Effect Of Co-infection On The Pathogenicity And Transmission Of Geminiviruses

Geminivirus is one of the most serious pathogens that threaten the agriculture production worldwide.Tomato yellow leaf curl virus(TYLCV),tomato yellow leaf curl China virus(TYLCCNV)and papaya leaf curl China virus(PaLCuCNV)all belong to the genus Begomviruses,family Geminiviridae and are transmitted by whitefly Bemisia tabaci cryptic species complex(Hemiptera: Aleyrodidae)in a circulative persistent manner.TYLCV is distributed all over the world and has erupted in more than 20 provinces in China,seriously threatening agricultural production and food safety.TYLCCNV was discovered and identified in Guangxi,China in the 1990 s,and is currently distributed in western and southwestern regions of China,such as Guangxi,Yunnan,Xinjiang,and Sichuan.PaLCuCNV was first discovered on papaya in Guangxi province in 2002 and is currently distributed in Sichuan,Yunnan,Henan and other regions.With the spread of Bemisia tabaci,the distribution of geminiviruses has gradually expanded,and co-infections often occur in the field.In this thesis,we studied the effect of geminivirus co-infection on their infectivity,whitefly-plant interaction and whitefly transmission efficiency.The following results were obtained:(1)The co-infection of TYLCV and TYLCCNV aggravates the viral symptoms of tobacco,advances the disease time and increase the accumulation of the two viruses.Observation of symptoms showed that the fresh weight of the co-infected tobacco was 74.5% lower than that of uninfected tobacco,16.2% lower than that of TYLCV-infected tobacco,and 12.0% lower than that of TYLCCNV-infected tobacco;Moreover,after 10 days of inoculation,70% of TYLCV and TYLCCNV co-infected tobacco showed new leaf curling,while 47% TYLCCNV-infected tobacco and 0.7% TYLCV-infected tobacco showed the same symptom.After 30 days of inoculation,the accumulation of TYLCV and TYLCCNV was significantly increased in co-infected tobacco than that of single-infected.Those results suggest that TYLCV and TYLCCNV have synergistic effects in tobacco.(2)The co-infection of TYLCV and TYLCCNV improves the performance and preference of whitefly,but there is no significant difference of the increased level between co-infection and single infection.Compared with uninfected tobacco,the survival rate and fertility of whitefly on co-infected tobacco are increased,but there is no significant difference from TYLCV/TYLCCNV single infected tobacco.Like virus single infection,TYLCV and TYLCCNV co-infection also can suppress the gene expression level of jasmonic acid pathway to suppress the defense response of host plant.Olfactory response experiment showed that whitefly prefers to feed on virusinfected tobacco compared to uninfected tobacco.Whiteflies have no preference to plants with TYLCV and TYLCCNV co-infection compared to plants with single virus infection.(3)Whiteflies were infected by TYLCV,TYLCCNV or PaLCuCNV,both individually and as double,the results showed that whiteflies can acquire and transmit all combinations of these viruses simultaneously.Importantly,the relative virus quantity of acquisition and transmission rate are only mildly affected by co-infection.Moreover,co-infection did not affect the virion to cross the barriers of midgut and salivary gland within whiteflies.To sum up,this thesis preliminary studies the interaction of geminiviruses,and the effect of co-infection on whitefly-host plant interaction and transmission efficiency,suggesting geminiviruses co-infection cause greater economic losses in the field and provide information for disease epidemic prediction.