Potato virus Y (PVY) Isolates from Physalis peruviana are Unable to Systemically Infect Potato or Pepper and Form a Distinct New Lineage Within the PVYC Strain Group

Diversity of the Rysto gene conferring resistance to potato virus Y in wild relatives of potato

BACKGROUND

Potato virus Y (PVY) is among the economically most damaging viral pathogen in production of potato (Solanum tuberosum) worldwide. The gene Rysto derived from the wild potato relative Solanum stoloniferum confers extreme resistance to PVY.

RESULTS

The presence and diversity of Rysto were investigated in wild relatives of potato (298 genotypes representing 29 accessions of 26 tuber-bearing Solanum species) using PacBio amplicon sequencing. A total of 55 unique Rysto-like sequences were identified in 72 genotypes representing 12 accessions of 10 Solanum species and six resistant controls (potato cultivars Alicja, Bzura, Hinga, Nimfy, White Lady and breeding line PW363). The 55 Rysto-like sequences showed 89.87 to 99.98% nucleotide identity to the Rysto reference gene, and these encoded in total 45 unique protein sequences. While Rysto-like26 identified in Alicja, Bzura, White Lady and Rysto-like16 in PW363 encode a protein identical to the Rysto reference, the remaining 44 predicted Rysto-like proteins were 65.93 to 99.92% identical to the reference. Higher levels of diversity of the Rysto-like sequences were found in the wild relatives of potato than in the resistant control cultivars. The TIR and NB-ARC domains were the most conserved within the Rysto-like proteins, while the LRR and C-JID domains were more variable. Several Solanum species, including S. antipoviczii and S. hougasii, showed resistance to PVY. This study demonstrated Hyoscyamus niger, a Solanaceae species distantly related to Solanum, as a host of PVY.

CONCLUSIONS

The new Rysto-like variants and the identified PVY resistant potato genotypes are potential resistance sources against PVY in potato breeding. Identification of H. niger as a host for PVY is important for cultivation of this plant, studies on the PVY management, its ecology, and migrations. The amplicon sequencing based on PacBio SMRT and the following data analysis pipeline described in our work may be applied to obtain the nucleotide sequences and analyze any full-length genes from any, even polyploid, organisms.

Two new withanolides from the whole plants of Physalis peruviana

Two new withaphysalin-type withanolides (18-O-ethylwithaphysalin R and 5-O-ethylphysaminimin C, 1 and 2), along with twelve known withanolides (3-14), were purified and identified from Physalis peruviana L. The chemical structures of these new isolates were elucidated through analyzing spectroscopic and HRESIMS data. All the obtained metabolites were appraised for their potential antiproliferative activity against the human breast cancer cell line MCF-7. Compound 7 was discovered to exhibit potent activity with an IC₅₀ value of 3.51 µM and compounds 2, 6 and 14 showed weak cytotoxic effect.

Prevalence of Recombinant Strains of Potato Virus Y in Seed Potato Planted in Idaho and Washington States Between 2011 and 2021

Potato virus Y (PVY) has emerged as the main reason for potato seed lot rejections, seriously affecting seed potato production in the United States throughout the past 20 years. The dynamics of PVY strain abundance and composition in various potato growing areas of the United States has not been well documented or understood up to now. The objective of this study was to find out the prevalence of PVY strains in potato fields in the Pacific Northwest (PNW), including seed potato production systems in the State of Idaho and commercial potato fields in the Columbia Basin of Washington State between 2011 and 2021. Based on the testing of >10,000 foliar samples during Idaho seed certification winter grow-out evaluations of seed potato lots and seed lot trials in Washington State, a dramatic shift in the PVY strain composition was revealed in the PNW between 2011 and 2016. During this time period, the prevalence of the ordinary, PVY^O strain in seed potato dropped 8- to 10-fold, concomitantly with the rise of recombinant strains PVY^N-Wi and PVY^NTNa, which together accounted for 98% of all PVY positives by 2021. In Idaho seed potato, PVY^NTNa strain associated with the potato tuber necrotic ringspot disease (PTNRD) was found to increase threefold between 2011 and 2019, accounting for 24% of all PVY positives in 2019. Mild foliar symptoms induced by recombinant PVY strains may be partially responsible for the proliferation of PVY^N-Wi and PVY^NTNa in potato crops. A spike of another PTNRD-associated recombinant, PVY-NE11, was recorded in the PNW between 2012 and 2016, but after reaching a 7 to 10% level in 2012 to 2013 this recombinant disappeared from the PNW potato by 2019. Whole genome sequence analysis of the PVY-NE11 suggested this recombinant was introduced in the United States at least three times. The data on PVY strain abundance in the PNW potato crops suggest that virus management strategies must consider the current dominance of the two recombinant PVY strains, PVY^N-Wi and PVY^NTNa.

Potato Virus Y Biological Strain Group YD: Hypersensitive Resistance Genes Elicited and Phylogenetic Placement

Potato virus Y (PVY) disrupts healthy seed potato production and causes tuber yield and quality losses globally. Its subdivisions consist of strain groups defined by potato hypersensitive resistance (HR) genes and whether necrosis occurs in tobacco, and phylogroups defined by sequencing. When PVY isolate PP was inoculated to potato cultivar differentials with HR genes, the HR phenotype pattern obtained resembled that caused by strain group PVYD isolate KIP1. A complete genome of isolate PP was obtained by high-throughput sequencing. After removal of its short terminal recombinant segment, it was subjected to phylogenetic analysis together with 30 complete nonrecombinant PVY genomes. It fitted within the same minor phylogroup PVYO3 subclade as KIP1. Putative HR gene Nd was proposed previously to explain the unique HR phenotype pattern that developed when differential cultivars were inoculated with PVYD. However, an alternative explanation was that PVYD elicits HR with HR genes Nc and Ny instead. To establish which gene(s) it elicits, isolates KIP1 and PP were inoculated to F1 potato seedlings from (i) crossing 'Kipfler' and 'White Rose' with 'Ruby Lou' and (ii) self-pollinated 'Desiree' and 'Ruby Lou', where 'Kipfler' is susceptible (S) but 'White Rose', 'Desiree', and 'Ruby Lou' develop HR. With both isolates, the HR:S segregation ratios obtained fitted 5:1 for 'Kipfler' × 'Ruby Lou', 11:1 for 'White Rose' × 'Ruby Lou', and 3:1 for 'Desiree'. Those for 'Ruby Lou' were 68:1 (isolate PP) and 52:0 (isolate KIP1). Because potato is tetraploid, these ratios suggest PVYD elicits HR with Ny from 'Ruby Lou' (duplex condition) and 'Desiree' (simplex condition) and Nc from 'White Rose' (simplex condition) but provide no evidence that Nd exists. Therefore, our differential cultivar inoculations and inheritance studies highlight that PVYD isolates elicit an HR phenotype in potato cultivars with either of two HR genes Nc or Ny, so putative gene Nd can be discounted. Moreover, phylogenetic analysis placed isolate PP within the same minor phylogroup PVYO3 subclade as KIP1, which constitutes the most basal divergence within overall major phylogroup PVYO.

Potato Virus Y (PVY) Isolates from Solanum betaceum Represent Three Novel Recombinants Within the PVYN Strain Group and Are Unable to Systemically Spread in Potato

Tamarillo, or tree tomato (Solanum betaceum), is a perennial small tree or shrub species cultivated in subtropical areas for fresh fruit and juice production. In Ecuador, tamarillo orchards are affected by several viruses, with one previously identified as potato virus Y (PVY); however, the specific strain composition of PVY in tamarillo was not determined. In 2015 and 2016, eight tamarillo plants exhibiting symptoms of leaf drop, mosaic, and mottled fruit were sampled near Tumbaco and Quito, Ecuador. These tamarillo PVY isolates were able to systemically infect tobacco, Nicotiana benthamiana, naranjilla, and tamarillo. Seven of the eight PVY isolates from tamarillo exhibited N-serotype, while one of the PVY isolates studied, Tam15, had no identifiable serotype. One isolate, Tam17, had N-serotype but produced asymptomatic systemic infection in tobacco. In tamarillo, four tamarillo isolates induced mosaic and slight growth retardation and were unable to systemically infect pepper or potato. Tamarillo, on the other hand, was unable to support systemic infection of PVY isolates belonging to the PVY^O and PVY^Eu-N strains. The whole genomes of eight PVY isolates were sequenced from a series of overlapping RT-PCR fragments. Phylogenetically, tamarillo PVY isolates were found to belong to the large PVY^N lineage, in a new tamarillo clade. Recombination analysis revealed that these tamarillo PVY isolates represent at least three novel recombinant types not reported before. The combination of the biological and molecular properties found in these eight PVY isolates suggested the existence of a new tamarillo strain of PVY that may have coevolved with S. betaceum.

Genetic Diversity of Nine Non-Recombinant Potato virus Y Isolates From Three Biological Strain Groups: Historical and Geographical Insights

Potato virus Y (PVY) isolates from potato currently exist as a complex of six biologically defined strain groups all containing nonrecombinant isolates and at least 14 recombinant minor phylogroups. Recent studies on eight historical UK potato PVY isolates preserved since 1984 found only nonrecombinants. Here, four of five PVY isolates from cultivated potato or wild Solanum spp. collected recently in Australia, Mexico, and the U.S.A. were typed by inoculation to tobacco plants and/or serological testing using monoclonal antibodies. Next, these five modern isolates and four additional historical UK isolates belonging to biological strain groups PVY^C, PVY^Z, or PVY^N obtained from cultivated potato in 1943 to 1984 were sequenced. None of the nine complete PVY genomes obtained were recombinants. Phylogenetic analysis revealed that the four historical UK isolates were in minor phylogroups PVY^C1 (Y^C-R), PVY^O-O (Y^Z-CM1), PVY^NA-N (Y^N-M), or PVY^Eu-N (Y^N-RM), Australian isolate Y^O-BL2 was in minor phylogroup PVY^O-O5, and both Mexican isolate Y^N-Mex43 and U.S.A. isolates Y^N-MT12_Oth288, Y^N-MT12_Oth295, and Y^N-WWAA150131G42 were in minor phylogroup PVY^Eu-N. When combined, these new findings and those from the eight historical UK isolates sequenced earlier provide important historical insights concerning the diversity of early PVY populations in Europe and the appearance of recombinants in that part of the world. They and four recent Australian isolates sequenced earlier also provide geographical insights about the geographical distribution and diversity of PVY populations in Australia and North America.