To better understand the genetic diversity of cucurbit-infecting poleroviruses in Taiwan, a survey was conducted in 2008 and 2009 as a prelude to screening germplasm for resistance. Out of 102 cucurbit samples showing yellowing symptoms collected across eight counties, 29 were identified as infected by polerovirus(es) by reverse transcription polymerase chain reaction (RT-PCR) using a set of universal polerovirus primers. Sequence analysis of a 1AE4-kb PCR product spanning part of the RNA-dependent RNA polymerase (RdRp) gene, the intergenic region (IR) and the complete coat protein (CP) gene of 13 of the 29 samples revealed the presence of three distinct Polerovirus species, namely Cucurbit aphid-borne yellows virus (CABYV), Melon aphid-borne yellows virus (MABYV) and Suakwa aphid-borne yellows virus (SABYV). In addition to the common strain of CABYV (CABYV-C) a recombinant strain of CABYV (CABYV-R) was identified. The recombinant strain probably arose by recombination in the IR, a recombination hot-spot of poleroviruses, between ancestors of MABYV and CABYV-C. RT-PCR protocols based on sets of specific primers were developed to distinguish between the different cucurbit-infecting polerovirus species and the two CABYV strains. These findings are discussed in relation to strategies for breeding for durable resistance against poleroviruses.

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Ceratothripoides claratris, the predominant thrips species on tomato in Thailand, was tested for vector competence and efficiency to transmit Capsicum chlorosis virus (CaCV) (isolate AIT) to tomato. The efficiency of adult-stage transmission was influenced by the larval stage at which virus was acquired. Adult C. claratris showed 69% transmission efficiency after acquiring the virus as freshly emerged (<1 h) first-instar larvae. However, when just molted (<1 h) second-instar larvae acquired the virus, the percentage of adult transmitters significantly decreased (48%). Transmission efficiency of up to 47% was detected with second-instar larvae of C. claratris which had acquired the virus as freshly emerged first-instar larvae. Transmission efficiency did not significantly differ between adult males and females, irrespective of the larval stage at which the virus was acquired. Highest transmission efficiency for CaCV was recorded in adult C. claratris derived from second-instar larvae collected from infected tomato plants in a greenhouse. Lowest transmission efficiency was observed in adults directly collected from infected tomato plants in the greenhouse. The spread of CaCV on tomato plants in greenhouses showed a close association with thrips infestations.

The complete genome sequence of an isolate of euphorbia ringspot virus (EuRSV) was determined by deep sequencing and rapid amplification of cDNA ends (RACE) RT-PCR. It has an RNA genome of 10,154 nucleotides in size, excluding the poly(A) tail, and encodes a polyprotein of 3265 amino acids. Phylogenetic analysis from this study supports the earlier taxonomic assignment to the genus Potyvirus; however, a gene encoding the HAM1h protein, inserted between NIb and CP of the EuRSV genome, which was previously only observed for cassava brown streak virus and Ugandan cassava brown streak virus of the genus Ipomovirus, is an unusual feature of this potyvirus, which otherwise has typical potyvirus genome features.