Barley yellow dwarf virus in relation to the breeding and assessment of herbage grasses for yield and uniformity

Abstract

Ryegrass plants (Lolium spp.) rarely developed obvious foliar symptoms when infected with barley yellow dwarf virus, but their yield was often substantially reduced. Perhaps of even greater importance, the virus modified their morphological development and seasonal growth rhythm. Consequently, the disease introduces considerable non-heritable variation into populations of grass plants so its possible presence may introduce difficulties into selecting varietal mother plants for specific growth characteristics and when assessing bred varieties for uniformity. Virus infection caused the greatest deviation in growth morphology and the smallest reduction in yield in early-flowering hay type varieties: the converse was true of late-flowering pasture type varieties. Unless a source of immunity or extreme resistance to the virus can be found therefore, it may be difficult to combine minimum deviation in growth morphology and minimum yield loss in a single variety.