Search for sources of resistance to Fusarium wilt (Fusarium oxysporum f. sp. vasinfectum) in okra germplasm

– Fusarium oxysporum f. sp. vasinfectum (FOV) is one the most destructive okra (Abelmoschus esculentus) pathogens in Brazil. Fifty-four okra accessions were evaluated for resistance to FOV. Greenhouse screening was initially carried out with one FOV isolate (‘Fus-194’). Inoculation (in all assays) was carried out with 21-day-old plantlets, using the root-dipping inoculation technique. Thirty-three accessions displaying differential responses in the first screening were re-evaluated in two additional assays, using two FOV isolates (‘Fus-194’ and ‘Fus-201’). Twelve accessions were rated as highly to intermediately resistant to ‘Fus-194’ during the dry/moderate temperature season, whereas nine accessions were classified as highly to intermediately resistant to ‘Fus-201’. In the assay carried out in the wet and warm season, 72% of the accessions were classified as having high and intermediate resistance to ‘Fus-194’, and 32% were resistant to ‘Fus-201’. The accessions ‘Santa Cruz-47’, ‘BR-2399’ and ‘BR-1449’ were the most promising resistance sources

Effects of wounding, humidity, temperature, and inoculum concentrations on the severity of corky dry rot caused by Fusarium semitectum in melon fruits

[EN] Corky dry rot, caused by Fusarium semitectum, is the main postharvest disease of melons in Brazil. This study investigated the effects of wounding, humidity, temperature, and inoculum concentration on the severity of corky dry rot under controlled conditions. Cantaloupe and honeydew melon types were inoculated by spraying conidial suspensions of three F. semitectum isolates. In all experiments, the tested F. semitectum isolates did not differ in relation to disease severity, but, the cantaloupe melon showed higher levels of severity. No lesions appeared on fruits that lacked wounds, and increasing wound age reduced lesion severity. Melons that were inoculated with F. semitectum developed symptoms regardless of the presence or absence of a moist chamber at the post-inoculation stage, but the lesions were larger under moist chamber conditions. There were no symptoms at 10°C, but a temperature increase from 15 to 25°C resulted in a disease severity increase. The largest lesions were observed when both melon types were inoculated with a concentration of 106 conidia mL-1, but even the lowest concentration (101 conidia mL-1) was sufficient for causing lesions. Injury reduction and/or the acceleration of melon healing, as well as environmental variable control and a reduction of inoculum sources, are essential to reducing corky dry rot severityDe Oliveira, MJ.; Laranjeira, D.; Saraiva Camara, MP.; Ferraz Laranjeira, F.; Armengol Fortí, J.; Michereff, SJ. (2014). Effects of wounding, humidity, temperature, and inoculum concentrations on the severity of corky dry rot caused by Fusarium semitectum in melon fruits. Acta Scientiarum. Agronomy. 36(3):281-289. doi:10.4025/actasciagron.v36i3.17656S28128936

Population structure of Monosporascus cannonballus isolates from melons produced in Northeastern Brazil based on mycelial compatibility groups

[EN] The population structure of Monosporascus cannonballus, which causes vine decline in melons, was assessed based on the determination of mycelial compatibility groups (MCGs) in a collection of 58 isolates obtained from seven melon fields in three municipalities of Northeastern Brazil. For comparison, an additional 11 isolates of M. cannonballus from Spain were included in the analysis. MCGs were determined through comparisons of paired isolates growing on PDA culture media in the dark at 30ºC in various combinations. The Brazilian isolates were assigned into four MCGs: MCG-1 (n = 35 isolates), MCG-2 (n = 20), MCG-3 (n = 2), and MGC-4 (n = 1). MCG-1 and MCG-2 included isolates from all surveyed areas. The Spanish isolates were assigned into six different MCGs, and none of them were compatible with the Brazilian isolates. The genetic structure was determined using the frequencies of MCGs and genotypic diversity indices. The maximum genotypic diversity was 6.9 and 54.5% for the Brazilian and Spanish populations, respectively. The low level of genetic diversity in the M. cannonballus population from Northeastern Brazil suggests that breeding melons for disease resistance may be a promising strategy for the region.This research was partially funded by CAPES (Project 203/2009 - International Cooperation CAPES-Brazil/DGU-Spain). We are thankful CNPq for the research fellowships granted to C. S. Bezerra, M. P. S. Camara, R. Sales Junior and S.J. Michereff. We thank Prof. Eduardo S. G. Mizubuti, Universidade Federal de Vicosa, Vicosa, Minas Gerais State, Brazil, for useful advice on data analyses.De Souza Bezerra, C.; Câmara Correia, K.; Saraiva Câmara, MP.; Sales Júnior, R.; Armengol Fortí, J.; Michereff, SJ. (2013). Population structure of Monosporascus cannonballus isolates from melons produced in Northeastern Brazil based on mycelial compatibility groups. Acta Scientiarum. Agronomy. 35(2):161-167. https://doi.org/10.4025/actasciagron.v35i2.15182S16116735

Fungal trunk pathogens associated with table grape decline in Northeastern Brazil

[EN] During the last five years a decline of table grape plants has been noticed in nurseries, young plantations and vineyards of the Northeastern region of Brazil, where the management systems for grapevine production are adapted to the specific environmental conditions of a tropical viticulture. Samples of table grape plants showing decline symptoms were obtained from grapevine nurseries, young plantations and vineyards located in the São Francisco, Assú and Siriji Valleys in 2010, and were subjected to fungal isolation. Grapevine trunk pathogens were identified using morphological and molecular methods. Species recovered included Botryosphaeria mamane, Campylocarpon fasciculare, C. pseudofasciculare, Lasiodiplodia crassipora, L. parva, L. pseudotheobromae, L. theobromae, Neofusicoccum parvum, Phaeoacremonium aleophilum, Pm. parasiticum and Phaeomoniella chlamydospora. They are all reported for the first time on grapevine in Brazil, with the exception of L. theobromae. Moreover, Botryosphaeria mamane, Lasiodiplodia parva and L. pseudotheobromae are reported for the first time on grapevine, and C. fasciculare is reported for the first time on the American continent.This research has been performed within the Programme VLC/Campus, Microcluster IViSoCa (Innovation for a Sustainable Viticulture and Quality), and was financially supported by the Project RTA2010- 00009-C03-03 (Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, INIA, Spain), the European Regional Development Fund (ERDF) and by CAPES (Project 203/2009 - International Cooperation CAPES-Brazil/DGU-Spain). We are thankful to CAPES (Brazil) for the research fellowships granted to K. C. Correia and S. J. Michereff.Correia, KC.; Saraiva Camara, MP.; Guimaraes Barbosa, MA.; Sales, RJ.; Agustí Brisach, C.; Gramaje, D.; León Santana, M.... (2013). Fungal trunk pathogens associated with table grape decline in Northeastern Brazil. Phytopathologia Mediterranea. 52(2):380-387. https://doi.org/10.14601/Phytopathol_Mediterr-11377S38038752

BIOLOGY OF COLLETOTRICHUM SPP. AND EPIDEMIOLOGY OF THE ANTHRACNOSE IN TROPICAL FRUIT TREES

The anthracnose is important disease in the pre an d postharvest phases. Several species of Colle- totrichum ( C. gloeosporioides, C. acutatum, C. musae e C. magn a ) are responsible for inciting this disease. The pathogen infects many fruit trees in tropical and t emperate regions, causing considerable damage and l oss in all phases of cultures. Characteristic symptoms are dar k necrotic lesions depressed, subcircular or angula r shaped, and there may be coalescing. Infections have a spec ial feature: the phenomenon of quiescence. This pro cess has important implications, particularly in post-harves t, because the damage from infections reflect only this phase. The intensity of the disease have been striking at temperatures from 24 to 28 °C and in the presence o f high relative humidity. The understanding of some aspect s of the biology of the pathogen (the process of qu ies- cence) and the epidemiology of the disease is cruci al, since much has not yet been fully clarified, es pecially when the aim is to achieve sustainable management

Elaboration and validation of diagrammatic key to evaluate white rust severity in Chrysanthemum

White rust, caused by Puccinia horiana, is considered the major disease of Chrysanthemum in Brazil, which results in severe losses for the growers. Despite of its economic importance, very few epidemiological studies have been carried out in Brazil. In order to conduct these studies it is necessary to develop standard methods to quantify disease severity under field conditions. Therefore, a diagrammatic key, including the levels 1, 3, 6, 10, 18, and 30% of diseased leaf area, was elaborated. The severity of the white rust was estimates using the key or not in order to test its accuracy, precision and reproducibility. The diagrammatic key was validated by 10 raters using 50 leaves with different levels of severity, which were previously measured by the AutoCAD® software. Two evaluations were performed with the key at 7-day intervals when different sequences of the same leaves were visually estimated by the same raters. The accuracy and precision of each rater were determined by using simple linear regression between actual and estimated severity. When the key was not used, all raters overestimated disease severity indicating the presence of constant positive errors for all levels of disease severity. The evaluations using the diagrammatic key were more accurate for the great majority of the raters and more precise for all the raters. In addition, the key also showed good repeatability and high level of reproducibility among the evaluations from the different raters. The diagrammatic key is suitable for the evaluation of severity of white rust of Chrysanthemum.A ferrugem branca, causada pelo fungo Puccinia horiana, é considerada a principal doença do crisântemo no Brasil, induzindo severas perdas aos produtores. Apesar da importância, inexistem estudos epidemiológicos no país, e para que estes estudos sejam realizados, é necessário o desenvolvimento de métodos padronizados de quantificação da severidade da doença no campo. Visando atender a essa demanda, foi elaborada uma escala diagramática com os níveis de 1, 3, 6, 10, 18 e 30% de área foliar lesionada, testando-se a acurácia, a precisão e a reprodutibilidade das estimativas de severidade da ferrugem branca com e sem a sua utilização. Na validação da escala diagramática, 50 folhas com diferentes níveis de severidade da doença, mensurados previamente com o programa AutoCADâ, foram avaliadas por 10 pessoas sem e com a utilização da escala diagramática. Foram realizadas duas avaliações com a utilização da escala, com intervalo de sete dias, onde seqüências diferentes das mesmas folhas foram estimadas visualmente pelos mesmos avaliadores. A acurácia e a precisão de cada avaliador foi determinada por regressão linear simples, entre a severidade real e a estimada. Sem o auxílio da escala, todos os avaliadores superestimaram consistentemente a severidade, indicando a presença de desvios positivos constantes para todos os níveis de severidade da doença. As avaliações realizadas com a escala diagramática foram mais acuradas nas estimativas da maioria dos avaliadores e mais precisas para todos os avaliadores, além de proporcionar boa repetibilidade e elevada reprodutibilidade entre avaliações de diferentes avaliadores. A escala diagramática mostrou-se adequada para avaliação da severidade da ferrugem branca do crisântemo.BARBOSA, M. A. G. Universidade Federal do Par

Amostragem, caracterização de sintomas e escala diagramática da mancha graxa dos citros (Mycosphaerella citri) no Recôncavo Baiano Sampling, characterization of citrus greasy spot (Mycosphaerella citri) symptoms in Recôncavo Baiano and development of a diagrammatic scale for assessment of severity

O Recôncavo da Bahia é uma região de clima propício à mancha graxa dos citros (Mycosphaerella citri), doença nunca antes estudada no Brasil. Os objetivos deste trabalho foram definir o tamanho mínimo de amostra para quantificar a incidência, caracterizar os sintomas da doença e elaborar uma escala diagramática para a avaliação de sua severidade. A partir de uma amostragem piloto realizada por avaliação de cinco folhas por quadrante, quatro quadrantes por planta e 30 plantas em cada um dos 10 pomares visitados no município de Cruz das Almas, foi determinado que o tamanho mínimo da amostra em quadrantes e folhas seria de quatro e 16 plantas, respectivamente. De 320 folhas coletadas de diferentes plantas em 11 pomares, foi constatada uma grande quantidade de lesões (média de 131) por folha sintomática, em sua maioria diminutas (média de 0,014cm²). A severidade variou de 0,15% a 35,85%, com média de 7,3%. Com base na severidade real em campo, foi elaborada uma escala diagramática com seis níveis: 1%, 2%, 5%, 9%, 18% e 36% de área foliar lesionada. Cinqüenta imagens de folhas foram submetidas a avaliadores por duas vezes, os quais estimaram a severidade com e sem a utilização da escala, constatando-se um discreto benefício no grau de precisão e de acurácia das estimativas com o uso da escala.<br>Weather conditions make the Recôncavo Region in the State of Bahia, a favorable region to the occurrence of citrus greasy spot (Mycosphaerella citri), a disease that hadn't been studied before in Brazil. Thus, this research aimed to develop a sampling method to quantify its incidence, to characterize its symptoms, and to develop a diagrammatic scale for assessing disease severity. The minimum sample size to estimate greasy spot incidence in leaves (16 plants) was calculated based on a prospective sampling of five leaves per quadrant, four quadrants per tree, and 30 trees per grove, in ten groves. From 320 mature leaves collected in different plants of 11 groves, it was observed a high number of lesions per symptomatic leaf (mean of 131&plusmn;102), most of them small (mean of 0.014&plusmn;.,011cm²). Greasy spot severity varied from 0,15% to 35,85%, with a mean of 7,3%. Based on those severity values, a six level (1%, 2%, 5%, 9%, 18% e 36% of lesioned leaf area) diagrammatic scale was developed. 50 images of symptomatic leaves were showed to evaluators, which estimated the severity with and without the use of the scale. The diagrammatic scale use, slightly increased the estimates accuracy and precision