Identification of a Potyvirus Causing Latent Infection in Calla Lilies.

Abstract

A new potyvirus designated as Calla lily latent virus (CLLV) was isolated from apparently healthy calla lilies (Zantedeschia spp.) collected from nurseries in Taichung County, Taiwan. Different from most calla lily-infecting potyviruses, CLLV infects Chenopodium quinoa and develops local lesions on inoculated leaves (3). Typical potyvirus particles approximately 780 nm long were detected from CLLV-induced C. quinoa local lesions. CLLV was transmitted readily to and established in C. quinoa. Attempts to establish CLLV infection in calla lilies from extracts of C. quinoa lesions were not successful. The virus was transmitted from infected to healthy calla lilies with difficulty. A 1.3-kb cDNA product was amplified by reverse transcription-polymerase chain reaction (RT-PCR) from CLLV-infected calla lilies and C. quinoa using potyvirus degenerate primers (2). The PCR product was cloned and sequenced. It was found to consist of 1,339 nucleotides (nt) (GenBank Accession No. AF469171) corresponding to the genome organization of the 3'terminal region of potyviruses. The deduced amino acid sequence contains 362 residues encoding the 3'terminal region of the nuclear inclusion b gene (80 residues) and the complete coat protein (CP) gene (282 residues). A 253-nt noncoding region (NCR) was found at the 3'terminal region of the cDNA. By comparing with known sequences of potyviruses, CLLV was identified as a new species of Potyvirus based on the uniqueness in the CP gene and 3' NCR. Soybean mosaic virus and Watermelon mosaic virus 2 are the potyviruses most similar to CLLV, but they share only approximately 80% nucleotide identity with CLLV in the CP and NCR regions. Attempts to purify sufficient CLLV from C. quinoa for antiserum preparation were not successful. Alternatively, polyclonal antibodies were produced using E. coli-expressed CLLV CP (1). The antibodies were useful for detection of CLLV and its CP in calla lilies using enzyme-linked immunosorbent assay, sodium dodecyl sulfate-immunodiffusion, immuno-specific electron microscopy, and western blot. Field surveys showed that calla lily plants found positive for CLLV by serological methods always remained symptomless throughout the six-month growing season. Occasionally, CLLV was detected in symptomatic calla lilies, but these plants were consistently confirmed dually infected by other viruses (Dasheen mosaic virus and Konjak mosaic virus found most commonly). Infection of CLLV alone in calla lilies may not have a direct impact on the production and marketing of the crop. Synergism is not currently known when calla lilies are coinfected with other viruses. CLLV is spread by vegetative propagation through infected rhizomes or tubers.