Partial Characterisation of a Filamentous Seedborne Virus Infecting New Zealand Citrus
SFV was seed transmitted in 17 from 19 seedlings species tested; only the seedlings of two rootstocks, Poncirus trifoliata cv. Benecke and Zhuluan, tested virus-free by ISEM. None of 25 field grown cultivars tested were found to be virus-free. The virus was symptomless in all of the seedling. The only symptoms noted in field plants were boat and spoon shaped leaves in satsumas and leaf flecking in Dweet tangor. Since most field grown citrus in New Zealand is contaminated with CTF it is not certain that SFV was responsible for these symptoms. With phosphate buffer extraction (pH 7) the virus was not mechanically transmitted to any 12 herbaceous hosts tested, belonging to 4 different families. On the basis of the evidence to date the host range of SFV appears limited to citrus.
The physical, biological and serological properties of SFV were compared with those of previously reported filamentous viruses of citrus, but there was no complete correlation with the properties of CTV, CTLV or CRSV (psorosis). Morphologically the SFV particles are similar to the L particles of CRSV (Indian isolates). There is a clear difference in morphology between SFV particles and those of CTV and CRSV (Florida isolate and California isolate). CTLV and CRSV (California and Florida isolates) are mechanically transmissible to several herbaceous hosts, while CRSV (Indian isolate) and SFV are not. SFV is seed transmitted at a high rate while none of the other filamentous citrus viruses are reported to be seed transmissible, except for CRSV where conflicting reports exist. SFV did react with an antiserum to CRSV (Indian isolate) although both the size and number of capsid proteins are different. It did not react with antisera to any of the other filamentous citrus viruses.
Samples of purified SFV gave two prominent protein bands in SDS-PAGE, with molecule weights of 33 kDa (upper hand) and 24 kDa (lower band). Partial amino acid sequence was obtained from these two protein species. On the basis of N-terminal sequence and portions of the internal sequence SFV-specific primers were designed and used in PCR. Nucleic acid extraction from purified virus produced a single high molecular weight band of approximately 11.5 kb in agarose gels. The purified RNA was used as a template for cDNA synthesis by reverse transcription followed by PCR which yielded two bands (700 and 200 bp) amplification products.
It is concluded that the properties of the short filamentous virus isolated from citrus in New Zealand did not consistently match those of any of the previously described flexous viruses from citrus. On the basis of the characteristics of SFV the name” citrus seedborne virus CSBV)” is suggested.
School Location:New Zealand
Source Type:Master's Thesis
Date of Publication:04/12/1999