Varieties of Calibrachoa, a genus of plants with petunia-like flowers in the Solanaceae family originating from South America, are becoming increasingly popular as bedding and balcony plants worldwide. In autumn 2018, chlorotic spots and vein chlorosis were observed on several plants in the greenhouse of a nursery in North-Rhine Westphalia, Germany (Fig. 1) where only calibrachoa is cultivated. From the first mild symptoms, a severe disease developed with necrosis of leaves and wilting of entire shoots (Fig. 2). Almost all plants in the glasshouse (c. 2000 m²) became infected rapidly leading to the total loss of the crop.
Left: Calibrachoa plant with initial necrosis of whole shoots; right: Chlorotic spots observed on calibrachoa leaves.
Investigations by electron microscopy showed the presence of rod-shaped virus-like particles (Fig. 3) indicative of tobamoviruses. This was confirmed by RT-PCR in samples from twelve randomly collected plants using a generic primer pair for the detection of tobamoviruses (Menzel et al., 2019). Two PCR products were sequenced directly in the forward and reverse directions (HZI, Braunschweig) revealing 100% sequence identity. Sequence comparison using blastn showed 98.7 % nucleotide sequence identity to Bell pepper mottle virus (BPeMV, genus Tobamovirus; GenBank Accession No. NC_009642) and 75.8% identity to Tomato mottle mosaic virus (KX898034). BPeMV was first described in the 1960's as an unusual strain of Tobacco mosaic virus infecting pepper in Argentina (Garcia et al., 1968). Wetter et al. (1987) later characterised it as a distinct virus species that led to lethal infections in inoculated Petunia hybrids. The complete genome sequence for BPeMV reported by Rhie et al. in 2007 confirmed this status.
The calibrachoa isolate of BPeMV showed a strong serological reaction in ELISA using a BPeMV-specific antibody raised against an eggplant isolate of this virus (DSMZ AS-0244). In Europe, its occurrence is documented only once from the Netherlands in 1980 (Tobias et al., 1982). The pathway of introduction of this obviously rarely occurring virus into the vegetatively propagated calibrachoa plants is so far unknown. This is the first evidence of the occurrence of BPeMV in Germany, and the first proof that it is infectious in an ornamental plant. Due to the economic importance of the ornamental host Calibrachoa, and the fast and fatal progression of the disease, the occurrence of similar symptoms in these plant cultures demands careful monitoring and early diagnosis. The BPeMV isolate from calibrachoa (MK770674) was deposited as PV-1239 in the DSMZ Plant Virus Collection.
source: New Disease Report