Candidate marker genes and enzymes for selection of potato with resistance to early blight, caused by Alternaria alternata

Early blight, caused by Alternaria alternata ( Fr.) Keissler is a serious disease of potato and other cultivated Solanum species. The molecular components defining defense responses to A. alternata in potato are limited. Host transcript accumulation after A. alternata inoculation of six potato genotypes (10/33/R1, 3/33/R2 and 21/33/R2, resistant to the pathogen, and 8707/106, 8703/804 and 8707/112, susceptible) was examined to develop understanding of mechanisms of their responses to A. alternata genotypes. The marker genes PR-2, ChtA, PR-5, PR1- b, PIN2, ERF3, PAL and LOX, activity of catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), polyphenol oxidase ( PPOs) and phenylalanine ammonia-lyase (PAL), as well as biomass growth parameters, were analysed. Expression of PR-2, ChtA, PR-5, PR1-b and PAL genes was greatly increased in the inoculated resistant genotypes compared to the susceptible genotypes and un-inoculated controls. Transcription levels of PIN2, ERF3 and LOX genes were decreased in resistant inoculated plants. Simultaneously, activities of POX, SOD and PPOs were greatly increased in the inoculated resistant host genotypes, compared to the susceptible and non-inoculated controls. CAT activity in genotype 21/33/R2 and PAL activity in resistant genotypes 21/33/ R2 and 10/ 33/R1 increased in the susceptible and non-inoculated. Host growth parameters of inoculated plants decreased compared to un-inoculated controls. Knowledge of changes in gene expression levels and enzyme production in defense processes in infected potato plants can inform future studies to identify the defense mechanisms, and assist generation of potato cultivars resistant to early blight.