Viruses of New Zealand pasture grasses and legumes: a review

Abstract

This article reviews knowledge of 23 plant viruses infecting pasture grasses and legumes in New Zealand. The incidence, ecology and impact of each virus and prospects for control using natural or artificial resistance genes or by vector control is discussed. The most prevalent viruses are Alfalfa mosaic virus and White clover mosaic virus in pasture legumes and Cocksfoot mottle virus, Ryegrass mosaic virus and Barley yellow dwarf virus in pasture grasses. Lucerne Australian latent virus is restricted to the North Island and Red clover necrotic mosaic virus is largely restricted to the South Island. These patterns are likely to be dynamic with ongoing changes in weather patterns, land use, the spread of insect vectors and the continuing introduction of viruses and vectors. The existing and potential threats to 12 pasture species are tabulated and the knowledge gaps for each species highlighted. Control of vectors including aphids, eriophyid mites and soil-borne fungi is probably not economic per se but could be an additional benefit of integrated pest management in pasture and cropping systems. The most cost-effective and practical preventative measures are likely to be the use of virus-tested seed to establish new pastures and the incorporation of resistance genes by conventional breeding or by genetic engineering. Finally, recommendations are made for future research for New Zealand, which is also relevant to other temperate regions of the world.