Overwintering of Tomato Mosaic

Abstract

1. Tomato mosaic may be carried over winter in hothouse tomato crops, but this does not account for the great bulk of mosaic infection in the canning crop. 2. In a total of 22,944 tomato plants grown from seed from mosaic plants, no evidence of seed transmission of the disease was obtained. 3. The mosaic disease has been found occurring in the field on the following perennial weed relatives of the tomato in Indiana: Physalis subglabrata, P. virginiana, P. heterophylla, and Solanum carolinense. Mosaic has been transmitted to tomatoes from each of these species. 4. It has been proved that the mosaic virus persists over winter in the rootstocks of P. subglabrata. The young mosaic shoots appear in the spring before tomatoes are transplanted to the field. From these shoots the disease has been transmitted to tomatoes. 5. Physalis subglabrata, with some admixture of the very similar P. virginiana, is a very prevalent weed in Indiana tomato fields. 6. Examination of these weeds in fields previously in tomatoes shows that a considerable percentage of the Physalis plants come up showing mosaic the next year, and likewise the second year after the tomatoes. The disease persists among these weeds year after year, and such weeds serve as a perennial reservoir of mosaic infection for future tomato crops. 7. Mosaic has not been found to any extent occurring spontaneously in Physalis, and is present in the weeds only in and near fields once used for tomatoes. As more and more new fields are used for tomatoes, however, the reservoir of mosaic infection in the perennial weed flora will increase each year. 8. Evidence of spread of the disease to Physalis plants 200 to 400 feet from tomato fields has been adduced. 9. In a field survey Physalis was observed in 65 out of 81 tomato fields, and mosaic was noted on Physalis in 35 of these fields, and on both Physalis and tomatoes in 29 fields. Tomato mosaic was noted in 60 fields, and in 48 of these Physalis was found. 10. In many fields the tomato mosaic was undoubtedly of plant-bed origin. Mosaic was found on tomatoes in plant-beds. Physalis is often present in and near plant-beds. 11. Aphids and flea-beetles may play a part in the transmission of mosaic between Physalis and tomatoes. 12. Physalis heterophylla was found in 7 of the 81 tomato fields examined, and in 3 fields showed mosaic. 13. Solanum carolinense was found in 13 of the 81 tomato fields examined, and in one field showed mosaic. 14. The eradication of perennial Solanaceous weeds in and near tomato fields, and particularly the plant-beds early in the season, is recommended as a mosaic control measure.