Potato is one of the most important agricultural crops in Algeria and worldwide.Each year, potato late blight, caused by Phytophthora infestans, is responsible for significant damage that leads to large production losses, and is thus a direct threat to food security in Algeria. In this study, 131 isolates of P. infestans and 92 DNA fingerprints captured on FTA cards were sampled from commercial and seed production fields in three major potato production regions (western, eastern, and central) during the main-season and late-season in Algeria over six cropping seasons (2010)(2011)(2012)(2013)(2014)(2015)(2016).Genotypes of P. infestans and population genetic diversity were analysed using a 17plex simple-sequence repeat (SSR) marker assay, and the mating type of all isolates was characterized. Both mating types (A1 and A2) were found, and often occurred in the same field. Differences in mating type proportion were observed between regions and between sampling periods. Analysis with SSR markers showed the prevalence of the EU_13_A2 lineage (70%) over EU_2_A1 (16%), EU_23_A1 (10%), and 4% of unknown multilocus lineage (MLL). The EU_13_A2 showed differentiation within the group. EU_23_A1 was found mainly in late-season crops. However, the cropping region did not influence the distribution of lineages due to the dispersal of the pathogen in Algeria by seeds. Genetic structure did not reveal a clear variation in distribution of the three lineages throughout the sampling regions. These data provide important new information on the composition and change over time of P. infestans populations in Algeria and open the way for a better understanding of the local epidemiology of this important pathogen.

The potato (Solanum tuberosum) is the 3 rd most important crop worldwide, and Phytophthora infestans is the most devastating pathogen to potato crops. In this study, it has identified markers for resistance and susceptibility to late blight using potato genotypes that differ in their resistance/susceptibility to Phytophthora infestans. Using Fourier transform infrared spectroscopy, many absorbance bands have been identified as specific to resistant potato plants, and others were specific to susceptible potato plants. For each case (resistance/susceptibility), three bands were identified: 941-1180 cm , respectively. As it is a simple, rapid, and inexpensive technology, FTIR (Fourier Transform Infrared) spectroscopy offers an excellent opportunity for studying potato resistance/susceptibility to late blight.

Phytophthora infestans is the most important potato disease. It is a hemibiotrophic pathogen, with a high evolution capacity. Resistance breeding is thought to be the most suitable solution. Gene pyramiding is advanced as a solution for late blight disease.

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