Endophytic occurrence of a pathogenic strain of Fusarium reticulatum in English Oak in Italy.

In autumn 2002, the uppermost leaf and bud, the stem, collar, main root and a randomly chosen lateral root wereexcised from 20 symptomless 3-year-old Quercus robur L. seedlings growing in a severely declining Italian oak forestat Cessalto (northern Italy). All samples were surface-sterilized with 0.5 % sodium hypochlorite, thoroughly rinsed with sterile water and tissue fragments from each of them were plated on potato dextrose agar (PDA) according to Montecchio (2005). Fusarium reticulatum Mont (Nelson et al., 1983) was isolated with other fungi from all parts of 6 of the 20 assayed plants. Ten symptomless 3-year-old container-grown English oaks seedlings were inoculated with arandomly chosen isolate of F. reticulatum (now deposited as 115133, CBS, Utrecht, The Netherlands) by gentlyscraping with a sterile scalpel the surface-sterilized epidermis surrounding the collar. After covering the rest of theplant with a plastic sheet, the wound was sprayed with a conidial suspension containing 103 macroconidia/cm3 in sterile water, and sealed with Parafilm. Ten control seedlings were wounded as above and sprayed with sterile water. All seedlings were placed in a greenhouse at 20±2°C, 80% relative humidity, and 12 h photoperiod. After 150 days, all inoculated plants showed wilted and desiccated leaves, and brownish longitudinal stripes on the outer bark, originating from the inoculation site. Stem sections 2 cm above the inoculation point showed dark brown necroses on about 70% of the area. Abundant mycelium was present in vessels and parenchyma tissue from which F. reticulatum was reisolated. Control plants remained symptomless, the wound healed, and isolations were unsuccessful. To our knowledge, this is the first report of F. reticulatum in the genus Quercus. Investigations on the involvement of environmental stresses in the pathogenic behaviour of this fungus and on its possible role in the expression of the oak decline syndrome, which includes seedling dieback, are in progress.