Rodrigo Véras da Costa

Incidência de Colletotrichum graminicola em colmos de genótipos de milho

Stalk rot (Colletotrichum graminicola) is one of the most serious disease affecting maize crop in Brazil, especially after the flowering phase, when yield losses can reach significant levels. The use of genetically resistant cultivars is the most efficient strategy to control the disease. The aim of this work was to evaluate the incidence of stalk rot in maize commercial hybrids sinde there is scarce information to allow the use of genetic resistance as a strategy to control this disease. Eighteen maize commercial hybrids were evaluated in 2005, 2006, and 2007 in the experimental area of EMBRAPA Maize and Sorghum Research Center Sete Lagoas, Minas Gerais State, Brazil, under conditions of natural infection. From each plot, three stalk segments of three plants were sampled: the second internode above the soil line, the internode of ear insertion, and the internode right bellow the tassel. Four tissue fragments of each stalk segment were surface sterilized and transferred to oatmeal agar plates, which were incubated under continuous fluorescent light at 25oC. Pathogen identification and quantification were performed after three to four days of incubation. The hybrids BR201 and BR206 showed the lowest infection level (below 30%) whereas the highest incidence (above 60%) was observed for the hybrid BRS1010. The pathogen was observed in all analyzed stalk segments, but was most frequently isolated from the internode right below the tassel. No evaluated hybrid could be considered to have high resistance to the pathogen.

First report of pathogenicity of Pantoea ananatis in sorghum (Sorghum bicolor) in Brazil

Bacterial isolates from sorghum plants showing leaf spot symptoms were identified through molecular and phenotypic traits, showing that the isolates belong to Pantoea ananatis. Sorghum plants inoculated with those isolates showed a pathogenic reaction. The causal agent was reisolated and Koch’s postulates were fulfilled. This is the first report of P. ananatis causing leaf spots on sorghum plants in Brazil.

Viabilidade técnica e econômica da aplicação de estrobilurinas em milho

Technical and economic feasibility of strobilurin fungicides application on maize In recent years, great emphasis has been given to the use of fungicides for managing foliar diseases in corn in Brazil. This study aimed to conduct an analysis of technical and economic feasibility of application of fungicides on maize in different growing regions. Trials were conducted to evaluate the effect of fungicides on the yield of different maize cultivars at three locations: Sete Lagoas (state of Minas Gerais), Londrina (state of Parana) and Rio Verde (state of Goias). The effect of one and two fungicide applications on each cultivar was evaluated. For each trial, the difference in mean yield and disease severities between treated and untreated plots for each cultivars was compared. For all trials, yield response of cultivars treated with fungicides was highly inconsistent under low disease severity. A higher frequency of positive yields and economic benefit occurred when fungicide applications were made under conditions of high disease pressure. More studies are needed to better clarify the effect of strobilurin fungicides on the physiology and production of corn plants.

Adubação nitrogenada e potássica na severidade da antracnose em dois cultivares de milho

O equilibrio nutricional pode contribuir para a resistencia das plantas as doencas. Com o objetivo de avaliar o efeito da interacao entre as adubacoes nitrogenada e potassica na severidade das lesoes da antracnose foliar e na nutricao mineral da cultura do milho, foram instalados dois experimentos, em casa de vegetacao com dois cultivares, o DAS 2B710 (moderadamente resistente a doenca) e o BRS 1010 (susceptivel), cinco doses de N (75, 150, 300, 600 e 1200 mg dm-3) e cinco doses de K 63, 125, 250, 500 e 1000 mg dm-3). O delineamento experimental para cada cultivar foi em blocos inteiramente ao acaso, em esquema fatorial 5 x 5, com 25 tratamentos e quatro repeticoes. Cada vaso com quatro plantas constituiu uma parcela experimental. As doses de N e K foram divididas em quatro parcelas, com intervalos de dez dias a partir da semeadura, para os dois cultivares. Aos 21 dias apos a semeadura, as plantas foram inoculadas e levadas para câmara umida, com fotoperiodo de 16 horas, no escuro durante tres dias consecutivos. Avaliou-se a severidade das lesoes diariamente, ate 11 dias apos a inoculacao. Aos 43 dias apos a semeadura, a parte aerea das plantas foi colhida, secada e moida para determinar os teores de N e de K. A quantidade de area foliar lesionada dependeu da interacao entre os nutrientes. Em ambos os cultivares, os menores valores de severidade foram observados na menor dose de N, combinada com a maior dose de K. A severidade das lesoes observada no cultivar moderadamente resistente foi 41% menor que a observada no cultivar susceptivel. A adubacao nitrogenada influenciou de forma negativa o teor de K da parte aerea.

Utilização de multilinhas dinâmicas para o manejo da antracnose do sorgo

The objective of this work was to evaluate the efficiency of dynamic multilines, using genetic mixing in populations of three-;way hybrids, in the management of sorghum anthracnose, caused by the fungus Colletotrichum sublineolum. Eighteen three-;way hybrids were obtained from seven different lines containing genes for resistance to the disease. The 25 genotypes of hybrids and lines were evaluated in field conditions. In some hybrids, a higher resistance level was observed when compared to that of the more resistant line used in the crosses, indicating an additive effect of the resistance genes of the different lineages in the composition of the final resistance of hybrids. The use of dynamic multilines reduced the disease intensity in field and increased productivity. This strategy makes it possible to use lineages that have desirable agronomic characteristics, but are susceptible to anthracnose.

Transposable elements belonging to the Tc1-Mariner superfamily are heavily mutated in Colletotrichum graminicola

Transposable elements are ubiquitous and constitute an important source of genetic variation in addition to generating deleterious mutations. Several filamentous fungi are able to defend against transposable elements using RIP(repeat-induced point mutation)-like mechanisms, which induce mutations in duplicated sequences. The sequenced Colletotrichum graminicola genome and the availability of transposable element databases provide an efficient approach for identifying and characterizing transposable elements in this fungus, which was the subject of this study. We identified 132 full-sized Tc1-Mariner transposable elements in the sequenced C. graminicola genome, which were divided into six families. Several putative transposases that have been found in these elements have conserved DDE motifs, but all are interrupted by stop codons. An in silico analysis showed evidence for RIP-generated mutations. The TCg1 element, which was cloned from the Brazilian 2908 m isolate, has a putative transposase sequence with three characteristic conserved motifs. However, this sequence is interrupted by five stop codons. Genomic DNA from various isolates was analyzed by hybridization with an internal region of TCg1. All of the isolates featured transposable elements that were similar to TCg1, and several hybridization profiles were identified. C. graminicola has many Tc1-Mariner transposable elements that have been degenerated by characteristic RIP mutations. It is unlikely that any of the characterized elements are autonomous in the sequenced isolate. The possible existence of active copies in field isolates from Brazil was shown. The TCg1 element is present in several C. graminicola isolates and is a potentially useful molecular marker for population studies of this phytopathogen.

First report of Lasiodiplodia brasiliense causing maize stalk rot

Maize stalk rot can lead to major corn yield losses in Brazil and worldwide. Maize stalks exhibiting tiny black specks or light brown lesions were collected in the city of Luís Eduardo Magalhães. Based on morphological characteristics and molecular assays, the fungus was identified as Lasiodiplodia brasiliense. This is the first report of maize stalk rot caused by L. brasiliense.

Nitrogen and potassium fertilization on the yield and intensity of the maize white spot

A plants nutritional balance can influence its resistance to diseases. In order to evaluate the effect of increasing doses of N and K on the yield and severity of the mayze white spot, two experiments were installed in the field, one in the city of Ijaci, Minas Gerais, and the other in the city of Sete Lagoas, Minas Gerais. The experimental delimitation was in randomized blocks with 5 x 5 factorial analysis of variance, and four repetitions. The treatments consisted of five doses of N (20; 40; 80; 150; 190 Kg ha-1of N in the experiments 1 and 2) and five doses of K (15; 30; 60; 120; 180 Kg ha-1of K in experiment 1 and 8.75; 17.5; 35; 50; 100 Kg ha-1of K in experiment 2). The susceptible cultivar 30P70 was planted in both experiments. The plot consisted of four rows 5 meters long, with a useful area consisting of two central rows 3 meters each. Evaluations began 43 days after emergence (DAE) in the first experiment and 56 DAE in the second one. There was no significant interaction between doses of N and K and the disease progress P+. The effect was only observed for N. The K did not influence the yield and the severity of the disease in these experiments. Bigger areas below the severity progress curve of the white spot and better yield were observed with increasing doses of N. Thus, with increasing doses of N, the white spot increased and also did the yield.

ETIOLOGY AND EPIDEMIOLOGICAL VARIABLES ASSOCIATED WITH MAIZE RESISTANCE TO WHITE SPOT DISEASE

SUMMARY Maize white spot disease (MWSD) has become most important in Brazil. With this study the susceptible maize hybrid DAS657 was artificially inoculated under greenhouse conditions with the bacterium Pantoea ananatis and the fungus Phaeosphaeria maydis, the two most likely candidate etiological agents of MWSD. Plants inoculated with P. ananatis reproduced the symptoms typical of MWSD, while several attempts to fulfill Koch’s postulates with P. maydis failed. The epidemiological variables associated with maize resistance to MWSD was assessed with eight simple hybrids, one double hybrid, one triple hybrid and five inbred lines evaluated in two trials in a randomized block design with three replicates in two planting times. The area under disease progress curve (AUDPC) and disease severity at the end of the epidemic (Y max ) were the epidemiological variables that better differentiated maize genotypes resistant to MWSD. One inbred line and three simple hybrids were highly resistant. Two inbred lines were identified as new sources of resistance and may be used in maize breeding programs.