VIRUSES AND VIRUS DISEASES IN DUTCH BULBOUS IRISES (IRIS-HOLLANDICA) IN THE NETHERLANDS

The occurrence in Dutch bulbous irises (Iris hollandica) of two viruses - iris mild mosaic virus (IMMV) and iris severe mosaic virus (ISMV) - in association with two diseases - mosaic (mozaïek) and grey (grijs) - was reported so far. In the Netherlands, three virus diseases have been distinguished: mild mosaic (mozaïek), mild yellow mosaic (bont), and severe mosaic (grijs). These diseases were associated with IMMV (750 nm), IMMV plus iris mild yellow mosaic virus (IMYMV, a newly recognized virus; 660 nm), and IMMV plus ISMV (750 nm), respectively. The viruses are antigenically distinct and their presence could be established serologically. Tobacco mosaic virus (TMV), tobacco rattle virus (TRV), and tobacco ringspot virus (TRSV) were also detected in irises, but not in association with particular symptoms. Generally, the symptoms of the diseases can be distinguished early in the growing season, particularly in March. Later on, the distinctive symptoms mostly disappear on plants showing mild symptoms but not on severely affected plants. Growing and forcing conditions influence the symptoms. The IMYMV and the ISMV transmitted in May and early in June by Macrosiphum euphorbiae cause more severe symptoms than those induced by transmissions late in June and in July. Problems related to disease control in irises are discussed. © 1979 Koninklijke Nederlandse Planteziektenkundige Vereniging.