DiVaPRA, Plant Pathology, University of Torino, via da Vinci 44, I-10095 Grugliasco (TO), Italy
Tubakia dryina (Sacc.) Sutt. (teleomorph Dicarpella dryina Belisario & Barr) is a widespread leaf pathogen in northern temperate zones and is mainly associated with Quercus spp. During 2000, T. dryina was isolated from seasonal samplings of endophytic fungal communities of Turkey (Q. cerris L.) and English (Q. robur L.) oaks. Samples were taken from healthy and declining trees showing no symptoms of T. dryina in a coppice with saplings in Piedmont (northwestern Italy). Fragments of freshly opened buds (1-year-old shoots) and leaves were surface-sterilized by immersion in 75% ethanol for 1 min, in a NaClO solution (3 to 4% active ingredient) for 3 min, and in 75% ethanol for 30 s, then plated on potato dextrose agar. T. dryina was found in all sampled tissues. Its frequency in buds was higher in healthy trees than in declining trees (≈25 versus 12%; analysis of variance test P < 0.05), whereas no difference was found in shoots. T. dryina was also isolated from asymptomatic leaves, but more often from declining trees than from healthy ones (≈40 versus 10%; P < 0.05). No differences were observed when comparing the two oak species. The fungus was previously reported in buds of Q. nigra L. in North America (2), and it has also been isolated from symptomatic leaves of Q. cerris in a 5-year-old plantation (1). T. dryina was found in other studies in leaves and dead twigs of Q. robur. To our knowledge, this is the first report of T. dryina in buds and shoots of European oak species, suggesting an important role of this fungus as either an endophyte or a latent pathogen associated with oak decline.
References: (1) A. Belisario. Plant Dis. 77:647, 1993. (2) Y. C. Zhang and J. T. Walker. Plant Dis. 79:568, 1995.