Chilli pepper is an important economic crop and virus diseases are constraints on its production. In 2018, disease surveys were conducted at a 15-ha chilli pepper plantation in Dehong, southwest of Yunnan Province, China. Throughout the chilli pepper growing season from March to September, pepper plants developed three different virus-like symptoms on leaves, including mosaic, yellow mottle and shrinkage (Fig. S1). Based on observation of virus-like symptomatic phenotypes, the field surveys indicated that the disease incidence ranged from 30% in March to a peak 100% in July, resulting in a significant loss of pepper fruit from 30 to 100% depending on plot of the field. Potyvirus-like filamentous particles, around 11*760 nm, were observed under electron microscopy in the sap of symptomatic leaves (Fig. S1). To further determine the viral species in these samples, total RNA was extracted from three symptomatic samples using a Trans ZolUp Plus RNA Kit (Trans Gene, Beijing, China). Complementary DNA (cDNA) was synthesized using oligo (dT) and M-MLV reverse transcriptase (Promega, Madison, Wisconsin, USA) according to the manufacturer’s instructions, and the polymerase chain reaction (PCR) was performed using degenerate primers specific to genus Potyvirus targeting HC-Pro region (HPFor: 5-TGYGAYAAYCARYTIGAYIIIAAYG-3; HPRev: 5-GAICCRWAIGARTCIAIIACRTG-3) (Ha et al. 2008) under the following conditions: an initial denaturation at 94°C for 4min, 30 cycles of denaturation at 94°C for 30 s, annealing at 56°C for 30 s, extension at 72°C for 30s, and a 10min final extension at 72°C. An expected 683-bp DNA fragment was amplified and cloned into the pMD 18-T Vector (Takara, Japan) for sequencing. Sequence analysis using BLAST revealed that the amplicons of phenotype I (Fig. S1a) shared highest nucleotide identity (85.6%) with wild tomato mosaic virus (WTMV) isolate from Vietnam (GenBank no. DQ851495) while the amplicons of phenotype III (Fig. S1c) showed the highest nucleotide identity (93%) with chilli veinal mottle virus (ChiVMV) isolate from Sichuan, China. (GenBank no. MK405594). Amplicons of phenotype II included both sequence of above WTMV and ChiVMV, indicating co-infection of phenotype II (Fig. S1b). Phenotype I sample was used for mechanical inoculation on chilli pepper as described previously (Yang et al.2013). After ten days, virus-like symptoms similar to phenotype I were observed on leaves, and WTMV infection, but not ChiVMV infection, was confirmed by RT-PCR tests on inoculated pepper plants (Fig. S1 e, f). To further ascertain the incidence of these two viruses in the field, primers WT-F: 5'-GTTGTTGAATGTGGTTTAGTT-3' and WT-R: 5'-AGATGTGCTTTGGAAGCGACC-3' were designed based on the WTMV sequence (GenBank no. DQ851495) to amplify a 476 bp product, and primers Ch-F/Ch-R (Ch-F: 5'-AAAGAAGAACAAGCGACAGAA-3', Ch-R: 5'-CATCACGCAAATATTCAAAGC-3') were designed based on ChiVMV sequence (GenBank no. MK405594.1) to amplify a 332 bp product. RT-PCR was conducted on 31 field-collected samples, and amplicons of expected sizes, 476bp and 332bp, corresponding to WTMV and ChiVMV, respectively, were obtained and sequenced to verify their identity. The results (Fig. S2) showed that 71% (22/31) of the samples tested positive for WTMV, 90% (28/31) tested positive for ChiVMV, and 65% (20/31) were co-infected with the two viruses. The WTMV was first reported infecting wild tomatoes in Vietnam in 2008 (Ha et al. 2008), and later reported in China in Nicotiana tabacum (Sun et al. 2015), Solanum nigrum (Zhang et al. 2019), and wild eggplant (Zhang et al. 2014). To our knowledge, this is the first report of WTMV infection on chilli pepper under natural conditions. Our study revealed that the chilli pepper disease in Dehong was caused by single or co-infection of WTMV and ChiVMV. It is necessary to find effective methods to control these two viruses.

Chilli pepper (Capsicum annuum L.) is an economically important crop worldwide. However, numerous plant pathogens, including potyviruses, affect its production (Kenyon et al., 2014;Parisi et al., 2020).Potyviruses are aphid-transmitted plant viruses belonging to the genus Potyvirus. Potyvirus virion is a flexuous filamentous capsid with a length of 700-900 nm and a diameter of 11-13 nm. The potyvirus genome consists of a 9.7 Kb single-stranded RNA (ssRNA), two untranslated regions in 5'-UTR and 3'-UTR, and a single major open-reading

The present study reports observation of a field chilli pepper disease consisting of a co-infection with two potyviruses: Wild tomato mosaic virus Dehong isolate (WTMV-Dh) and Chili veinal mottle virus Dehong isolate (ChiVMV-Dh). We obtained the complete genome sequences of these two viruses by NGS sequencing. The WTMV-Dh is 9,598 nucleotides (nt) in length and encodes a complete polyprotein of 3,075 amino acids (aa). The polyprotein of WTMV-Dh shares 76.1–82.6% nt and 85.3–89.5% aa identities with the other three WTMV isolates reported previously. The ChiVMV-Dh is 9688 nt in length and encodes a complete polyprotein with 3, 089 aa. The polyprotein of ChiVMV-Dh shares 80.8–92.2% nt and 85.3–95.6% aa identities with the other ChiVMV isolates reported previously. Following phylogenetic analysis based on the polyprotein sequences of other potyviruses, WTMV-Dh clustered with the Vietnam strain WTMV-Laichau while ChiVMV-Dh clustered with several ChiVMV Sichuan isolates. Evaluation of the recombination events within the WTMV and ChiVMV subgroups indicated that some putative recombination events occurred in critical regions. These regions include the N-terminal of HC-Pro and P1 region of WTMV-Dh, CP and the P3 to CI region of ChiVMV-Dh, which may be new evidence of adaptive evolution of potyviruses.