G.R.G. Clover*, D.R. Elliott, Z. Tang and B.J.R. Alexander
National Plant Pest Reference Laboratory, Ministry of Agriculture and Forestry, PO Box 2095, Auckland, New Zealand.

*cloverg@maf.govt.nz

Accepted for publication 22/10/01

In May 2001, unusual symptoms were observed on less than 1 % of cucumber plants (Cucumis sativus) growing in a glasshouse in Tuakau, south Auckland, New Zealand. These symptoms, which included leaf chlorotic spotting and inter-veinal chlorosis, resembled those induced in cucumber elsewhere by Beet pseudo-yellows virus (BPYV) the vector of which, Trialeurodes vaporariorum (greenhouse whitefly), also occurred on the plants. Flexuous, filamentous virus particles resembling those of BPYV were observed in sap from affected plants using electron microscopy. Testing of these plants by indirect ELISA (Liu & Duffus, 1990) using specific polyclonal antiserum diluted 1/1000 (v/v) and anti-rabbit conjugate diluted 1/8000 (v/v), revealed that the plants were infected by BPYV. This diagnosis was confirmed by RT-PCR using specific primers which yielded a single band of 450 bp with nucleic acid extracted from the diseased, but not healthy, plants (Rubio et al., 1999). The sequence of the specific product of the BPYV isolate was almost identical to that of the isolate previously sequenced by Tian et al. (1996). No other viruses were detected in affected plants by electron microscopy or mechanical inoculation of common herbaceous indicator plant species, and specific tests for other cucumber pathogens (including Cucumber mosaic virus and Potato spindle tuber viroid) were negative. The distribution of BPYV in New Zealand is unknown, but similar symptoms in cucumber have been observed for a number of years in this region and around Nelson. It is also not known how the virus was introduced, but viruliferous T. vaporariorum may have been inadvertently imported with plant material. This outbreak is the first confirmed occurrence of BPYV in New Zealand and also of a virus of the genus Crinivirus in the country. Glasshouse cucumbers are of some importance in New Zealand where 499,000 m² were grown in the year to March 2001. Severely affected cucumber plants may not yield at all (Liu & Duffus, 1990). More significantly, the virus also has the potential to infect a number of other crops grown in New Zealand including sugar beet, lettuce, endive, squash and melon.

Figure 1: Cucumber leaf infected with Beet pseudo-yellows virus from a New Zealand glasshouse.

Acknowledgement

The authors thank Dr. Hsing-Yeh Liu, USDA-ARS, Salinas, USA, for providing specific antiserum to Beet pseudo-yellows virus.

Liu H-Y, Duffus JE, 1990. Beet pseudo-yellows virus: Purification and serology. Phytopathology 80, 866-9.

Rubio L, Soong J, Kao J, Falk BW, 1999. Geographic distribution and molecular variation of isolates of three whitefly-borne closteroviruses of cucurbits: Lettuce infectious yellows virus, cucurbit yellow stunting disorder virus and beet pseudo-yellows virus. Phytopathology 89, 707-11.

Tian T, Klaasen VA, Soong J, Wisler G, Duffus JE, Falk BW, 1996. Generation of cDNAs specific to lettuce infectious yellows closterovirus and other whitefly-transmitted viruses by RT-PCR and degenerate oligonucleotide primers corresponding to the closterovirus gene encoding the heat shock protein homolog. Phytopathology 86, 1167-73.

The British Society for Plant Pathology