Influence of day-length and isolates of Phytophthora infestans on field resistance to late blight of potato |
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Authors: | E Mihovilovich S Munive M Bonierbale |
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Institution: | (1) International Potato Center, Lima 12, P.O. Box 1558, Lima, Peru; |
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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 × isolate × 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. |
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