Between 2001 and 2007, samples from three California native plants showing canker symptoms were submitted to the California Department of Food and Agriculture's Plant Pest Diagnostics laboratory. Giant sequoia (Sequoiadendron giganteum) and coast redwood (Sequoia sempervirens) showed branch cankers and dieback, whereas tanoak (Lithocarpus densiflora) had bleeding bole cankers. Samples were collected from mature trees in private landscapes in El Dorado, Sacramento, and Alameda counties in California. A fungus was isolated on one-half strength acidified potato dextrose agar (APDA) from the canker margins of all three hosts. Colonies were moderately fast growing, initially white, later turning olivaceous black. Pycnidia developed singly or in small groups and contained conidia that measured 18 to 29 × 6 to 8 μm (average 21.5 × 6.8 μm). Conidia were aseptate, hyaline, and fusiform, with truncate bases. rDNA sequences of the internal transcribed spacer (ITS) region of the isolates (GenBank JQ282157 through JQ282159), amplified using primers ITS1 and ITS4 (2), were 100% identical to the holotype isolate of Neofusicoccum nonquaesitum Inderb., Trouillas, Bostock & Michailides (1) by a BLAST query (GenBank GU251163). Pathogenicity of the N. nonquaesitum isolate from giant sequoia (CDFA4) was tested on five saplings using cultures grown on APDA for 14 days. A single wound was made approximately 2 cm above the soil line on the cambium of each plant using a 3-mm cork borer. One 3-mm colonized agar plug was placed on each wound and secured with Parafilm. Plugs of APDA were placed onto wounds of five plants as controls. All plants were kept in a growth chamber at 23°C with a 12-h photoperiod. After 4 days, Parafilm was removed to reveal dark brown cankers measuring 12 to 43 mm long on the inoculated plants. Fourteen days after inoculation, cankers were black, sunken, and measured 79 to 117 mm (average 91.4 mm) long. Most of the inoculated plants were wilted with chlorotic to necrotic foliage. Mature pycnidia with cirri developed in most of the cankers. N. nonquaesitum was reisolated on APDA from all of the cankers. No symptoms developed on the control plants. The experiment was repeated once with similar results. Botryosphaeria dothidea, also in the Botryosphaeriaceae, has been reported to cause similar cankers on giant sequoia and coast redwood in California (3). However, rDNA sequencing of the ITS region of this isolate obtained from the American Type Culture Collection (ATCC 60344) (GenBank JQ284384) showed it matched the type specimen of Neofusicoccum australe (GenBank GU251219), not our isolate. To our knowledge, this is the first report of N. nonquaesitum as a pathogen of giant sequoia in North America. This study expands the host range of N. nonquaesitum from almond (Prunus dulcis), California bay (Umbellularia californica), and blueberry (Vaccinium spp.) (1) to include giant sequoia, coast redwood, and tanoak, which are economically important trees in California forests and landscapes.
References: (1) P. Inderbitzin et al. Mycologia 102:1350, 2010. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990. (3) J. J. Worrall et al. Plant Dis. 70:757, 1986.
