Scielo RSS <![CDATA[Tropical Plant Pathology]]> http://www.scielo.br/rss.php?pid=1982-567620120001&lang=en vol. 37 num. 1 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<b>Letter from the Editors</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100001&lng=en&nrm=iso&tlng=en <![CDATA[<b>Research approaches, adaptation strategies, and knowledge gaps concerning the impacts of climate change on plant diseases</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100002&lng=en&nrm=iso&tlng=en This review discusses the present trends in studies on the impacts of climate change on plant diseases. Firstly, the approaches used for studying the potential effects of altered temperature, water availability, CO2 and O3 air concentrations, and UV-B radiation on components of the disease cycle are explained and discussed. Next, the impact of changes in climate patterns on the geographic and temporal distribution of diseases by integrating biological and epidemiological models into geographic and climate databases are assessed. Finally, adaptation strategies are discussed and areas where there is a recognized lack of knowledge are highlighted. The literature shows that different pathosystems respond in different ways to climate change. Thus, case-by-case studies on the responses of crop species or varieties and their diseases to climate change are necessary. In addition to that, wide-scale projections of disease risk are necessary in order to identify research priorities, whereas industry must be strategically directed and public policies developed to establish adaptation measures and to prevent potential food security crisis. Only by conducting long-term and multidisciplinary studies can we reduce the uncertainty regarding the effects of climate change on plant diseases. <![CDATA[<b>Effects of variety, cropping system and soil inoculation with <i>Aspergillus flavus </i>on aflatoxin levels during storage of maize</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100003&lng=en&nrm=iso&tlng=en The effects of soil inoculation with A. flavus, variety and cropping system on the level of aflatoxin in stored maize were investigated under crop storage conditions in Benin. The experiment was organized in a factorial scheme (two varieties x two cropping system x with or without A. flavus soil inoculation) with eight treatments carried out in a completely randomized block design with three replications. A. flavus incidence in the plots soil was assessed both before and after soil inoculation. The harvested maize was stored for four months and cobs were sampled in a monthly interval and analyzed for the determination of Fusarium spp. colonization, Penicillium spp. and A. flavus cfu levels, insect pests population size and aflatoxin content. Multi-factorial analysis of variance and linear regression analyses with dummy variables were used to compare treatments. The concentrations of aflatoxin B1 and B2 in the kernels tended to increase with time during storage. Variety and fungal inoculation were the main factors influencing the levels of aflatoxins in stored maize. The improved variety showed a higher number of A. flavus cfu and aflatoxin B1 and B2 levels as compared to the local variety.Intercropping with Vigna unguiculata decreased the aflatoxin concentration in the improved variety but not in the local variety. The local variety had higher levels of Penicillium spp. and lower levels of Fusarium spp. than the improved variety. The treatments had no effect on the populations of the most common storage insect pests, but their levels were positively correlated with aflatoxin content. Both the initial inoculum level and the variety effect on the water content of the kernels after harvest played a significant role in A. flavus infection. <![CDATA[<b>Genetic variability of papaya lethal yellowing virus isolates from Ceará and Rio Grande do Norte States, Brazil</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100004&lng=en&nrm=iso&tlng=en The papaya (Carica papaya) is a fruit crop of great economic importance throughout the Brazilian northeast, which is responsible for 60% of the national output. Papayas in the states of Ceará and Rio Grande do Norte are affected by lethal yellowing disease, caused by papaya lethal yellowing virus (PLYV). Previous work suggested that PLYV is a putative sobemovirus. To assess the genetic variability of PLYV, foliar samples were collected in October 2008 and October 2009 in commercial fields from Ceará and Rio Grande do Norte states, and total RNA was extracted. Specific primers based on the sequence of a previously characterized PLYV isolate were used for the RT-PCR-based amplification of a 900 bp fragment corresponding to the central region of the viral genome. Fragments from 21 viral isolates were cloned and sequenced. Sequence analyses indicated >97% nucleotide sequence identity among the isolates, 94-100% identity with the previously sequenced PLYV isolate, and a lower but significant identity with sobemoviruses (43-48.5%). These results suggest a low genetic variability among PLYV isolates, and are in agreement with the provisional placement of PLYV in the genus Sobemovirus. Definitive taxonomic conclusions, however, can only be drawn after the determination of the full-length genomic sequence.<hr/>O mamão (Carica papaya) é uma fruta de grande importância econômica em todo o Nordeste brasileiro, região responsável por 60% da produção nacional. Mamoeiros nos estados do Ceará e Rio Grande do Norte são afetados pela doença denominada amarelo letal do mamoeiro, causada pelo papaya lethal yellowing virus (PLYV). Trabalhos anteriores indicaram que o PLYV é um possível sobemovírus. A fim de estimar a variabilidade genética do PLYV, amostras foliares de mamoeiro foram coletadas em outubro de 2008 e de 2009 em regiões produtoras do Ceará, e Rio Grande do Norte. Oligonucleotídeos específicos baseados na sequência de um isolado de PLYV previamente caracterizado foram utilizados para a amplificação via RT-PCR de um fragmento com 900 pb, correspondente à região central do genoma viral. Fragmentos de 21 isolados virais foram clonados e sequenciados. A análise das sequências de nucleotídeos indicou >97% de identidade entre os isolados, entre 94-100% com o isolado de PLYV previamente sequenciado, e uma identidade baixa, porém significativa, com sobemovírus (43-48,5%). Estes resultados sugerem um baixo grau de variabilidade genética entre isolados de PLYV, e estão de acordo com a classificação provisória do PLYV como membro do gênero Sobemovirus. Conclusões de ordem taxonômica, no entanto, só podem ser tiradas após a determinação da sequência genômica completa. <![CDATA[<b>Spatial dispersal of <i>Metarhizium anisopliae </i>and <i>Beauveria bassiana</i> in soybean fields</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100005&lng=en&nrm=iso&tlng=en The dispersal and persistence of Beauveria bassiana and Metarhizium anisopliae following application in soybean fields as kaolin dust and sprays of soybean oil formulations were investigated. Fungal dispersion was evaluated from a centrally-treated area by sampling leaflets on eight transects at 20-m intervals in concentric rings up to 100 m from the central area. Density of colony-forming units (CFU) per unit leaf area was determined by washing the soybean leaflets in water containing Tween 80, and plating the aqueous suspensions on an oatmeal-dodine semi-selective agar medium. Spatial dispersal of B. bassiana in soybean field was significantly higher when conidia were applied as an oil formulation compared with a kaolin dust formulation. No significant differences were observed in M. anisopliae CFU number between sprayed or dusted plots. Oil-based formulations favor the dispersal of B. bassiana in soybean crops, but not the dispersal of M. anisopliae. Kaolin-based formulations are not suitable for B. bassiana or M. anisopliae dispersal.<hr/>A dispersão e a persistência de Beauveria bassiana e Metarhizium anisopliae mediante aplicações por polvilhamento e pulverização em óleo de soja em campos de soja foram estudados. A dispersão fúngica foi avaliada a partir de uma área central mediante a amostragem de folíolos sobre oito transectos dispostos em anéis concêntricos em intervalos de 20 m até 100 m da área central. A densidade de unidades formadoras de colônias (UFC) por unidade de área foliar foi determinada mediante lavado dos folíolos de soja em água contendo Tween 80 e plaqueamento das suspensões em água em meio seletivo dodine-aveia-agar. A dispersão espacial de B. bassiana no campo de soja foi significativamente maior quando os conídios foram aplicados com óleo em comparação com a aplicação por polvilhamento. Não foram observadas diferenças significativas no número de UFC de M. anisopliae entre as parcelas pulverizadas ou polvilhadas. As aplicações em óleo favoreceram a dispersão de B. bassiana na cultura da soja, mas não a de M. anisopliae. As misturas em caulim não são apropriadas para a dispersão de B. bassiana ou de M. anisopliae. <![CDATA[<b>Epidemiological components of coffee rust affected by foliar application of potassium silicate</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100006&lng=en&nrm=iso&tlng=en A ferrugem, causada por Hemileia vastatrix, é a doença mais importante do cafeeiro. Existe uma necessidade urgente de se obter métodos alternativos de controle dessa doença que sejam menos nocivos ao meio ambiente. Este estudo avaliou o efeito da aplicação foliar de soluções de silicato de potássio (SP) nas doses de 0, 8, 20, 40 e 60 g/L, em pH 5,5 e 10,5, na intensidade da esporulação (IE) de H. vastatrix, número total de pústulas (NTP) por folha e severidade da ferrugem. Avaliou-se também o efeito dessas doses de SP, do fungicida oxicloreto de cobre (7,5 g/L) e da água destilada estéril em pHs 5,5, 7,5 e 10,5 na inibição da germinação de uredósporos de H. vastatrix. A concentração foliar de silício (Si) e de potássio (K) também foi determinada. A IE, o NTP e a severidade responderam de forma quadrática e negativa às doses crescentes de SP em pH 5,5 ou 10,5. Para as doses crescentes de SP em pH 5,5 ou 10,5, a resposta da IE, do NTP e da severidade foi linear e negativa. A concentração foliar de Si respondeu de forma linear e positiva às doses crescentes de SP com pH 5,5. Não houve efeito significativo das doses crescentes de SP em pH 10,5 na concentração foliar de Si e nem das doses crescentes de SP, nos dois valores de pH, na concentração foliar de K. A inibição da germinação dos uredósporos de H. vastatrix respondeu de forma linear e positiva às doses crescentes de SP nos três valores de pH. O fungicida oxicloreto de cobre reduziu significativamente a germinação dos uredósporos em comparação com as aplicações de SP. Os resultados desse trabalho apontam para a possibilidade da pulverização de solução de SP, em pH mais alcalino, visando reduzir a intensidade da ferrugem do cafeeiro.<hr/>Leaf rust, caused by Hemileia vastatrix, is the most important coffee disease. Alternative methods of management of this disease that are less damaging to the environment than fungicide applications are urgently needed. This study aimed at evaluating the effect of foliar applications of potassium silicate (PS) solutions at concentrations of 0, 8, 20, 40, and 60 g/L, at pHs 5.5 and 10.5, on sporulation intensity of H. vastatrix (SI), total number of pustules (TNP) per leaf, and on coffee leaf rust severity. The effect of the applications of PS at the selected rates, of copper oxychloride (7.5 g/L), and of sterile distilled water at pH 5.5, 7.5, and 10.5 on the inhibition of H. vastatrix uredospores germination was also tested and the foliar concentration of silicon (Si) and potassium (K) was determined. A quadratic regression model best described the effect of PS applications, at pH 5.5 or 10.5, on SI, TNP, and severity. The relationship between SI, TNP, or severity and PS applications, at pH 5.5 or 10.5, was linear and negative. Si concentration in leaves increased as the concentration of PS solutions utilized (at pH 5.5) increased from 0 to 60 g/L. There was no effect of PS applications, at pH 10.5, on Si concentration in leaves. K concentration did not change as the PS rates increased from 0 to 60 g/L, both at pHs 5.5 and 10.5. A linear regression model adequately described the relationship of inhibition of uredospores germination versus PS concentrations at the three pHs values. Copper oxychloride significantly reduced uredospore germination as compared with the PS applications. The results from this study highlight the possibility of using PS spray, in a more alkaline pH, as a treatment for reducing coffee leaf rust intensity. <![CDATA[<b>Detection method for <i>Leifsonia xyli </i>subsp<i>. xyli </i>and effect of thermotherapy on bud germination in sugarcane varieties</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100007&lng=en&nrm=iso&tlng=en O raquitismo-da-soqueira [Leifsonia xyli subsp xyli (Lxx)] é uma das principais doenças da cana-de-açúcar. Sua identificação no campo é difícil e sua disseminação para plantas sadias e novas áreas é feita exclusivamente por toletes contaminados ou mecanicamente. A termoterapia (regime de 52ºC/30min) é o controle adotado no Brasil para fornecer mudas sadias para novas áreas. O outro regime recomendado (50ºC/2h) não tem sido muito usado no Brasil. Os objetivos do presente trabalho foram estudar a eficiência de diferentes métodos de detecção de Lxx em canas-de-açúcar de períodos de maturação diferentes com 4-9 meses de idade e o efeito da termoterapia (50ºC/2h) sobre a brotação das gemas, inclusive em função de sua localização no colmo. A microscopia foi o melhor método de detecção, pois detectou Lxx em cana-planta de quatro meses, enquanto que o método sorológico - "dot blot" e o de PCR não permitiram identificar Lxx em colmos de cana-planta infectados com até nove meses. Modificação do procedimento envolvendo uma concentração do caldo permitiu que se detectasse Lxx eficientemente com "dot blot". Observou-se falha na erradicação de Lxx em material tratado com termoterapia (regime 50ºC/2h). Essa condição prejudicou a brotação de gemas na variedade RB935744, mas não nas variedades RB855156 e RB867515. Observou-se que a termoterapia aumentou a brotação das gemas do terço basal da RB867515 e diminuiu a das gemas dos terços médio e apical da RB935744.<hr/>Ratoon stunting disease [Leifsonia xyli subsp xyli (Lxx)] is one of the main diseases of sugarcane and it is of difficult detection in the field. Its spread to uninfected plants and into new areas occurs exclusively through contaminated planting material or mechanically. Thermotherapy at a 52ºC/30 min regime is broadly employed in Brazil for producing healthy seed cane. Another recommended regime (50ºC/2h) has not been commonly used in Brazil. The purposes of this research were to examine the efficacy of different methods of detection of Lxx in 4-9 months-old plants in cane varieties having different periods of maturity and the effect of thermotherapy (50ºC/2h) on bud germination including a consideration on the location of individual buds in the stalks. Microscopy was the best method allowing the detection of Lxx in plants of all ages whereas identification of Lxx in infected plants through dot blot and PCR methods, performed according to published protocols, failed for all treatments. A modification of the dot blot test involving the use of concentrated cane sap was successful in improving the method, allowing the identification of Lxx in infected nine-month old plants. Thermotherapy at a regime of 50ºC/2h did not completely eradicate Lxx from infected planting material. This regime was harmful for the germination of buds in var. RB935744 but not for vars RB855156 and RB867515. It increased the percentage of germination of basal buds of RB867515 and decreased that of apical and mid length buds of RB935744. <![CDATA[<b>Neonicotinoid insecticide induces resistance to citrus canker in sweet orange</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100008&lng=en&nrm=iso&tlng=en A atividade antimicrobiana de acetamipride, imidaclopride (IMI) e tiametoxam foram testadas in vitro em isolados de Xanthomonas citri subsp. citri (Xcc). Plantas de laranja 'Valência' foram tratadas com IMI por rega e infiltradas com suspensão de Xcc em casa-de-vegetação. Os neonicotinóides não apresentaram efeito antimicrobiano in vitro para Xcc. Plantas de laranja 'Valência' tratadas com IMI apresentaram lesões menores e em menor número, e alteração nos teores de macro e micronutrientes em relação às plantas controle. Foram observadas reduções entre 10% e 70% na incidência de cancro cítrico em plantas tratadas com IMI. A incidência da doença em folhas foi significativamente menor em plantas tratadas previamente com 1,5 g e 3,0 g de IMI (p.a.), enquanto redução significativa de até 4,7 unidades logarítmicas na população bacteriana foi observada em plantas tratadas com 3,0 g de IMI (p.a.). Plantas tratadas no mesmo dia da inoculação também apresentaram redução significativa no número de lesões de cancro cítrico e na população bacteriana.<hr/>The antimicrobial activity of acetamiprid, imidacloprid (IMI), and thiamethoxam was tested in vitro against Xanthomonas citri subsp. citri (Xcc) isolates. Plants of 'Valencia' sweet orange were treated by drenching with IMI and infiltrated with Xcc suspension in the greenhouse. The neonicotinoids showed no in vitro antimicrobial effect against Xcc. Plants of 'Valencia' sweet orange treated with IMI showed fewer and smaller lesions of citrus canker, as well as changes in the levels of macro and micronutrients when compared with control plants. Reductions in the incidence of citrus canker between 10% and 70% were observed in plants treated with IMI. Disease incidence was significantly lower in plants treated with 1.5 g and 3.0 g of IMI (a.i.), while a significant reduction of up to 4.7 log units in the bacterial population was observed in plants treated with 3.0 g IMI (a.i.). Plants treated with IMI at the same time of inoculation also showed significant reduction in the bacterial population and in the number of citrus canker lesions. <![CDATA[<b>'<i>Candidatus </i>Phytoplasma cynodontis' associated with white leaf disease of golden beard grass (<i>Chrysopogon acicalatus</i>)</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100009&lng=en&nrm=iso&tlng=en A phytoplasma was detected in golden beard grass (Chrysopogon acicalatus) displaying white leaf symptoms near vegetative fields at the Tatkone region in Myanmar, 2011. Based on restriction fragment length polymorphism analysis of PCR-amplified 16S rRNA genes, including the 16S-23S spacer region and part of the 23S rRNA gene, the phytoplasma was identified as a member of the Bermuda grass white leaf phytoplasma (BGWL) group. The golden beard grass white leaf phytoplasma (GBGWL) 16S rRNA gene sequence exhibited over 98.7% similarity with all members of BGWL group phytoplasmas and 99.5% similarity with Thailand Bermuda grass white leaf phytoplasma (AF248961). In addition, the GBGWL phytoplasma was confirmed to be a member of 'Candidatus Phytoplasma cynodontis' by phylogenetic analyses. <![CDATA[<b><i>Malva sylvestris</i></b><b>, new host of <i>Puccinia heterospora</i> in Brazil</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100010&lng=en&nrm=iso&tlng=en Observou-se a ocorrência de ferrugem em Malva sylvestris, causada por Puccinia heterospora, no Município de Garanhuns (PE). Esta espécie fúngica é microcíclica e apresenta apenas o estádio sexual, com a produção de teliósporos, com morfologia variada, podendo produzir, em menor número, teliósporos bicelulares do tipo Puccinia e, predominantemente teliósporos unicelulares do tipo Uromyces (mesosporos). A produção abundante de mesosporos é uma das características morfológicas mais marcantes da espécie. Essa ferrugem possui ampla distribuição geográfica, infectando plantas pertencentes à família Malvaceae. Este representa o primeiro registro dessa ferrugem sobre o gênero Malva no Brasil. Uma amostra de referência foi depositada no Herbário Dimitri Sucre Benjamin do Instituto de Pesquisas Jardim Botânico do Rio de Janeiro (JBRJ-RB). São apresentadas a descrição da morfologia do fungo com base na amostra coletada, ilustrações e comentários sobre a distinção entre essa espécie e outras morfologicamente semelhantes.<hr/>A rust was observed attacking Malva sylvestris plants in Garanhuns, state of Pernambuco, Brazil. The fungus involved was identified as Puccinia heterospora. This is a microcyclic species and has only the sexual stage: teliospores. Such teliospores are of two kinds in this species: bicellular typical of Puccinia and unicellular Uromyces-like (mesospores), which are abundantly produced in that species. This rust species has a broad geographical distribution and infects plants belonging to the family Malvaceae. This is the first report of P. heterospora attacking a species belonging to the genus Malva in Brazil. A representative specimen was deposited in the Herbarium Dimitri Sucre Benjamin of the Instituto de Pesquisas Jardim Botânico do Rio de Janeiro (JBRJ-RB). Herein are presented the description of the fungal morphology, illustrations and comments about the distinction of this species from morphologically similar rust species. <![CDATA[<b>Relationship between chlorophyll content in leaves and panicle blast in upland rice</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1982-56762012000100011&lng=en&nrm=iso&tlng=en A brusone (Magnaporthe oryzae) é um dos principais fatores limitantes da produtividade do arroz de terras altas no Brasil. A época de plantio e o nível de adubação nitrogenada determinam o grau de severidade da brusone nas panículas. Foi realizado um experimento de campo com a cultivar BRS Bonança, visando determinar a relação entre o conteúdo de clorofila nas folhas superiores e a severidade de brusone nas panículas. O delineamento experimental foi blocos ao acaso em esquema de parcelas subdivididas com três repetições. Os tratamentos consistiram de 12 épocas de plantios em intervalos semanais e cinco níveis de nitrogênio (0, 30, 60, 120 e 240 kg ha-1 de N). As leituras do teor de clorofila foram feitas na folha bandeira com um clorofilômetro. A brusone nas panículas aumentou significativamente com o aumento dos níveis de N. Houve correlação significativa e positiva entre os níveis de N e o conteúdo de clorofila na folha bandeira (r=0,98; p < 0,01). A relação entre a severidade de brusone nas panículas e o teor de clorofila foi linear e positiva (r= 0,99; p < 0,01). Estes resultados mostram que o teor de clorofila pode ser incluído como variável independente no desenvolvimento de modelo matemático para a previsão de brusone nas panículas.<hr/>Rice blast (Magnaporthe oryzae) is the most important yield limiting factor of upland rice in Brazil. The nitrogen application rate and planting date determine the level of panicle blast severity. A field experiment was conducted with the cultivar BRS Bonança to establish the relationship between chlorophyll content in leaves and panicle blast severity. The layout was a randomized split plot design with three replications. The treatments included 12 planting dates at weekly intervals and five rates of nitrogen (0, 30, 60, 120 and 240 kg ha-1 of N). The chlorophyll content was measured on flag leaf with a chlorophyll meter. Panicle blast severity increased significantly with the increase in nitrogen fertilization. The correlation between nitrogen rate and chlorophyll content in flag leaf was positive and significant (r=0.98; p < 0.01). The relationship between panicle blast severity and chlorophyll content was linear and positive (r= 0.99; p < 0.01). The chlorophyll content in the flag leaf can be included as independent variable in the development of a mathematical model for panicle blast forecasting.