Beginning in the summer of 1996, a disease of high-bush blueberry (Vaccinium corymbosum L.) appeared on cvs. Sparta and Berkeley in commercial plantings near Cuneo and in a nursery in Pinerolo (northwest Italy). In the field, the disease became evident 5 to 8 months after planting. Symptoms included stunting, pale green-to-reddish leaves, premature defoliation, and root and crown rot. The root system was reduced, with few feeder roots and a dark discoloration of the root cortex. Root, crown, and basal stem rot led to death of the plants. Pieces of the discolored organs were surface-sterilized in sodium hypochlorite (2%) for 5 min, rinsed in sterile water, dried on sterile filter paper, and plated on acidified malt extract agar (pH 4.6) (MEA) and a selective medium for oomycetes (2). Slow-growing colonies developed on MEA, whereas colonies characteristic of Phytophthora spp. grew on the selective medium for oomycetes. Six isolates from plants collected from the field and the nursery were inoculated as V8 juice culture homogenate on the roots of blueberry cv. Berkeley, azalea, and 1-year-old chestnut plants in pots. All six isolates reproduced the symptoms in blueberry and caused root and foot rot in the other hosts. The original fungus was reisolated from all inoculated hosts. The isolates were examined and compared with strain 0229 of P. cinnamomi Rands from the International Mycological Institute. They were identified as P. cinnamomi on the basis of morphological characteristics and total mycelial soluble protein patterns on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In Italy, blueberry is a new host for this pathogen that was previously observed in rhododendron (1), and recently in chestnut (3) and other forest species. Because of the high risk of spreading the pathogen to areas where susceptible plants are grown, it is recommended that high-bush blueberry nursery stock be tested for the pathogen.
References: (1) G. Gullino and A. Garibaldi. La difesa delle piante 10:273, 1987; (2) H. Masago et al. Phytopathology 67:425, 1977. (3) A. M. Vettraino et al. Plant Pathol. 50:90, 2001.
