Phenotypic and DNA Marker-Assisted Characterization of Russian Potato Cultivars for Resistance to Potato Cyst Nematodes

Potato is one of the most important food crops in the world and also in the Russian Federation. Among harmful organisms reducing potato yield potential, the potato cyst nematodes (PCN) are considered to be ones of the most damaging pests. Information on PCN resistant cultivars is important for potato breeding and production. Russian potato cultivars are characterized in the state-bio-test program for resistance to only one PCN species Globodera rostochiensis and one pathotype Ro1 which is reported to be present in the country. This study aimed to find domestic cultivars with multiple resistances to different PCN species and different pathotypes using phenotyping coupled with molecular marker analysis due to the risk of the occasional introduction of new pests. The phenotypic response was determined by the inoculation of plants with pathotypes Ro5 of G. rostochiensis and Pa3 of G. pallida. The obtained results were supplemented by the state-bio-test data on resistance to Ro1 of G. rostochiensis. Nine of 26 Russian cultivars were resistant both to Ro5 and Ro1 pathotypes and two cultivars possess multiple resistances to both PCN species. Most tested molecular markers associated with the Gpa2, GpaVvrn, GpaVsspl, Grp1 loci showed discrepancies with phenotyping. However, a predictive haplotype and epistatic effect were detected

Evaluation of Responses of Potato Cultivars to Potato Spindle Tuber Viroid and to Mixed Viroid/Viral Infection

Potato spindle tuber viroid (PSTVd) is a harmful quarantine disease with wide geographic distribution. To date, experimentally proved resistance or tolerance of potato cultivars to PSTVd has not been reported. The aim of this study was to evaluate responses to four PSTVd strains of 39 modern potato cultivars of different origin. Four PSTVd strains of different origin, the intermediate VP35, VP87, and two sever strains FP10-13 and NicTr-3, deposited in GenBank, were used. Transcripts of these strains were used to inoculate tomato plants of the cv. Rutgers. Before PSTVd inoculation with tomato sap, all plants were tested for viral infection by ELISA. The presence of PSTVd in infected plants was verified by RT-PCR as well as by RT-qPCR at sixty days post-inoculation (dpi). The strain-specificity in the response of cultivars to viroid infection was revealed. Five cultivars were identified in which, after the first inoculation of plants with all PSTVd strains, normal in shape tubers were formed. All plants of the next generation derived from infected but normally shaped tubers showed strong symptoms of disease. PSTVd and mixed viroid/viral infection (PVY + PSTVd, PVM + PSTVd, and PVY + PVS + PSTVd) led to a significant decrease in the number and weight of tubers in most of the cultivars studied

NLR Genes Related Transcript Sets in Potato Cultivars Bearing Genetic Material of Wild Mexican Solanum Species

The long history of potato breeding includes the numerous introgressions of resistance genes from many wild species of South and Central America as well as from cultivated species into the breeding genepool. Most R genes belong to the NLR family with nucleotide-binding site–leucine-rich repeat. The aim of this research concerns an evaluation of NLR genes expression in transcriptomes of three potato cultivars (Evraziya, Siverskij, Sudarynya), which combine genetic material from wild and cultivated potato species, and each bears intragenic markers of RB/Rpi-blb1/Rpi-sto1 genes conferring broad-range resistance to late blight. The transcriptomes of the cultivars were compared before and 24 h after the Phytophthora infestans inoculation. The induction of RB/Rpi-blb1/Rpi-sto1 transcript after 24 h of inoculation was detected in the resistant cultivars Siverskij and Sudarynya but not in susceptible cv. Evraziya. This demonstrates the importance of transcriptomic assay for understanding the results of marker-assisted selection and phenotyping. Interestingly, assembling the transcriptomes de novo and analysis with NLR-parser tool revealed significant fractions of novel NLR genes with no homology to the reference genome from 103 (cv. Siverskij) to 160 (S. stoloniferum, 30514/15). Comparison of novel NLRs demonstrated a relatively small intersection between the genotypes that coincided with their complex pedigrees with several interspecific hybridization events. These novel NLRs may facilitate the discovery of new efficient R genes