BackgroundAcid 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 AltSB locus on chromosome 3 and confers Al tolerance via Al-activated root citrate release.MethodologyPopulation 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 AltSB and SbMATE expression was undertaken to assess a possible role for AltSB 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/SignificanceSix 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. AltSB 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.

RESUMO. Estudou-se a variabilidade genética de 17 cultivares de alface, tipos Lisa, Crespa e Americana, com base em características agronômicas e em procedimentos multivariados, visando selecionar cultivares divergentes e com melhor desempenho em cultivo hidropônico -NFT. Avaliou-se, também, a importância das características para a divergência, pelo descarte seqüencial das variáveis, segundo suas contribuições relativas. O experimento foi conduzido em casa-de-vegetação, na Epamig, Viçosa-MG, no verão de 1999, em blocos casualizados, com 3 repetições. 6 plantas foram colhidas, a 46 dias da semeadura, e avaliadas em 10 características relacionadas à produção. Os dados foram analisados pelos métodos de agrupamento de Tocher, do vizinho mais próximo e da análise de variáveis canônicas. As cultivares Mimosa, Brisa, Regina, Monalisa e OGR são mais indicadas para integrar programas de cruzamentos dirigidos, visando produzir novas cultivares destinadas ao cultivo hidropônico, pois mostraram-se mais divergentes geneticamente, apresentando boas qualidades agronômicas, principalmente a matéria fresca da planta. As características matéria seca de folhas e de caule e matéria fresca de raiz e da planta inteira não alteraram o agrupamento original, podendo ser eliminadas de futuros estudos de divergência genética em alface. Palavras-chave:Lactuca sativa, variabilidade genética, análise multivariada, agrupamento, características agronômicas.ABSTRACT. Genetic divergence and discard of variables in lettuce cultivated under hydroponic system. It was studied the genetic variability of 17 lettuce cultivars, types Butter, Crisp and Iceberg, according to agronomic traits and multivariate procedures. It aims to select divergent cultivars with better performance designed to hydroponic system culture. The importance of the traits for divergence was, also, evaluated by the sequential discards of the variables, according its relative contributions. The trial was carry out in greenhouse, Epamig, Viçosa-MG, in summer of 1999, using randomized blocks with three replicates. Six plants were harvested 46 days after the sowing, and evaluated in ten traits related to the yield. The data were analyzed by Tocher, single linkage, and canonical variables grouping methods. The Mimosa, Brisa, Regina, Monalisa and OGR are the most appropriated cultivars to integrate in specific crossings programs for hydroponic culture. They were more genetically divergent and had good agronomic qualities. Some traits did not affect the original grouping, so they could be eliminated in future studies of lettuce genetic divergence.

Estudou-se a divergência genética de 21 progênies de meios-irmãos - 19 do grupo Congolês e duas do grupo Guineano - de introduções do germoplasma de café robusta (Coffea canephora) do IAC. O estudo baseou-se em análises multivariadas de 14 características morfo-agronômicas, com o propósito de selecionar as progênies mais divergentes, visando à definição de população-base para posterior seleção e produção de híbridos. Avaliou-se também a importância das características discriminantes para análises de divergência, visando ao descarte das variáveis, segundo suas contribuições relativas. O experimento foi plantado e desenvolvido em campo experimental localizado no Pólo Regional do Nordeste Paulista, Mococa (SP), em blocos casualizados, com 21 tratamentos e 24 repetições. O agrupamento dos genótipos foi realizado com base nos métodos de Tocher e UPGMA. A matriz de dissimilaridade genética foi obtida por meio da distância generalizada de Mahalanobis, que serviu de base para a formação dos grupos. Os métodos empregados foram eficientes em detectar ampla variabilidade genética entre as progênies avaliadas. Vários grupos dissimilares foram identificados. As progênies IAC 2262, IAC 2290, IAC 2286, IAC 2292 e IAC 2291 são indicadas para compor programas de intercruzamentos, por terem sido consideradas as mais promissoras na obtenção de populações segregantes ou híbridos heteróticos. As características que menos contribuíram para a divergência genética foram, hierarquicamente: diâmetro da copa antes da poda, altura da planta antes da poda e área foliar.

Coffee leaf rust (CLR) caused by Hemileia vastatrix Berk. et Br. is one of the major Coffea arabica diseases worldwide. CLR resistance has been attributed to at least nine dominant genes, as single or in combination. We present an inheritance study and mapping loci involved in the Híbrido de Timor (HDT) UFV 443-03 resistance to race I, race II, and pathotype 001 of H. vastatrix. Molecular markers were used to ascertain the phenotypic results and to map the putative resistance loci. For all tree isolates, the inheritance study indicated that the resistance of HDT UFV 443-03 is conditioned by two independent dominant loci or by three independent loci (two dominant and one recessive). Molecular marker analyses ascertained that the resistance of HDT UFV 443-03 to race II is conditioned by at least two independent dominant loci, while the resistance to race I and pathotype 001 is conditioned by at least four independent dominant loci. Gene pyramiding might result in a cultivar with durable resistance; however, it is difficult to distinguish between plants with one or more resistance genes due to epistatic effects. Molecular markers linked to these genes were indicated for marker-assisted selection, as it is an efficient breeding alternative for CLR resistance with no such epistatic effects.

Histrionicotoxin from the Colombian frog Dendrobates histrionicus and its perhydro derivative reversibly block the acetylcholine-sensitive ion conductance system in frog neuromuscular preparations. The perhydro derivative ana [3Hlperhydrohistrionicotoxin, like histrionicotoxin, caused a significant decrease in the peak amplitude of the end-plate current and shortened its rise time and half-decay time. In membrane preparations from Torpedo electroplax, [3Hjperhy-drohistrionicotoxin bound reversibly to a limited number of high-affinity sites [dissociation constant, (KD) = 0.4 ,uMM. The ratio of perhydrohistrionicotoxin to acetylcholine binding sites in these membrane preparations approached 2. Histrionicotoxins, local anesthetics, and certain cholinergic agonists inhibited binding of perhydrohistrionicotoxin. Binding of perhydrohistrionicotoxin to membranes was decreased bylheat or treatment with proteases. Treatment of membranes with Triton X-100 solubilized acetylcholine binding proteins and apparently also perhydrohistrionicotoxin-binding proteins. However, the detergent Triton X-100 also bound [3H perhydrohistrionicotoxin. This nonspecific binding was not saturable and complicated studies on the antagonism by drugs of binding of [3Hjperhydrohistrionicotoxin. In solubilized preparations the binding protein for acetylcholine could be removed by affinity chromatography or immunoprecipitation without affecting binding ofrperhydrohistrionicotoxin. Sephadex chromatography also separated acetylcholine-from perhydrohistrionicotoxinbinding proteins. Perhydrohistrionicotoxin did not bind significantly to purified acetylcholine-receptor protein but presumably bound to an ion conductance modulator protein that was associated with the acetylcholine-receptor in intact membrane and readily separable from the receptor protein after solubilization.The excitatory action of acetylcholine (ACh) at the postsynaptic membrane involves its binding to a specific recognition site followed by activation of the ion conductance modulator (1) and a marked increase in ionic conductance. The ion conductance modulator may represent an ionic channel or ionophore comprising part of the same macromolecule as the ACh receptor or it may be separate from, but somehow coupled with, the receptor. The ACh receptor, purified in several laboratories (2-5), has generally been assumed to contain, as part of the molecule, the ion conductance modulator. However, in no case did the purified ACh receptors, in the presence of lipid membranes, recover the specificity, magnitude, and kinetics of the ion flux or conductance increase characteristic of the intact system (6-8). This may be due either to lack of incorporation of the receptor molecules into the lipid bilayer or to the absence of parts or all of the ion conductance modulator in the purified receptor preparation.It has been proposed that histrionicotoxin (HTX), an alkaloid isolated from the skin extracts of the Colombian frog, Dendrobates histrionicus (9), modifies responses to ACh in neuromusc...

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The coefficient of parentage among 121 cultivars of Coffea arabica L. in Brazil released from 1939 to 2009 was estimated and used to study the genetic diversity and the breeding pattern of the breeding programs. A low genetic diversity was observed within the C. arabica cultivars of Brazil. The genetic base of 121 cultivars released in Brazil between 1939 and 2009 was defined by 13 ancestors. Seven ancestors contribute with 97.55% of the genetic base of C. arabica cultivars. Bourbon Vermelho contributed with 52.76% for the genetic pool of the C. arabica cultivars of Brazil followed by Sumatra (19.05%) and Híbrido de Timor (11.59%). Mundo Novo and Icatu Vermelho contributed with 87.65% for the genetic base of the C. arabica cultivars. It was calculated that 97.55% of the genetic base of the Brazilian C. arabica cultivars is derived from seven ancestors, indicating a narrow genetic base. Among the first progenies, Mundo Novo contributed with 69.39% of the genetic base of C. arabica cultivars in Brazil. The increase in the genetic diversity among C. arabica cultivars observed in recent decades is due to the introduction of parental lines with diverse genetic base. High genetic diversity was observed among cultivars released by Empresa de Pesquisa Agropecuária de Minas Gerais/Universidade Federal de Viçosa, Fundação Procafé, and Instituto Agronômico do Paraná. The 121 Brazilian cultivars were clustered into four groups based on coefficient of parentage. The distributions of genotypes over the cluster groups showed the effect of parental line contribution.

Genomic Selection (GS) has allowed the maximization of genetic gains per unit time in several annual and perennial plant species. However, no GS studies have addressed Coffea arabica, the most economically important species of the genus Coffea. Therefore, this study aimed (i) to evaluate the applicability and accuracy of GS in the prediction of the genomic estimated breeding value (GEBV); (ii) to estimate the genetic parameters; and (iii) to evaluate the time reduction of the selection cycle by GS in Arabica coffee breeding. A total of 195 Arabica coffee individuals, belonging to 13 families in generation of F2, susceptible backcross and resistant backcross, were phenotyped for 18 agronomic traits, and genotyped with 21,211 SNP molecular markers. Phenotypic data, measured in 2014, 2015, and 2016, were analyzed by mixed models. GS analyses were performed by the G-BLUP method, using the RKHS (Reproducing Kernel Hilbert Spaces) procedure, with a Bayesian algorithm. Heritabilities and selective accuracies were estimated, revealing moderate to high magnitude for most of the traits evaluated. Results of GS analyses showed the possibility of reducing the cycle time by 50%, maximizing selection gains per unit time. The effect of marker density on GS analyses was evaluated. Genomic selection proved to be promising for C. arabica breeding. The agronomic traits presented high complexity for they are controlled by several QTL and showed low genomic heritabilities, evidencing the need to incorporate genomic selection methodologies to the breeding programs of this species.