Psiguria triphylla: a new natural host of Papaya ringspot virus – type W in Brazil

D.H. Nakano¹, D.M.F. Sansini¹, J.E. Buriolla¹, N.T.V. Junqueira², E.W. Kitajima¹ and J.A.M. Rezende^1*

¹ Departamento de Entomologia, Fitopatologia e Zoologia Agrícola, ESALQ, Universidade de São Paulo, 13418-900 Piracicaba, SP, Brazil
² Embrapa Cerrados, 73310-970 Planaltina, DF, Brazil

*jamrezen@esalq.usp.br

Accepted for publication 04/12/06

  Psiguria triphylla is a monoecious neotropical forest vine, belonging to subtribe Guaraniinae, family Cucurbitaceae, in which individual vines undergo two kinds of sex change viz. size-related and intraseazonal (Condon & Gilbert, 1988).  A plant of this species exhibiting symptoms of mosaic and severe leaf malformation was found in an experimental field of a germplasm collection of passion flower (Passiflora sp.) in the Experimental Station of Embrapa Cerrados, Planaltina County, DF, Brazil.  Preliminary electron microcopy examination of a negatively-stained extract of infected tissue showed the presence of filamentous potyvirus-like particles ca. 700-800 nm long.  Further electron microscopy analysis of ultra thin sections confirmed the infection by a potyvirus, based on the presence of filamentous particles scattered randomly or in parallel aggregates, and type I cylindrical inclusions in the cytoplasm of infected cells.  The virus was mechanically transmitted to healthy Psiguria triphylla (Fig. 1) and Cucurbita pepo cv. Caserta, causing severe symptoms. 

Figure 1: Psiguria triphylla experimentally infected with Papaya ringspot virus – type W (right; uninfected plant is on left).  Note that the leaves in the inoculated vine are unifoliate, as opposed to trifoliate in the control; this change is probably due to infection with PRSV-W.

Sap from these infected plants reacted in PTA-ELISA with polyclonal antiserum against Papaya ringspot virus – type W (PRSV-W), but not with antisera against Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus (WMV) and Passion fruit woodiness virus (PWV).  Total RNA extracted from infected and healthy P. triphylla and C. pepo was analysed by RT-PCR using specific primer pairs for the coat protein gene of PRSV-W (Vecchia et al., 2003) and ZYMV (Thomson et al., 1995).  A fragment of approximately 750bp was amplified only with PRSV-W coat protein primers.  This is the first report of P. triphylla as a natural host of PRSV-W.  This species might also be a host for ZYMV and WMV, since these potyviruses were successfully transmitted mechanically to healthy plants, causing severe mosaic.  Infection was confirmed by positive reaction of the extracts from infected plants with specific polyclonal antisera against ZYMV and WMV, respectively, in PTA-ELISA.

References

Condon MA, Gilbert LE, 1988. Sex expression of Gurania and Psiguria (Cucurbitaceae): neotropical vines that change sex. American Journal of Botany 75, 875-884.

Thomson KG, Dietzgen RG, Gibbs AJ, Tang YC, Liesack W, Teakle DS, Stackebrandt E, 1995. Identification of Zucchini yellow mosaic potyvirus by RT-PCR and analysis of sequence variability. Journal of Virological Methods 55, 83-96.

Vechia MGSD, Camargo LEA, Rezende JAM, 2003. Nucleotide sequence comparison of the coat protein gene of severe and protective mild strains of Papaya rigspot virus. Fitopatologia Brasileira 28, 678-681.

The British Society for Plant Pathology