Evidence for loss of ontogenetic resistance of apple leaves against Venturia inaequalis

• Published in: European journal of plant pathology 1996-10, Vol.102 (8), p.773-778
• Main Author: Kollar, A. (Federal Biological Research Centre for Agriculture and Forestry, Dossenheim (Germany). Inst. for Plant Protection in Fruit Crops)
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; BIOLOGICAL DEVELOPMENT; DESARROLLO BIOLOGICO; DEVELOPPEMENT BIOLOGIQUE; DISEASE RESISTANCE; FEUILLE; Fundamental and applied biological sciences. Psychology; Genetics and breeding of economic plants; HOJAS; LEAVES; MALUS; Pest resistance; Plant pathogens; RESISTANCE AUX MALADIES; RESISTENCIA A LA ENFERMEDAD; Varietal selection. Specialized plant breeding, plant breeding aims; VENTURIA INAEQUALIS
• ISSN: 0929-1873; 1573-8469
• DOI: 10.1007/BF01877152

The susceptibility of apple leaves to Venturia inaequalis was investigated by assessing disease on individual leaves of seedlings and labelled shoots of orchard trees. Four sets (A-D) of potted seedlings of cv. `Golden Delicious', which had been grown in a glasshouse, each with approximately 30 mature leaves, were exposed to a high-inoculum orchard. Sets A and B were exposed after each other for 47 and 42 days, respectively. As a result of the six and three infection periods during exposure, 94% and 81%, respectively of the seedling shoot tips in set A and set B became infected. However, due to ontogenetic resistance, disease incidence was low in both sets on leaves which were fully expanded at the beginning of exposure. Set C was exposed during both periods (89 days) in which sets A and B were exposed. Not only were all the seedling shoot tips in set C infected, but also - due to the loss of ontogenetic resistance - nearly all of the mature leaves. Ontogenetic resistance was also lost in set D, which was exposed for 57 days at the end of the growing season. The symptoms on fully expanded leaves on plants in sets C and D were typical and similar to those on young leaves. A time course symptom assessment was performed on leaves which had developed early in the season on labelled, field-grown shoots of cv. `Golden Delicious' trees. A steady increase of disease incidence was detected, which could not only have resulted from infections followed by extended incubation periods. In addition to the increase of typical lesions on both leaf surfaces, there was also an abundance of diffuse mycelial development on the lower surfaces of the leaves of the field-grown trees.