Abstract
In 2006, the release and cultivation of the genetically modified papaya cultivar ‘Huanong No.1’ successfully controlled the destructive papaya ringspot disease caused by Papaya ringspot virus (PRSV) in South China. However, some transgenic papaya plants from Guangdong and Hainan are found infected by PRSV. In this study, Field investigation was carried out and susceptible transgenic papaya samples were collected during 2012–2016. Twenty representative isolates were artificially inoculated into Cucurbita pepo and commercialised ‘Huanong No.1’ papaya, and results indicated that the plants showed obvious disease symptoms. Phylogenetic analysis of CP genes of 120 PRSV-infected isolates showed that PRSV can be divided into three groups. Isolates from Guangdong and Hainan belong to Group III, which is further divided into two subgroups. The isolates collected in this study have greatly diverged from the previously reported dominant strains Ys, Vb and Sm in South China, indicating that they belong to a new lineage. Further analysis showed a highly genetic differentiation between isolates, and 27.1% of the isolates were identified as recombinants on the basis of CP nucleotide sequences. These results indicate that the genetic variation of PRSV and the formation of the new virus lineage may explain the loss of transgenic papaya resistance in South China.
Highlights
Papaya ringspot virus (PRSV) of the genus Potyvirus and the family Potyviridae is a threat to the papaya and cucurbit industries in tropical and subtropical regions
Recent studies have found that PRSV infects ‘Huanong No.1’ transgenic papaya plants in some regions of South China[24], and the occurrence tendency increases gradually with time
To explain the loss of transgenic papaya resistance against PRSV in South China, we investigated the virus occurrence in ‘Huanong No.1’ papaya plantations in Guangdong and Hainan during 2012–2016, and found that transgenic papaya plants were respectively infected by two kinds of the viruses, PRSV and Papaya leaf-distortion mosaic virus
Summary
Papaya ringspot virus (PRSV) of the genus Potyvirus and the family Potyviridae is a threat to the papaya and cucurbit industries in tropical and subtropical regions. Cai et al.[18] identified four PRSV isolates, Ys, Vb, Sm and Lc, in South China, based on the different symptoms on Cucurbita pepo They collected and analysed 313 papaya virus samples in 1994 and showed that 40.57% of diseased plants are infected with Ys, 10.22% with Vb, 4.47% with Lc, 0.64% with Sm, and 44.08% with Ys and Vb mixed. A few scholars have reported some PRSV isolates in Hainan[23,24] but not in Guangdong, where ‘Huanong No.1’ is widely cultivated These isolates have yet to be compared with the four dominant strains identified by Cai et al in South China[18]. This study may serve as a theoretical basis for further prevention and control of PRSV
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