A new species of Phytophthora reported to cause root and collar rot of common boxwood, Nordmann fir and Port Orford cedar in Hungary

Collar and root necroses associated with severe wilting and desiccation of foliage were observed on box (Buxus sempervirens) growing in a public garden in Budapest (2002), and on Nordmann fir (Abies nordmanniana) and Port Orford cedar (Chamaecyparis lawsoniana) produced in a 12 ha ornamental nursery of Western Hungary (2007). The disease was sporadic on Nordmann fir, but was abundant on box and Port Orford cedar, resulting in 25-30% mortality.

Isolations from lower stems and roots consistently yielded cultures typical of Phytophthora, developing stellate-radiate colonies with low aerial mycelium on carrot agar (CA) and V8 juice agar, or were featureless on potato dextrose agar at 25°C (Fig. 1). Cultures lacked sexual structures, sporangia or chlamydospores. Three isolates (IMI 390920, CBS 124086, CBS 123840), one from each host plant, were further characterised. Optimum and maximum temperatures for growth on CA were 30°C and 38°C, respectively. Mean radial growth-rate at 30°C ranged from 9.2 to 9.4 mm/day. In non-sterile stream water, persistent, ellipsoid-ovoid, non-papillate, rarely internally proliferating sporangia were produced with dimensions of 73±7 x 33±4 µm (average of the three strains) (Fig. 2.). The rDNA ITS sequences (GenBank Accession Nos. FJ801357, GU230789 and GU230790) showed 100% congruence with accessions deposited as 'P. sp. niederhauserii' (Abad & Abad, 2003). The morphological characteristics are also consistent with published descriptions given the same name. However, a valid name according to nomenclatural rules has not yet been published for this species of Phytophthora and we refrain from naming it here.

Pathogenicity to the original host plant species was verified by wound-inoculating at the root collar of two-year-old potted plants with mycelial CA discs. Symptoms identical to those observed on naturally infected plants developed within three to six weeks, and our Phytophthora alone was re-isolated. Control plants inoculated with sterile CA remained healthy. A species of Phytophthora named as 'P. sp. niederhauserii' has been reported on other hosts in Europe (e.g., Cacciolaet al., 2009; Herrero et al., 2008; Moralejo et al., 2009). This is the first record of this formally unnamed Phytophthora from Hungary.