"European apple canker" caused by the fungus Nectria gallígena Bres. is the most serious disease of this tree in Chile, specially in the south of the country. The prevalence of the disease south of the Bío-Bío river is accounted for the climatic conditions in this zone favouring the fungus and the difficulty in its eradication once established in an orchard.
Unfortunately, all the varieties of apples now cultivated in the country are susceptible to this disease. After a survey of the most important orchards the author has been able to prepare a ranking of cultivated apple varieties in relation to their susceptibility to the disease.
Studying the morphology of the fungus two different conidial types or races, Osorno and San Clemente, are described.
The pathogenicity test, which shows the greater power of infection of the Osorno race, is given.
During the study of the etiology of the fungus, the author has determined that peritecia are formed preferentaly, in the months of May to August in the south of Chile. Cold weather is not a limiting factor in the reproduction of the fungus, as the author foundapple trees with cankers covered by peritecia in Winter. These trees are placedin precordilleran localities where temperatures of 2° and 3°C. over 0° are common in Winter.
The pH (acidity) of the soil of a lot of orchards was determined and the results of these tests lend to conclusion that the higher acidity helps the development of the "European canker."
In the course of this investigation a new host for this fungus in Chile has heen found: the serbal (Sorbus Aucuparia L.).
Favorable conditions that the fungus finds in the south of Chile are also studied in detail.
Suggested control measures are based on tests made by the author and on foreign information. These are based on removal of diseased tissue, use of fungicides, use of wild roots, cultural practices and use of resistant varieties.

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1 Ingeniero Agronómo Fitopatólogo del Departamento de Investigaciones Agrícolas, Ministerio de Agricultura

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