Disease development and changes in the natural Pseudomonas syringae pv. tomato populations on field tomato plants

The probe TPRI, derived from the Pseudomonas syringae pv. tomato gene cluster controlling production of the phytotoxin coronatine, was used in conjunction with the semiselective medium VBTar to trace natural populations of the pathogen on tomato plants from just before planting to harvest. In a survey of transplant seedlings in greenhouses, P. syringae pv. tomato populations ranged from 8 x 10(0) to 3.2 x 10(5) CFU/g of leaf tissue. Copper-sprayed seedlings had similar populations to nonsprayed plants, but copper tolerance was common among the P. syringae pv. tomato strains surveyed. Transplant seedlings from three greenhouses were tagged, randomly planted in three grower fields, and monitored for P. syringae pv. tomato and disease severity over two growing seasons. Statistical analysis indicated that, when the P. syringae pv. tomato populations of greenhouse plants were small, as recorded in this study, there was no correlation between greenhouse infestation and disease severity in the field. Environmental conditions played a greater role than greenhouse infestation in disease development. Once formed, leaf lesions remained a good inoculum source (10(4) to 10(5) CFU) throughout the 7-week life of the leaf. Bacterial speck damage correlated well in both years (r = 0.80 and r = 0.86, respectively) with P. syringae pv. tomato population levels.