Angelonia flower mottle, a new disease of Angelonia angustifolia caused by a hitherto unknown carmovirus

S. Winter ¹*, A. Hamacher², J. Engelmann³ and D.-E. Lesemann³

1 DSMZ Plant Virus Division, c/o BBA, Messeweg 11-12, 38104 Braunschweig, Germany
2 Institute for Plant Diseases, Dept. Plant Diseases, Rheinische Friedrich-Wilhelms-Universität Bonn, Nussallee , 53115 Bonn, Germany
3 Federal Biological Research Centre for Agriculture and Forestry, Institute for Plant Virology, Microbiology and Biosafety, Messeweg 11-12, D-38104 Braunschweig, Germany

*S.Winter@bba.de

Accepted for publication 05/10/05

Angelonia angustifolia (family Scrophulariaceae), a Central American ornamental, is receiving increasing attention in the USA and Europe for its attractive flowers. In Germany, a number of accessions from commercial companies, subjected to evaluation for varietal release, exhibited conspicuous flower mottling symptoms (Fig. 1), suggestive of virus infection. Carmovirus-like isometric particles (approx. 30 nm in diameter) were detected in symptomatic plants by electron microscopy. Sap inoculation studies revealed that the virus is mechanically transmissible to Angelonia plants, leading to mottling symptoms on the petals of flowers. When inoculated to Nicotiana hesperis, N. occidentalis, N. glutinosa and N. clevelandii, latent infections confined to the site of inoculation site resulted. An antiserum (DSMZ AS-858) raised against a purified virus preparation, reacted specifically with homologous antigen in western blot analyses (Fig. 2). Virus was detected in flowers and in non-symptomatic leaves. Immunoelectron microscopic decoration tests showed no detectable cross-reaction to several other carmoviruses.

Figure 1: Dark flower mottling symptoms on Angelonia cultivars with purple and light pink primary colours.

Clones of the complete coat protein gene were obtained by RT-PCR from viral RNA isolated from purified particles. Sequence analysis of the 1053 nucleotide coat protein gene (EMBL Acc. No. AM050058; encoding a predicted 351 amino acid product) confirmed this virus to be a typical, but distinct, carmovirus with 49 and 48% nucleotide sequence identity (37% and 35 % amino acid sequence identity) to Pelargonium flower break virus and Carnation mottle virus respectively.

Figure 2: SDS Page (left) and western blot analysis using Antiserum DSMZ AS-858 (right), of purified virus preparations and total plant protein extracts. Samples loaded on the gels were: a purified preparation of virus particles from infected Angelonia plants (1), total soluble protein extracts from flowers (2) and leaves of symptomatic Angelonia plants (3) total soluble protein extracts from non-symptomatic Angelonia plants (4), a purified preparation of Carnation mottle virus (5), a purified preparation of Pelargonium chlorotic line pattern virus (6). The arrow indicates the position of the coat protein. The minor band in purified virus preparations is presumed to be due to proteolytic degradation. The sizes (kDa) of co-electrophoresed molecular weight markers are indicated.

During cultivation of Angelonia, transient mild chlorotic spots appeared on the leaves of infected and non-infected plants, which are suspected to be stress induced. Since the flower mottle symptoms consistently correlate with infection by the carmovirus, we propose naming this tentative new carmovirus species Angelonia flower mottle virus.

The British Society for Plant Pathology