Prevalence, host range, and characterization of multiple Palo verde broom emaravirus genomes and eriophyid mites from Parkinsonia spp. in Arizona

The palo verde tree is native to the Sonoran Desert and consists of multiple species classified in the genus Parkinsonia, family, Fabaceae. Palo verde broom virus (PVBV), Fimoviridae, Emaravirus, is the suspect causal agent of witches' broom disease of blue palo verde, P. florida. Here, PVBV was detected in four palo verde species and two hybrids by reverse transcription polymerase chain reaction (RT-PCR) amplification of a 679-base pair (bp) fragment of RNA3, which encodes the nucleocapsid gene (NP). The prevalence of witches' broom symptoms among the different Parkinsonia species (n = 70), collected from naturally-occurring, nursery- or urban landscape trees was 54 %. Within-species PVBV infection spanned 50-100 % and 81 % across four species and two hybrids combined. The PVBV genome segments RNAs 1-5 were de novo and reference based-assembled from Illumina® RNAseq reads obtained from total RNA isolated from PVBV-positive trees. Pairwise nucleotide identity and amino acid identity for 29 field isolates and GenBank reference PVBV RNA1-5 segments/predicted proteins was 73-100 % and 68-100 %, respectively. Phylogenetic analysis of concatenated RNA1-5 segments resolved four sister clades with no basis in host range among the four palo verde species or hybrids. Five predicted recombinants were identified with breakpoints in either tfhe RNA1 or RNA5 genomic segment. Consistent recovery of PVBV full-length genomes from four Parkinsonia spp. and two hybrids indicated that additional Parkinsonia species and hybrids besides blue palo verde, the only previously reported host, harbored PVBV. Previous studies have linked emaravirus transmission with Eriophyidae mite vectors. Here, the palo verde mite Aculus cercidii Keifer (Eriophyidae) (1965) counts ranged from eight to >1000 per tree. Prolific or minimally-detectable colonization of PVBV-infected trees by A. cercidii, together with consistent detection of PVBV in symptomatic and asymptomatic trees implicate the palo verde mite as the vector of and PVBV as the causal agent of witches' broom disease.