Molecular Identification Of Geminiviruses Infecting Weeds In Hainan And Viral Pathogenicity

Geminiviruses have caused severe diseases in several economically important crops. In China, several begomoviruses have been reported infecting some crops in Yunnan, Guangxi and Guangdong provinces. In an attempt to provide a better understanding of the species, distribution and spread of begomoviruses in China, begomoviruses collected from weeds in Hainan province were identified with molecular technique, and their pathogenicity was studied in this dissertation..Three viral isolates Hn8, Hn40 and Hn41 were obtained from Sida acuta showing yellow mosaic symptom in Danzhou, Hainan province. Comparison of partial sequences confirmed the existence of single type of begomovirus. The complete nucleotide sequence of the DNA-A-like molecule of Hn8 was determined to be 2749 nucleotides. Hn8 DNA-A had the highest sequence identity (78%) with that of Ageratum yellow vein China virus (AJ558120), and had less sequence identity with other begomoviruses. Hn8 was thus considered as a new Begomovirus species, for which the name Sida yellow mosaic China virus (SiYMCNV) is proposed. Satellite DNAβ molecules (Hn8β, Hn40β and Hn41β) were found to be associated with Hn8, Hn40 and Hn41 and their complete nucleotide sequences were determined. Sequence analysis demonstrated that they had 1346, 1341 and 1346 nucleotides (AJ810093-95), respectively, and shared more than 84% nucleotide sequence identity each other. They were different from other characterized DNAβ, sharing the highest nucleotide sequence identity (47.8%) with DNAβ of Ageratum yellow vein virus (AYVV).Begomoviruses samples were collected from Stachytarpheta jamaicensis plants showing leaf curl symptom in Haikou, Hainan province. The complete sequences of isolates Hn30 and Hn34 were determined. Both of them have highest sequence identities (above 93%) with two isolates (Hn5-4, Hn6-1) of Stachytarpheta leaf curl virus (StaLCV). The above molecular data show that Hn30 and Hn34 are isolates of StaLCV. PCR and Southern blot analyses demonstrate that all the collected field samples are not associated with DNAβ or DNA-B components. Infectious clone of StaLCV isolate Hn5-4 DNA-A was constructed and its infectivity was tested. Hn5-4 DNA-A alone could efficiently infect host plants and induced typical begomoviral symptoms. The interaction between Hn5-4...