AbstractMechanical inoculation of seedlings of 26 tomato cultivars with an attenuated strain of tomato aspermy virus (TAV‐M, ATCC # PV361) resulted in development of only mild symptoms, which had largely disappeared by the time the infected plants had begun to set fruit. Yield trials revealed that plants inoculated with TAV‐M when transplanted at the 6–8 leaf stage displayed no delay in fruit set and had yields only slightly less than uninoculated plants. Cross protection studies carried out in the greenhouse revealed that TAV‐M has the potential to interfere with infection of tomato seedlings by a more severe TAV strain (ATCC # PV127). ‘Pik‐Red’ seedlings inoculated with TAV‐M showed a significant reduction in symptom expression when challenged with the Blencowe strain of TAV 21 days after the initial inoculation with TAV‐M; interference was incomplete