Effects of the Age-Related Resistance to Potato virus Y in Potato on the Systemic Spread of the Virus, Incidence of the Potato Tuber Necrotic Ringspot Disease, Tuber Yield, and Translocation Rates Into Progeny Tubers

Dynamics of Potato Virus Y Infection Pressure and Strain Composition in the San Luis Valley, Colorado

The San Luis Valley (SLV), Colorado, is the second-largest fresh-potato-growing region in the United States, which accounts for about 95% of the total production in Colorado. Potato virus Y (PVY) is the leading cause of seed potato rejection in the SLV, which has caused a constant decline in seed potato production over the past two decades. To help potato growers control PVY, we monitored the dynamics of PVY infection pressure over the growing seasons of 2022 and 2023 (May through August) using tobacco bait plants exposed to field infection weekly. PVY infection dynamics were slightly different between the two seasons, but July and August had the highest infection in both years. The first PVY infection was detected in the second half of June, which coincides with the emergence of potato crops in the valley. PVY infection increased toward the beginning of August and declined toward the end of the season. Three PVY strains were identified in tobacco bait plants and potato fields, namely PVYO, PVYN-Wi, and PVYNTN. Unlike other producing areas of the United States, PVYO is still the major strain infecting potato crops in Colorado, comprising ∼40% of total PVY strain composition. This could be explained by the prevalence of the potato cultivar Russet Norkotah that lacks any identified N genes, including the Nytbr that controls PVYO, which imposes no negative selection against this strain. The current study demonstrated the usefulness of bait plants to understand PVY epidemiology and develop more targeted control practices of PVY.

Coordinated recruitment of conserved defense-signaling pathways in PVYO-Infected Nicotiana benthamiana

Potato virus Y (PVY) is an aphid-transmitted potyvirus that affects economically important solanaceous species. In this study, the phenomena and mechanisms following infection with PVY were investigated in tobacco (Nicotiana benthamiana). In tobacco plants, infection with a mild strain of PVY (PVYO) induced stunted growth in the first two leaves at the shoot apex starting 7 days post-infection (dpi), and mosaic symptoms began to appear on newly developing young leaves at 14 dpi. Using enzyme-linked immunosorbent assay and ultrastructure analysis, we confirmed that viral particles accumulated only in the upper developing leaves of infected plants. We analyzed reactive oxygen species (ROS) generation in leaves from the bottom to the top of the plants to investigate whether delayed symptom development in leaves was associated with a defense response to the virus. In addition, the ultrastructural analysis confirmed the increase of ATG4 and ATG8, which are autophagy markers by endoplasmic reticulum (ER) stress, and the expression of genes involved in viral RNA suppression. Overall, our results suggested that viral RNA silencing and induced autophagy may play a role in the inhibition of viral symptom development in host plants in response to PVYO infection.

Molecular perspectives on age-related resistance of plants to (viral) pathogens

Age-related resistance to microbe invasion is a commonly accepted concept in plant pathology. However, the impact of such age-dependent interactive phenomena is perhaps not yet sufficiently recognized by the broader plant science community. Toward cataloging an understanding of underlying mechanisms, this review explores recent molecular studies and their relevance to the concept. Examples describe differences in genetic background, transcriptomics, hormonal balances, protein-mediated events, and the contribution by short RNA-controlled gene silencing events. Throughout, recent findings with viral systems are highlighted as an illustration of the complexity of the interactions. It will become apparent that instead of uncovering a unifying explanation, we unveiled only trends. Nevertheless, with a degree of confidence, we propose that the process of plant age-related defenses is actively regulated at multiple levels. The overarching goal of this control for plants is to avoid a constitutive waste of resources, especially at crucial metabolically draining early developmental stages.

Managing the deluge of newly discovered plant viruses and viroids: an optimized scientific and regulatory framework for their characterization and risk analysis

The advances in high-throughput sequencing (HTS) technologies and bioinformatic tools have provided new opportunities for virus and viroid discovery and diagnostics. Hence, new sequences of viral origin are being discovered and published at a previously unseen rate. Therefore, a collective effort was undertaken to write and propose a framework for prioritizing the biological characterization steps needed after discovering a new plant virus to evaluate its impact at different levels. Even though the proposed approach was widely used, a revision of these guidelines was prepared to consider virus discovery and characterization trends and integrate novel approaches and tools recently published or under development. This updated framework is more adapted to the current rate of virus discovery and provides an improved prioritization for filling knowledge and data gaps. It consists of four distinct steps adapted to include a multi-stakeholder feedback loop. Key improvements include better prioritization and organization of the various steps, earlier data sharing among researchers and involved stakeholders, public database screening, and exploitation of genomic information to predict biological properties.

Infection Dynamics of Potato Virus Y Isolate Combinations in Three Potato Cultivars

The United States potato industry has recently experienced a strain shift; recombinant potato virus Y (PVY) strains (e.g., PVY^NTN) have emerged as the predominant strains over the long dominant ordinary strain (PVY^O), yet both are often found as single infections within the same field and as mixed infections within individual plants. To understand mixed infection dynamics in potato plants and in daughter tubers, three potato varieties varying for PVY resistance, 'Red Maria', 'CalWhite', and 'Pike', were mechanically inoculated either at the pre- or postflowering stage with all possible heterologous isolate combinations of two PVY^O and two PVY^NTN isolates. Virus titer was determined from leaves collected at different positions on the plant at different times, and tuber-borne infection was determined for two successive generations. PVY^NTN accumulated to higher levels than PVY^O at nearly all sampling time points in 'Pike' potato. However, both virus strains accumulated to similar amounts in 'Red Maria' and 'CalWhite' potato early in the infection when inoculated preflowering; however, PVY^NTN dominated at later stages and in plants inoculated postflowering. Regardless of inoculation time, both virus strains were transmitted to daughter plants raised from the tubers for most isolate combinations. The relative titer of PVY^NTN and PVY^O isolates at the later stages of mother plant development was indicative of what was found in the daughter plants. Although virus titer differed among cultivars depending on their genetics and virus isolates, it did not change the strain outcome in tuber-borne infection in subsequent generations. Differential virus accumulation in these cultivars suggests isolate-specific resistance to PVY accumulation.

Insight into aphid mediated Potato Virus Y transmission: A molecular to bioinformatics prospective

Potato, the world's most popular crop is reported to provide a food source for nearly a billion people. It is prone to a number of biotic stressors that affect yield and quality, out of which Potato Virus Y (PVY) occupies the top position. PVY can be transmitted mechanically and by sap-feeding aphid vectors. The application of insecticide causes an increase in the resistant vector population along with detrimental effects on the environment; genetic resistance and vector-virus control are the two core components for controlling the deadly PVY. Using transcriptomic tools together with differential gene expression and gene discovery, several loci and genes associated with PVY resistance have been widely identified. To combat this virus we must increase our understanding on the molecular response of the PVY-potato plant-aphid interaction and knowledge of genome organization, as well as the function of PVY encoded proteins, genetic diversity, the molecular aspects of PVY transmission by aphids, and transcriptome profiling of PVY infected potato cultivars. Techniques such as molecular and bioinformatics tools can identify and monitor virus transmission. Several studies have been conducted to understand the molecular basis of PVY resistance/susceptibility interactions and their impact on PVY epidemiology by studying the interrelationship between the virus, its vector, and the host plant. This review presents current knowledge of PVY transmission, epidemiology, genome organization, molecular to bioinformatics responses, and its effective management.

The carbohydrate elicitor Riclinoctaose facilitates defense and growth of potato roots by inducing changes in transcriptional and metabolic profiles

Promoting both root growth and defense is conducive to the production of potatoes (Solanum tuberosum L.), while the role of elicitors in this topic hasn't been fully understood. To investigate the effect of Riclinoctaose (RiOc) on root growth and defense, potato tissue cuttings were cultivated with different concentration of RiOc (0, 50, 200 mg/L) for 5 weeks and changes in root morphology, transcription, enzymatic and metabolomic profiles were monitored over time. The results indicated that RiOc triggered the salicylic acid (SA)-mediated defense response and facilitated the growth of adventitious and lateral roots in a dose- and time-dependent manner. MPK3/MPK6, SA- and auxin-signaling pathways and transcription factors such as WUS, SCR and GRAS4/GRAS9 participated in this process. Moreover, the ¹H NMR based metabolome profiling demonstrated that potato roots altered the primary metabolism to respond to the RiOc elicitation and efficiency in production and allocation of defense and growth-related metabolites was improved. After 5-week treatment, the level of glucose, N-acetylglucosamine, glutamine, asparagine, isoleucine, valine, 3-hydroxyisovalerate and ferulate increased, while acetate, acetoacetate, fucose, and 2-hydroxyphenylacetate declined. In conclusion, RiOc played dual roles in activating the SA-mediated defense response and in promoting growth of potato roots by inducing changes in root transcription and metabolism.

Phloem connectivity and transport are not involved in mature plant resistance (MPR) to Potato Virus Y in different potato cultivars, and MPR does not protect tubers from recombinant strains of the virus

The aims of this study were: i) to investigate mature plant resistance (MPR) against four strains of Potato virus Y (PVY^O, PVY^N, PVY^NTN and PVY^N-Wi) in potato cultivars that differ in maturity (e.g. early or maincrop) at different developmental stages, and ii) to determine whether phloem translocation of photoassimilates at different stages including the source-sink transition influences MPR. The data showed that MPR was functional by the flowering stage in all cultivars, and that the host-pathogen interaction is highly complex, with all three variables (potato cultivar, virus strain and developmental stage of infection) having a significant effect on the outcome. However, virus strain was the most important factor, and MPR was less effective in protecting tubers from recombinant virus strains (PVY^NTN and PVY^N-Wi). Development of MPR was unrelated to foliar phloem connectivity, which was observed at all developmental stages, but a switch from symplastic to apoplastic phloem unloading early in tuber development may be involved in the prevention of tuber infections with PVY^O. Recombinant virus strains were more infectious than parental strains and PVY^NTN has a more effective silencing suppressor than PVY^O, another factor that may contribute to the efficiency of MPR. The resistance conferred by MPR against PVY^O or PVY^N may be associated with or enhanced by the presence of the corresponding strain-specific HR resistance gene in the cultivar.

The prevalence of recombinant strains of potato virus Y in the East Kazakhstan region

The eastern region of Kazakhstan is an important territorial district producing seed potatoes. Since 2022, the region has been divided into the Abay region (administrative center in Semey city) and the East Kazakhstan region (administrative center in Ust-Kamenogorsk city). One of the largest elite seed farms producing potatoes is East Kazakhstan Agricultural Station LLP (Ust-Kamenogorsk). Potato Virus Y (PVY) was reported as problem for the production of Solanum tuberosum L. in Kazakhstan more than 25 years ago, however, over the past 5 years the spread of recombinant strains of PVY has become more serious problem (Loebenstein, Manadilova 2003). The purpose of this study was to find out the prevalence of PVY strains in the fields of the eastern region of Kazakhstan, including the fields of elite seed farm and commercial potato fields of the Glubokovsky district for the period from 2020 to 2021. Previously, the presence of recombinant strains (PVYN, PVYNTN, PVYN-Wi, PVYO) was shown in the west of Kazakhstan (Khassanov et al. 2020), but there is no data on the variety of PVY strains in the east region of Kazakhstan. Considering the geographical remoteness of these regions by more than 2000 km, the study of the prevalence of PVY in the fields of Kazakhstan needs to be supplemented with new data. PVY strains show a range of symptoms in different potato cultivars. The most damaging of these symptoms is tuber necrosis (Karasev and Gray 2013) associated with PVYNTN and some other recombinant strains. The pathogenesis of a viral infection of the PVYN strain and its recombinants is associated with the development of severe necrotic lesions of the tuber material, because of which yield losses can reach 60% (Chikh-Ali at al., 2020). In July 2021 leaf samples of 240 plants of two local regional potato varieties (Tavria and Izolda) were randomly selected to study PVY strains circulating in seed potatoes. 120 samples of the Tavria variety (seed material of the Elita class) and 120 samples of the Izolda variety (seed material of the Elita class) grown on seed potato fields of the East Kazakhstan Agricultural Experimental Station (GPS: N50.03324°, E82.53346°) were tested for the presence of potato viruses (PVA, PVS, PVM, PLRV, PVY) using commercial ELISA test systems (Russian Potato Research Center, Russia). In most samples (43 leaf samples), PVY is identified in the presence of a number of other potato viruses, mainly with PVM and PVS viruses. In order to type of PVY recombinant strains, samples containing PVY monoinfection have been selected. According to the results of ELISA, 21 PVY monoinfection positive samples have been detected: 14 plants of the Tavria variety, 7 plants of the Izolda variety. Serotype analysis using anti-rabbit polyclonal antibodies (Bioreba Ag, Switzerland) specific for PVYO, PVYC and PVYN serotypes identified PVYO serotype in 14 samples of the Tavria variety and in 7 samples of the Izolda variety, PVYN serotype in 2 samples of the Tavria variety and in 2 samples of the Izolda variety. All 21 PVY-positive samples were tested for strain by reverse transcription polymerase chain reaction (RT-PCR) using the strain-specific primers described by Chikh Ali et al. (2010). The products of PCR analysis showed the presence of bands characteristic of the recombinant N:O strain, 853, 633, and 441 bp - in 17 samples and characteristic of the NTNa strain, 1307, 633 and 441 bp in 4 samples. After determining the results of the analysis of leaf material samples, PVY-infected plants were removed from the soil and the tuber material was visually analyzed for signs of necrosis. According to the results of visual diagnostics, the symptoms of tuber necrosis were found in 80% of cases of infection with recombinant strains of PVYNTNa. In terms of severity, the symptoms of tuber necrosis were identical in both strains and caused to the damage of 35-50% of tubers on each plant of the Tavria and Isolda varieties, which indicates the absence of resistance to these recombinant strains. As is known, at present, many potato varieties have strain-specific resistance to PVYO (Funke at al. 2017). However, N:O and NTNa recombinant strains are the most difficult to develop resistance (Green et al. 2017). This is the first report on the Tavria and Izolda potato varieties as a susceptible host to recombinant strains of PVYN:O and PVYNTNa. Over the past five years, recombinant strains PVYN:O and PVYNTNa were introduced in two regions of Kazakhstan. In this regard, research and development of effective strategies to reduce the spread of recombinant strains PVYN:O and PVYNTNa in Kazakhstan, is particularly relevant. The authors declared no conflicts of interest. Funding: research was carried out within the framework of the scientific project "Development and implementation of innovative technology aimed at imparting antiviral resistance to crop varieties", funded by the Ministry of Education and Science of the Republic of Kazakhstan, Individual registration number (IRN): AP08052163.

Prevalence of Recombinant Strains of Potato Virus Y in Seed Potato Planted in Idaho and Washington States Between 2011 and 2021

Potato virus Y (PVY) has emerged as the main reason for potato seed lot rejections, seriously affecting seed potato production in the United States throughout the past 20 years. The dynamics of PVY strain abundance and composition in various potato growing areas of the United States has not been well documented or understood up to now. The objective of this study was to find out the prevalence of PVY strains in potato fields in the Pacific Northwest (PNW), including seed potato production systems in the State of Idaho and commercial potato fields in the Columbia Basin of Washington State between 2011 and 2021. Based on the testing of >10,000 foliar samples during Idaho seed certification winter grow-out evaluations of seed potato lots and seed lot trials in Washington State, a dramatic shift in the PVY strain composition was revealed in the PNW between 2011 and 2016. During this time period, the prevalence of the ordinary, PVY^O strain in seed potato dropped 8- to 10-fold, concomitantly with the rise of recombinant strains PVY^N-Wi and PVY^NTNa, which together accounted for 98% of all PVY positives by 2021. In Idaho seed potato, PVY^NTNa strain associated with the potato tuber necrotic ringspot disease (PTNRD) was found to increase threefold between 2011 and 2019, accounting for 24% of all PVY positives in 2019. Mild foliar symptoms induced by recombinant PVY strains may be partially responsible for the proliferation of PVY^N-Wi and PVY^NTNa in potato crops. A spike of another PTNRD-associated recombinant, PVY-NE11, was recorded in the PNW between 2012 and 2016, but after reaching a 7 to 10% level in 2012 to 2013 this recombinant disappeared from the PNW potato by 2019. Whole genome sequence analysis of the PVY-NE11 suggested this recombinant was introduced in the United States at least three times. The data on PVY strain abundance in the PNW potato crops suggest that virus management strategies must consider the current dominance of the two recombinant PVY strains, PVY^N-Wi and PVY^NTNa.

Enhanced Age-Related Resistance to Tomato Yellow Leaf Curl Virus in Tomato Is Associated With Higher Basal Resistance

Tomato yellow leaf curl virus (TYLCV) is one of the most notorious plant pathogens affecting the production of tomato worldwide. While the occurrence of age-related resistance (ARR) against TYLCV has been reported, the factors impacting its development remain unknown. We conducted a series of experiments with three tomato cultivars that vary in basal resistance to TYLCV to explore factors involved in the development of ARR. Our data indicate that ARR is more pronounced in tomato cultivars with higher basal resistance. Additionally, increased plant biomass in older plants does not contribute to ARR. Virus source plants with a younger age at initial inoculation facilitates virus acquisition by whiteflies. Finally, an analysis on plant hormones suggests that salicylic acid (SA) may play a major role in the development of ARR in tomato against TYLCV. These findings provide new insights into the developmental resistance in tomato against TYLCV as well as clues for the deployment of ARR in the management of diseases caused by TYLCV.

Current-Season Infection With Ordinary and Recombinant Strains of Potato virus Y Has Detrimental Effects on Chipping Potato Yield and Tuber Quality

Potato virus Y (PVY) is the most economically important virus infecting potatoes worldwide. Current-season spread of PVY occurs when aphids transmit the virus from infected to noninfected plants during the growing season. The impact of current-season PVY infection on yield and quality of chip processing potatoes is not well documented. In a replicated, greenhouse experiment conducted over 2 years, we measured the effect of current-season infection with four PVY strains (PVY^O, PVY^N-Wi, PVY^NTN, and PVY^N:O) on chip processing varieties Atlantic, Lamoka, and Snowden. PVY infection decreased yield and tuber specific gravity for some combinations of potato variety and virus strain but did not affect the appearance of chips including the prevalence of stem-end chip defects. This work suggests that current-season infection of chipping potatoes imposes a cost on producers and emphasizes the need for continued investment in seed certification and development of PVY-resistant cultivars.