| Sumario: | Peach-associated luteovirus (PaLV) belongs to the genus Luteovirus,
family Tombusviridae. To date, PaLV has only been reported in peach
(Prunus persica) and its presence detected in the Republic of Georgia (Wu
et al. 2017), China (Zhou et al. 2018), and a range of European countries
(Khalili et al. 2023). PaLV-infected peach plants have been reported to show
pitting of the fruit surface (Sorrentino et al. 2018) or leaf yellowing
and mosaic (Zhou et al. 2018). However, the association between PaLV
and symptoms in peach remains very doubtful (Khalili et al. 2023). In
October 2021, a plot of almond trees (cv. Lauranne) located in Valencia,
Spain, was surveyed because of an outbreak of almond foamy canker, a
syndrome of unknown etiology characterized by the presence of foam on the
main trunk that leads to sudden tree death. Foliar and subcortical trunk tissue
collected from both a symptomatic (IVIA_12111S) and an asymptomatic
(IVIA_12111A) tree was analyzed by high-throughput sequencing. Total RNA
extracted from each sample was individually sequenced using TruSeq
Ribo-Zero Illumina technology on a Novaseq 6000 platform. Bioinformatic
analysis (CLC Genomics Workbench version 10.1.1) generated 9,175 and
5,039 de novo contigs, respectively. Interestingly, BLASTX analysis of the
asymptomatic plant dataset revealed a contig of 5,820 nt (covered by 5,297 out
of 1,251,368 reads), representing a near complete PaLV genome. The sequence
of this isolate PaLV-12111A (GenBank accession no. PQ660174) shares highest nucleotide (nt) identity (97.1%) with a peach isolate from Spain
(IVIM18, KY635989.1). The presence of PaLV in this almond tree was
confirmed by RT-PCR using PaLV-specific primers (Sorrentino et al. 2018)
followed by amplicon Sanger sequencing. Moreover, the RT-PCR analysis of
27 additional trees from the same plot showed the presence of two additional
PaLV-infected almonds, which were also asymptomatic. These results identify
almond as a new natural host of PaLV, which confirms the otherwise unpublished
existence in GenBank of a PaLV genomic sequence from Iran
reportedly from almond (ON192959). In order to further confirm the presence
of PaLV in almond, two publicly available Sequence Read Archives independently
generated in Spain but also involving the Lauranne variety
(ERR8601621 and ERR8601618) were datamined, allowing the recovery of two
additional near-complete PaLV genomes sharing 99.68% nt identity and
showing 95.6% nt identity with PaLV-12111A. The phylogenetic analysis of
available PaLV genomes revealed that both almond and peach Spanish
PaLV isolates grouped together in a cluster genetically distant from the
Iranian almond isolate. These results suggest phylogenetic relationships
associated with geography rather than host adaptation. Interestingly, the
presence of PaLV in Spain was observed in almond cultivars grafted onto
almond/peach hybrid rootstocks (GF677 and Garnem), which might account
for the presence of PaLV in this crop. To our knowledge, this is the first
confirmed report of almond as a natural PaLV host. The finding of PaLV in
trees that did not show almond foamy canker symptoms rules out its involvement
in this syndrome of unknown etiology and further contributes to a
growing list of reports of asymptomatic PaLV infections in Prunus. Additional
studies are however needed to evaluate the biological and agronomical significance
of these findings and unambiguously establish whether PaLV should
be a cause of concern or not.
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