Genomic diversity of Capillovirus uniheveae (Betaflexiviridae) infecting Hevea brasiliensis Muell. Arg. in Hainan, China.

Abstract

Background: Rubber tree (Hevea brasiliensis Muell. Arg.) is a significant commercial crop in tropical areas worldwide, with rubber production threatened by Tapping Panel Dryness (TPD). Rubber tree virus 1 (Capillovirus uniheveae; RTV1) was identified in rubber tree samples with TPD symptoms through RNA-seq. However, its genetic diversity may have hindered the detection of RTV1 via RT-PCR, complicating the further identification of RTV1 as the causative agent of TPD. To assess RTV1 prevalence and genomic diversity, rubber tree bark samples with TPD syndrome were collected from various sites in Hainan, China, for RNA-seq and RTV1 genome determination.

Results: Twenty complete RTV1 genomes were determined from 22 samples with TPD syndrome via RNA-seq and RT-PCR. Using degenerate primers based on conserved sequences in the 3'- and 5'-UTR, 20 complete RTV1 genomes were identified directly from 48 trees affected by TPD via RT-PCR. The 40 RTV1 genome sequences showed significant variations, particularly in the RdRp domain. Phylogenetic analysis of full-genome nucleotide sequences divided RTV1 isolates into three phylogroups (A, B, and C), with phylogroup A being the most prevalent (67.5%). Similar results were observed based on RdRp and CP phylogenetic analysis. Additionally, mixed infections with different genotypes were identified in the same tree. Notably, no genetic recombination was observed among different phylogroups, while ten recombination events were identified within phylogroup A.

Conclusions: RTV1 was identified in approximately 50% of samples with TPD syndrome collected in Hainan, China, with phylogroup A being the most prevalent. Considerable variations were observed in RTV1 nucleotide sequences among different phylogroups. These findings lay a foundation for accurate diagnostics, etiological characterization, and elucidation of the evolutionary relationships of RTV1 populations, providing a strong guarantee for obtaining virus-free rubber tree seedlings, and promoting the healthy and sustainable development of rubber tree plantations.