Resistance to Pseudomonas syringae pv. tomato Race 1

Bacterial speck caused by Pseudomonas syringae pv. tomato (Pst) presents a serious problem to tomato growers in many countries. The first line of control is the genetic resistance. For a long time race 0 of Pst has been successfully controlled by Pto1 gene. The resistance of this gene was overcome by race 1 detected in 1982 in Canada. For the present there are not commercial tomato cultivars resistant to race 1 although several wild tomato species have been reported to carry such resistance. The objective of this investigation was to screen breeding materials coming from crosses with several wild tomato species with California race 1 isolates, as well as to perform tests aiming to determine the genetics of resistance to race 1 in selected tomato lines. The evaluation of plant responses was based on the number of bacterial lesions per plant, using a scale of 1 to 5. Disease severity index (DSI) was calculated. The results indicated the existence in the investigated tomato lines of a high level of resistance to California race 1 isolates. The DSI of the best lines ranged from 1.00 to 1.93 depending on the virulence of the isolate. At the same time the DSI of the susceptible control cultivars Chico III and ONT 7710 (Pto1) were between 4.70 and 5.00. The results from the genetic test lead us to the conclusion of one major dominant gene was involved in controlling resistance to race 1 in two of the best lines. The level of resistance of F1 plants was comparable to that of the resistant parent line.