The incidence and phylogenetic analysis of viruses infecting New Zealand's native grasses

Abstract

Grasses form the basis for the meat, dairy, wool and deer industries, which contribute to nearly 50% of New Zealand exports, and are also an important component of natural ecosystems. Worldwide >100 plant viruses infect grass species and even mild and symptomless infections can adversely effect plant populations through reduced reproductive rates and greater susceptibility to environmental extremes. The only previously published study on viruses in New Zealand’s natural grasslands found that cereal viruses have invaded the native grass flora of the South Island. This research provided an extensive survey of New Zealand native grasses, showing that barley yellow dwarf virus diseases (BYDV, Luteoviridae) and Cocksfoot mottle virus (CoMV, Sobemovirus) are widespread in the North and South islands of New Zealand. Significant findings include seven new virus hosts amongst the New Zealand native flora, the first report of BYDV-PAS in New Zealand, detection in Hierochloe redolens of a novel virus in the Luteoviridae family (proposed name BYDV-To), and in Festuca novae-zelandiae a novel dsRNA virus possibly belonging to the Partitiviridae family. New virus host reports in New Zealand include CoMV in Poa anceps, P. cita, F. novae-zelandiae, and Chionochloa rubra; BYDV-PAV and BYDV-PAS in Microlaena stipoides and Dichelacne crinita; BYDV-MAV in P. cita, F. novae-zelandiae and H. redolens; and CYDV-RPV in P. cita and M. stipoides. Molecular techniques for virus detection and identification were developed or improved during this study. Phylogenetic analyses of viral coat protein sequences from native and exotic grass species indicate either frequent or recent virus movement into native ecosystems, and multiple virus introduction events in New Zealand. The likely origins of the virus species are discussed. Two CoMV variants were identified, one of which caused severe necrosis in susceptible cocksfoot cultivars. Reciprocal aphid transmission of BYDV-PAV using cereals and native grasses showed that although transmission to natives was low, the efficiency of transmission from natives to cereals was comparable to that between cereal species, suggesting virus adaptation to the cereal host species. The findings from this study are discussed in respect to disease management and bio-security in New Zealand, and recommendations are made for future research.