This study compared different temperatures and dormancy-reversion procedures for preservation of Phakopsora pachyrhizi uredospores. The storage temperatures tested were room temperature, 5°C, )20°C and )80°C. Dehydrated and non-dehydrated uredospores were used, and evaluations for germination (%) and infectivity (no. of lesions⁄cm 2 ) were made with fresh harvested spores and after 15, 29, 76, 154 and 231 days of storage. The dormancy-reversion procedures evaluated were thermal shock (40°C⁄5 min) followed or not by hydration (moist chamber⁄24 h). Uredospores stored at room temperature were viable only up to a month of storage, regardless of their hydration condition. Survival of uredospores increased with storage at lower temperatures. Dehydration of uredospores prior to storage increased their viability, mainly for uredospores stored at 5°C, )20°C and )80°C. At 5°C and )20°C, dehydrated uredospores showed increases in viability of at least 47 and 127 days, respectively, compared to non-dehydrated spores. Uredospore germination and infectivity after storage for 231 days (7.7 months), could only be observed at )80°C, for both hydration conditions. At this storage temperature, dehydrated and non-dehydrated uredospores exhibited 56 and 28% of germination at the end of the experiment, respectively. Storage at )80°C also maintained uredospore infectivity, based upon levels of infection frequency, for both hydration conditions. Among the dormancyreversion treatments applied to spores stored at )80°C, those involving hydration allowed recoveries of 85 to 92% of the initial germination.
European canker, caused by Neonectria ditissima, is an important disease of apple in the temperate climate of southern Brazil. Monthly inoculations of this fungus were carried out on various wound types on cvs 'Gala' and 'Fuji' over two productive cycles to better understand the seasonal susceptibility of apple trees. Wound types were: bud scars (September), petal scars (October), fruit-thinning scars (November), leaf scars (from November to May), fruit-picking wound scars for 'Gala' (February) and 'Fuji' (March), and pruning wounds (June to August). One hundred plants of each cultivar were used and inoculation sites were monitored periodically for symptom expression. At each assessment, visible lesions were counted and pruned, and wounds were painted. Differences in wound susceptibility occurred throughout the year. Most lesions resulted from inoculations of pruning wounds. Inoculations performed in spring on bud and petal scars resulted in lower disease expression than inoculations later in the season.
RESUMOObjetivou-se detectar a influência do estádio fenológico e da idade da folha de soja na infecção por Phakopsora pachyrhizi, agente causal da ferrugem asiática (FA). Plantas das cultivares BRS 154 e BRS 258 foram inoculadas, com suspensão de 10 5 urediniósporos/mL, nos estádios fenológicos V 3 , R 1 e R 5 . Após 24 horas de câmara úmida, as plantas foram acondicionadas em condições de casa de vegetação por 20 dias. Avaliou-se o período latente médio (PLM) e a severidade. Para a avaliação da suscetibilidade de trifólios à FA utilizou-se a cultivar BRS 154 (V 5 ). A inoculação foi realizada nos quatro primeiros trifólios. Aos 15 dias após a inoculação, os folíolos foram avaliados quanto à severidade, tamanho médio de lesão e freqüência de infecção. O estádio das plantas de soja não influenciou no PLM. As cultivares BRS 154 e BRS 258 tiveram PLM de 8 e 9 dias, respectivamente. As cultivares não se diferenciaram quanto à severidade da doença. Não houve diferença de severidade nos estádios V 3 e R 1 , porém, os valores de severidade nesses estádios foram superiores ao valor de severidade no estádio R 5 , na avaliação realizada 8 dias após a inoculação. Em relação à suscetibilidade de folhas, o trifólio mais velho apresentou maiores valores de doença. Palavras-chave: Glycine max, ferrugem asiática, estádios de inoculação. ABSTRACT Influence of soybean phenological stage and leaflets age on infection by Phakopsora pachyrhiziThis work was conducted to study the influence of soybean growth stage and leaf age on the infection of Phakopsora pachyrhizi, the soybean rust pathogen. Soybean plants (cv. BRS 154 and BRS 258) at the V 3 , R 1 and R 5 growth stages were inoculated with a 1 x 10 5 urediniospores per mL suspension. After a period of 24 hours in dew chambers, all plants were removed from the chambers and placed under greenhouse conditions for 20 days. Mean latent period (PLM) and disease severity were estimated. The susceptibility of trifoliate leaves to soybean rust was estimated on cv. BRS 154 at the growth stage R 5 . Pathogen inoculation was done at the first four trifoliate leaves. Fifteen days after inoculation, leaflets of each trefoil were evaluated for disease severity, lesion mean size and infection frequency. Plants' growth stage did not influence the PLM. Cultivars BRS 154 and BRS 258 presented PLM of 8 and 9 days, respectively. There was no difference in disease severity at the growth stages V 3 and R 1 , but those values were higher than at the R 5 growth stage, 8 days after inoculation. The oldest trefoil showed the highest disease values.
European Canker and Neonectria fruit rot (NFR), caused by Neonectria ditissima, has become a major problem for the production of apples (Malus domestica) in Brazil. This study characterized environmental factors affecting in vitro growth and germination of Neonectria ditissima as well as infection, colonization and reproduction, ex vivo, on 'Gala' and 'Eva' fruit. Temperatures between 17 to 20 °C were optimum for mycelial growth, and minimal growth occurred at 35 °C. Micro/ macroconidia sporulation ratio was lower at 10 °C for most of the isolates tested, and no macroconidia were produced at 30 °C. More than 70% of conidia germinated after 12 h of exposure to constant humidity incubation and a temperature of 25 °C. Germination rate as high as 90% occurred after 48 h regardless of the temperature. Incubation of 2 h with high humidity is not sufficient for germination of 10% of conidia at any temperature between 10 to 30 °C. The cultivars Eva and Gala did not differ in relation to incubation period. A minimum of 25 days was necessary for sporulation on fruit incubated at 16.8-21.7 °C. Unwounded fruit did not present symptoms even 40 days after inoculation on intact epidermis, demonstrating the need of wounds for NFR development.
Rod. BR 285, km 115, CP 1543, CEP 95200-000, Vacaria-RS. Autor para correspondência: Silvio André Meirelles Alves (silvio@cnpuv.embrapa.br) Data de chegada: 06/10/2011. Aceito para publicação em: 01/08/2012. 1781F a b r a e a l e a f s p o t , c a u s e d b y t h e f u n g u s E n t o m o s p o r i u m mespili, is one of the major diseases affecting pear (Pyrus sp.) in Brazil. Considering the lack of standardized methods to quantify this disease on leaves, the aim of this study was to develop a diagrammatic scale to quantify the severity of Fabraea leaf spot o f p e a r. To s t a n d a r d i z e t h e a s s e s s m e n t , w e d e v e l o p e d a diagrammatic logarithmic scale with seven levels (0.3, 1.0, 2.3, 5.1, 11.1, 22.4 and 40.0% diseased leaf area). To validate the scale, nine raters estimated the severity of 60 scanned leaf images Nunes, C.C.;Alves, S.A.M. Development and validation of a diagrammatic scale to quantify the severity of Fabraea leaf spot of pear. Summa Phytopathologica, v.38, n.3, p.239-244, 2012. at different severity levels. The evaluations were done in two steps: with and without the aid of the scale. The actual severity was obtained through the program Quant. v.1.0. The accuracy and the precision of raters were determined by simple linear regression between actual and estimated severity. The proposed scale provided good levels of accuracy and precision, good repeatability of estimates, and rapid and easy assessment, constituting thus a useful tool in epidemiological studies and for the development of strategies to control Fabraea leaf spot of pear.Additional keywords: Entomosporium mespili, leaf diseases, severity, phytopathometry. ABSTRACTA entomosporiose, causada pelo fungo, Entomosporium mespili (DC.) Sacc. (forma perfeita: Fabraea maculata Atk.), é uma das principais doenças da pereira (Pyrus sp.) (9). Também conhecida como requeima, esta doença é caracterizada por apresentar pequenas lesões no limbo foliar e causar desfolha, o que afeta a capacidade fotossintética das plantas e reduz o rendimento.Os sintomas são visíveis em ambas as faces das folhas jovens como lesões pequenas, avermelhadas a púrpuras, as quais coalescem, tornando-se marrom-escuras, podendo aparecer rodeadas por um halo clorótico; as folhas severamente infectadas apresentam aspecto necrótico, amarelecem e caem. Nos frutos há formação de manchas necróticas semelhantes às folhas, porém ficam deprimidas à medida que o fruto cresce, além disso, podem aparecer rachaduras, favorecendo a entrada de outros micro-organismos. A principal fonte de inóculo primário são as folhas caídas do ano anterior (6).Essa doença ocorre na maioria das regiões produtoras do mundo (6) com maior severidade onde há verões quentes e úmidos (14). Por esse motivo, a importância da entomosporiose no Brasil é relativamente maior do que nos principais países produtores. O programa de melhoramento da pereira no Brasil busca desenvolver variedades adaptadas às condições locais e resistentes a entomosporiose (Oliveira, comunicação pessoal). A entomo...
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