Understanding pasture performance: the interaction between perennial ryegrass and viruses

Abstract

In New Zealand livestock-based agriculture is an essential component of the economy, and at the very core of the majority of livestock-based farming systems in New Zealand is a pasture comprised of perennial ryegrass (Lolium perenne L.). Therefore, the productivity and profitability of livestock industries is inextricably linked to, and influenced by, the quality and performance of the underlying perennial ryegrass pasture. However, previous research indicates that ryegrass pastures in New Zealand could be infected with multiple viruses, and that the incidence or “load” of viruses within ryegrass pastures could potentially increase over time. Considering the significance of ryegrass to agricultural productivity, and current targets to increase the output of ryegrass pastures, these findings are concerning, as 1) multiple virus infections could have synergistic effects, in which the impact of one pathogen could potentially be exacerbated by the concurrent presence of other pathogens within a single host, and 2) increasing viral load or incidence within a pasture could potentially undermine the productivity and persistence of a ryegrass pasture over time. However, the extent to which multiple virus infections and/or increasing viral load undermines the persistence and productivity of perennial ryegrass is yet to be ascertained. Therefore, the purpose of this research is to elucidate the potential impact of multiple virus infections and increasing viral load upon the yield and persistence of ryegrass. To determine the impact of viral load and/or multiple viruses upon ryegrass, tillers obtained from 10-year-old and 1-year-old ryegrass were screened for multiple viruses, viral load was quantified, and the yield of old and new ryegrass was compared over time, to ascertain if there was or is potentially a link between viral load and ryegrass performance. The results of this project indicate 1) that multiple viruses are present within the ryegrass material examined, 2) that viral load is higher in 10-year-old ryegrass, and 3) 10-year-old old ryegrass produced less biomass (4-29%) than young ryegrass. Overall, the results of this research demonstrate that there is a potential correlation or link between increasing and/or high viral load and yield deficit in old ryegrass.