A novel population of Phytophthora, similar to P-infestans, attacks wild Solanum species in Ecuador

Twenty-six isolates of a Phytophthora population from two wild solanaceous species, Solanum tetrapetalum (n = 11) and S. brevifolium (n = 15), were ch aracterized morphologically, with genetic and phenotypic markers, and for p athogenicity on potato and tomato. Based on morphology, ribosomal internal transcribed spacer region 2 (ITS2) sequence, and pathogenicity, all isolate s closely resembled P. infestans and were tentatively placed in that specie s. Nonetheless, this population of Phytophthora is novel. Its primary host is neither potato nor tomato, and all isolates had three restriction fragme nt length polymorphism (RFLP) bands (probe RG57) and a mitochondrial DNA ha plotype that have not been reported for P. infestans. All the isolates were the A2 mating type when tested with a P. infestans A1 isolate. The A2 mati ng type has not been found among isolates of P. infestans from potato or to mato in Ecuador. Geographical substructing of the Ecuadorian A2 population was detected. The three isolates from the village of None, identical to the others in all other aspects, differed by three RFLP bands; those from None lacked bands 10 and 16, but possessed band 19. Most of the Ecuadorian A2 i solates were nonpathogenic on potato and tomato, but a few caused very smal l lesions with sparse sporulation on necrotic tissue. Cluster analysis of m ultilocus genotypes (RFLP, mating type, and two allozymes) dissociated this A2 population from genotypes representing clonally propagated populations of P. infestans worldwide. The current hypotheses for the historical global movements of P. infestans do not satisfactorily explain the origin or poss ible time of introduction into Ecuador of this A2 population. Assuming the population is P. infestans, its presence in Ecuador suggests either a hithe rto unreported migration of the pathogen or an indigenous population that h ad not previously been detected.