The objective of this work was to evaluate the resistance of 30 Chilean potato landraces to natural infection by Phytophthora infestans during two growing seasons in Southern Chile. Control cultivars were 'Désirée', which has moderate susceptibility to late blight, and 'Karú', which is characterized by moderate resistance to the disease. The response of the potato landraces to late blight infection was assessed weekly by scoring the percentage of foliage destruction during the growing season. Subsequently, the relative area under the disease progress curve (AUDPCr) was calculated. A wide response variation was observed among the landraces during the occurrence of late blight. The comparative analysis of the AUDPCr showed that three landraces achieved high resistance to the disease (low AUDPCr values). These were UCT-34Cor (0.05), UCT-26Ach (0.06) and UCT-27Mu (0.10). Most of the potato landraces were classified into the range moderately resistant to moderately susceptible. The estimated values of heritabilities of the means were moderate to high for the joint analysis of the two years tested (0.65). The wide range of AUDPCr observed within potato landraces suggests the presence of partial resistance in response to the complex virulence pattern of the P. infestans populations present in Southern Chile.

Background: The object of this work was to determine the genetic and allelic diversity of Solanum species present in Chile, assessing allelic distribution among native varieties and commercial cultivars of Solanum tuberosum ssp. tuberosum L., using microsatellite markers. Results: A high level of allelic richness was found in the potatoes studied. The seven microsatellite markers used presented a total of 64 allelic variants among native varieties and commercial cultivars of Solanum tuberosum ssp. tuberosum. The SSR loci generated an average of 9.16 alleles/locus. The group with the highest PIC was that of native varieties collected in the Chiloe archipelago. The high PIC values found indicate that the native varieties from Chiloe have a low level of interrelation, representing wide genetic diversity. Conclusions: The markers with the highest number of alleles in native varieties corresponded to loci STG 0016 and LEMALX. Commercial cultivars do not present the same genetic variability as native varieties, and the allelic richness of commercial cultivars is lower than that of native varieties of S. tuberosum ssp. tuberosum. Most of the native varieties were clustered in accordance with their geographical location, while commercial cultivars, were clustered in accordance with their breeding programs in Chile and Europe, with the exception of Shepody.