Papers by Douglas Parreira
A survey of fungal pathogens associated with cane tibouchina, Tibouchina herbacea (Melastomatacea... more A survey of fungal pathogens associated with cane tibouchina, Tibouchina herbacea (Melastomataceae), was conducted in the neotropics, concentrated in south and southeastern Brazil and aimed at finding potential biological control agents for this herbaceous invasive weed for introduction into Hawaii. Numerous fungal species were found, including five cercosporoid fungi. Four new taxa are described and illustrated here: Passalora tibouchinae, Pseudocercospora subsynnematosa, Pseudocercospora tibouchina-herbaceae and Pseudocercospora tibouchinicola. A phylogenetic analysis of the ITS and TEF-1α regions of the three new species of Pseudocercospora was conducted and confirmed their separation as distinct taxa as indicated by morphological and cultural features. Additionally, Cercospora apii is reported for the first time on T. herbacea. Among the species of fungi described in this study, two appear particularly promising for use in a biological control program because they were found to cause severe disease on T. herbacea: Passalora tibouchinae and Pseudocercospora subsynnematosa. Additional tests, including host-specificity screening, will be required in order to confirm this potential.
The main objective of this research is to determine the influence of leaf position on corn plants... more The main objective of this research is to determine the influence of leaf position on corn plants with white spot caused by Pantoea ananatis, which better represents the infection on the whole plant. A diagrammatic scale to quantify the severity of the disease was elaborated and validated. For scale elaboration, the minimal and maximal limits of the disease severity observed in the field were considered, and intermediate levels followed logarithmic increments according to the WebereFechner stimulation law. The scale has nine classes: 0.1, 1, 2, 4, 8, 16, 24, 32 and 64%. For scale evaluation, a severity evaluation for white spot was performed by 10 raters with no experience in disease evaluation. Initially, severity estimation was performed without a scale for 41 leaves with different levels of severity. Afterward, the same raters used the proposed diagrammatic scale. Through linear regression to compare the actual and estimate severity values, the raters' accuracy and precision were analyzed. Satisfactory accuracy and precision were achieved when estimation was performed with a diagrammatic scale. To determine the best leaf disease severity evaluation, correlation and regression analyses were performed with 25 plants of five genotypes, for a total of 284 leaves analyzed. Results analysis leads us to conclude that the severity of white spot on corn plants significantly correlates with the disease mean severity of leaves 0 and -1, i.e., a leaf of the corn ear and the one immediately below it. This scale provided good levels of accuracy and precision (a mean R 2 of 94%), with errors concentrating around 10%. Raters presented increased reproducibility (R 2 > 90% in 82% of cases) of severity estimates. The proposed diagrammatic scale is considered adequate to estimate the severity of white spot in corn for germplasm evaluations, for epidemiological studies and for evaluation of control strategies for this disease.
The anthracnose stalk rot of corn (ASR), caused by Colletotrichum graminicola, is a major disease... more The anthracnose stalk rot of corn (ASR), caused by Colletotrichum graminicola, is a major disease of this crop and occurs in most Brazilian regions where corn is grown. Despite its widespread occurrence, there are no estimates of the effect of ASR on the yield of corn under the Brazilian conditions. In this study, we evaluated the effect of ASR on corn hybrids yield. Two experiments were conducted (first crop 2007/2008 and second crop, 2009) in areas with a history of occurrence of leaf anthracnose and ASR. Five hybrids were evaluated in the first and second crops: AG1051, BRS 1001, BRS 1010, BRS 1035, P30F80 and BRS 1010, 2B710, P30F80, DKB390, BRS 1035, respectively. At harvest, we evaluated the incidence of plants with anthracnose stalk rot (IPASR), and we selected pairs of healthy and diseased plants to quantify the effect of ASR in the ear weight (EW), grain weight (GW) and the weight of a sample containing 100 kernels (W100). The IPASR was higher in the hybrid BRS 1010 (21.87 and 45.28%, first and second crops, respectively). The EW, GW and W100 were lower in diseased plants in all hybrids. The mean weight loss in the first season was EW 29.03%, GW 27.83% and W100 17.08%, and the second season was EW 27.75%, GW 25.60% and W100 16.99%. The most affected hybrids with weight loss in the first crop were AG1051 (EW 34.31%, GW 33.05%, W100 19.96%) and BRS 1035 (EW 34.74%, GW 34.65%, W100 22.31%). In the second crop, were P30F80 (EW 30.72%, GW 30.92%, W100 19.24%), DKB390 (EW 30.61%, GW 29.81%) and 2B710 (W100 19.27%). Corn yield was strongly affected by ASR.
Bacteria of the genus Pantoea have become important plant pathogens worldwide in recent years. Pa... more Bacteria of the genus Pantoea have become important plant pathogens worldwide in recent years. Pantoea ananatis was reported as the cause of maize white spot, a serious maize disease in Brazil, causing significant yield losses. However, very little information is available about how to detect this pathogen, its genetic variability and the putative alternative hosts in maize-growing areas. To address these issues, we implemented a rapid and efficient PCR-based method to identify P. ananatis isolated from leaves showing white spot symptoms and evaluated its genetic diversity in maize, sorghum and crabgrass. Of the 29 bacteria isolated from typical water-soaked lesions of white spot disease that produced yellow colonies, 15 isolates were identified as P. ananatis by 16S rDNA sequencing and correctly detected by the PCR reaction, amplifying a specific fragment of the ice nucleation gene (ina). These P. ananatis isolates included 13 from maize, one from sorghum and one from crabgrass, while the other 14 yellow colony isolates were from other bacterial species, including two Pantoea species (Pantoea dispersa and Pantoea agglomerans) that were not amplified by the ina primers. These results indicate that the optimized PCR assay can be used to detect P. ananatis isolated from white spot lesions and could be used as a large-scale and cost-effective method of detecting this pathogen in leaf lesions on maize and other grasses. All isolates were evaluated for hypersensitive response (HR) on tobacco, revealing that some P. ananatis were able to induce HR. The high genetic variability revealed by rep-PCR did not differentiated the P. ananatis isolates based on their hosts or HR reaction. The detection, characterization and diversity of P. ananatis from maize, sorghum and crabgrass in our study can be applied in understanding epidemiology and designing control strategies for maize white spot disease in Brazil.
Bacterial isolates from sorghum plants showing leaf spot symptoms were identified through molecul... more 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.
Pseudocercospora muntingiae is recorded as the cause of leaf spots on Muntingia calabura (Tiliace... more Pseudocercospora muntingiae is recorded as the cause of leaf spots on Muntingia calabura (Tiliaceae), for the first time from Brazil and also in South America. (a) (b) Fig. 1. Leaves of Muntingiae calabura, with leaf spots: (a) adaxial surface, (b) abaxial surface (bar 2 cm).
Resumo -O pinhão-manso (Jatropha curcas) é considerado uma importante fonte de óleo para produção... more Resumo -O pinhão-manso (Jatropha curcas) é considerado uma importante fonte de óleo para produção de biodiesel. Devido à expansão desta cultura pelo país, fitopatógenos podem ser disseminados por meio de sementes infectadas. Desta forma, o objetivo deste trabalho foi avaliar o aspecto sanitário de sementes de pinhão-manso provenientes dos Vales do Jequitinhonha e Mucuri. A presença de patógenos associados a sementes foi avaliada por meio de teste de sanidade (Blotter test) e germinação em leito de areia em casa de vegetação. Fusarium sp., Rhizoctonia sp. e Alternaria sp. foram os principais fungos encontrados no teste de sanidade. A germinação das sementes foi de 68%. Baseados nestes resultados, estratégias fitossanitárias devem ser estabelecidas com o objetivo de reduzir a disseminação de patógenos por meio de sementes de pinhão-manso.
Stalk rot (Colletotrichum graminicola) is one of the most serious disease affecting maize crop in... more 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 i s the most efficient strategy to control the disease. The aim of this work was to evalua te the incidence of stalk rot in maize commercial hybrids sinde there is scarc e informa tion 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: Costa, R.V.; Silva, D.D; Cota, L.V.; Parreira, D.F.; Ferreira, A. S.; Casela, C.R.. Incidence of Colletotrichum graminicola in stalk from maize genotypes.
Uma muda de tomate com 20 dias de idade foi transplantada por vaso com dois litros de capacidade ... more Uma muda de tomate com 20 dias de idade foi transplantada por vaso com dois litros de capacidade contendo mistura de solo argiloso e areia na proporção 1:1 (v:v). Após dois dias, o substrato foi infestado com 5.000 ovos de Meloidogyne javanica. Decorridos 90 dias da inoculação do nematóide, as plantas foram retiradas e o substrato dos vasos foi misturado em betoneira, para homogeneizar a distribuição dos nematóides, e recolocado nos vasos. Cem gramas de parte aérea fresca e picada de repolho (Brassica oleracea var. capitata), mostarda (Brassica juncea), brócolis (Brassica oleracea var. italica) ou couve-flor (Brassica oleracea var. botrytis) foram depositadas na superfície do substrato de cada vaso, na proporção de 50 g por litro de substrato. Após seis dias, o material orgânico foi incorporado e os vasos cobertos com polietileno transparente. Os tratamentos constaram de incorporação de material vegetal com ou sem cobertura com plástico. No tratamento testemunha, não foi feita a incorporação de material vegetal nem a cobertura do solo com o plástico. Decorridos os 30 dias, foi feita a retirada do plástico e, 24 horas depois, uma muda de tomate foi transplantada em cada vaso. Sessenta dias após o transplantio, foram avaliados os números de galhas e ovos por sistema radicular, a altura e a massa da parte aérea das plantas. Os tratamentos de biofumigação com couve-flor, brócolis e mostarda reduziram o número de galhas em 61,3, 60,8 e 46,8 %, respectivamente, em relação à testemunha, da qual diferiram estatisticamente. Todos os tratamentos diferiram da testemunha em relação ao número de ovos de M. javanica por sistema radicular e a massa da parte aérea das plantas foi superior em todos os tratamentos em que a matéria orgânica foi incorporada ao solo. Palavras-chave: Meloidogyne javanica, biofumigação, brássicas.
Summa Phytopathologica, 2006
Resumo -Um grande problema no controle de doenças na agricultura é a ocorrência de populações res... more Resumo -Um grande problema no controle de doenças na agricultura é a ocorrência de populações resistentes aos produtos utilizados. Nos últimos anos, uma classe de fungicidas que vem ganhando destaque são os QoI's, que atuam na respiração mitocondrial se ligando ao sítio Qo do citocromo bc1. Devido ao uso excessivo desses produtos, vários casos de resistência já foram relatados em condições de campo. Estudos moleculares identificaram algumas mutações no sítio alvo, sendo a mais comum a troca de glicina por alanina na posição 143 (G143A). Outros mecanismos de resistência também foram identificados, como a ocorrência de respiração alternativa e o bombeamento do produto para fora da célula fúngica por um processo de xenobiose. A compreensão sobre os mecanismos de resistência auxilia na elaboração de estratégias anti-resistência para serem empregadas nos programas de manejo das culturas.
Two new species of Mycosphaerella (Ascomycota, Mycosphaerellaceae) are described on Sapium glandu... more Two new species of Mycosphaerella (Ascomycota, Mycosphaerellaceae) are described on Sapium glandulosum from Brazil. Both Mycosphaerella sapiicola and M. sapii differ in ascospore shape and size from the other species of Mycosphaerella described on Sapium (M. sodiroana). An anamorph belonging to Septoria was also found associated with M. sapii. The type of M. sodiroana was reexamined and is illustrated here for the first time.
Meliola thalliformis var. major var. nov., associated with leaf spots on Bathysa australis (Rubia... more Meliola thalliformis var. major var. nov., associated with leaf spots on Bathysa australis (Rubiaceae), is described and illustrated.
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Papers by Douglas Parreira