Glomerella leaf spot (GLS) of apple is caused by three different Colletotrichum species complexes. This study evaluated the dispersal of Colletotrichum spores related to GLS temporal progress and defoliation. Spores were monitored by air and water runoff in different plant heights, and the temporal progress of GLS and defoliation were assessed. Spores of the pathogen were first cached in the lower part of the tree closer to the ground, confirming the importance of dead leaves on the ground as main source of primary inoculum. In plots with high primary inoculum, the disease increases exponentially during favorable weather conditions. The highest initial inoculum was found in the lower part of the tree, but the highest rate of the disease progress in the upper.
Glomerella leaf spot (GLS) and bitter rot (BR) on apples are often caused by Colletotrichum acutatum in Paraná State, Brazil. GLS control is difficult because of its rapid development, with an incubation period of only 2 days under favorable conditions. Therefore, producers use successive fungicide applications every season; however, failure to control GLS has been commonly reported. The objectives of this study were to determine the sensitivity of isolates of the C. acutatum species complex obtained from apple orchards in Brazil to mancozeb, thiophanate-methyl, and azoxystrobin fungicides. Isolates from the different parts of the plant (leaves, flowers, buds, and twigs) and cultivars (Gala and Eva) showed different levels of sensitivity to mancozeb, thiophanate-methyl, and azoxystrobin. For mancozeb, the frequencies of isolates were 25% highly resistant, 50% low-resistance, and 25% sensitive. For thiophanate-methyl, the frequencies of isolates were 72.2% highly resistant, 11.1% resistant, and 16.7% moderately resistant. For azoxystrobin, the frequencies of isolates were 11.1% highly resistant, 5.6% resistant, and 83.3% sensitive. Interestingly, no mutations in the β-tubulin and cytochrome b genes were observed in any of the isolates resistant to thiophanate-methyl and azoxystrobin fungicides.
The Glomerella leaf spot (GLS) and bitter rot (BR) are important apple diseases in Brazil, caused by species of Colletotrichum, which are usually related with quiescent infection. This study aimed to detect quiescent infections of Colletotrichum spp. in flowers and in unripe fruits from apple commercial orchard cultivars Eva and Gala. The pathogen was observed in various structures of the flower in both cultivars. In unripe fruits, the pathogen was recovered only from 'Eva'. Five isolates were obtained and were inoculated by mycelial (with and without wound) on ripe apple fruits and by conidia suspension (without wound) on ripe apple fruits and leaves of 'Gala'. On inoculated fruits by mycelial, the isolates induced symptoms of BR, and on inoculated fruits by conidia without wound the isolates induced symptoms of GLS. On inoculated leaves, isolates induced symptoms of GLS. The isolates were characterized by cultural, morphological and pathogenic aspects. Detection of Colletotrichum spp. in asymptomatic apple flowers is epidemiologically important, since the flowers can be a route for infection in unripe fruits. This is the first investigation of quiescent infection of this pathogen on apple flowers.
RESUMOColletotrichum gloeosporioides e C. acutatum são os agentes etiológicos da Mancha da Gala (MG), na cultura da macieira, no Brasil. Programas de melhoramento visando o desenvolvimento de resistência genética à doença necessitam do conhecimento pleno das características das espécies do patógeno envolvidas. Uma maneira de separar estas espécies é através do estudo da sensibilidade de isolados ao fungicida benomyl. Através do teste de sensibilidade de 39 isolados de C. acutatum e C. gloeosporioides relacionados à MG, em que foram avaliados a taxa de crescimento micelial e o índice de redução deste crescimento, observou-se que dentre os isolados de C. gloeosporioides há um grupo resistente ao fungicida e que difere de todos os isolados desta espécie relatados neste patossistema. Este grupo mostrou-se resistente às concentrações de 5 e 100 µg.mL -1 com índice de redução (IR) variando entre 0% e 8%, e entre 15 e 30%, respectivamente, enquanto o isolado padrão (CG197) apresentou IR de 100% em ambas as concentrações testadas. Os isolados de C. acutatum foram todos resistentes ao fungicida. Devido à resistência de alguns isolados de C. gloeosporioides, a separação de espécies de Colletotrichum associadas à macieira, baseada apenas na resistência ou suscetibilidade ao fungicida benomyl, não deve ser utilizada isoladamente. Palavras-chave: Malus spp., resistência a fungicida, crescimento in vitro. ABSTRACT In vitro assessment of sensitivity to benomyl of Colletotrichum spp. isolates associated with Gala leaf spot of appleIn Brazil, Colletotrichum gloeosporioides and C. acutatum are responsible for the occurrence of Gala leaf spot or Glomerella Leaf Spot (GLS) on apple. Breeding programs aiming to develop genetic resistance to disease need a complete understanding of the characteristics of involved species. A study of the sensibility of the isolates to benomyl is a way to separate those species. A sensitivity test of 39 isolates of C. acutatum and C. gloeosporioides involved with GLS, evaluated by growth rate and reduction rate of mycelium, revealed a group of C. gloeosporioides isolates that are resistant to the fungicide. This group showed resistance to concentrations of 5 and 100 µg.mL -1 with reduction rate varying between 0% and 8%, and between 15 and 30%, respectively. While the standard C. gloeosporioides isolate (CG197) showed a reduction rate of 100% at both tested concentrations, all isolates of C. acutatum were resistant to the fungicide. Due to the resistance of some isolates of C. gloeosporioides, the separation of Colletotrichum species on apple should not be based only on resistance or susceptibility to benomyl.
RESUMOEste trabalho objetivou avaliar fungicidas em associação ou não com fosfito de potássio na redução da mancha foliar de glomerela (MFG) e desfolha da planta e selecionar modelo de crescimento para o progresso temporal da doença em plantas não tratadas, entre novembro e abril, safras 2004/05 e 2005/06. O delineamento foi em blocos ao acaso, quatro repetições, e as pulverizações a cada 10 dias. Avaliações de incidência, severidade e desfolha, foram quinzenais em dois ramos/tratamento. Avaliaram-se: mancozebe, clorotalonil, tiofanato metílico, e fosfito de potássio (00-20-20). Procedeu-se à análise de variância e comparação de médias entre tratamentos e se ajustaram modelos para descrever a epidemia, comparados pelo critério de informação de Akaike (AIC). O tiofanato metílico mostrou-se eficiente na redução da desfolha precoce mas não diminuiu a área abaixo da curva de progresso (AACP) da incidência e da severidade. A associação de fosfito com tiofanato metílico reduziu a AACP da incidência e da severidade. Na safra 2005/06 clorothalonil foi superior ao padrão mancozebe reduzindo a AACP da incidência e severidade. Os ajustes dos modelos foram semelhantes (R 2 >85% e valores próximos de AIC); o modelo logístico foi escolhido por melhor descrever a epidemia. Palavras-chave: Colletotrichum spp, epidemiologia, progresso temporalFungicides associated or not with phosphite for controlling glomerella leaf spot on apple ABSTRACTThe aim of study was to test fungicides and their association with potassium phosphite in reduction of glomerella leaf spot (GLS) and plant defoliation and select a grown model of the temporal progress of GLS in untreated plants during November and April, 2004/05 and 2005/06 seasons. The experimental design was random blocks with four replications and the applications at intervals of 10 days. Evaluations of incidence, severity and defoliation took place every 15 days (two branches per treatment). The fungicides evaluated were: mancozeb, chlorothalonil, methyl tiophanate, and potassium phosphite (00-20-20). Analysis of variance was performed and mean comparison between treatments, and models were adjusted to describe the epidemic, compared themselves through Akaike information criteria (AIC). Methyl tiophanate showed efficient in defoliation reduction, but it did not reduce the area under progress curve (AUPC) for incidence and severity. Association of phosphite with methyl tiophanate reduced the AUPC of incidence and severity. During 2005/06 season the fungicide chlorothalonil was better than standard mancozeb, reducing the AUPC of incidence and severity. Adjustments of models are similar (R 2 >0.85 and similar values of AIC); the logistic model had the better epidemic adjustment.
Several diseases are difficult to control specially in subtropical regions and perennial hosts where the pathogen survive easily within the plant. The aim of this study was to identify which pathogens are surviving after end of one season and at the beginning of the next season to inform which pathogens represent potential risk as primary inoculum to the next season. Survival of pathogens on apple tree twigs was evaluated during dormancy and on beginning of vegetative growth in four orchards located in the two main apple production regions: Palmas and metropolitan region of Curitiba, in Paraná State, Brazil. For this purpose, 10 cm long asymptomatic twigs were collected from 10 randomly selected plants, 24 twigs per plant. Half of the twigs were left directly (without disinfection) in humid chambers for 30 days at 25ºC. The other half of the twigs were disinfected and kept in a freezer for 12 hours at -16ºC by the Over Night Freezing Incubation Technique (Onfit) and then kept in a humid chamber for 30 days at 25ºC. The fungi Colletotrichum sp., Botryosphaeria sp., Alternaria sp., and Fusarium sp. were detected in the two sampled dates and methodologies in all evaluated regions. Neonectria ditissima was only detected in both orchards from Palmas. The genera found surviving on twigs were confirmed molecularly by BLASTn and were pathogenic in wounded fruits from the cultivar ‘Gala’. Our results indicate that pathogens are surviving in orchards after winter treatment and throughout the apple season, being potential sources of inoculum for infections in flowers and fruits, where the pathogens detected cause important diseases as bitter rot, Neonectria fruit rot, white and black rots, and possibly cause Alternaria and Fusarium rots which have not been extensively studied in Brazil.
Palmas, a capital paranaense da maçã e do frio recebe este título devido as suas condições climáticas e geográficas, que fazem da região um lugar propicio para o cultivo de maçãs. Por possuir um inverno frio e um verão com chuvas regulares o município produz frutos de bons calibres, sabor e coloração. A introdução da cultura no município se deu em 1978, com o cultivo de 4 hectares. A produção de maçã de Palmas passou por grandes mudanças desde a sua implantação. Observa-se um período de incremento de área e produção até por volta do ano de 2004, devido principalmente a qualidade e a quantidade da produção, que já em seus primeiros anos alcançava números acima das médias nacionais. Entretanto, após o ano de 2006 houve uma redução de 11% da área cultivada e consequentemente da produção. Dados de 2018 registraram que o município conta com 380 ha de área plantada e produção total de 7.932 toneladas. Os fatores climáticos ao longo dos anos, de forma geral, não prejudicaram a produção, uma vez que se apresentam em ciclos regulares; desta forma uma das hipóteses é de que fatores mercadológicos e referentes a outros fatores de produção tenham sido responsáveis pela queda da área cultivada com a cultura.
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