Scielo RSS <![CDATA[Tropical Plant Pathology]]> vol. 39 num. 6 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>New records of plant parasitic Asterinaceae (Dothideomycetes, Ascomycota) with intercalary appressoria from Central America and Panama</b>]]> New records of species of Asterinaceae with intercalary appressoria infecting plants in Central America and Panama are described and illustrated in detail. New records are Asterolibertia licaniicola on the new host Licania arborea (Chrysobalanaceae), Asterolibertia nodulosa on the new hosts Oxandra venezuelana and Xylopia sp. (Annonaceae), and Cirsosia splendida on the new hosts Chrysobalanus icaco and Hirtella triandra (Chrysobalanaceae). The teleomorph C. splendida is linked for the first time to the asexual morph Homalopeltis chrysobalani based on morphological observation. For the presented fungi an identification key is provided and infection strategies are discussed. Nomenclatural novelties are introduced, Leprieuria radiata becomes a synonym of H. chrysobalani and Asterina nodulifera is recombined into Asterolibertia nodulifera. <![CDATA[<b>Favorable conditions for <i>Xanthomonas</i> axonopodis infection in <i>Eucalyptus</i> spp.</b>]]> Currently, Xanthomonas axonopodis is one of the main foliar pathogens for Eucalyptus spp. in Brazil. It induces leaf blight and defoliation of seedlings in the nursery and young plants in the field. However, little is known about thefavorable conditions for infection. The establishment and development of bacterial leaf blight caused by X. axonopodis in eucalyptus was studied for different leaf ages, temperatures and leaf wetness durations. Disease severity increased with leaf age, and the highest severity was observed on the fourth pair of completely expanded leaves (from the apex to the base). A higher level of bacterial colonization was also observed on the fourth pair of leaves quantified as bacterial cells/cm2 of leaf area. Twelve hours of free water on the leaf surface, prior to inoculation, was essential to promote a severe infection. However, with the increase in the leaf wetness duration, a decrease in disease severity was observed. The optimal temperature for disease development was 26-30ºC. <![CDATA[<b>High-density chitosan reduces the severity of bacterial spot and activates the defense mechanisms of tomato plants</b>]]> Bacterial spot, caused by Xanthomonas gardneri, is a disease of great importance for tomato crops, especially due to yield reduction. The objective of this study was to evaluate the effectiveness of low - and high-density chitosan for the control of bacterial spot and whether such control was due to activation of defense mechanisms in tomato. Tomato plants were treated with high-density (HD; 0.8 g/cm³) or low-density chitosan (LD; 0.4 g/cm³) at concentrations ranging from 0.0 to 3.0 mg/mL, and then inoculated with a bacterial suspension three days later. The effect of varying intervals (7, 5, 3 and 1 day) between the application of HD chitosan (3 mg/mL) and the inoculation of the pathogen was also assessed. The effect of chitosan on the in vitro growth of X. gardneri and the activities of peroxidases and polyphenol oxidases in leaves were also determined. HD chitosan (3.0 mg/mL) was able to greatly reduce disease severity by up to 85% compared to the control. The application of HD-chitosan at five days before inoculation showed larger reduction in disease severity and high level of peroxidase activity. The in vitro growth of X. gardneri was not affected by the treatment with chitosan, thus suggesting that the disease was controlled due to mechanisms related to induced resistance. <![CDATA[<b>Agronomic performance of Pera and related sweet orange accessions naturally infected with Citrus tristeza virus in northern Paraná State, Brazil</b>]]> Despite of the susceptibility to the Citrus tristeza virus (CTV), Pera sweet orange is the most important citrus cultivar in Brazil. The objective of this study was to evaluate the CTV aggressiveness and the relationship with the agronomic performance of 24 accessions of Pera and related sweet oranges. Accessions belonging to the Citrus Germplasm Collection of the Instituto Agronômico do Paraná (IAPAR), Londrina, PR, were included in the study. Citrus tristeza disease was rated based on the severity of stem pitting symptoms. Yields were evaluated in the 2010/2011, 2011/2012, and 2012/2013 seasons, and tree growth in 2012. The best performance regarding stem pitting severity was shown by Redonda accession, followed by Ipiguá II. Vegetative tree vigor was more evident for Redonda, Tardia CO3, and Guilherme Spagnol accessions. These Pera and related sweet oranges accessions also showed the highest fruit yields, along with Vimusa, Santa Tereza, Ipiguá, Ipiguá II, D-6, and Paulo Rosa. Vegetative tree vigor, yield and number of fruits were inversely correlated with citrus tristeza disease stem pitting severity. Therefore, the poor agronomic performance of some Pera and related sweet oranges is probably related to the presence of severe CTV complexes infecting these accessions. <![CDATA[<b>High incidence of <i>Tomato chlorosis virus</i> alone and in mixed infection with begomoviruses in two tomato fields in the Federal District and Goiás state, Brazil</b>]]> Tomato chlorosis virus (ToCV), a species in the Crinivirus genus, was first reported in tomatoes in Brazil (state of São Paulo) in 2008. This was followed by reports in several other Brazilian states. Tomato plants with chlorotic spots and leaf roll symptoms are frequently observed in tomato fields with high whitefly populations in Central Brazil. These plants could be infected with a begomovirus, a crinivirus, or with both viruses. A survey of two selected tomato fields in the Federal District and Goiás State was conducted in 2012 and 2013 specifically to determine the occurrence of begomoviruses and criniviruses. A total of 150 samples were collected and subjected to RT-PCR for ToCV detection and PCR for begomovirus detection. About 48% of the tested plants were infected with both viruses, 32% were infected with ToCV alone and 20% were only infected with the begomovirus ToSRV. The increasing incidence of ToCV associated with high whitefly populations in the field highlights the need for studying this virus disease to clarify its impact on tomato crops and minimize its potential damage. <![CDATA[<b>Pathogenicity and aggressiveness of Macrophomina phaseolina isolates to castor (Ricinus communis)</b>]]> Charcoal rot, caused by Macrophomina phaseolina, is one of the most important diseases of castor (Ricinus communis) in the growing regions of Northeastern Brazil, particularly in the State of Bahia, which concentrates 65% of the country's production. The pathogenicity and aggressiveness of the charcoal rot pathogen was assessed in twenty-seven isolates of M. phaseolina obtained from six plant species: Ricinus communis (n=21), Gossypium hirsutum (n=2), Sesamum indicum (n=1), Helianthus annuus (n=1), Jatropha gossypifolia (n=1) and Arachis hypogaea (n=1). All isolates were pathogenic and exhibited a range of aggressiveness towards BRS Energia cultivar regardless of their host of origin. <![CDATA[<b>Silicon potentiates the activities of defense enzymes in the leaf sheaths of rice plants infected by <i>Rhizoctonia solani</i></b>]]> This study aimed to assess the ability of silicon (Si) to potentiate defense enzyme activities in rice leaf sheaths and thus reduce sheath blight, caused by Rhizoctonia solani, development. Rice plants of BR-Irga 409 and Labelle cultivars were grown in a hydroponic solution containing 0 (-Si) or 2 mM (+Si) Si and inoculated with R. solani. Silicon concentration in the leaf sheaths was significantly higher in the +Si plants than the -Si plants by 727% for BR-Irga 409 and 714% for Labelle. The area under relative lesion expansion progress curve was significantly lower for +Si plants than -Si plants, by 34.2% for BR-Irga 409 and 30.59% for Labelle. Increases in the activities of phenylalanine ammonia-lyases, peroxidases, polyphenoloxidases and chitinases in the leaf sheaths of plants supplied with Si, especially of those from BR-Irga 409, led to reduced progress of sheath blight lesions. <![CDATA[<b>New occurrences of Botryosphaeriaceae causing black root rot of cassava in Brazil</b>]]> Despite the occurrence of several diseases of cassava, the cassava black root rot (CBR) represents one of the main limiting factor for crop rentability in the world. However, the etiology of CBR is complex and it needs to be revised based on current molecular analysis. On this work, molecular and morphological studies allowed for the identification of three species of Botryosphaeriaceae causing black root rot disease of cassava in the states of Maranhão and Paraíba, Brazil, namely: Lasiodiplodia euphorbicola, Lasiodiplodia pseudotheobromae and Neoscytalidium hyalinum. This is the first report of these three fungal species as causal agents of CBR in the world. <![CDATA[<b>Sclerotia morphology traits and mycelial growth rate are not informative variables for population studies of <i>Sclerotinia sclerotiorum</i></b>]]> The usefulness of sclerotia morphology traits and mycelial growth rate to infer phenotypic variability in populations of Sclerotinia sclerotiorum associated with common beans in Minas Gerais State (MG) was assessed in two experiments. Isolates (131) were collected in the Northwestern, Alto Paranaíba, Zona da Mata and Southern regions of MG and the mycelial growth rate, the number, weight and dimensions (length, width and thickness) of sclerotia and mycelial pigmentation were assessed. There was a high variability among isolates, even among colonies of the same isolate. The variance of the first experiment for the mycelial growth rate, number, weight, length, width and thickness of sclerotia, were 0.01, 190.15, 0.01, 0.62, 0.12 and 0.05, whereas in the second, the variances were 0.01, 28.48, 0.002, 0.18, 0.06 and 0.03, respectively. Most correlations between traits were of low magnitude except that between length and width (r = 0.84, 'P < 0.001). Regarding colony pigmentation, non-pigmented, pigmented and highly pigmented isolates were identified, but for most isolates this characteristic varied between experiments. No groups based on phenotypic traits were detected. The morphological traits evaluated in the present study are not suitable for characterization of populations of S. sclerotiorum. <![CDATA[<b>Incidence of postharvest diseases on 'Kumagai' and 'Pedro Sato' guavas at wholesale markets in Brazil</b>]]> The time after harvest is characterized by physiological changes in the fruit that favor the occurrence of postharvest diseases, which are often observed only after sale. As a result, the damage resulting from the action of quiescent pathogens can be underestimated. From November to April of the years 2009/2010 and 2010/2011, a survey was conducted to quantify the postharvest diseases in 'Kumagai' and 'Pedro Sato' guavas at two large wholesale markets in Brazil. The incidence of postharvest diseases differed significantly between the two cultivars evaluated. The most frequent postharvest diseases for 'Kumagai' guavas were anthracnose, black spot and fusicoccum rot, ranging in incidence from 23.6 and 31.6%. For 'Pedro Sato' guavas, the most frequent postharvest disease was anthracnose, with an incidence of approximately 72.3%. <![CDATA[<b>Identification and sequence analysis of five allexiviruses species infecting garlic crops in Brazil</b>]]> Garlic plants are naturally infected by a mixture of viruses, including allexiviruses. Symptomatic garlic plants with mosaic and distorted leaves from garlic producing regions in Brazil were analyzed for the presence of Garlic virus A (GarV-A), Garlic virus B (GarV-B), Garlic virus C (GarV-C), Garlic virus D (GarV-D) and Garlic mite-borne filamentous virus (GarMbFV), five allexivirus species previously reported in the country. Fifty-nine virus isolates from five distinct allexivirus species were identified and the complete coat protein region of each genome was sequenced. Mixed infections were very frequent and corresponded to 43% of the positive samples. The nucleotide identity of the coat protein ranged between 75% and 98% for GarV-A isolates, 83% and 90% for GarV-B, 69% and 98% for GarV-C, 87% and 97% for GarV-D, and 72% and 91% for GarMbFV. <link></link> <description/> </item> </channel> </rss> <!--transformed by PHP 11:01:40 23-01-2018-->