Luciano Viana Cota

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.

Comparative transcriptomic analysis indicates genes associated with local and systemic resistance to Colletotrichum graminicola in maize

The hemibiotrophic fungus Colletotrichum graminicola may cause severe damage to maize, affecting normal development of the plant and decreasing grain yield. In this context, understanding plant defense pathways at the inoculation site and systemically in uninoculated tissues can help in the development of genetic engineering of resistance against this pathogen. Previous work has discussed the molecular basis of maize - C. graminicola interaction. However, many genes involved in defense have not yet been exploited for lack of annotation in public databases. Here, changes in global gene expression were studied in root, male and female inflorescences of maize under local and systemic fungal infection treatments, respectively. RNA-Seq with qPCR was used to indicate genes involved in plant defense. We found that systemic acquired resistance induction in female inflorescences mainly involves accumulation of salicylic acid (SA)-inducible defense genes (ZmNAC, ZmHSF, ZmWRKY, ZmbZIP and PR1) and potential genes involved in chromatin modification. Furthermore, transcripts involved in jasmonic acid (JA) and ethylene (ET) signaling pathways were also accumulated and may participate in plant immunity. Moreover, several genes were functionally re-annotated based on domain signature, indicating novel candidates to be tested in strategies involving gene knockout and overexpression in plants.

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.

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.

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.