Etiology of Ageratum Yellow Vein Diseases in South China.

Ageratum conyzoides is a common weed in agricultural regions in Asia. A. conyzoides plants exhibiting yellow vein symptoms were collected from Yunnan and Guangxi provinces of China. Polymerase chain reaction detection and sequence analysis showed that samples collected from Yunnan were mainly infected by Tobacco curly shoot virus (TbCSV) associated with Ageratum yellow vein China betasatellite (AYVCNB), while samples from Guangxi were mostly infected by Papaya leaf curl China virus (PaLCuCNV) and AYVCNB, or by Ageratum yellow vein China virus (AYVCNV) and AYVCNB, with a few exhibiting dual infections by PaLCuCNV, AYVCNV, and AYVCNB. Agrobacterium-mediated inoculation of infectious clones showed that both TbCSV and AYVCNB or PaLCuCNV and AYVCNB produced typical yellow vein symptoms in A. conyzoides. Consequently, Ageratum yellow vein diseases in Yunnan and Guangxi provinces were caused by TbCSV/AYVCNB, PaLCuCNV/AYVCNB, or AYVCNV/ AYVCNB. The implications of these results in relation to the prevalence of begomoviruses in cultivated plants are discussed.