Assessment of potato varieties preserving at VIR’s collection to (Phytophthora infestans) resistance for late blight in field and laboratory evaluation

Thirty-eight varieties of potato Solanum tuberosum L. from the N. I. Vavilov All-Russian Institute of Plant Genetic Resources (VIR) collection were studied for leaf and tuber resistance to late blight. Аn aggressive Phytophthora infestans isolate collected from VIR experimental field was used for inoculation at a concentration of 50,000 zoospores/ml. The disease severity was evaluated using a scale from 1 to 9 grades, where grade 9 means resistant. Recent field observations revealed that most of the variety accessions were sensitive to late blight. In the present study, some of the varieties identified as foliar resistant in field evaluation were further tested under artificial inoculation. Resistance of some varieties found in field observations was not confirmed in laboratory assays. The data obtained in tuber inoculation tests did not show a direct correlation between resistance levels in leaves and tubers. Only some varieties possessed both characteristics, while varieties with leaf resistance and tuber sensitivity and with tuber resistance and leaf sensitivity were also identified. To develop potato varieties that combine resistance to late blight with good agronomic characteristics, resistant lines identified in this study can be potentially hybridized with varieties of high consumer value that are susceptible to late blight.

QTLs for potato tuber resistance toDickeya solaniare located on chromosomes II and IV

Soft rot is a bacterial disease that causes heavy losses in potato production worldwide. The goal of this study was to identify quantitative trait loci (QTLs) for potato tuber resistance to bacteriumDickeya solaniand for tuber starch content to study the relationship between these traits. A highly resistant diploid hybrid of potato was crossed with a susceptible hybrid to generate the F1 mapping population. Tubers that were wound-inoculated with bacteria were evaluated for disease severity expressed as the mean weight of rotted tubers, and disease incidence measured as the proportion of rotten tubers. Diversity array technology (DArTseq™) was used for genetic map construction and QTLs analysis. The most prominent QTLs for disease severity and incidence were identified in overlapping regions on potato chromosome IV and explained 22.4% and 22.9% of the phenotypic variance, respectively. The second QTL for disease severity was mapped to chromosome II and explained 16.5% of the variance. QTLs for starch content were detected on chromosomes III, V, VI, VII, VIII, IX, XI, and XII in regions different than the QTLs for soft rot resistance. Two strong and reproducible QTLs for resistance toDickeya solanion potato chromosomes IV and II might be useful for further study of candidate genes and marker development in potato breeding programs. The relationship between tuber resistance to bacteria and the starch content in potato tubers was not confirmed by QTL mapping, which makes the selection of genotypes highly resistant to soft rot with a desirable starch content feasible.

POPULATION STRUCTURE OF PHYTOPHTHORA INFESTANS ON WORLDWIDE SCALE: A REVIEW

Phytophthora infestans is a destructive pathogen that causes late blight of potato worldwide. Several sexually and asexually reproducing lineages of the pathogen have been identified and new lineages are more virulent as compared to their parental lineages. A new highly aggressive clonal lineage EU13_A2 has spread into potato fields of Europe, Africa and Asia in place of the older lineages. In North America, 24 clonal lineages US1to US24 have been identified. Despite of sexual reproduction, the overall population of P. infestans in potato and tomato fields is dominated by asexual lineages. Breeding has been done to transfer 'R' genes into commercial potato cultivars through classical breeding and by pyramiding of genes. Defender is the only potato cultivar that has foliar and tuber resistance to late blight. Genetically modified potato with RB gene from Solanum bulbocastanum has been developed but it lacks tuber resistance to disease. This review discusses population structure of P. infestans worldwide and breeding efforts to produce late blight resistant potato.

Assessment of Potato Tuber Resistance Against Dry Rot

Fungi of the genus Fusarium display inter- and intraspecific variation in their pathogenic capabilities. Although no resistance genes against dry rot have been identified, some indications of the possible defense responses are noticeable, since a single isolate might cause lesions of various sizes when infecting tubers of different potato cultivars. Pathogenicity tests are routinely used to assess potato tubers resistance against dry rot; a setup of pathogenicity test performed at Młochów Research Center is described in this work.

Tuber and root resistance of potato genotypes against Meloidogyne chitwoodi in the presence of Avena strigosa, related to tuber quality

Relative tuber infestation and quality of two Meloidogyne chitwoodi resistant potato genotypes, AR04-4096 and 2011M1, were compared in glasshouse experiments at initial population density () = 16 second-stage juveniles (g dry soil)−1 in the presence and absence of the bristle oat, Avena strigosa. When A. strigosa was added, ( final population) on both AR04-4096 and 2011M1 increased 130×, increased 1.9 and 3.7×, respectively, while × fresh root weight (FRW)−1 was the same. Nematode hatch from peel of AR04-4096, without A. strigosa, was delayed by 3 weeks but relative hatching rate was increased. Although the RStuber (RS = Relative Susceptibility) of both AR04-4096 and 2011M1 were lower than 1%, in the presence of A. strigosa tuber quality of 2011M1 dropped below the marketable level, while that of AR04-4096 was hardly affected. We conclude that: i) is influenced by root mass; ii) root quality influences nematode hatch; iii) tuber quality is not an estimator for tuber resistance, and the reverse; iv) root resistance is equal to tuber resistance.