Preliminary studies on discula pascoe, a fungus associated with rotted chestnut fruits, new for Italy

Since 2005s, an uncommon and severe mummification of sweet chestnut fruits was noted in southern Piedmont. In 2007-2008 a survey was carried out on flowers and fruits at different developing stages collected in chestnut stands suited in 4 resorts on the south of Cuneo. Small pieces of fruit stem, burrs, stigmas, styles and developing seeds were plated on malt agar, pH 4.75, and incubated at 25°C. A fungus was isolated with a variable frequency from stigmas and styles, constantly from the bark of flower/fruit stems, but not from the xylem and the inner layer of the hylum. From the fruits it was isolated sporadically just after the setting and with frequency increasing until 25-80% in 2007 and 4-84% in 2008, in complete ripened fruits. In the immature nuts the disease was asymptomatic, whereas in the ripening ones it caused small chalky areas in the endosperm out layers, developing inwards the kernel, and progressively turning brown, conducing to the complete mummification of the endosperm. On the pellicle and the shell the pathogen produced 122x85 – 251x171 m, globose, black, pycnidium-like acervuli, that split open along the top releasing a slimy, globular mass of conidia. Conidia were pale brown, one-celled, ovoid-oblong, biguttulate, 6.1-7.32 x 2.44-2.68 m. This fungus resulted constantly associated with the symptoms and reproduced the disease in artificially inoculated healthy nuts. On the bases of such characters, the pathogen has been identified as Discula pascoe (teleomorph Gnomonia pascoe), a pathogen recently reported in the rainy areas of Australia and New Zealand