Possible Nonpathogenic Origin of Hydrangea. Distortion

Abstract

Florists’ hydrangea, Hydrangea macrophylla subsp. macrophylla var. macrophylla (Thunb.) Ser., is susceptible to a foliar malformation that appears during high day temperature (>30C) per iods of summer production. This condition previously has been termed hydrangea distortion (Weiler and Lopes, 1974). Affected plants produce thickened laminae that are sometimes mottled and reduced in width (Fig. 1). The plant apex becomes irregularly shortened, distorted apices often produce abnormal inflorescences, and many of the affected plants do not flower. In many respects, the symptoms of hydrangea distortion are similar to symptoms expressed by plants infected with a virus. Hydrangeas are known to be susceptible to nine viruses: alfalfa mosaic, cucumber mosaic, hydrangea ringspot, tobacco necrosis, tobacco rattle, tobacco ringspot, tomato ringspot, and tomato spotted wilt virus. A mycoplasma-like organism (MLO) also has been identified within hydrangeas (Kleinhempel et al., 1972; Lawson and Smith, 1980). The etiology of hydrangea distortion has not been described, and we therefore examined the possibility of a viral or MLO origin of this problem. Virus indicator plant species (Catharanthus roseus ‘Dwarf Bright Eyes’, Chenopodium amaranticolor, Chenopodium quinoa, Cucumis sativus, Gomphrena globosa ‘Buddy Purple’, Lycopersicon esculentum ‘Rutgers’, Nicotiana clevelandii, Nicotiana glutinosa, Nicotiana tabacum ‘Samsun NN’, Phaseolus vulgaris ‘Bountiful’, and Vigna sinensis ‘Early Ramshorn’) were inoculated with sap from distorted foliage of H. macrophylla ‘Rose Supreme’ or ‘Merritt’s Supreme’. Inoculum was prepared by grinding distorted leaves in