Cultivated Calibrachoa hybrids were previously thought to be resistant to powdery mildew, but infections have been recently encountered in Germany, USA and Nicaragua. The exclusive development of asexual morphs (anamorphs) led to the question as to which powdery mildew species might be involved as causal agents. Based on inoculation experiments and molecular sequence analyses, it was determined that powdery mildew infections on Calibrachoa in Europe (Germany), North America (USA), and Central America (Nicaragua) were found to be caused by the plurivorous Podosphaera xanthii. The anamorph is a typical Fibroidium characterized by conidia formed in chains (catenescent), containing distinct fibrosin bodies. Calibrachoa powdery mildew caused by P. xanthii could be easily transferred to cucumber, squash and Verbena ×hybrida and vice versa in the latter case. Attempts to inoculate petunias failed. In addition to P. xanthii, two additional powdery mildew species were found infecting Calibrachoa ×hybrida in Germany. The first, characterized by having lobed hyphal appressoria and conidia formed singly, can be assigned to Pseudoidium neolycopersici, and the second species, readily distinguishable by its very long conidiophores, conidia in chains with sinuate outline and nipple-shaped hyphal appressoria, belongs to Euoidium longipes. In the course of the current examinations, E. longipes was also found on Verbena ×hybrida, which represents the first record of this species on a non-solanaceous host.

In August 2011, a severe shoot dieback was observed on several hundred plants of 1-year-old Euonymus fortunei cv. Emerald 'n Gold in a nursery in Lower Saxony and on a cemetery in Berlin. Single shoots or the whole plant were affected. Chocolate brown lesions around the shoots spread primarily acropetally to be followed by wilting of the shoot tip, reddish discoloration, dropping of leaves, and finally plant death. Two fungal isolates, JKI 2187 and JKI 1288, forming white mycelium on 2% malt extract agar (MEA) were obtained from symptomatic shoots. Both were identified by their morphology as Cylindrocladiella parva (P.J. Anderson) Boesewinkel (syn. Cylindrocladium parvum). After incubation for one week at 25°C in the dark, the reverse side of the colony became buff to ochreous and this was associated with development of long chains of chlamydospores. Microsclerotia and fruiting bodies were not observed. Morphological characteristics were determined on synthetic nutrient agar (SNA) after 7 days at 25°C under near-ultraviolet light. The conidiophores were penicillately branched. The stipe extensions were thick-walled with clavate to naviculate vesicles. Conidia measured 12.7 to 17.1 (14.9) × 2.2 to 3.3 (2.7) μm. The molecular studies confirmed the morphological identification. Genomic DNA was isolated from the mycelia. The rDNA internal transcribed spacer (ITS) region was amplified with the primers ITS1 and ITS4 and a part of the β-tubulin gene with the primers Bt2a and Bt2b (2). The sequences generated in this study were compared with sequences obtained from GenBank. A BLAST analysis showed that the ITS sequence had a 99% similarity with that of C. parva GenBank Accession No. AY793454 and the β-tubulin gene had a 100% similarity with AY793489. So far, pathogenicity of C. parva has been demonstrated for only a few plant species. Its pathogenicity was confirmed on grapevine (Vitis vinifera) in New Zealand (3), on common oak (Quercus robur) in Italy (4), and on eucalyptus in South Africa (1). To fulfill Koch's postulates for the pathogen on E. fortunei, the isolate JKI 2188 of C. parva was inoculated on 40 two-year-old plants of cv. Emerald 'n Gold. The leaves around one node were removed on five shoots per plant. After wounding the nodes with a needle, colonized agar plugs were placed on them. The plugs were covered with moist cellulose swabs and sealed with Parafilm. To act as negative controls, 20 plants were treated with sterile agar plugs. All the plants were incubated in a growth chamber at 21/16°C (day/night), with a day length of 12 h and a relative humidity of 90 to 100%. Seven weeks after inoculation, all inoculated plants showed symptoms identical to those of the diseased plants from which C. parva was originally isolated. The negative controls remained healthy. The strains reisolated were identical to the original isolates. To our knowledge, this is the first report of C. parva as a pathogen of Euonymus. Since 2011, there were no further reports of this disease. At present, the disease is not of economic importance. References: (1) P. W. Crous et al. Plant Pathol. 42:302, 1993. (2) N. L. Glass and G. C. Donaldson. Appl. Environ. Microbiol. 61:1323, 1995. (3) E. E. Jones et al. Plant Dis 96: 144, 2012. (4) L. Scattolin and L. Monteccio. Plant Dis. 91:771, 2007.

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