The severe strain of Beet curly top virus (BCTV-svr) and Beet curly top Iran virus (BCTIV) are known as the causal agents of curly top disease in beet and several other dicotyledonous plants. Seed transmission of BCTV-svr and BCTIV in Petunia (Petunia X hybrida) and Dianthus barbatus, two ornamental hosts of these viruses, have been already reported. To investigate the seed transmission rate of these viruses in petunia, symptomatic petunia plants showing yellowing and leaf deformation were collected from green areas in Shiraz. DNA was extracted from leaves of the plants and subjected to PCR using specific primers of each virus to detect the viruses. The infection rate of the collected plants was determined. Seeds produced from infected plants were harvested and cultivated for two generations. The presence of viruses in seedlings developed from seeds of the infected plants were tested at 6 to 8 leaf stage by PCR using specific primers of each virus and infection rate of seedlings in the first and second generations was investigated. The infection rates of BCTV-Svr and BCTIV in infected plants collected from Shiraz street sides (23 plants) were determined to be 52.85% and 32.85%, respectively. The infection rates 45 seedlings developed from seeds of the infected plants were 47 and 40% in the first generatin, and 40 and 33% in the second generation for BCTV-Svr and BCTIV, respectively. The results of this study indicated that BCTV-Svr infected the petunia plants and their developed seeds in Shiraz street sides with a higher rate than that of BCTIV. In another experiment, 20 petunia seedlings were inoculated separately with the infectious clone of either virus by agroinoculation. Three weeks after inoculation, the infection rate was assessed in four growth stages. Seeds produced by infected plants were collected and seed infection rates of seedlings developed from the seeds were determined in the next generation. The infection rate of BCTIV inoculated seedlings at each 6-8 leaf stage, before flowering stage and after flowering stage was 94% and at seed production stage was 100%. Seedling infection rate with BCTIV in the next generation was determined to be 76% at 4-6 leaf stage. The infection rate of BCTV-Svr inoculated seedlings at 6-8 leaf stage was 72%, at pre- and post-flowering stages was 83% and reached to 100% at seed production stage. The infection rate of seedlings developed from the seeds of infected plants (first generation) was determined to be 83% at 4-6 leaf stage.This study shows That curlytop viruses are transmitted through seeds of petunia and probably some other plants to high rate.