Ricardo Ribeiro de Oliveira

Diagrammatic scale for assessment of grapevine rust

A diagrammatic scale with six levels of disease severity (1, 5, 12, 25, 50 and 75%) was developed to assess grapevine (Vitis spp.) rust severity, caused by the fungus Phakopsora euvitis. Two versions of the scale, in black-and-white and in color, were validated by seven raters without previous experience with grapevine rust, who estimated the severity of 30 grapevine leaves showing rust symptoms, with and without the use of the scales. Precision and accuracy were determined by linear regression, relating the assessments using the scales to actual severity. Actual severity was assessed with the software ASSESS®. Using the diagrammatic scales, some raters were able to improve precision and accuracy. The color scale provided slightly more precise and accurate estimates than the black-and-white scale.

Patogenicidade de isolados de Corynespora cassiicola a diferentes espécies de plantas

Corynespora cassiicola, causes target leaf spot on a wide host range, including several economically important crops. This study investigated the pathogenicity of 15 C. cassiicola isolates on several hosts, in greenhouse. The fungal isolates were collected from several hosts. These isolates were inoculated on 12 different plant species. The isolates from cucumber showed the widest host range, infecting also six other hosts. The isolates from C. benghalensis and lettuce showed the narrowest host range, since they infected their host of origin and only another host plant. Most of the isolates lacked host specificity. Papaya plant, which showed the greatest susceptibility to the C. cassiicola isolates, were colonized by 12 of the 15 isolates tested. On the opposite, Vernonia sp. and C benghalensis were susceptible to only two and three C. cassiicola isolates, respectively.

Genome-Wide Analysis of Corynespora cassiicola Leaf Fall Disease Putative Effectors

Corynespora cassiicola is an Ascomycetes fungus with a broad host range and diverse life styles. Mostly known as a necrotrophic plant pathogen, it has also been associated with rare cases of human infection. In the rubber tree, this fungus causes the Corynespora leaf fall (CLF) disease, which increasingly affects natural rubber production in Asia and Africa. It has also been found as an endophyte in South American rubber plantations where no CLF outbreak has yet occurred. The C. cassiicola species is genetically highly diverse, but no clear relationship has been evidenced between phylogenetic lineage and pathogenicity. Cassiicolin, a small glycosylated secreted protein effector, is thought to be involved in the necrotrophic interaction with the rubber tree but some virulent C. cassiicola isolates do not have a cassiicolin gene. This study set out to identify other putative effectors involved in CLF. The genome of a highly virulent C. cassiicola isolate from the rubber tree (CCP) was sequenced and assembled. In silico prediction revealed 2870 putative effectors, comprising CAZymes, lipases, peptidases, secreted proteins and enzymes associated with secondary metabolism. Comparison with the genomes of 44 other fungal species, focusing on effector content, revealed a striking proximity with phylogenetically unrelated species (Colletotrichum acutatum, Colletotrichum gloesporioides, Fusarium oxysporum, nectria hematococca, and Botrosphaeria dothidea) sharing life style plasticity and broad host range. Candidate effectors involved in the compatible interaction with the rubber tree were identified by transcriptomic analysis. Differentially expressed genes included 92 putative effectors, among which cassiicolin and two other secreted singleton proteins. Finally, the genomes of 35 C. cassiicola isolates representing the genetic diversity of the species were sequenced and assembled, and putative effectors identified. At the intraspecific level, effector-based classification was found to be highly consistent with the phylogenomic trees. Identification of lineage-specific effectors is a key step toward understanding C. cassiicola virulence and host specialization mechanisms.

Caracterização morfofisiológica e identificação molecular de isolados de Guignardia citricarpa, agente patogênico da mancha preta dos citros

O presente trabalho teve como objetivo identificar 11 isolados de Guignardia citricarpa, agente causal da mancha preta dos citros (MPC), obtidos de frutas citricas sintomaticas de diferentes regioes geograficas, por meio da PC R e caracterizacao morfofisiologica das estruturas propagativas, esporulacao e crescimento micelial em diferentes meios de cultura, temperaturas e regimes de luz, nas condicoes de laboratorio. Pelo teste de PCR, todos os isolados foram identificados como o patogeno G. citricarpa. Os isolados caracterizados foram submetidos as temperaturas de 20, 25 e 30oC, em regime de luz continua, escuro continuo e fotoperiodos de 12 horas, durante 24 dias. Utilizaram-se os meios de cultura aveia-agar (AA), batata-dextrose-agar (BDA) e cenoura-dextrose-agar (CDA). Os resultados mostraram que ocorreu interacao entre os diferentes meios de cultura, temperaturas e fotoperiodos. O meio de cultura que melhor estimulou o crescimento micelial foi o CDA a 25oC sob o fotoperiodo de 12h. A maior producao de esporos (conidios) foi verificada no meio BDA a 20oC, no fotoperiodo de 12 horas. No meio CDA, nao ocorreu esporulacao de nenhum isolado. Sob a temperatura de 30oC, foi verificada apenas a producao de hifas e picnidios para a maioria dos isolados, em todos os meios de cultura e fotoperiodo testados.

Progress of Asian soybean rust and airborne urediniospores of Phakopsora pachyrhizi in southern Brazil

Asian soybean rust, caused by the fungus Phakopsora pachyrhizi, was reported at epidemic levels in 2003/2004 and is the main soybean disease in Brazil. The aim of this study was to investigate the spread of Asian soybean rust and to quantify airborne urediniospores in the region of Campo Mourao, Parana State, Brazil. Three experiments were conducted under field conditions during the 2007/08 and 2008/09 crop seasons. Using the disease gradient method, provided by the application of increasing levels of the fungicide tebuconazole, four Asian soybean rust epidemics at different intensities were obtained in each experiment. To quantify the urediniospores, weathercock-type spore collectors were installed during and between the two crop seasons. Disease progress curves were plotted for each epidemic, and maximum severity was estimated. The curves were fit to the logistic model, which provided higher coefficients of determination and more randomly distributed residuals plotted over time. Analyses of the area under the disease progress curve showed that the largest epidemics occurred in the 2007/2008 crop season and that the progress rates were higher for severity, even among plants protected with the fungicide. The number of urediniospores collected in the air was related to the presence of soybean plants in the cultivated crops. The quantity of urediniospores was also positively correlated to the disease severity and incidence, as well as to cumulative rainfall and favorable days for P. Pachyrhizi infection.

Chlamydospore formation by Corynespora cassiicola

The fungus Corynespora cassiicola is an important pathogen that causes necrotic lesions in several plant species. Saprophytism and parasitism habits of plants are common survival strategies for this pathogen. Few studies referred to the formation of chlamydospores by C. cassiicola. The objective of this study was to test the formation of chlamydospores by several C. cassiicola isolates from different agronomic crops and weeds. Fifteen isolates were analysed by in vivo and in vitro tests. Six isolates from four host plants (Cucumis sativus, Lantana camara, Malpighia glabra and Vernonia cinerea) were able to produce chlamydospores, both in vitro and in vivo. In vitro, chlamydospore production was highest for the Malpighia glabra isolate and one Cucumis sativus isolate, intermediate for two other C. sativus isolates, and lowest for the Vernonia cinerea and Lantana camara isolates. However, no difference in the relative number of chlamydospores produced among isolates was observed in vivo.