Viruses are associated with buffalo grass yellowing in Australia

Abstract

Stenotaphrum secundatum (Buffalo grass or St Augustinegrass) is a hardwearing and vigorous warm season turfgrass popular in many countries including the USA and Australia. In Australia, buffalo grass ranks first in importance based on farmgate value. Buffalo grass yellowing is an emerging disease syndrome that affects both the appearance and vigour of the turf. We tested the hypothesis that buffalo grass yellowing is caused by one or more viruses. We surveyed turf farms in NSW, QLD and WA and found sugarcane mosaic virus (SCMV) to be widespread, while panicum mosaic virus (PMV) was only detected in cultivar Palmetto and a new cultivar recently imported from the USA. Satellite panicum mosaic virus was not associated with these PMV isolates. Network analyses of the coat protein gene indicated that there are two strains of SCMV on buffalo grass in Australia, one matching that found in panicoid grasses in Florida and the second on Digitaria didactyla (blue couch) in Queensland. The Australian PMV isolates from buffalo grass have only 86% nucleotide identity across the entire genome sequence to the exemplar isolate from pearl millet in Kansas, confirming that it is a very distinct strain. A new virus named Stenotaphrum nepovirus was also identified by high-throughput sequencing and it was common in all regions and cultivars but symptoms of infection were not obvious. We conclude that SCMV is a major cause of the buffalo grass yellowing disease syndrome.