Brief Summary of Minutes of Annual Meeting

Minutes Summary: WERA-89 Annual Meeting Wyndham San Diego Bayside San Diego, CA on March 4-5, 2015 Chair: Mark Pavek; Vice Chair: Carrie Wohleb; Secretary: vacant The meeting started at 8:00 am March 4, 2015. The minutes of the WERA-89 Annual Meeting of March 20-21, 2014 were unanimously approved. Administrative Advisor Report: Don Thill said that WERA-89 will need to file paperwork this year to renew for another five years. The current project will expire on September 30. The Chair will need to prepare a termination report for WERA-89 and a new proposal needs to be submitted into NIMSS by January 15, 2016. Thill announced that he is retiring so a new Administrative Advisor will be assigned to WERA-89. A copy of the new proposal should be sent to this person by mid-December. R. Davidson, P. Hamm, M. Pavek, and H. Pappu agreed to work on the draft proposal. All of the members of WERA-89 will need to re-enroll in January, 2016. State Certification Reports: CA - Pablo Guzman reported that CA had about 1,000 acres in the certification program in 2014, which is an increase of about 200 acres. He noted that a lot of “Banana” seed was infected with PVY, but the mosaic symptoms are difficult to see. CO - Kent Sather reported that total acreage in the certification program in CO decreased in 2014. A lot of acres were rejected in 2013 mostly due to unacceptable levels of PVY. In 2014, there were 582 seed lots = 7,541 acres (not including “Canela Russet” and experimental varieties). He said 303 lots had mosaic and 56 of them had PVY >8%. Sather also noted that “Banana” has lots of PVY problems, and said that it is being replaced by varieties like “Austrian Crescent” and “LaRatte”. The top five russets in the program are “Norkotah”, “Classic”, “Rio Grande”, “Teton”, and “Centennial”. Some are difficult to rogue. In a PVY survey they found that 36% were N:Wi, 38% O, and 2% NTN. Colorado will be requiring a PHT with a 5% mosaic maximum (and no more than 1% N strain) for both recertified and commercial seed sales, including imported lots. This is a change from the zero tolerance for the NTN strain. Sather says they are focused on reducing the overall inoculum level. ID - Alan Westra reported that acres in the certification program are down 2% from last year. He said many new varieties are being entered in the program and it is a challenge to get to know how each of these express PVY symptoms. He mentioned that three lots in 2014 had PLRV. These lots came from Canada and a couple of them were withdrawn because they were not able to clean them up with rogueing. He said that 109 of 811 lots had mosaic in the summer readings, which is a slight increase in PVY but not enough to affect the amount of certified seed available. Westra also mentioned bacterial ring rot inspection results from a survey conducted in 2014. They inspected 114 stems from 71 seed lots (agglutination). Two lots tested positive and were confirmed with PCR. They also did trace back tests of sister lots; 4400 tuber cores were tested and all were negative. MT - Nina Zidack reported that 10,200 acres were in the certification program in 2014. Acreage has been steady. She discussed the winter grow out tests and said that emergence of varieties and lots was mostly good. They have been using Rindite instead of GA to encourage emergence. Results of PVY testing were as follows: 0% = 70 lots, 0.5% = 12 lots, 0-5-1% = 7 lots, 1-2% = 7 lots, and >2% = 4 lots. She noted that “Umatilla” is the easiest to see symptoms and rogue, followed by “Russet Burbank”. “Alturas” can be more difficult depending on the PVY strain. “Ranger” is difficult to see symptoms with N strains. “Norkotah” is very difficult to see symptoms and rogue. Zidack reported that growers that separated nuclear and G1 in 2013 had 96% clean G1 in 2014. But, growers that had nuclear and G1 together in 2013 had 73% clean G1 in 2014. Separation of nuclear and G1 is now a recommendation that they are making to growers. Zidack reported less current season spread in 2014 vs. 2013. She suggested this might be attributed to fewer aphids, mineral oil sprays, and/or earlier vine kill and harvest in 2014 (hail damage extended the season in 2013). They are recommending separation of nuclear and GI seed crops and surrounding them with their cleanest G3. They are also suggesting use of a legume or annual rye border, planting as far from other potatoes as possible, a neonicotinoid insecticide at planting, mineral sprays in-season, insecticides that are feeding inhibitors (ex. Beleaf, Fulfill) applied in-season, or new-generation systemics like Movento in-season, and paying attention to when adjacent crops are harvested. WA - Mark Pavek discussed the Commercial Seed Lot Trial that has been conducted in WA every year since 1978. In 2014, the lots originated from Canada (9%), Idaho (34%), Montana (37%), North Dakota (1%), Oregon (2%), and Washington (13%). Though not totally representative of what is grown, the varieties entered were “Russet Burbank” (20%), “Ranger” (13%), “Russet Norkotah” (15%), “Umatilla” (13%), “Alturas” (7%), “Clearwater” (6%), and other cultivars (27%). PVY symptoms were found in 30% of the lots, blackleg in < 10% of lots, and no PLRV. Some lots had severe PVY infection. It was suggested that Pavek contact state certification agencies about the most severe lots, since this would be helpful information for them. WI - Amy Charkowski reported that about 8,500 acres were in the certification program in WI in 2014. Acreage is holding steady. She said that they moved the winter grow out to Hawaii this year (instead of Florida) and it cost less. She said the highest rejection rate they have had for PVY was in 2013, but 2014 had fewer rejections. Herbicide damage was a big issue in 2014. Charkowski noted that the N:Wilga strains have been the most problematic in WI and they have not seen much NTN. Project Reports: Jonathan Whitworth: New varieties with full or partial resistance to PVY. Whitworth reported on a study to characterize strain specific infection reactions in some potato cultivars including “Premier”, “Ranger Russet “, “Yukon Gold”, and “Mountain Gem Russet”. Nina Zidack: PVY management in seed. Zidack reviewed the results of a study to integrate rogueing, stylet oils, and induced resistance to minimize PVY transmission in seed fields. They found that an insecticide program alone did not reduce aphid transmission of PVY. Mineral oil provided the most significant reduction in PVY transmission and it was enhanced when paired with an insecticide program. Rogueing decreased virus spread when paired with other control measures. Application of BmJ (a Bacillus myccoides isolate) did not reduce PVY spread alone. Mathuresh Singh said application instructions for mineral oils are vague. Rates should be 1.5 to 2.0 L/A, because higher rates can cause phytotoxicity. Mathuresh Singh: Current season spread of PVY and PVY transmission and translocation studies. Singh said that they have been tracking current season PVY spread in 12-13 fields per year since 2010. They have noted a decrease in PVY spread and severity over the years. This is attributed to the use of mineral oils and insecticides, and improved timing of applications. They have noted that insecticide applications alone are not effective. He also discussed the results of a study comparing mechanical transmission methods. Seed cutting resulted in no transmission, but plant wounding did. Hammering resulted in 90% transmission. Singh also talked about a greenhouse PVY translocation study. They found that PVY travels upward faster than downward. They established a time line of PVY movement in leaves above and below the infected leaf (middle) and also for movement into the tubers. Hanu Pappu: Update on PVY, PVS, PMTV and TRV work. Pappu reported on the work that his lab has been doing to understand several important potato viruses. His lab has been comparing small RNA profiles of different PVY strains. They are also comparing various PMTV isolates from the U.S. and have found that all carry three overlapping genes (triple gene block) that are important for suppressing host defense response. They are comparing the U.S. PMTV isolates to European PMTV isolates. They are also studying TRV isolates and are creating a database of TRV genome sequences from different areas. Pappu also said that his lab has been studying a common association of late blight resistance and PVS susceptibility in in potato varieties. Cassandra Funke (and Alex Karasev): Changes in PVY strains circulating in potato in the PNW, and reactions of potato cultivars to different strains of PVY. Funke said they have documented a decrease in PVY-O incidence in the PNW, but an increase in PVY-N:O. She also discussed some work they have done to learn about reactions of several varieties to PVY strains and sources of resistance. They have been looking at the practical consequences of HR-resistance, which may restrict virus movement and prevent systemic PVY infections under certain conditions. Silvia Rondon: Brief update of aphid work in Hermiston. Rondon has been studying PVY in volunteers and weeds and has found a mixture of PVY strains. In one study she reports that green peach aphids did not appear to differentiate between healthy vs. PVY infected plants when given choice. She has also been comparing PVY transmission rates from weeds to potato with green peach aphids and potato aphids. She reported that green peach aphid transmission of PVY from lambsquarters to potato was 44%, but from potato to potato was 57.5%. Transmission with potato aphids from lambsquarters to potato was 37.5%. Additional Research/Extension Reports: Andy Jensen reported that seed potato growers in some areas are in need of more education about aphids and aphid monitoring. Some do not monitor aphids and are not familiar with identification of aphids. These growers make regular insecticide applications but do not check to ensure that those applications were effective. Erik Wenninger and Shaonpius Mondal have been studying aphid transmission of PVY strains. He noted green peach aphids were the most efficient vectors of PVY in their studies, potato aphids were the least efficient, and bird cherry oat aphids in the middle and much more efficient vectors than previously thought. Wenninger reported that the aphid species complex has varied from year to year at their study sites in Idaho. Absolute abundance has also varied. Silvia Rondon also reported year to year variations in the predominant aphid species in the Columbia Basin. Some of the more common non-colonizing species were bird cherry oat aphid, mint aphid, rose-grain aphid, mealy plumb aphid, cowpea aphid, and pea aphid. Amy Charkowski opened a discussion about a proposal to lift the 1912 quarantine on importing tubers from countries other than Canada. Mini tubers imported from other countries go through six-month quarantine. Rob Davidson explained that some Colorado growers are pushing to allow PVY-resistant material from Scotland so it can be planted immediately. Jorge Abad said that temporary release permits are already an option for importing potato plant material. A temporary expedited release usually takes six weeks. Davidson said that the temporary permit process should be explained to John Keeling (U.S. Potato Council). It was suggested that a letter from WERA 89 could help and Charkowski would start the process. Everyone agreed that a lift of the quarantine, even for Scotland which is considered an origin of low-risk, would be bad since there is nothing to verify the earlier origins of the material. Status Report – SCRI PVY: Amy Charkowski reported that the SCRI-PVY project was approved for funding but they have not heard what the funding amount will be. Election: Carrie Wohleb will move from Vice Chair to Chair. Andrew Houser was unanimously elected as the Vice Chair. Ken Frost was unanimously elected to serve as the Secretary. The meeting adjourned at 10:00 am March 5, 2015.

PVY Strain Diversity and Strain Specific Resistance in Potato Cultivars – Karasev et al. Interactions of the main strains of PVY with potato cultivars grown in Idaho, Washington, and Oregon were studied to understand the drastic change in strain composition of PVY isolates circulating in the Pacific Northwest. Special attention was paid to strain-specific resistance genes available in North American potato cultivars. PVY strains have been defined based on genetic reactions in potato indicators expressing hypersensitive reaction (HR) response due to the presence of three different N genes. The genetic background of the majority of North American potato cultivars has so far been poorly characterized for the presence of N genes inducing HR towards different PVY strains. To fill this knowledge gap, the HR response was studied in eight potato cultivars elicited by the five strains of PVY (PVY-N:Wi, PVY-NA-N, PVY-O, PVY-Z and PVY-N) circulating in North America. Potato cultivars tested included Russet Burbank, Russet Norkotah, Shepody, Ranger Russet, Western Russet, Alturas, Rio Grande Russet, and Yukon Gem, and standard indicators Desiree and Maris Bard with the known genetic background. Three additional strains (PVY-N:O, PVY-NE11, and PVY-E) were tested on Yukon Gem. This systematic approach allowed the investigators to identify Nytbr and Nztbr genes present in several North American cultivars. Two more new, putative N genes were postulated to be expressed in the cultivar Yukon Gem, and one additional putative N gene was postulated to be expressed in two cultivars, Yukon Gem and Rio Grande Russet. These N genes may represent valuable sources of resistance against multiple strains of PVY. Presence of strain-specific resistance genes in new cultivars, in addition to the decline in acreage of Russet Burbank, may explain the observed shift in PVY strain composition from non-recombinant PVY-O to different recombinant strains that do not elicit HR in the majority of potato cultivars. The two practical conclusions from this research are: 1) presence of strain-specific N genes in commercial cultivars needs to be understood and taken into account to correctly manage PVY threat; 2) breeding for PVY resistance must address the most common PVY strains circulating in the field. Developing Potato Cultivars Resistant to PVY – Whitworth et al. Efforts to develop PVY resistant potato varieties involved the use of putative PVY resistant and susceptible breeding clones and new varieties for screening trials in Idaho, Wisconsin and New York. Two sets of clones were screened each over a two year period. Clones that were submitted for screening trials came from seven breeding programs across the USA. Each set was planted in three separate strain blocks and one block was inoculated with PVY-O, one with PVY-N:O, and one with PVY-NTN. In addition, no insecticides for aphid control were used in the plots. In the first set there were 15 clones in addition to Russet Burbank and Yukon Gold used as controls. Two of the 15 were known to have markers for the PVY resistance gene, Ryadg. A total of four clones, including the two with the Ryadg gene, were not infected by PVY during the season or in subsequent grow-out tests of daughter tubers. Foliar and tuber symptoms were recorded on all clones in the trials. A second set of nine clones for these screening trials had four clones with the presence of Ry genes, with two from Ryadg, one from Rysto, and one from Rychc. Results from the two years (2013 and 2014) are not yet complete, but preliminary results show that six of the nine clones are resistant to PVY. The Ryadg, Rysto, and Rychc genes are reported to provide resistance against all strains of PVY. In addition to these trials, an example of the multiplying effect of advanced breeding lines with PVY resistance is that in 2013, one of the clones in the first set of trials was used in 12 crosses to develop chip, tablestock, and yellow varieties. These crosses were made with a clone developed by Dave Douches at Michigan State University. These 12 crosses resulted in 2973 individuals, all with the potential to have extreme resistance to PVY. The molecular markers for genes conferring extreme PVY resistance are now being used by breeding programs in the USA. In the USDA-ARS potato breeding program in Idaho, both the Rysto and the Ryadg markers are routinely used to identify second field year selections with these genes. Both genes have been introgressed into the program, and Rychc is currently being introgressed. A variety to be released this year named Payette Russet has the Rysto marker and in two years of field testing at high virus pressure shows no PVY in grow-out tests of daughter tubers. In the same trial, the Russet Burbank controls averaged 85% PVY. In addition to virus resistance, this variety has been trialed by multiple cooperators and scored high in agronomic, processing, and culinary trials. Another PVY resistant variety, Eva, released in 1999 is a round white chipping potato that also has extreme resistance to PVY. These releases and the increase in the number of putative PVY resistant clones submitted for these trials between the first and second set of clones shows clear progress in developing PVY resistant varieties that are acceptable to the industry. They also demonstrate an emphasis on PVY resistance in breeding programs. As these and other PVY resistant varieties become accepted and more widely grown, the impact is great for the seed grower as rejections and downgrading of seed will decrease and to the commercial grower as yield reduction and quality defects caused by necrotic strains of PVY will be reduced. Best Management Practices to Minimize PVY Spread – Singh et al. Potato is the most valuable agricultural crop in New Brunswick, Canada. The province is an important seed producer both for Canada and for export to foreign markets. About 47,000 acres of the limited agriculture land in this small province is used for potato seed production every year. Up to 2011, many potato seed lots were testing with high levels of PVY (5 to 10% or more). Specifically, in 2011, 33% tested >5% PVY, and less than 43% tested at or below 2% PVY. Subsequent efforts of the research community to develop and communicate science-based best management practices and strict certification thresholds set by the government have resulted in drastic improvements over the past several years. In 2014, only 1.1% of tested lots were >5% PVY and over 93% were at or below 2% PVY. A project tracking PVY spread in commercial potato fields across the potato growing region of New Brunswick was conducted from 2010 to 2014. In total, 16 commercial growers participated, including 56 separate fields and 13 different potato varieties. PVY inoculum was determined at the beginning of the growing season, and then its spread to marked initially virus-free plants was measured through the season and correlated with initial inoculum, aphid abundance, and management practices used in the field. The results make clear that frequent mineral oil spraying at moderate rates (ca. 2 liters/acre, every 5 to 7 days) beginning early (prior to full crop emergence) and continuing season-long helps to reduce PVY spread to uninfected plants. The effectiveness was substantially increased when several of these oil sprays (at least 5) were combined with contact insecticide sprays, especially when more effective lambda-cyhalothrin or flonicamid type insecticides were used. Control fields that were not sprayed with either oil or insecticide showed an average PVY spread ranging 27% to 31% in the first years of the study, which dropped to 11% by 2014. At the same time, intensively sprayed fields had average PVY spread of 14% in 2010, dropping to only 1.2% in 2014. The near 30-fold reduction in on-farm spread of PVY between unsprayed fields in 2010 to intensively sprayed fields in 2014 is largely due to more frequent and better-timed oil spraying combined with numerous insecticide applications of known-effective chemistries. Also contributing to the decline, however, was a better recognition among growers of the value of planting clean seed. This led to a general trend toward lower inoculum in the field over the years; it went from averaging 2.2% PVY-positive plants in 2010 to only 0.6% in 2014. In 2013 and 2014, controlled and replicated experimental field trials were undertaken to test various treatment combinations of mineral oil and insecticide sprays in many small plots within the same field. In 2013, 13 replicated mineral oil and insecticide treatments were planted, but with low PVY inoculum, thus only a slight amount of spread to new plants occurred. It was difficult to distinguish the different effects of each individual treatment in 2013; despite this, trends in the broad categories of the treatments reflected what was observed on commercial farmers' fields. In a redesigned trial in 2014, higher initial inoculum (2.3%) ensured far more potential for PVY spread (up to 17% in control plots). These data more clearly showed that frequent mineral oil spray and combination of mineral oil and insecticide spray significantly reduces PVY spread (down to 7% to 9%) in these controlled experiments, similar to observations on commercial farms. Other important results from the field trials, however, are that increased rates of mineral oil spray (4 liters/acre rather than 2 liters/acre) do not increase the effectiveness of the spray, and confirm the suspicion that insecticide sprays alone (not in combination with mineral oil) do not significantly reduce PVY spread compared to unsprayed control plots. From both experimental field trials and the long study surveying PVY spread and management practices in commercial potato fields, best management practice recommendations have been developed for reducing on-farm spread of PVY. The practices are effective, economically viable and now widely adopted by the local industry. Planting the lowest possible PVY inoculum in seed is recommended as the most cost-effective deterrent against PVY spread. Furthermore, mineral oil sprays are recommended early (before full crop emergence or large aphid abundances) and frequently (every 5 to 7 days; 12 to 15 sprays per season) until top-kill; oil rates at 2 liters/acre mixed as 2-3% oil in water are sufficient, with several of these sprays (at least 5) tank-mixed with foliar contact insecticides such as lambda-cyhalothrin or flonicamid. Spray programs should increase in intensity during the rapid early growth of the crop or periods of higher aphid activity. The large-scale survey of New Brunswick growers' practices and PVY spread in commercial fields has been completed, but the experimental field trial will continue and expand to include investigating effects of different strains. By planting known-positive tubers of three major strains of PVY, consistency of inoculum in the treatment plots can be maximized and the possibility of differential rates of spread of the strains can be investigated. Symptom Expression of Major PVY Strains in Different Potato Varieties – Singh et al. PVY exists in nature as a complex of several distinct and evolving strains. In many major potato producing regions of the world several novel strains (e.g. PVY-N:O and PVY-NTN) have recently emerged that are quickly displacing the traditional "ordinary" strain PVY-O. These novel strains are concerning, as they typically show more cryptic symptoms, hampering field detection, and distinct phytopathology compared to PVY-O. The responses of eleven commercial potato varieties commonly grown across Canada were characterized to infection with different PVY strains. Plants of each variety grown in the greenhouse were artificially infected with one of the PVY-O, PVY-N:O and PVY-NTN strains. While ten of the varieties were easy to infect with all strains, one variety "Eva" could not be infected by any of the tested strains. In infected varieties, visual symptoms on leaves and effects on tubers varied greatly depending on the infecting strain. Generally, most varieties showed strongest visual symptoms and tuber yield reduction with PVY-O; notably, however, varieties "Bintje" and "Innovator" showed mild symptoms and no significant plant vigor or tuber yield reductions with any PVY strain. There was no clear correspondence between the typically more mild visual symptoms from PVY-N:O or PVY-NTN and effects on tuber yield or quality, though several varieties were identified (e.g. "Atlantic", "Chieftain", "Norland" and "Sangre") that showed no significant tuber effects from these strains. A particular concern about PVY-NTN is its potential to cause tuber necrosis, yet only one variety "Envol" showed these symptoms from the eleven varieties tested thus far. The characterization of symptom expression in different variety-strain combinations will continue in 2015, with the addition of more potato varieties as well as the replanting of progeny tubers from the 2014 trials to investigate symptoms in secondary infection. Mechanical Transmission of PVY and Within-plant Transduction of PVY – Singh et al. In the greenhouse, the potential of mechanical transmission of PVY through seed cutting or plant wounding was studied. There is substantial concern in the local industry that these events during planting, field operations or even violent weather phenomena may transfer PVY to neighboring plants. To investigate seed-cutting, known-infected tubers each carrying the PVY-O, PVY-N:O or PVY-NTN strains were manually cut as though being prepared for planting. Without sterilizing the knife, five more known-negative tubers were immediately cut, then all the seed were planted in marked pots to later test if the resulting plant was infected with PVY. Despite testing all three strains and replicating the experiment twice, in no case did PVY spread to the negative tubers. Mechanical transmission between the foliage of the plants, however, did occur easily in the greenhouse setting. Simply hammering together the leaves of an infected and non-infected plant with a pair of stones was sufficient to transfer the virus in 90% of attempts. Firmly squeezing two stems together, as may happen by stepping on plants or striking them with farm equipment, was 60-70% effective at transferring PVY, and even only jostling plants together by blowing a fan on them for a few days caused up to 40% transmission in some trials. Clearly, mechanical transmission of PVY with realistic treatments is a significant potential. In 2015, the investigators will study the potential for mechanical spread in several growers' fields by testing plants adjacent to known-infected plants. These infected plants will be intentionally planted in high-traffic rows (along tractorways) and compared to infected plants in low-traffic control rows. After artificially infecting greenhouse-grown plants, the transduction of the virus through the plant was also studied. From inoculation on a leaf half-way up the stem of a ca. 75 day old plant, the results show faster transduction upward into the youngest growing leaves (59% of plants after 12 days) than toward older leaves lower on the plant (53% of plants after 24 days). Downward transduction into developing tubers may be slightly faster, however, as 63% of plants showed infected tubers after 24 days. Further research into rates of virus transduction and distribution in the plant may produce important advice for management, such as the timing and method of top-kill. All three PVY-O, PVY-N:O or PVY-NTN strains were tested individually for the mechanical transmission and transduction experiments, though there were no clear differences between the strains. Aphid Vectors and Alternative Sources of PVY on Potatoes – Rondon et al. Several strains of PVY have been problematic in potatoes in the Pacific Northwest causing reduction in quality and yield loss. This disease has increased in severity in recent years and represents one of the most common reasons for rejections of seed lots for certification. Potato Virus Y can be vectored by many aphid species and has several alternative weed hosts; however, alternative weed hosts have not been thoroughly investigated in this region. Therefore, weeds and neighboring crops were surveyed for PVY and aphid vectors in Oregon (Umatilla, Morrow, Baker, Union, Klamath counties) and Washington (Franklin and Benton counties) in 2013 and 2014. Fields were monitored for aphids using green tile traps, buckets, inverted leaf blower, berlese funnel, leaf samples and yellow sticky cards. Weeds such as lambsquarters, tumble mustard, prickly lettuce, redstem filaree and bittersweet nightshade were surveyed for presence of aphids and PVY; neighboring volunteer potatoes, wheat and alfalfa were also sampled. Total number of aphids in the lower Umatilla and Morrow counties were some of the highest seen in the last 30 years. Numbers were relatively high in Klamath Basin and in Union-Baker counties as well. Over 20,000 aphids were collected for species identification. The weed and/or crop species that supported the greatest percent of aphids included: alfalfa, wheat, redstem filaree, prickly lettuce, tumble mustard and bittersweet nightshade. Over 30 species of aphids were identified from traps in potato fields. Potato aphid, cereal aphids (bird cherry-oat aphid, corn leaf aphid, etc.), mint aphids and mealy plum aphids were the most abundant species. PVY was found in 50% of the potato fields surveyed, and approximately 30% of the volunteer potatoes sampled in neighboring fields. Transmission Efficiency of PVY Isolates by Three Aphid Species – Wenninger et al. PVY is transmitted by aphids in a non-persistent, non-circulative manner. Green peach aphid is the most efficient vector in laboratory studies, but potato aphid and bird cherry-oat aphid can also transmit the virus. Studies were conducted with all three of these aphids to evaluate PVY transmission efficiencies for two isolates of each of three PVY strains (PVY-O, PVY-N:O, and PVY-NTN). Treatment also included a sham inoculation. Infected plantlets (Russet Burbank cv.) were used as the virus source and virus-free plantlets were used as the virus recipients. Recipient plants were tested using quantitative DAS-ELISA to assess virus titer and infection percentage five weeks post-inoculation. Positive recipient plants were also tested using RT-PCR to verify the virus strain present. Transmission efficiency in general was highest with the green peach aphid. Green peach aphid and bird cherry-oat aphid transmitted PVY-NTN with greater efficiency than PVY-O and PVY-N:O. Transmission efficiency for all aphid species did not differ significantly between isolates within strains. There were no correlations between plant titer, infection percentage, and recipient plant titer. Bird cherry-oat aphid transmitted PVY at higher efficiency than previously reported, suggesting that it is more important to PVY spread than was once thought. Factors Influencing PVY Transmission – Wenninger et al. A study was conducted to compare factors that might influence PVY transmission. Infection rates in aphid-inoculated and mechanically inoculated plants were compared across two potato genotypes (Yukon Gold and A98345-1), three PVY strains (PVY-O, PVY-N:O, and PVY-NTN), and two growth stages (pre- and post-flowering). Infection rate and virus titer was measured using DAS-ELISA. Yukon Gold had a higher PVY infection rate than A98345-1 regardless of PVY strain, especially when inoculated mechanically. Infected Yukon Gold plants had higher virus titer and lower tuber mass compared to A98345-1. Yukon Gold was most susceptible to PVY-O, while A98345-1 was most susceptible to PVY-N:O. Across potato genotypes, plants infected with PVY-O had the highest virus titer while plants infected with PVY-N:O had the lowest virus titer. Both cultivars demonstrated age-based resistance, with higher infection rates when inoculated pre-flowering versus post-flowering. This study demonstrates that many factors influence PVY transmission. These factors should be considered when screening genotypes for resistance. Potato Mop Top Virus (PMTV) – Pappu et al. Potato mop-top virus (PMTV; family Virgaviridae) was reported recently in the Pacific Northwest USA. To better understand the genetic diversity of the virus, the complete genome of an isolate from Washington State (WA) was characterized. Sequence comparisons of the WA isolate with other known sequences revealed that the RNA Rep-encoded RdRp protein and the RNA CP-encoded coat protein displayed >99% amino acid identity with those of two Nordic (RdRp) and several European and North American isolates (CP) respectively. The RNA TGB-encoded TGB 1 and TGB 3 protein sequences had >99% amino acid identity with the corresponding proteins of the Czech and Danish isolates, whereas the TGB 2 protein is identical to the Colombian isolates. Phylogenetic analysis of the viral genes of the WA isolate reflected the close relationship among the WA and European isolates. RFLP analysis of corresponding DNA of RNA TGB and RNA CP revealed that the WA isolate is considered RNA TGB-II and RNA CP-B types, which are prevalent in Europe and other parts of world. This is the first report of the complete genome characterization of PMTV from the Americas.

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