Seedlings of Nicotiana species of Australian and American origin were tested for resistance to an Australian strain of P. tabacina. American species were less resistant than Australian species and differences in 12 results of similar tests in both countries could have been due to differences in the pathogen or in the seed lines tested. The data suggest that the pathogen would have difficult in surviving on the highly resistant Australian species of Nicotiana in their natural arid habitat. Field observations have shown that survival occurs on the introduced susceptible species N. tabacum and N. glauca.