Articles
POPULATION SUBSTRUCTURING OF PHYTOPHTHORA INFESTANS ON AMERICAN POTATO CLONES IN THE TOLUCA VALLEY, MÉXICO
Article number
619_20
Pages
183 – 188
Language
English
Abstract
A recent study highlighted the degree of genetic variability typical for a sexually reproducing population of the late blight pathogen Phytophthora infestans, in the Toluca valley, México (Grünwald et al., 2001). This study lends support to the idea that the valley is an ideal location for testing potato clones for genetic resistance to the pathogen by exposing the plants to natural infection in the absence of fungicides.
More than 100 P. infestans isolates, each from a single discrete lesion of resistant American potato clones, were obtained between 1998 and 2000. Mating type was identified by pairing each isolate with known A1 and A2 tester strains on Rye-A agar.
The allozyme genotypes for peptidase (Pep) and glucose-6-phosphate isomerase (Gpi) were determined by cellulose acetate membrane electrophoresis, and in vitro metalaxyl resistance was assessed as radial growth on metalaxyl amended relative to non-amended medium.
The A1 mating type was predominant, occurring at a 6:1 ratio with respect to A2 in the population isolated from three multiple-sampled potato clones (n=105), and homothallic cultures were identified in about 22 % of the isolates.
The 100/100 Pep genotype predominated with just two isolates being of the 96/100 genotype.
For Gpi six genotypes were identified, the most frequent one being 122/122, followed by 86/122. The predominant multilocus genotypes were A1, 100/100, 122/122 (mating type, Pep, Gpi), especially on the potato clones AWN86514-2 and A90586-11. Frequency distribution of metalaxyl resistance at four dosages was dependent on the host.
Isolates from two clones were susceptible, while genotypes from the other three clones were resistant.
No new P. infestans genotypes were isolated from the American clones in Toluca, nor did the level of resistance show signs of diminishing, and selection towards higher virulence is not occurring.
More than 100 P. infestans isolates, each from a single discrete lesion of resistant American potato clones, were obtained between 1998 and 2000. Mating type was identified by pairing each isolate with known A1 and A2 tester strains on Rye-A agar.
The allozyme genotypes for peptidase (Pep) and glucose-6-phosphate isomerase (Gpi) were determined by cellulose acetate membrane electrophoresis, and in vitro metalaxyl resistance was assessed as radial growth on metalaxyl amended relative to non-amended medium.
The A1 mating type was predominant, occurring at a 6:1 ratio with respect to A2 in the population isolated from three multiple-sampled potato clones (n=105), and homothallic cultures were identified in about 22 % of the isolates.
The 100/100 Pep genotype predominated with just two isolates being of the 96/100 genotype.
For Gpi six genotypes were identified, the most frequent one being 122/122, followed by 86/122. The predominant multilocus genotypes were A1, 100/100, 122/122 (mating type, Pep, Gpi), especially on the potato clones AWN86514-2 and A90586-11. Frequency distribution of metalaxyl resistance at four dosages was dependent on the host.
Isolates from two clones were susceptible, while genotypes from the other three clones were resistant.
No new P. infestans genotypes were isolated from the American clones in Toluca, nor did the level of resistance show signs of diminishing, and selection towards higher virulence is not occurring.
Authors
H. Lozoya-Saldaña, N.J. Grünwald, C. Brown, E. Garay-Serrano, A. Sturbaum-Abud, C. Belmar
Keywords
Potato late blight, mating type, allozyme, metalaxyl resistance
Online Articles (56)