ABSTRACT. 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.

ABSTRACT 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.

Colletotrichum 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.

In 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.