First Report of Inonotus rickii Causing Canker Rot on Boxelder in Europe.

Abstract

In November 2001, during an examination of ornamental trees in Seville, Spain, several boxelders (Acer negundo L.) were observed with symptoms and signs of canker rot disease. Symptoms and signs occurred mainly 2 to 4 m above ground and included bulges of the stem and bark necrosis. Golden brown masses of fungal tissue up to 20 cm wide and 15 cm thick occurred over the affected areas, but were sometimes hidden behind bark scales. Cultures were obtained from decayed wood and hyphal strands. On potato dextrose agar (PDA), mycelium was initially white and cottony, later changing to cream color, ochre, and finally dark brown. In 4-week-old cultures, abundant brown chlamydospores of varying shape, but usually globose and 5 to 14 μm in diameter, were often formed in chains. Also present on PDA and diseased trees were dark brown setal hyphae, 80 to 250 μm long and 5 to 15 μm in diameter. Based on morphological characteristics, the fungus was identified as Ptychogaster cubensis Pat., the anamorph of Inonotus rickii (Pat.) Reid. I. rickii is a white rot fungus found in living trees in tropical and subtropical areas. In Europe, it has been previously reported only from Sicily, Italy, where it was found sporadically on living Parkinsonia sp. and Schinus molle L. (1,2). In Seville,I. rickii is widespread and appears to be well adapted to the area. Classified as a canker rot pathogen, this introduced fungus not only has the ability to cause decay of heartwood, resulting in structural damage to the tree, but it also can parasitize the sapwood and cambium resulting in a progressive crown dieback. To our knowledge, this is the first record of I. rickii in Spain and on boxelders in Europe.