Antonio Carlos Baião de Oliveira

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

Background Acid soils comprise up to 50% of the worlds 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. 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 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/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. 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.

Identification of citrus hybrids through the combination of leaf apex morphology and SSR markers

Citrus breeding programs normally face several biological obstacles such as apomixis and polyembryony that result in a cumbersome identification of hybrid seedlings. The main purpose of this work is to describe the combined use of visual selection based on the leaf apex morphology and SSR analysis to differentiate hybrid from nucellar seedlings derived from the cross between the ‘Murcott’ tangor [Citrus reticulata Blanco × Citrus sinensis (L.) Osb.] and ‘Pêra’ sweet orange [Citrus sinensis(L.) Osb.]. A new morphological variable named leaf apex morphometric index is also described as the quantitative basis of the visual selection. The efficiency of visual selection of hybrids was tested under two growth conditions, seedlings germinated in seedbeds and in plastic tubes. Putative hybrid seedlings were also confirmed through the analysis of simple sequence repeats (SSR). The visual selection of hybrid seedlings resulted in an increase of 87.2% (p < 0.01) and 202.2% (p <0.001) in the number of correctly identified hybrids when compared to the method of random picking of seedlings in seedbeds and plastic tubes,respectively. The results indicate that the combination of visual selection and SSR analysis for the identification of hybrids derived from the cross of polyembryonic citrus cultivars will improve the accuracy of the selection,save time, and reduce the costs involved in the use of molecular markers alone in citrus breeding programs.

Frequency and distribution of microsatellites from ESTs of citrus

Nearly 65,000 citrus EST (Expressed Sequence Tags) have been investigated using the CitEST project database. Microsatellites were investigated in the unigene sequences from Citrus spp. and Poncirus trifoliata. From these sequences, approximately 35% of the non-redundant ESTs contained SSRs. The frequencies of different SSR motifs were similar between Citrus spp and trifoliate orange. In general, mononucleotide repeats appeared to be the most abundant SSRs in the CitEST database, but we also identify di-, tri-, tetra-, penta- and hexanucleotide repeats. The AG/CT and AAG/CTT were the most common dinucleotide and trinucleotide motifs, with frequencies of 54.4% and 25.2%, respectively. Primer sequences flanking SSR motifs were successfully designed and synthesized. After in silico polymorphism analysis, a subset of sixty-eight primers was validated in different Citrus spp. and Poncirus trifoliata. PCR-amplification revealed polymorphism in citrus with all tested primer pairs and showed the potential of these markers for linkage mapping. Our study showed that the CitEST database can be exploited for the development of SSR markers that can amplify Citrus spp. and related genus for comparative mapping and other genetic analyses.

Divergência genética entre progênies de café robusta

Estudou-se a divergencia genetica de 21 progenies de meios-irmaos - 19 do grupo Congoles e duas do grupo Guineano - de introducoes do germoplasma de cafe robusta (Coffea canephora) do IAC. O estudo baseou-se em analises multivariadas de 14 caracteristicas morfo-agronomicas, com o proposito de selecionar as progenies mais divergentes, visando a definicao de populacao-base para posterior selecao e producao de hibridos. Avaliou-se tambem a importância das caracteristicas discriminantes para analises de divergencia, visando ao descarte das variaveis, segundo suas contribuicoes relativas. O experimento foi plantado e desenvolvido em campo experimental localizado no Polo Regional do Nordeste Paulista, Mococa (SP), em blocos casualizados, com 21 tratamentos e 24 repeticoes. O agrupamento dos genotipos foi realizado com base nos metodos de Tocher e UPGMA. A matriz de dissimilaridade genetica foi obtida por meio da distância generalizada de Mahalanobis, que serviu de base para a formacao dos grupos. Os metodos empregados foram eficientes em detectar ampla variabilidade genetica entre as progenies avaliadas. Varios grupos dissimilares foram identificados. As progenies IAC 2262, IAC 2290, IAC 2286, IAC 2292 e IAC 2291 sao indicadas para compor programas de intercruzamentos, por terem sido consideradas as mais promissoras na obtencao de populacoes segregantes ou hibridos heteroticos. As caracteristicas que menos contribuiram para a divergencia genetica foram, hierarquicamente: diâmetro da copa antes da poda, altura da planta antes da poda e area foliar.

Efeito da palha e da mistura atrazine e metolachlor no controle de plantas daninhas na cultura do milho, em sistema de plantio direto

The objective of this work was to study the effect of corn plant residue and mixture of atrazine plus metolachlor on weed control in no-till corn system. This experiment was performed in an Oxisol, and the weed desiccation was done using glyphosate, 15 days before planting. The experimen- tal design was a randomized block, with three replications. Before corn planting, five levels of corn plant residues (0, 3, 6, 9 e 12 t ha -1 ) were equally distributed in the plots. Two treatments were applied in subplots after corn planting: one without herbicide and the other one using the commercial mixture of atrazine plus metolachlor (1,200 + 1,800 g ha -1 ). Different weed species were evaluated, at 26 and 41 days after planting. The total grass weeds number was significantly affected by the plant residue levels, independently of herbicide treatments and of evaluation period. The herbicide did not show a significant effect in the first evaluation period. However, in the second evaluation period, the herbicide reduced about 53% the total number of weeds compared to the plots without herbicide. It was verified that in the herbicide absence the total population of weeds were significantly higher in the second evaluation period. However, in the herbicide presence there was no significant difference in the total population of weeds between the two evaluated periods.

A role for root morphology and related candidate genes in P acquisition efficiency in maize

Phosphorus (P) is an essential nutrient for plants and is acquired from the rhizosphere solution as inorganic phosphate. P is one of the least available mineral nutrients, particularly in highly weathered, tropical soils, and can substantially limit plant growth. The aim of this work was to study a possible effect of root morphology and the expression pattern of related candidate genes on P efficiency in maize. Our field phenotyping results under low and high P conditions enabled us to identify two contrasting genotypes for P acquisition efficiency that were used for the root traits studies. Root morphology was assessed in a paper pouch system to investigate root traits that could be involved in P acquisition efficiency. The genes, Rtcs, Bk2 and Rth3, which are known to be involved in root morphology, showed higher expression in the P efficient line relative to the P inefficient line. Overall, root traits showed high heritability and a low coefficient of variation. Principal component analysis revealed that out of the 24 root traits analysed, only four root traits were needed to adequately represent the diversity among genotypes. The information generated by this study will be useful for establishing early selection strategies for P efficiency in maize, which are needed to support subsequent molecular and physiological studies.

Application rate trials with a nuclear polyhedrosis virus to control Spodoptera frugiperda (Smith) on maize

Diferentes concentracoes de virus da poliedrose nuclear (VPN) foram aplicadas em suspensao aquosa, usando-se pulverizador (acoplado a um trator ou costal-manual), para o controle de larvas de Spodoptera frugiperda (Smith), em milho (Zea mays L.). A mortalidade das larvas variou com o equipamento de aplicacao. Na aplicacao via trator, foi necessaria uma dose de pelo menos 2,5 x 1012 corpos de inclusoes poliedricas (CIP)/ha para se ter eficiencia comparavel a que se obteve com o pulverizador costal-manual (70,2%). Para este tipo de pulverizador pode-se usar 2,5 x 1011 CIP/ha, porem o efeito residual foi muito curto. Maior persistencia foi obtida com doses acima de 1,25 x 1012 CIP/ ha (93,4% de mortalidade). A ocorrencia de parasitoides na area experimental propiciou um aumento medio na taxa de mortalidade larval (16,4%), independente da metodologia de aplicacao. Entre os parasitoides, a maior ocorrencia foi de Campoletis flavicincta (Ashmead) (53,0%), seguido por Chelonus insularis (Cresson) (31,3%), e Eiphosoma spp. (15,6%).

Change in root apical protein and peroxidase activity in response to aluminum in tolerant and sensitive maize inbred lines

The effects of a short-term (80 min) exposure to 222 µM aluminum (Al) on the protein content and expression and on peroxidase activity and isoenzymes in the primary root of maize were evaluated. Two inbred lines differing in their level of tolerance to Al were used: Cateto 237 (tolerant) and L36 (sensitive). The apical 20 mm of the primary root was divided into 2-mm-long segments that were analyzed for total protein content and peroxidase activity. These results demonstrate that the total protein content along the root apex was not affected by Al in the tolerant inbred line, but decreased in the sensitive line. In the apical 2 mm of the root of the sensitive line, the expression of low molecular weight proteins (43 kDa or smaller) was decreased. Expression of low molecular proteins increased in the tolerant inbred line, even though total protein content did not increase. This suggests that some of these proteins could play a role in metal tolerance, perhaps as binding peptides. While the peroxidase activity of the tolerant inbred line did not change with exposure to Al, peroxidase activity in the apical 6 mm of the root of the sensitive line decreased. The tolerant inbred line constitutively expressed more anionic peroxidase isoforms. These results demonstrate that maintenance of protein expression may be an important component of the plants resistance to Al stress, and that resistance to Al stress is associated with the higher expression of anionic peroxidase isoforms.

Desempenho agronômico de cultivares de café resistentes à ferrugem no estado de Minas Gerais, Brasil

The purpose of this study was to evaluate the agronomic performance of 24 coffee cultivars (22 rust resistant cultivars and 2 susceptible control varieties) in different environments of Minas Gerais State, Brazil. The coffee plants were planted in four locations (Lavras, Campos Altos, Patrocinio and Turmalina) in three agroclimatic regions. The experiments were arranged in randomized complete block design, with three replications in plots measuring 3.5x0.7 m, with 10 plants per plot. The following traits were analyzed: yield, percentage of grains retained in sieve size 16 and vegetative vigor from four cropping years (2008 to 2012) and the adaptability and stability in yield. The cultivars showed differential performance in the four environments. The cultivars Sabia Tardio, Pau Brasil MG1, Obata IAC 1669-20, Catucai Amarelo 24/137 and IPR 103 were the most promising because they combined higher agronomic stability and adaptability in favorable and unfavorable environments.

Prediction of genetic gains from selection in Arabica coffee progenies

Gains from selection for yield were estimated in Arabica coffee progenies carrying rust-resistance genes. The experiment in augmented block design was installed in Tres Pontas, state of Minas Gerais. Three blocks were established with six plants per plot, spaced 3.50 x 0.90 m, in 96 regular (F2 progenies) and two control treatments. The plant response to rust was evaluated on a grade scale in 2008. Yield (bags per hectare) was estimated in the growing seasons 2005 to 2008. Significant differences between treatments for yield were observed in all harvests, except 2005. The presence of genetic variability among progenies allowed significant gain from selection for yield. Under the experimental conditions of this study, selection for yield can be performed in the first high-yield year, without major losses compared to genetic gain from selection for yield when based on the mean of four harvests.