SEROLOGICAL AND MOLECULAR PROPERTIES OF FIVE POTYVIRUSES INFECTING CALLA LILY

Abstract

Calla lily (Zantedeschia spp.), an aroid plant species indigenous to Africa, is a popular ornamental crop in Taiwan and many other countries. Dasheen mosaic virus (DsMV) is the first potyvirus species reported to infect calla lilies. Besides DsMV, several potyviruses with distinct serological and molecular properties were isolated from calla lilies in Taiwan. In 2001, a potyvirus with serological and molecular properties distinct to those of DsMV was recognized and widely distributed in calla lily fields in Taiwan. The virus inducing mosaic symptoms similar to those caused by DsMV was provisionally designated as Zantedeschia mosaic virus (ZaMV). The ZaMV was later identified as a strain of Konjak mosaic virus (KoMV), a potyvirus infecting aroid plants reported from Japan. This was based on the analysis that they shared more than 90% of identity between their coat protein (CP) gene sequences. In 2002, Turnip mosaic virus infecting calla lilies causing yellow spot and stripe foliar symptoms was recognized. TuMV was found frequently occurring in calla lily fields adjacent to cruciferous crops. In addition, TuMV was also detected in calla lily bulbs imported from other countries including USA and Vietnam. The same year, another potyvirus discovered from calla lilies showing mild mosaic symptoms. It was evidently different from those already reported calla lily-infecting potyviruses, and named Zantedeschia mild mosaic virus (ZaMMV) based on its distinct symptoms. ZaMMV was identified coincidentally by two working groups novel molecular properties that a sequence of 38-39 repeated glutamine residues located on the N-terminal of the CP gene. The biological and molecular significance of the unusual glutamine repeats is not known. Finally, Calla lily latent virus (CLLV) was discovered and detected from a calla lily plant dually co-infected with DsMV and KoMV. It is so named for its inability to induce any visible symptoms on calla lilies. This characteristic was confirmed by the consistent observation in field surveys that none of the calla lily plants singly infected by CLLV developed symptoms. Serological and molecular studies reveal that CLLV is a new species of Potyvirus.