Prevalence and Diversity of Aphid-Vectored Yellow Dwarf Viruses in Oregon Perennial Grass Seed Crops

Abstract

Oregon produces 70% of the world’s cool-season grass seed, many species of which are susceptible to yellow dwarf viruses (YDVs). This virus complex has numerous defined virus species vectored by multiple aphid species. The diversity of YDVs associated with Oregon grass seed production has not been determined and is needed to provide insight to develop a risk prediction framework and improve management guidelines to mitigate disease severity. Commercial grass seed fields (n = 57) across the Willamette Valley and central and eastern Oregon were surveyed across 2021 and 2022 to determine the incidence and diversity of YDVs associated with crop species (perennial ryegrass, tall fescue, and Kentucky bluegrass) and the abundance and incidence of YDVs associated with aphid vectors. Virus incidence and diversity were determined using multiple previously-published endpoint reverse-transcriptase multiplexes specific for YDV genera and species. Across commercial grass seed crop hosts and growing seasons, 82% of fields had at least one plant sample detection of a luteovirus-type YDV, and 65% had at least one detection of a polerovirus-type YDV. Both perennial ryegrass and tall fescue crops hosted diverse YDV populations, especially apparent during the spring sampling season, when similarly diverse YDV communities were found associated with alate aphids. Only polerovirus-type YDVs were detected in Kentucky bluegrass, reflecting a highly variable landscape compared to Oregon’s western Willamette Valley. This study provides a current understanding of the spatial composition and diversity of the aphid-YDV virus-vector system in grasses grown for seed in Oregon.