SEASONAL COLONISATION BEHAVIOUR OF CANDIDATUS PHYTOPLASMA MALI IN APPLE TREES IN TRENTINO
Apple proliferation (AP) disease is a serious problem in the apple growing region of Trentino (Northern Italy). The knowledge of the periods in which phytoplasma is certainly either present or absent in the canopy of the plant is extremely important especially to determine the most suitable moment for a correct diagnosis and the collection of scions for vegetative propagation. The colonisation dynamic and the distribution of Candidatus Phytoplasma mali was followed for two years in a valley bottom environment in Trentino-Alto Adige. Samples were collected at 7 different levels of two infected apple trees Golden Delicious every two weeks from May 2003 until October 2004. The phytoplasma distribution was studied by epifluorescence microscopy with DAPI staining. This method permitted a semi-quantitative evaluation of the phytoplasma concentration at the different heights of the trees. The colonisation has a seasonal trend found also in other species, such as Prunus and Pyrus. The phytoplasma is absent from the aerial part of both plants in all the examined levels in late spring, whereas it reappears progressively during summer, with a maximum peak between the middle of July and the end of December. Its distribution is less homogeneous and random in winter, decreasing with the sieve tube degeneration. The results indicate that the phytoplasma survives in the roots in winter and migrate with the phloematic fluid to the upper parts of the tree each spring and summer. The results show that, in the environmental and climatic conditions of Trentino Alto-Adige, the phytoplasma is absent from the aerial part between April and May, which is crucial for the success of the control of the disease spread by the development of resistant rootstocks.
Pedrazzoli, F., Ciccotti, A.M., Bianchedi, P.L., Salvadori, A. and Zorer, R. (2008). SEASONAL COLONISATION BEHAVIOUR OF CANDIDATUS PHYTOPLASMA MALI IN APPLE TREES IN TRENTINO . Acta Hortic. 781, 483-489
Malus domestica, Apple Proliferation, phloem, DAPI, infection index