title: Influence of day-length and isolates of Phytophthora infestans on field resistance to late blight of potato.
abstract: Main and interaction effects of day-length and pathogen isolate on the reaction and expression of field resistance to Phytophthora infestans were analyzed in a sample of standard clones for partial resistance to potato late blight, and in the BCT mapping population derived from a backcross of Solanum berthaultii to Solanum tuberosum. Detached leaves from plants grown in field plots exposed to short- and long day-length conditions were independently inoculated with two P. infestans isolates and incubated in chambers under short- and long photoperiods, respectively. Lesion growth rate (LGR) was used for resistance assessment. Analysis of variance revealed a significant contribution of genotype x isolate x day-length interaction to variation in LGR indicating that field resistance of genotypes to foliar late blight under a given day-length depended on the infecting isolate. An allele segregating from S. berthaultii with opposite effects on foliar resistance to late blight under long- and short day-lengths, respectively, was identified at a quantitative trait locus (QTL) that mapped on chromosome 1. This allele was associated with positive (decreased resistance) and negative (increased resistance) additive effects on LGR, under short- and long day-length conditions, respectively. Disease progress on whole plants inoculated with the same isolate under field conditions validated the direction of its effect in short day-length regimes. The present study suggests the occurrence of an isolate-specific QTL that displays interaction with isolate behavior under contrasting environments, such as those with different day-lengths. This study highlights the importance of exposing genotypes to a highly variable population of the pathogen under contrasting environments when stability to late blight resistance is to be assessed or marker-assisted selection is attempted for the manipulation of quantitative resistance to late blight.
authors.affiliation: International Potato Center, Lima 12, P.O. Box 1558, Lima, Peru.
authors.forename: E
authors.initials: E
authors.lastname: Mihovilovich
authors.forename: S
authors.initials: S
authors.lastname: Munive
authors.forename: M
authors.initials: M
authors.lastname: Bonierbale
mesh_terms: D000383:Agriculture; D001681:Biological Assay; D005838:Genotype; D007113:Immunity, Innate / Q000276:immunology*; D008126:Lod Score; D017440:Photoperiod; D055750:Phytophthora infestans / Q000302:isolation & purification*; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology* / Q000469:parasitology*; D018515:Plant Leaves / Q000254:growth & development / Q000469:parasitology; D040641:Quantitative Trait Loci / Q000235:genetics; D011198:Solanum tuberosum / Q000235:genetics / Q000254:growth & development / Q000276:immunology* / Q000469:parasitology*