Further studies of green petal and other leafhopper‐transmitted viruses infecting strawberry and clover

Abstract

SUMMARYStrawberry green petal, clover witches' broom, stolbur and Delphinium yellows viruses were distinguished from one another and from aster yellows, tomato big bud (lucerne witches' broom) and cranberry false blossom viruses by vector species, host range, host symptoms and reactions to heat in vivo. Euscelis plebejus (Fall.) leafhoppers transmitted green petal virus from, but not to, strawberry plants. Aphrodes bicinctus (Schrank) was an efficient vector and is probably chiefly responsible for green petal disease in strawberry crops.Green petal virus did not protect clover plants from the effects of witches' broom virus, but the latter seemed to interfere with the transmission of green petal virus by E. plebejus. The witches' broom virus also retarded the development of E. plebejus vectors and apparently reduced their longevity. This virus was not transmitted by A. bicinctus.Strawberry plants did not become infected with stolbur virus, but did with Delphinium yellows virus, which caused a bronze‐leaf‐wilt syndrome indistinguishable from that caused by clover witches' broom virus. Stolbur and Delphinium yellows viruses both killed clover; stolbur was occasionally transmitted by E. plebejus and frequently by A. bicinctus, neither of which transmitted Delphinium yellows. Cuscuta campestris Yunck. transferred Delphinium yellows virus from Vinca rosea L. to strawberry and V. Yosea but not to clover or aster; only a single white clover plant was infected by Macrosteles sexnotatus (Fall.). Delphinium yellows virus was inactivated in V. Yosea plants kept at 42°C. for 3 weeks, whereas green petal virus was not, although virus‐free cuttings were propagated from heat‐treated plants.