Abstract

The late blight pathogen, P. infestans, is a hemi biotrophic, heterothallic, diploid oomycete that remains a major constraint for potato and tomato production worldwide and causes economic losses yearly calculated to be over four billion euros. This study was undertaken to test the following hypotheses: i) P. infestans isolates from Nicaragua do not differ in their aggressiveness toward potato or tomato; and ii) the P. infestans population from Nicaragua is formed exclusively by a single clonal lineage. Five SSR multilocus genotypes among 72 isolates of P. infestans were detected and all of them were of the Ia mtDNA haplotype and A2 mating type. The NI-1 single multilocus genotype continued to be dominant within the clonal lineage. The genotypic analysis revealed neither host specificity nor population differentiation between potato and tomato isolates. Aggressiveness tests revealed that tomato isolates showed a general, but not exclusive, host-specificity and were more aggressive on tomato. In contrast, potato isolates showed host-preference toward tomato leaflets and were more aggressive on them. The findings of this study provide useful information regarding late blight disease management on potato and tomato crops in Nicaragua.

Keywords: Quantitative pathogenicity; Plant pathogen diversity; Molecular markers; Population structure