GENETIC CONTROL OF MAIZE DWARF MOSAIC VIRUS IN TROPICAL MAIZE INBRED LINES

The continuous cropping in the major corn growing areas has contributed to the increase in the incidence and severity of diseases, including the diseases caused by potyvirus. It has been predominantly observed that one strain of the maize dwarf mosaic virus (MDMV) is the causal agent of the potyvirus - induced - mosaic in Brazil. The use of resistant cultivars is the most efficient method to protect crops against this virus disease. However, the identification of resistance sources and its genetic control are important requirements to establish successful breeding programs aiming the production of resistant cultivars. Thus, the objective of this study was to determine the genetic basis of resistance to maize dwarf mosaic virus using two resistant (L18 and L520) and one susceptible (L19) maize inbred lines. The parents and their respective generations F1, F2, BC1.1 and BC1.2 were artificially inoculated and the symptoms evaluation was done at 15 and 30 days after inoculation. The genetic-statistic results analyzed by the chisquare test showed that the resistance to maize dwarf mosaic virus is conditioned by a single gene with complete dominance in both resistant inbred lines. Besides, the allelism test between L18 and L520 detected a phenotypic proportion of 15 (R): 1 (S) in the F2 generation, suggesting that the resistant inbred lines carry different genes

PEROXIDASE ACTIVITY IN MAIZE INBRED LINES RESISTANT OR SUSCEPTIBLE TO MAIZE DWARF MOSAIC VIRUS

Peroxidase (EC 1.11.1.7) activity levels were analyzed in maize seedling inbred lines contrasting with their resistance to maize dwarf mosaic virus (MDMV). Groups of noninoculated resistant and susceptible inbred lines showed different levels of guaiacol peroxidase activity at the seedling stage, with 78 % of susceptible inbred lines presenting enzyme activity values below 91.46 A470 min–1g FW –1. However, the zymogram patterns of peroxidase did not allow the differentiation of non-inoculated resistant or susceptible inbred lines. The virus complex induced a general enhancement of enzyme activity, without qualitative changes in the isoenzymes, when inoculated into resistant or susceptible inbred lines. However, a quantitative change, with 19% OD average increase in a moderately anionic isoform was observed in some resistant inbred lines in response to virus inoculation. Our results could suggest that peroxidase activity prior to infection, and the increase in activity of an specific anionic isoform in some resistant inbred lines, due to virus inoculation, could be related to a defense mechanism against MDMV

PHENOLICS CONTENTS IN MAIZE ROOTS UNDER ALUMINUM TOXICITY

Aluminum (Al) tolerance mechanisms proposed in the literature can beclassified as exclusion and internal tolerance mechanisms. Exclusion mechanisms preventthe Al from crossing the plasma membrane and penetrating the simplast. Internal tolerancemechanisms immobilize, compartmentalize or detoxify Al that penetrates the simplast.It has been suggested that phenolic compounds act in both mechanisms, due to its capacityto chelate metals as Al and to act as a strong antioxidant in response to abiotic stresses.The objective of this work was to identify differences in the content of total solublephenolics and phenolic acids (ferulic acid, 5-5‘diferulic and para-cumaric), bounded tothe cell wall of maize roots between inbred lines contrasting in their tolerance to Al,Cateto 237 (tolerant) and L53 (sensitive), when exposed to Al toxicity. Seedlings were cultivated in nutrient solution in the absence (0 h period) and presence of Al (AlK(SO4)2)39 μM activity (12, 24, 48 and 72 h period). Total soluble phenolics were analyzed bythe Prussian Blue method, and phenolic acids bounded to cell wall were analyzed byHigh Performance Liquid Chromatography (HPLC). Results obtained suggested thatphenolics may participate in Al tolerance mechanisms, considering that the tolerant inbredline Cateto 237 was capable of maintaining total soluble phenolics concentration, andincreased the concentration of ferulic, 5-5‘diferúlic and p-cumáric acids under Al toxicit

Análise do N-terminal da proteína capsidial de SCMV infectando milho e sorgo no Brasil

Os objetivos do presente estudo foram (i) identificar por meio do sequenciamento da proteína capsidial a espécie de potyvírus causando sintomas de mosaico em milho e sorgo no Brasil, e (ii) analisar a sequência de aminoácidos (aa) do N-terminal do gene da proteína capsidial.Fil: Souza, Isabel Regina Prazeres de. Embrapa Milho e Sorgo, Sete Lagoas; BrasilFil: Carneiro, Newton Portilho. Embrapa Milho e Sorgo, Sete Lagoas; BrasilFil: Giolitti, Fabian. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Patología Vegetal; ArgentinaFil: Lenardon, Sergio Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Patología Vegetal; ArgentinaFil: Oliveira Sabato, Elizabeth de. Embrapa Milho e Sorgo, Sete Lagoas; BrasilFil: Gomes, Eliane Aparecida. Embrapa Milho e Sorgo, Sete Lagoas; BrasilFil: Noda, Roberto Willians. Embrapa Milho e Sorgo, Sete Lagoas; BrasilFil: Souza, Francisco Adriano de. Embrapa Milho e Sorgo, Sete Lagoas; Brasi

PROTEIN OXIDATION AND LIPID PEROXIDATION OF SEVERAL ‘SARACURA’MAIZE SELECTION CYCLES UNDER CONTINUOUS FLOODING

This work aimed at studying, under continuous flooding, biochemicalmechanisms such as total protein concentration, proteic oxidation, and membrane lipidperoxidation in leaf and root of the maize BRS 4154 (Saracura) seedlings, after 1 (C1), 8(C8) and 16 (C16) selection cycles under intermittent flooding. The variety BR 107 wasused as control. Seeds of the selection cycles from Saracura: C1, C8 and C16, and controlBR 107 were sowed with the embryo facing up, 1 cm deep, in perforated 200 ml plasticcups filled with lowland soil. The treatments were composed of the periods 0 h (withoutflooding) 8, 24, 48, 72, 96, 120 and 144 h under continuous flooding, using distilledwater up to the soil surface. Protein oxidation and concentration, root and leaf lipid peroxidation were responsive to flooding, showing the same tendency in all genotypesanalyzed

Abundance and Species Richness of Leafhoppers and Planthoppers (Hemiptera: Cicadellidae and Delphacidae) in Brazilian Maize Crops

Fil: De Oliveira, Charles Martins. Embrapa Cerrados. Planaltina. Brasília/DF; BrazilFil: De Oliveira, Elizabeth. Embrapa Milho e Sorgo. Sete Lagoas/MG; BrazilFil: Prazeres De Souza, Isabel Regina. Embrapa Milho e Sorgo. Sete Lagoas/MG; BrazilFil: Alves, Elcio. DuPont do Brazil S.A. DivisÆo Pioneer Sementes. Itumbiara/GO; BrazilFil: Dolezal, William. Pioneer Hi-Bred International. Itumbiara/GO; BrazilFil: Paradell, Susana Liria. División Entomología. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Marino de Remes Lenicov, Ana María. División Entomología. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Frizzas, Marina Regina. Universidade de Brasília. Departamento de Zoologia. Instituto de Ciências Biológicas. Brasília/DF; Brazi

Variabilidade genética de fitoplasma e espiroplasma isolados de plantas de milho no Brasil

The objective of this work was to characterize the genetic variability of phytoplasma and Spiroplasma kunkelii isolated from maize plants showing symptoms of stunt collected from different Brazilian geographic regions. A DNA fragment of 500 base pairs (bp) was amplified from the spiralin gene in S. kunkelii and one fragment of 1,200 bp was generated from 16S rDNA gene in phytoplasma. The partial sequences of the spiralin gene showed similarity of 98% among the isolates of S. kunkelii analyzed. These sequences were compared with the sequence of the spiralin gene from other Spiroplasma species deposited in the GenBank, resulting in a similarity varying from 76.9% to 88.1%. The 16S rDNA sequence from the phytoplasma were completely similar within the Brazilian isolates and showed up to 98% of the similarity with sequences already found from other phytoplasmas. A very narrow genetic variability was detected by these gene fragments within phytoplasma and Spiroplasma analyzed. However, other genomic regions with higher polymorphic levels shall be identified in order to better evaluate the genetic diversity within these microorganisms population.O objetivo deste trabalho foi caracterizar a variabilidade genética de isolados de fitoplasma e de Spiroplasma kunkelii obtidos de plantas de milho, apresentando sintomas de enfezamento, coletados em diferentes regiões do Brasil. Um fragmento de 500 pares de bases (pb) do gene que codifica a espiralina de S. kunkelii foi amplificado e um produto de amplificação de 1.200 pb foi gerado a partir do gene 16S rDNA de fitoplasma. As seqüências parciais do gene da espiralina mostraram similaridade de 98% entre os isolados de S. kunkelii analisados. Essas seqüências foram comparadas com a seqüência do gene da espiralina de outras espécies de Spiroplasma depositadas no GenBank, resultando em similaridade variável entre 76,9% e 88,1%. As seqüências do gene 16S rDNA dos isolados de fitoplasma foram completamente similares entre todos os isolados brasileiros e apresentaram até 98% de similaridade com seqüências do mesmo gene de outros fitoplasmas já publicadas. Uma variabilidade genética muito estreita foi detectada para esses genes entre os isolados de fitoplasma e Spiroplasma analisados. No entanto, outras regiões genômicas, que apresentem um maior polimorfismo precisam ser identificadas para melhor avaliar a diversidade genética dentro da população desses microrganismos

AGRONOMICAL AND MOLECULAR EVALUATION OF ACCESSIONS FROM MAIZE CORE COLLECTION, SUBGROUP FLINT ENDOSPERM

The utilization efficiency of maize germplasm accessions that consist of a core collection can be incremented using molecular and morpho-agronomical characteristics, getting more detailed descriptions about these accessions. The objective of this work was to valorize maize core collection, sub-group endosperm flint of the Brazilian Agricultural Research Corporation (Embrapa), through the use of morphological descriptors and AFLP molecular markers. Fifty-eight accessions from the core collection were used, thirty-two morphoagronomical descriptors considered, and six AFLP primers combinations were tested to obtain the genetic patterns. The most contributions of morpho-agronomical variables for core collection genetic divergence were grain thousand weight (31.0%), ear height (21.7%) and ear weight (16.4%). The core collection principal component analysis was done with 14 morphoagronomical variables and indicated that variance accumulated by the first three components was 70.57%. The six primers AFLP combinations used in 58 accessions generated 207 bands, with 32.8 polymorphic bands average. Dendrograms of core collection showed similar general structure and did not indicate homogeneous group formation. The observed allele number average was 1.95, allele effective number average was 1.47 and the heterosigosity (h), (Nei’s index of genetic diversity) used for polymorphic information content evaluation was 0.28. Molecular characterization allowed valorization of each accession, indicating new information on the core collection genetic structure, and confirming high variability among accessions

SEQUENCE DIVERSITY IN THE COAT PROTEIN OF SCMV INFECTING MAIZE AND SORGHUM IN BRAZIL

The “maize common mosaic”, caused by potyvirus, is among the major virus diseases of this crop inBrazil. Although there were evidences indicating Sugarcane mosaic virus (SCMV) as the most common potyvirusspecies in maize (Zea mays L.) in Brazil, information about those species that infect sorghum plants [Sorghum bicolor(L.) Moench] are few. Leaves showing characteristic mosaic symptoms were collected from maize and sorghum andused in serological and sequencing analysis of the coat protein (CP) gene for potyvirus species identification. Amino acid(aa) analysis of the CP N-terminal sequence of our samples showed a different repeated sequence, a higher content of thedipeptide GT, and a 15 aa longer than the majority of the SCMV sequences used for comparisons. The Brazilian maizeand sorghum potyviruses formed a monophyletic group, suggesting that they can be classified within a new SCMV strain.Studies using potyvirus CP gene sequencing from Brazilian sorghum potyvirus have been reported for the first time