Abstract：Potato late blight, ranks as world agriculture's most destructive disease, which are caused by Phytophthora infestans (Mont.) de Bary, and potato production has been seriously limited by this disease. Research on molecular mechanism of resistance against P. infestans is a very important issue in potato breeding program. To date, many ESTs involved in potato late blight resistance have been isolated by the molecular biology methods such as suppression subtractive hybridization, DNA microarray and cDNA-AFLP. To screen and analysis of key candidate genes of potato against P. infestans, functional studies of these ESTs are the most urgent thing. In the present study, two potato ESTs EL732276 and EL732318 which involved in late blight resistance were silenced in Nicotiana benthamiana using virus-induced gene silencing(VIGS). The gene silenced N.benthamiana leaves were inoculated with P. infestans and length grow rate (LGR) of lesions were measured. The RT-PCR results showed that the fragments of candidate genes EL732276 and EL732318 have been successfully cloned into Tobacco rattle virus (TRV) vector. The N.benthamiana leaves infected with TRV carrying the phytoene desaturase gene(PDS) were bleached, indicating that the VIGS system was successful. One month late, the N.benthamiana leaves infected with TRV carrying the genes EL732276 and EL732318 fragment individually were inoculated with P. infestans. The results showed that, compared to the control, LGR values were significantly increased in the EL7322276 and EL732318 silenced N.benthamiana plants, suggesting that P. infestans resistance was dramatically decreased after these two genes silenced in N.benthamiana. This founding was consistent with the results that water soaked lesions and white mycelium obviously observed on EL732276 or EL732318 silenced N.benthamiana leaves after P. infestans inoculation, whereas the lesions developed very slowly on the control leaves which infected with TRV empty vector. The results suggest that functions of potato genes involved in late blight resistance can be rapidly confirmed in N.benthamiana by VIGS technique
