Camellias are widely cultivated in gardens and grown in nurseries for plant and flower production in northwestern Spain. Camellia japonica L. is most frequently grown, but many other camellia species and hybrids are also produced. In spring 1998, plants of Camellia sp. from a garden were observed to be affected by a root fungal pathogen, that formed a white mycelium that covered most of the roots, while aboveground plant parts showed a general decline. Infected roots were macerated and discolored. Fragments of the infected roots were surface-sterilized and placed in petri dishes containing potato dextrose agar and incubated at 24°C in the dark. The fungus formed a white mycelium that turned black in 1 week, developing pyriform swellings characteristic of Rosellinia necatrix Prill (1). To confirm pathogenicity, inoculum of the isolate was produced on wheat (Triticum aestivum L.) seeds autoclaved in glass vessels for 30 min at 120°C. Wheat seed cultures were started from disks of R. necatrix mycelium and grown at 24°C in the dark for 30 days. Pathogenicity tests were conducted on 48 2-year-old plants of the hybrid Camellia × williamsii cv. Mary Phoebe Taylor, which had been grown in 1.5-liter pots (one plant per pot) filled with soil in a glasshouse. The R. necatrix isolate was inoculated by adding 30 g of infected wheat seeds to each pot. The inoculum was mixed thoroughly with the substrate before potting. Another set of pots was left uninoculated, and served as a control. All pots were randomly arranged in a growth chamber at 22 to 24°C with a 12-h photoperiod. Seventeen days after inoculation, aerial symptoms of chlorosis and leaf fall were observed, while control plants remained symptomless. Inoculated plants died 3 months after inoculation. R. necatrix was reisolated from roots of all infected plants. To our knowledge, this is the first report of a root rot of camellia caused by R. necatrix, a pathogen causing white root rot mainly in deciduous fruit crops.
Reference: (1) S. Freeman and A. Sztejnberg. Pages 71--73 in: Methods for Research on Soilborne Phytopathogenic Fungi. The American Phytopathological Society, St. Paul, MN, 1992.
