritability

Pollen viability and meiotic analysis of Solanum commersonii commersonii Dun., Solanum commersonii malmeanum Bitt. and Solanum tuberosum L.

Meiotic abnormalities in potato hamper sexual recombination, due to their influence on pollen production andviability rate. In this study we evaluated pollen viability and meiosis of three clones of Solanum commersonii commersoniiDun. (SCC), two of Solanum commersonii malmeanum Bitt. (SCM) and seven clones and four cultivars of Solanum tuberosumL., with the purpose of indicating promising genotypes for genetic breeding of potato. Early chromosome migration atmetaphases I and II and chromosome pairing anomalies were the main causes of pollen inviability in the evaluated genotypes.Clones SCC 07 and SCM 60 are the most suitable for sexual recombination, owing to the high percentage of viable pollengrains and low frequencies of meiotic abnormalities

Hierarchical genetic clusters for phenotypic analysis

Methods to obtain phenotypic information were evaluated to help breeders choosing the best methodology for analysis of genetic diversity in backcross populations. Phenotypes were simulated for 13 characteristics generated in 10 populations with 100 individuals each. Genotypic information was generated from 100 loci of which 20 were taken at random to determine the characteristics expressing two alleles. Dissimilarity measures were calculated, and genetic diversity was analyzed through hierarchical clustering and graphic projection of the distances. A backcross was performed from the two most divergent populations. A set of characteristics with variable heritability was taken into account. The environmental effect was simulated assuming x~N(0, σ2). For hierarchical clusters, the following methods were used: Gower Method, average linkage within the cluster, average linkage among clusters, the furthest neighbor method, the nearest neighbor method, Ward's method, and the median method. The environmental effect and heritability of the analyzed variables had an influence on the pattern of hierarchical clustering populations according to the backcrossed generations. The nearest neighbor method was the most efficient in reconstructing the system of backcrossing, and it presented the highest cophenetic correlation. The efficiency of the nearest neighbor method was the highest when the analysis involved characteristics of high heritability.Visando auxiliar o melhorista na escolha da melhor metodologia para análises de diversidade genética em populações de retrocruzamento avaliaram-se os métodos baseados em informações fenotípicas. Os fenótipos foram simulados para 13 características, geradas em 10 populações com 100 indivíduos cada. Geraram-se informações genotípicas de 100 locos, dos quais 20 foram tomados ao acaso para determinar as características, manifestando dois alelos. Medidas de dissimilaridade foram calculadas, e analisou-se a diversidade genética por meio agrupamento hierárquico e projeção gráfica das distâncias. A partir das duas populações mais divergentes fez-se o retrocruzamento. Considerou-se um conjunto de características com herdabilidade variável. Simulou-se o efeito ambiental admitindo distribuição normal, com média zero e variância σ2. Para as análises de agrupamentos hierárquicos utilizaram-se os métodos: Método de Gower, Ligação média dentro de grupo, Ligação média entre grupo, Vizinho mais distante, Vizinho mais próximo, Método de Ward, Método da mediana. O efeito ambiental e a herdabilidade das variáveis analisadas influenciaram o padrão de agrupamento de populações sob retrocruzamento. Em características de herdabilidade elevada, o método do Vizinho mais próximo foi o mais eficiente em reconstituir o retrocruzamento, além de ter apresentado a maior correlação cofenética, sendo considerada a melhor metodologia a priori e a posteriori

Colchicine and oryzalin effects on tetraploid induction and leaf anatomy of Solanum commersonii ssp.

The aim of the present study was to evaluate the effect of the colchicine and oryzalin anti-mitotic substances on the induction of tetraploid plants and foliar anatomy of two diploids clones of Solanum commersonii ssp. Nodal segments of Solanum commersonii subsp. commersonii Dun. and Solanum commersonii subsp. malmeanum Bitt. were treated with colchicine (3.5, 5.0, and 6.5mM; 72h) or oryzalin (10, 30, and 50μM; 24h). After the treatment with anti-mitotic substances, nodal segments were inoculated in the MS culture medium and cultivated in vitro (60 days). After in vitro cultivation, the plants were transferred to vases with the substrate Plantmax ® and kept in the greenhouse (45 days). Plant ploidy level was assessed by flow cytometry and leaf anatomy was assessed by anatomic cuts. An increase was observed in the polar and equatorial diameter of stomata (“gigas effect”) of the Solanum commersonii subsp. commersonii (SCC) and Solanum commersonii subsp. malmeanum (SCM) clones, which was due to the use of the anti-mitotic substances. Treatments with colchicine (6.5mM; 72h) and oryzalin (50μM; 24h) caused death of the SCC plants cultured in vitro. In the others treatments of the SCC clone, the use of oryzalin and colchicine caused production of chimeric plants. The treatment of nodal segments of SCM with oryzalin (10-50μM; 24h) was effective on induction of tetraploid plants, which can be employed in genetic breeding programs in crossbreeding with cultured potato.O objetivo deste estudo foi avaliar o efeito das substâncias antimitóticas colchicina e orizalina na indução de plantas tetraploides e na anatomia foliar de dois clones diploides de Solanum commersonii ssp. Segmentos nodais de Solanum commersonii subsp. commersonii Dun. e Solanum commersonii subsp. malmeanum Bitt. foram tratados com colchicina (3,5, 5,0 e 6,5mM; 72h) ou orizalina (10, 30 e 50μM; 24h). Após o tratamento com as substâncias antimitóticas, os segmentos nodais foram inoculados em meio de cultura MS e cultivados in vitro (60 dias). Após o cultivo in vitro, as plantas foram transferidas para vasos contendo o substrato Plantmax ® e mantidas em casa de vegetação (45 dias). O nível de ploidia das plantas foi avaliado por citometria de fluxo e a anatomia foliar foi avaliada através de cortes anatômicos. Foi observado um aumento no diâmetro equatorial e polar dos estômatos (“efeito gigas”) dos clones de Solanum commersonii subsp. commersonii (SCC) e Solanum commersonii subsp. malmeanum (SCM), que foi produzido pelo uso de substâncias antimitóticas. O tratamento com colchicina (6,5mM; 72h) e orizalina (50μM; 24h) causou morte nas plantas de SCC cultivadas in vitro. Nos demais tratamentos do clone de SCC, o uso de orizalina ou colchicina causou a produção de plantas quiméricas. O emprego de orizalina (10-50μM; 24h), nos segmentos nodais de SCM, resultou na obtenção de plantas tetraploides consistentes, as quais podem ser usadas nos programas para melhoramento genético em cruzamentos com a batata cultivada

Colchicine and oryzalin effects on tetraploid induction and leaf anatomy of Solanum commersonii ssp.

ABSTRACT: The aim of the present study was to evaluate the effect of the colchicine and oryzalin anti-mitotic substances on the induction of tetraploid plants and foliar anatomy of two diploids clones of Solanum commersonii ssp. Nodal segments of Solanum commersonii subsp. commersonii Dun. and Solanum commersonii subsp. malmeanum Bitt. were treated with colchicine (3.5, 5.0, and 6.5mM; 72h) or oryzalin (10, 30, and 50µM; 24h). After the treatment with anti-mitotic substances, nodal segments were inoculated in the MS culture medium and cultivated in vitro (60 days). After in vitro cultivation, the plants were transferred to vases with the substrate Plantmax(r) and kept in the greenhouse (45 days). Plant ploidy level was assessed by flow cytometry and leaf anatomy was assessed by anatomic cuts. An increase was observed in the polar and equatorial diameter of stomata ("gigas effect") of the Solanum commersonii subsp. commersonii (SCC) and Solanum commersonii subsp. malmeanum (SCM) clones, which was due to the use of the anti-mitotic substances. Treatments with colchicine (6.5mM; 72h) and oryzalin (50µM; 24h) caused death of the SCC plants cultured in vitro. In the others treatments of the SCC clone, the use of oryzalin and colchicine caused production of chimeric plants. The treatment of nodal segments of SCM with oryzalin (10-50µM; 24h) was effective on induction of tetraploid plants, which can be employed in genetic breeding programs in crossbreeding with cultured potato

Pólen 2n e mecanismos meióticos de formação em Solanum commersonii ssp 2n pollen and meiotic mechanisms of Formation in Solanum commersonii ssp

Solanum commersonii subsp. commersonii Dun. e Solanum commersonii subsp. malmeanum Bitt. (2n=2x=24 - 1EBN) não podem ser diretamente cruzadas com a batata cultivada de S. tuberosum subsp. tuberosum L. (2n=4x=48 -4 EBN) em razão da barreira da ploidia e do número de equilíbrio do endosperma (EBN). No entanto, a produção de pólen não reduzido por S. commersonii ssp. (2x=2n=24 - 1EBN), permite o cruzamento desta com dihaplóides de batata e com as espécies diplóides S. phureja Juz. & Bukasov. e S. chacoense Bitt., que possuem 2 EBN. Conduziu-se este trabalho, com o objetivo de determinar o mecanismo meiótico e a freqüência dos grãos de pólen não reduzidos em cinco clones de Solanum commersonii ssp. Foram avaliados três clones de S. commersonii subsp. commersonii (SCC) e dois de S. commersonii subsp. malmeanum (SCM). Nas avaliações, duzentos grãos de pólen viáveis foram corados (carmim acético 2%) e mensurados, sendo considerados não reduzidos aqueles com o diâmetro igual ou superior a 25 µm. O clone Solanum commersonii subsp. commersonii Dun. (SCC 100) produz 26.1% de polen não reduzido, por fusos fundidos e fusos paralelos, o qual pode ser utilizado em programas de melhoramento.<br>Solanum commersonii subsp. commersonii Dun. and Solanum commersonii subsp. malmeanum Bitt. (2n=2x=24 -1EBN) cannot be directly crossed with the cultivated Solanum tuberosum subsp. Tuberosum L. (2n=4x=48 - 4EBN) species due to ploidy barriers and endosperm balance number (EBN). However, non-reduced pollen production by the wild species S. commersonii ssp. (2x=2n=24 -1EBN), allows the crossing of these species with dihaploids of potato and with the diploids species, S. phureja Juz. & Bukasov. and S. chacoense Bitt., all with 2EBN. The aim of this work was to determine the meiotic mechanism and frequency of non-reduced pollen production of five clones of S. commersonii ssp. Three different clones of S. commersonii subsp. commersonii Dun. (SCC) and two of S. commersonii subsp. malmeanum Bitt. (SCM) were evaluated. In the evaluation, two hundred viable pollen grains were stained (2% acetic carmin) and measured. The pollen grains measuring 25 µm in diameter or more were considered nonreduced. The clone Solanum commersonii subsp. commersonii Dun. (SCC 100) produces 26.1% of non-reduced pollen grains caused by parallel spindles and fusion spindles, which may be used in breeding program