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Potato spindle tuber viroid (PSTVd) is a small infectious non-coding circular RNA causing diseases of important crops, including tomato and potato. The symptoms vary from mild to severe depending on the viroid strain, the host plant variety, and the environmental conditions. The molecular mechanisms underlying the development of particular disease phenotypes remain elusive. The PSTVd strain NicTr-3 causes severe disease symptoms on Solanum lycopersicum cv. Rutgers and Solanum tuberosum cv. Colomba. It was found that after three cycles of propagation in tomato cv. Rutgers, infection of potato cv. Colomba with NicTr-3 resulted in very mild symptoms including smaller size of tubers and delayed leaf senescence. Sequence analysis of PSTVd clones isolated from tomato inoculum revealed the presence of mutated variants of genomic RNA. Transcriptome analysis carried out on leaves showed a considerable difference between infected and healthy plants at 14 dpi and 30 dpi. Interestingly, the response of potato plants to the attenuated PSTVd strain revealed a large number of DEGs associated with initiation of dormancy with a considerable increase in the vegetation period. The second vegetative generation (tuber-derived plantlets from control healthy and PSTVd-infected plants) was characterized by similar phenotypes and transcriptomes. Thus, here we describe a case of attenuation of a severe PSTVd strain after continuous propagation in tomato. It would be of interest to consider the attenuated viroid strains as a potential biocontrol agent or vaccine against this type of pathogenic RNA. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: Spot blotch, caused by Cochliobolus sativus, is one of the most widespread and harmful diseases in barley. Identification of genetic loci associated with resistance to C. sativus is of importance for future marker-assisted selection. The goal of the current study was to identify loci conferring seedling resistance to two different pathotypes of C. sativus in the Siberian spring barley core collection. Results: A total of 96 spring barley cultivars and lines were phenotyped at the seedling stage with two C. sativus isolates (Kr2 and Ch3). According to the Fetch-Steffenson rating scale 16%/17% of genotypes were resistant and 26%/30% were moderate-resistant to the Kr2/Ch3 isolates respectively. A total of 94 genotypes were analyzed with the barley 50 K Illumina Infinium iSELECT assay. From 44,040 SNPs, 40,703 were scorable, from which 39,140 were polymorphic. 27,319 SNPs passed filtering threshold and were used for association mapping. Data analysis by GLM revealed 48 and 41 SNPs for Kr2 and Ch3 isolates, respectively. After application of 5% Bonferroni multiple test correction, only 3 and 27 SNPs were identified, respectively. A total of three genomic regions were associated with the resistance. The region on chromosome 3H associated with Ch3-resistance was expanded between markers SCRI_RS_97417 and JHI-Hv50k-2016-158003 and included 11 SNPs, from which JHI-Hv50k-2016-157070, JHI-Hv50k-2016-156842 had the lowest p-values. These two SNPs were also significant in case of Kr2 isolate. The region on chromosome 2H included 16 loci (7 of them with the lowest p-values were tightly linked to BOPA2_12_11504). Three loci corresponding to this region had suggestive p-values in case of Kr2 tests, so the locus on chromosome 2H may also contribute to resistance to Kr2 isolate. The third region with significant p-value in case of Kr2 tests was identified on chromosome 1H at the locus JHI-Hv50k-2016-33568. Conclusions: Three genomic regions associated with the resistance to one or both isolates of C. sativus were identified via screening of the Siberian spring barley core collection. Comparison of their location with QTLs revealed previously either with biparental mapping populations studies or with GWAS of distinct germplasm and other isolates, demonstrated that resistance to isolates Kr2 and Ch3 is conferred by known spot blotch resistance loci. Information on SNPs related can be used further for development of DNA-markers convenient for diagnostics of resistance-associated alleles in barley breeding programs. [ABSTRACT FROM AUTHOR]