THE POPULATION STRUCTURE OF PHYTOPHTHORA INFESTANS FROM THE TOLUCA VALLEY OF CENTRAL MEXICO SUGGESTS GENETIC DIFFERENTIATION BETWEEN POPULATIONS FROM CULTIVATED POTATO AND WILD SOLANUM SPP.

Authors: FLIER, W - PLANT RES INTL,NETHERLAND; Grunwald, Niklaus - Nik; KROON, L - PLANT RES INTL,NETHERLAND; STURBAUM, A - PICTIPAPA, MEXICO; VANDEN BOSCH, T - PLANT RES INTL,NETHERLAND; GARAY-SERRANO, E - PICTIPAP, MEXICO; LOZOYA-SALDANA, H - UNIV AUTONOMA CHAPINGO; FRY, W - CORNELL UNIV; TURKENSTEEN, L - PLANT RES INTL,NETHERLAND

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2002
Publication Date: 4/1/2003
Citation: FLIER, W.G., GRUNWALD, N.J., KROON, L.P., STURBAUM, A.K., VANDEN BOSCH, T.B., GARAY-SERRANO, E., LOZOYA-SALDANA, H., FRY, W.E., TURKENSTEEN, L.J. THE POPULATION STRUCTURE OF PHYTOPHTHORA INFESTANS FROM THE TOLUCA VALLEY OF CENTRAL MEXICO SUGGESTS GENETIC DIFFERENTIATION BETWEEN POPULATIONS FROM CULTIVATED POTATO AND WILD SOLANUM SPP. PHYTOPATHOLOGY. 2003. 93:382-390.

Interpretive Summary: This study investigated the population structure of Phytophthora infestans, the oomycete plant pathogen that causes potato late blight, in the Toluca Valley of central Mexico where this pathogen originated. A total of 170 pathogen isolates were collected from cultivated potatoes and the native wild Solanum species S. demissum and S. x edinense. All isolates were analyzed for mitochondrial DNA (mtDNA) haplotype and amplified fragment length polymorphism (AFLP) multilocus fingerprint genotype. Isolate samples were monomorphic for mtDNA haplotype as all isolates tested were of the Ia haplotype. A total of 158 multilocus AFLP genotypes were identified among the 170 P. infestans isolates included in this study. P. infestans populations sampled in the Toluca Valley were highly variable, and almost every single isolate represented a unique genotype, based on the analysis of 165 AFLP marker loci. Populations of P. infestans collected from the commercial potato-growing region in the valley, the subsistance potato production area along the slopes of the Nevado de Toluca and from native Solanum species on the forested slopes of the volcano showed a high degree of genetic diversity. Significant differentiation was found at the population level, between strains originating from cultivated potatoes and wild Solanum species. Indirect estimation of gene flow between populations indicated restricted gene flow between both P. infestans populations from cultivated potatoes and wild Solanum hosts. There was no evidence fround for the presence of sub-structuring at the field level. We hypothesize that population differentiation and genetic isolation of P. infestans in the Toluca Valley is driven by host specific factors (i.e. R-genes) widely distributed in wild Solanum species and random genetic drift.

Technical Abstract: The population structure of Phytophthora infestans in the Toluca Valley of central Mexico was assessed using 170 isolates collected from cultivated potatoes and the native wild Solanum species S. demissum and S. x edinense. All isolates were analyzed for mitochondrial DNA (mtDNA) haplotype and amplified fragment length polymorphism (AFLP) multilocus fingerprint genotype. Isolate samples were monomorphic for mtDNA haplotype as all isolates tested were of the Ia haplotype. A total of 158 multilocus AFLP genotypes were identified among the 170 P. infestans isolates included in this study. P. infestans populations sampled in the Toluca Valley in 1997 were highly variable, and almost every single isolate represented a unique genotype, based on the analysis of 165 AFLP marker loci. Populations of P. infestans collected from the commercial potato-growing region in the valley, the subsistence potato production area along the slopes of the Nevado de Toluca and from native Solanum species on the forested slopes of the volcano showed a high degree of genetic diversity. The number of polymorphic loci varied from 20.0% to 62.4% for isolates collected from the field station and wild Solanum species. On average, 81.8% (135) of the AFLP loci were found to be polymorphic. Heterozygosity varied between 7.7 and 19.4%. Significant differentiation was found at the population level, between strains originating from cultivated potatoes and wild Solanum species (P = 0.001 to 0.022). Private alleles were observed in individual isolates collected from all three populations, with numbers of unique dominant alleles varying from 9 to 16 for isolates collected from commercial potato crops and native Solanum spp. respectively. Four AFLP markers were exclusively found present in isolates collected from S. demissum. Indirect estimation of gene flow between populations indicated restricted gene flow between both P. infestans populations from cultivated potatoes and wild Solanum hosts. There was no evidence found for the presence of sub-structuring at the subpopulation (field) level. We hypothesize that population differentiation and genetic isolation of P. infestans in the Toluca Valley is driven by host specific factors (i.e. R-genes) widely distributed in wild Solanum species and random genetic drift.