Characterization of late blight resistant potato genotypes using phenotypic and molecular approaches

Abstract:

Late blight, caused by Phytophthera infestans, destroys an estimated 6 billion USD worth of potato production globally each year, and fungicide-based control adds another layer of cost and environmental concern. Identifying genotypes that carry durable resistance genes remains the most sustainable path forward. This research characterized 25 potato genotypes from the Caspian region of Iran for late blight resistance using both phenotypic evaluation and molecular marker analysis. Detached leaf assays and field inoculations with two aggressive P. infestans isolates (Pi-GI-01 and Pi-GI-04) were conducted at the Caspian Institute of Agricultural Sciences, Rasht, during the 2022-23 growing season. Disease severity was scored on a 1-5 scale, and the area under the disease progress curve (AUDPC) was calculated for each genotype. Five sequence-characterized amplified region (SCAR) and simple sequence repeat (SSR) markers linked to R-genes (R1, R3a, R3b, R8, R10) were used for molecular screening. Phenotypic evaluation identified seven genotypes with severity scores below 2.0 and AUDPC values under 180. Molecular analysis revealed that four of these seven genotypes carried resistance alleles at three or more marker loci. Genotypes G-01, G-07, and G-22 showed the strongest combined phenotypic-molecular resistance profile, carrying alleles at four of five screened loci and maintaining AUDPC values of 94.3, 78.6, and 102.1, respectively. Polymorphism information content (PIC) values for the markers ranged from 0.31 to 0.68. These three genotypes are recommended as donor parents for late blight resistance breeding in the humid Caspian lowlands.