Stability in Population of Phytophthora infestans Attacking Tomato in Ecuador Demonstrated by Cellulose Acetate Assessment of Glucose-6-Phosphate Isomerase.

Cellulose acetate electrophoresis was used to examine glucose-6-phosphate (Gpi) isomerase banding patterns of the population of Phytophthora infestans attacking tomato in Ecuador. All but two of 160 sporulating lesions from tomato leaflets collected from 25 tomato fields between January 1998 and March 1999 produced the 86/100 Gpi isozyme electromorph. This isozyme type is characteristic of the US-1 clonal lineage, indicating that no change in the population of P. infestans attacking tomato in Ecuador has occurred since a more exhaustive study was done using isolates collected between 1993 and 1995. The two lesions that produced a different Gpi electromorph in the current study came from a field that was located approximately 80 m from a potato field that had been severely affected by late blight. These two isolates produced a single large band for Gpi with a relative migration distance of 100. This electromorph is characteristic of the clonal lineage EC-1, which was shown previously to be the predominant clonal lineage attacking potato in Ecuador. Therefore, we assume that the two tomato lesions with the EC-1 phenotype were caused by inoculum originating from the potato field. During the current study, 34 infected potato leaflets were collected from five potato fields found in close proximity to blighted tomato fields. All of the potato leaflets produced banding patterns characteristic of EC-1. Our data are consistent with earlier studies indicating that, in Ecuador, tomato and potato are attacked by separate populations of P. infestans, which belong to two different clonal lineages.