Chlorotic dwarf (CD), the most important disease in the sweet potato-producing regions of Argentina, is caused by the synergistic combination of two aphid-transmitted potyviruses with a whitefly-transmitted crinivirus. Sweet potato feathery mottle virus, sweet potato mild speckling virus, and a crinivirus (serologically related to sweet potato chlorotic stunt virus) were associated with CD. The synergistic combination of these three viruses reproduced the disease.

Cassava is an important crop with great economic and social significance in many countries. Most of its biomass is usable: storage roots can be destined for industry or fresh consumption, leaves are a source of protein, vitamins, and minerals, and stems can be used as propagation material. Due to its vegetative propagation, cassava yield is greatly constrained by viral diseases. Cassava common mosaic virus (CsCMV), one of the most widely spread viruses in Latin America, is the only cassava‐infecting potexvirus able to cause disease in a single infection: cassava common mosaic disease (CCMD). Here, we evaluated the effect of an Argentinian strain of CsCMV on several agronomic traits. Field trials were established in north‐eastern Argentina for three successive cropping seasons, 2016/17, 2017/18, and 2018/19. CsCMV presence was confirmed by PCR or ELISA tests in mechanically inoculated cassava plants. The evaluated traits were plant height (PH), total fresh weight (TFW), shoot fresh weight (SFW), diameter and FW of tuberous root per plant (TRD and FWTR), FW of each individual tuberous root (FWiTR), length and number of tuberous roots (TRL and TRN), harvest index (HI), and estimated yield of tuberous root (EY) in both infected and noninfected plants. Significant yield losses were recorded in infected plants. The most affected traits were EY and FWTR (both showing 44.3% of losses), followed by TFW, SFW, TRN, and FWiTR (37.8%, 33.5%, 29.9%, and 24.8% of losses, respectively). These losses are extremely high for Argentina, where this crop provides food security and demand for the raw material is unsatisfied.

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454-pyrosequencing was applied as a tool to identify etiological agents involved in the symptoms observed in a sweet potato sample from Argentina. RNA was purified from symptomatic material and sequenced using a Roche 454 GS-FLX+. BLAST analysis of the viral reads identified the presence of Sweet potato feathery mottle virus (SPFMV)-O and SPFMV-RC strains and Sweet potato virus C (SPVC). For SPFMV-O and SPFMV-RC, 10 878 and 10 812 nucleotides, respectively, were sequenced, whereas a sequence of 10 793 nucleotides was obtained for SPVC. Pairwise comparison of polyprotein nucleotide sequences of O and RC Argentinian isolates (Arg) showed 99% and 98.4% sequence identities with SPFMV-O and SPFMV-RC-M2-41, respectively, whereas SPVC-Arg showed 94.2%, 92.9% and 94.6% sequence identities with SPVC-Il, SPVC-C1 and SPVCBungo, respectively. These results allowed us to develop a one-step multiplex reverse transcription-polymerase chain reaction assay (mRT-PCR) for the simultaneous detection and differentiation of SPFMV-O-Arg and SPFMV-RC-Arg and SPVC-Arg. Three specific forward primers unique to each virus and one reverse primer based on a region conserved in all three viruses were designed and used in the assay. These primers were further evaluated using field samples collected from four provinces of Argentina. The results showed that SPVC was the most common virus in samples analysed. This study shows the usefulness of deep sequencing not only to rapidly identify mixed infections between SPFMV-O and SPFMV-RC and SPVC, but also to develop a reliable mRT-PCR assay for detection of these sweet potato pathogens, which cannot be discriminated by serological techniques.

Sweet potato virus G belongs to the largest plant virus genus Potyvirus. This virus was detected for the first time in Argentina and then sequenced using the method of next-generation pyrosequencing. The complete genome was found to be 10,798 nucleotides excluding the poly-A tail with a predicted genome organization typical for a member of the genus Potyvirus. This is the first report of the complete genomic sequence of a SPVG isolated from South America.

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Sweet potato (Ipomoea batatas (L.) Lam) is one of the most important crops worldwide. Recently, the appearance of severe viral symptoms has been observed in sweet potato crops in the pampas region of Argentina and both begomovirus and crinivirus, exclusively transmitted by whiteflies, have been identified. The aim of this study was to identify B. tabaci species from sweet potato crops in Colonia Caroya by analysing mitochondrial cytochrome c oxidase subunit I (mtCOI) sequences. Two previously described haplotypes were identified: New World2 (indigenous species) and MEAM1 (introduced species). The results indicate the presence of both species, which are potential vectors of begomovirus and crinivirus in Argentina.