First Report of Phytophthora citrophthora Causing Root and Basal Stem Rot of Woody Ornamentals in Hungary

From 2007 to 2009, necrotic bark lesions at the root collar and lower stem associated with root rot were observed on container-grown cork-bark r (Abies lasiocarpa var. arizonica, Port-Orford-cedar (Chamaecyparis lawsoniana (A. Murray) Parl. Barabits Gold ), lavender (Lavandula angustifolia Mill. Hidcote ), Fowering currant (Ribes sanguineum Pursh King Edward VII ), and lilac (Syringa vulgaris L. Belle de Nancy ) in six ornamental nurseries in western Hungary. Symptoms also included reduced growth, wilting, and desiccation of branches. Mortality of affected plants ranged from a low level in Fowering currant to a high frequency in cork-bark r (1,000 plants; 50%) and lavender (2,500 plants; 50%). Isolations from necrotic tissues onto PARPB medium (1) yielded 13 isolates of a Phytophthora sp. None of the isolates produced sexual structures, sporangia, or chlamydospores butdeveloped slightly stellate or patternless colonies with loose, aerial mycelium onnonselective carrot agar (CA) at 25C. One isolate from each host species was furthercharacterized and tested for pathogenicity. Growth on CA was fastest at 25C (7.9 to 8.6mm per day) and no growth occurred below 5C or above 34C. In nonsterile stream water,persistent, mono-and bipapillate, mostly ovoid, rarely distorted sporangia, measuring 40.5to 49.4 × 29.8 to 37.3 um were produced. In pairings on CA with A1 and A2 strains of P.cambivora and P. nicotianae, used as testers, none of our isolates produced gametangia. Onthe basis of these characteristics, the pathogen from ornamentals appeared to be P.citrophthora (Smith & Smith) Leon. (1). Species identity of all 13 isolates was determined insingle-round PCR assays with the P. citrophthora-specic primer-pair Pc2B/Pc7 (2) and/or bysequencing the rDNA internal transcribed spacer (ITS) regions amplied with the universalITS1/ITS4 primers. The primers Pc2B and Pc7 generated a single DNA fragment of theexpected size (approximately 210 bp), and the rDNA ITS sequences (NCBI Accession Nos.GU723282, GU723284, GU723285, and GU723287) showed 99 to 100% homology withmany GenBank sequences (e.g., HQ697232) of P. citrophthora as the closest match.Pathogenicity to the original host plant cultivars was tested on 2-or 3-year-old healthyplants potted in sterile soil and inoculated at the root collar (2 replicates per isolate). A 4-mm-diameter bark plug was removed and a mycelial disc of the same size from an activelygrowing CA culture was placed into the hole. Control plants received sterile CA plugs.Inoculation points were sealed with sterile moist cotton and Paralm, covered with sterilesoil, and then the plants were kept in a greenhouse at 24 4C. Symptoms identical tothose observed on the naturally diseased hosts developed on inoculated plants within 3months. Control plants remained healthy. P. citrophthora could be reisolated only from theinfected plants. The pathogen is polyphagous, widely distributed (1), and has beenassociated with woody ornamentals in nurseries (3). However, to our knowledge, this is therst record of P. citrophthora in Hungary. The pathogen has to be considered as a threat toornamental production within Hungary. © 2011 American Phytopathological Society. All rights reserved.