Brief Summary of Minutes of Annual Meeting

WERA-089 Potato Virus Disease Control Committee Annual Meeting 14-15 March 2007 San Diego, CA Chair: Juan Manuel Alvarez, University of Idaho, Aberdeen Vice-Chair: James Crosslin, USDA-ARS, Prosser, WA Secretary: Steven Marquardt, North Dakota State Seed Department Chair Juan Manuel Alvarez welcomed everyone to the meeting and presented opening remarks regarding the format for the meeting and began the meeting with special introductions. Greg Bohach (CSREES Administrator for our group) presented information regarding the reapproval of the committee and encouragement regarding the status of the organization and its continued recognition. The WERA-089 was approved almost immediately after last years meeting (one of 3 was rejected last year). The approbation process went through with no suggested changes where most that go through are with suggested changes. The impact statements were well received by CSREES. Attendees represent the states of Colorado, Idaho, Minnesota, Oregon, New York, North Dakota, Washington, and Wyoming/Nebraska. Certification Agencies Presentations and Reports Rob Davidson (Colorado) talked about current and recent virus disease levels occurring in Colorado seed over the past several years and included several studies. Rob illustrated the dramatic increase of virus in seedlots when replanted for one and two years out from certification and the corresponding yield decreases with that rising virus level. He explained that in Colorado Certification, the first rejections for mosaic occurred in 1991, three years after the introduction of Russet Norkotah. There were no rejections for mosaic in the post harvest test until 2003, with the most acres rejected for the year and for the winter test in the 2006 crop. Russet Norkotah is by far the leading cause for rejections for certification in both summer and winter inspections. Until recently, rejections in other varieties had remained at a very low level but now they are starting an upward trend as well. Additionally, earlier generations are increasing in size in recent years and PVY has begun to become a problem there as well. The Russet Norkotah variety and selections represent 60% of the acres in the San Luis Valley, and about 45 to 50% of the seed acres. The aphid trapping data presented indicates rising numbers compounding with drought and cultural trends in other crops leading to increased numbers of aphids moving to potatoes. With the continued increase in inoculum, vectoring and seed demand, growers need the seed to fill contracts. This is where a seed law is needed. It will be difficult, but he believes that over the next two or three years they can get control over this. The difficulty has to do with the strains maturing later, and a roguer's ability to detect PVY anytime in a plant. It's not the vectors, it's the inoculum. Summary: The Russet Norkotah variety is problematic at best but most of the other varieties were pretty clean, although they are concerned about seeing the virus moving into the non- Russet Norkotah -type varieties. They have over 150 varieties. The only real problems are the mosaics and they are seeing more TRV in commercial acres (not seed). They may be reduced in acreage next year due to water availability. The certification system has been able to hold in check the various diseases afflicting seed potatoes. However, with a 'symptomless expresser' like Russet Norkotah, commercial demand and / or interference can pull the disease situation out of control if the hands of certification are tied. Phil Nolte (Idaho) presented current year Idaho datasets provided by Doug Boze (ICIA Area Manager) regarding virus pressure and rejection rates and explained the changes taking place in Idaho regarding their post harvest test. The virus levels in the 1990s were PLRV until acreages of Shepody and Russet Norkotah increased. Then PVY levels began to ramp up and are currently a problem. The worst years were probably 2000 and 2001. The current year winter test is not complete. According to Alvarezs suction trap data, mid-July to 1st of August is usually when a spike of Bird Cherry Oat Aphids occurs. Leafroll is very minimal. In 2006, they had the highest aphid activity in the last four years and the virus level may increase consequently. Steve Marquardt (North Dakota) presented various data sets from ND, WI and ME ranging from 1968 including summer and post harvest test inspections. Rising and falling rejection levels in line graphs were noted for several diseases, virus and non-virus. They rose and fell with time. All of the inspections are done on a visual basis with laboratory testing for support information, especially for 'symptomless expressers'. In general, PVY levels are rising and becoming more difficult with the new strains and milder symptoms on many varieties, but it is manageable. Discussion ensued regarding the importance of the PVY problem. Consensus seemed to be that there is an increase of PVY infection rates. Several other topics in the discussion included whether the PVY epidemic is a problem of varieties that do not express symptoms adequately and / or a problem that the newer PVY strains do not seem to express visually for as long in the season (narrowing visual window), and that the yields are not always dramatically affected. It was not a problem until the commercial growers found that they could not get seed. As long as seed is available and there are no apparent symptoms, the perspective of the commercial grower of Russet Norkotah seems to be that, PVY is not a problem to them. They will have taken the cap off the virus. This is another problem that needs to be addressed. Clearly, PVY is a problem. But the strains are another issue as they may present different outcomes when infecting different cultivars. It was especially noted the case of Russet Norkotah selections, presenting milder infection symptoms with not major yield reductions. There is still a lot to learn about the new virus strains. As was acknowledged by many, earlier generations of seedlots are increasing in size in recent years, which makes not them practical to rogue. It is necessary to look for virus management / control strategies that we can take back to our grower / board / commission meetings for further consideration as they get final say in rulemaking on the state level. Are there levels of virus that our current standards or techniques cannot manage? One of the problems is the varieties, but we do not have the ability to control that. There is a limitation to what growers and certification can do. We cannot spend a fortune testing for every combination of variety and strain and end up with nothing meaningful. It's a visual based system and the ability of roguers is variable, but we have studies showing that a good roguing crew can stay on top of it. Additionally, other non- Russet Norkotah varieties out there have PVY problems. So it's more problematic than a laboratory can resolve without the insight of the people in the field. Dave Ragsdale (Minnesota) presented some data indicating the current situation in Minnesota. PVY strain information illustrated a complicated picture in Minnesota. Fungicide use for late blight exacerbates green peach aphid flights in the field. Fungicide and pyrethroid sprays in combination balloon huge populations. He has seen circles killed by green peach aphid. Minnesota had suction traps and pan traps for the past three years in Hawaii. It may be 12 aphids for the six week period. Aphis gossypii and Aphis glycines, in the field can mate. They are very closely related. Although soybean aphids (A. glycines) do not colonize potato, they do feed on the phloem for as long as 10 to 12 minutes. Minnesota had a very mild winter translating into early aphid movement. They are watching movement of virus strains. Virus levels seem to be high. The rejection rates did increase. Jeff McMorran (Oregon State University). Very low levels of PVY were observed this year in winter grow-outs relative to 2 or 3 years ago. This is attributed to a couple of different factors: 1) growers are replacing seed with clean seed and it stayed clean 2) they are growing some Russet Norkotahs, but not a lot of acres of the varieties that cause them a lot of problems in the past. Growers are moving away from some of the problematic varieties. They are seeing more mild-type symptoms. Gary Franc (University of Wyoming, Wyoming / Nebraska). 5700 acres certified last year, no rejections for PVY. About 500 of those acres are in WY and all acres in WY are certified, even though a portion of those acres are just for the commercial market. No real problems the last couple of years. Dallas Batchelor, Andy Jensen (Washington). Most of the seed is confined to the west side of the state. The east side has a few growers in the northeast, but most of that is consumed internally. Commercially, it has been quite a few years since leafroll has been of any consequence, however, the last 2 years have seen a steady increase of leafroll plants observed. They believe that they will see a resurgence in leafroll in the very near future. Spraying for leafhoppers has been stepped up. Andy Jensen put out the yellow cards for monitoring leafhoppers. Jensen indicates that they do not colonize (in terms of reproducing) potato plants, but they are consistently found on potato fields for quite some time. There is data that says that in the lab they feed on the plants for weeks. So, presumably, you can spray with some residual activity, you can knock them out for some time. It takes several minutes to hours to spread the phytoplasmas. So if the insects feed for anytime, they will probably spread the phytoplasmas that cause the disease. It appears leafhoppers are not afraid to stay for days on the crop. They think the insects have 3 generations per season. Question: Do you spray 3 times, only in spring or only when they move from weeds to potatoes? Some growers spray once, some all season. There are some that think the insects produce damage all through the season. But, from a grower's meeting, they put down almost anything from mid-May to almost the 3rd week in June and get good control but there are those who continue to see additional infection beyond that and how important that is no one seems to know. If you look at the symptomology, its about 3 weeks from infestation to symptoms. Jim Crosslin: The data that exists (Munyaneza) with row cover in Moxie and uncovered at various times definitely indicates that it is the early crop exposure to the phytoplasma vectors is when the plants are most susceptible to infection. The older plants are less susceptible. So, control of leafhopper in early May to possibly early June is fairly good to control purple top. The early leafhopper invaders are the ones that transmit early in the life of the potato plants causing the disease problems. It is now also known from leafhopper colonies that the insects overwinter as adults with the phytoplasma in them. So as soon as it warms up in March, they will move into whatever plants happen to be available and will have phytoplasmas in them ready to be vectored. They find phytoplasma in tumble mustard, wild radish, but never found it in Russian thistle until last year. Russian thistle is a great host for the leafhopper. They have infected kochia in the greenhouse, but have never had a wild kochia test positive for phytoplasmas. Discussion: Growers mostly use pyrethroids and the carbamate Vydate. Vydate is used in furrow in the growers nematode program but it is much more expensive than pyrethroids. Someone may have seen some effectiveness of this insecticide reducing phytoplasma infection by accident. It was noted that: the earlier the phytoplasma infection, the more devastating the disease. After plants reach maturity, you may or may not see signs of infection. It all depends on the physiological stage of the crop. The processing quality does not seem to deteriorate at that point in time. There is a yield loss. The most efficacious control of phytoplasma vectors is about 4 weeks after plant emergence. [Crosslin: The phytoplasma does infect the daughter tubers at a fairly high rate (looks like about 35% on controlled, unsprayed plots) and fairly high rate (20%) of those tubers will produce a phytoplasma-affected plant with no symptoms, esp. in the potato variety Katahdin]. Other Disease-Related Presentations Emmanuel Jacquot (INRA). Reported on the Detection and Characterization of the Potato virus Y using FRITN (Fast Reliable Innovative Tools for Necrotic Potato Virus Y) Assay and Potato virus Y: A variable pathogen with numerous not yet described variants. The invited speaker presented an overview of the current PVY detection tools, indicating that the serological tools are not reliable for detection of the virus and that they fail to characterize the different strains. Then he also presented some biological and molecular tools for PVY detection and characterization. Biological tools, he argued, are reliable for characterization of strains but inappropriate for large scale testing. Recombination events that occur in molecular targets used by molecular assays may make these tools inefficient for strain characterization. Then he presented some molecular markers that are related to the necrotic ability of the different PVY strains. A new set of detection tools based on these markers have been patented by his lab in France. There are qualitative, quantitative and multiplex versions available. The FRITN PVY assay targets a single nucleotide polymorphism linked to the necrosis property of PVY isolates. FRITN assay allows accurate assignment of the 46 tested PVY isolates in their corresponding YN or YO groups. Samples containing PVYN or PVYO RNA copies are efficiently detected by the developed FRITN assay. Detection of PVYN and PVYO isolates in mixed fractions is reliable using the FRITN assay. The quantitative FRITN assays are 10 to 1000 times more sensitive than available molecular and serological assays and allow detection and quantification of PVY in fractions containing from 103 to 107 copies of PVYN or PVYO RNA. The quantitative FRITN assays quantify PVY isolates according to the specificity of the probe. In mixed samples, the specific quantitative FRITN assays quantify the target copy number whatever the YN/YO ratio. From GH to diagnostic you can perform 200 tests in 1/2 day on leaf tissue. Add 1 to 2 hours for tubers. These are detections from total RNA extractions. They have not checked these assays against isolates from our hemisphere. Cost is approximately 4 to 10 times that of ELISA. He would like to coordinate a worldwide project to characterize all isolates with the assay and confirm the necrosis-causing gene. As with most tests, it is not as reliable before dormancy is broken. The extraction method is not yet developed to use this technique to test plants a week before kill date. Luis Salazar (Agdia, Inc.) presented some new information from Agdia, Inc. regarding the availability of a new lateral flow test. With emphasis on the Immunostrip tests, Luis Salazar was placing focus on accuracy rather than sensitivity. They are working to include all the common potato viruses. Future plans are in this area. They are also developing rapid detection technology for TRV without coat protein. The NASH technique is also being developed for commercial use at Agdia. This may be more accurate than PCR. PCR requires an extraction which may be given to lose some of the target. Stewart Gray (USDA-ARS, Cornell U.) gave an update on the 3-year national PVY survey. There is data for 2 years completed. There are 4 PVY groups now: PVYO, PVYN:O, PVYN, and now PVYO5. PVYO seem to be the predominant isolate in most states. PVYN:O is widely distributed and seems to be spreading. In some of the states they are seeing a shift of strains but the PVYNTN seem to be localized and stable. Most lots have low or undetectable levels of PVY infection but with the very low number of tubers per acre (2), more data are needed. The Canadians are finding the same things in Canada. PVYN:O is being seen more now locally than nationally. Theories were that 1) perhaps that more of the tubers are infected per plant, and that 2) aphids transmit the new PVY recombinant strains more easily, but neither of the theories have been proven. He does not know whether the mild symptoms produced by some strains allow more infection in the system. The high level of virus infection seems to him to be more environment- than cultivar- dependant. Perhaps some kind of competitive advantage, but it is not clear what it is. Rangers now live longer, and aphids seem to be unable to transmit PVYO after acquiring PVYN:O, and the reverse is not true. Science Panel recommendations included: dropping the P1 sequence information, and simply going with the multiplex information; discontinuing the Year 2 testing, managing PVY as a species not as strains, making post harvest lab-testing mandatory, developing national standards for PVY tolerances, and sharing more information between the US and Canada. Jason Cavatorta (Cornell University) talked on the lack of availability of PVY-resistant varieties to growers, even though there are some known sources of PVY resistance. A number of resistance genes have been introgressed into varieties. There are a number of tolerant (Shepody) and resistant varieties (e.g. Eva, Cornell University, bred for GN resistance). In addition to conventional resistance, there is also transgenic resistance that includes pathogen-derived resistance such as coat, replicase, and other resistance such as antiviral proteins from pokeweed, plantibodies targeting protease in the plant. Transgenic resistance, however, has a strong consumer rejection at this time. He presented an approach that for transgenic resistance using only potato DNA (intragenic) which may be more accepted for consumers and could be more durable. Babu Srinivasan (University of Idaho) talked about an alternate host and possibly a different biotype of potato aphid (PA) which may influence the epidemiology of PVY. Hairy nightshade (HNS, annual solanaceous weed) is found everywhere in Idaho and the Pacific Northwest. Studies to evaluate the performance of the PA on different host plants were undertaken. Host plants included HNS, potato, ground cherry, Chinese cabbage and wild rose and it was found that the aphid does very well only on HNS. HNS outperformed any other host plant. This finding was not expected considering that this aphid is a highly polyphageous. Field experiments also demonstrated the preference of PA for HNS. Virus transmission experiments found that HNS and can be infected with PLRV and PVY. Additional experiments were conducted to determine the effect of plant host and viral infections on the biology of PA. Longevity of PA was longer on HNS when compared to potato and even longer on infected plants when compared to non infected plants of both species. Fecundity was higher on PLRV infected plants of both species than on healthy plants. In fact, PA did not survive to reproduce at all on potato plants. Summary: The PA lives longer and produces more nymphs on HNS than on potato. PA lives longer and produces more nymphs on PLRV-infected plants than on healthy plants. Virus infection alter the physiology of the plant making it more conducive for the PA survival. Andrew Jensen confirmed species identity of this colony as PA. However, since PA did not survive on potato plants, it is believed that this is a new PA biotype exclusively adapted to HNS. 80% of the nymphs turn into adult winged aphids making PA a more effective virus vector. PA is also more active than GPA. Survives less on potato plant, but probes more. PA transmits several strains of PVY. HNS could be one of the causes that we see so much inoculum at the end of the season. Since HNS is an excellent plant host for green peach aphid and PA, and also harbors potato viruses, it should be considered in the management plan of potato viruses. Luis Salazar commented that phloem parenchyma cells are infected by leafroll when co-infected by PVY or PVX. Jonathan Whitworth (USDA-ARS, Idaho) provided information on the Canadian Quality Assurance Survey (CQAS). This survey was developed from discussions held during the negotiations of the Virus Management Plan. Due to the change in Canada of shipping point inspections being done under an audit system instead of a direct federal inspection on every load, USDA-APHIS made plans to randomly check incoming seed loads for the presence of PVYN strains. This work was initiated last April after the WERA89 meeting using some year-end money from APHIS with support from the National Potato Council. Jim Crosslin, Jonathan Whitworth (both USDA-ARS) and John Rascoe (Agdia) developed a check set of PVYN tubers that were tested in all three labs. Results were used by Crosslin and Jim Lorenzen (Univ. of Idaho) to make adjustments to the S6 Singh primer for RT-PCR. A modified S6m primer was subsequently used by Agdia this year on a new check set of tubers. The new primer was able to detect PVYN in the check tubers and is now being used by Agdia (Elkhart, IN) and STA labs (Gilroy, CA). Whitworth provided results of the testing process and made available a list of labs and people for each state that would be involved in the CQAS. This program provides money for testing imported Canadian seed lots with a receiving point inspection that evaluates tubers for internal necrosis and collects a sample of tuber stem ends for a bacterial ring rot test. The money comes from APHIS through a TASC (specialty crop) grant. The work that has been done now provides seed growers and agencies with commercial labs (AGDIA and STA) that can test tubers for PVYN strains as well as Tobacco Rattle Virus, Alfalfa Mosaic Virus and other tuber-necrosing viruses. Hanu Pappu (Washington State University) reported on the continuation of a study of a necrotic reaction of Defender to PVS. Originally found in 2003 in Othello in potatoes in the Washington State seedlot trials from MT in 2003. Some plants exhibited a very severe necrotic type of response on potato and these symptoms persisted in 2004, 2005, and 2006. Symptoms also included severe stunting, necrotic lines, some necrosis on the leaves and sometimes severe malformation. It was interesting that these symptoms are only in one cultivar, Defender, which is one cultivar fully resistant to late blight. For a number of reasons, it is not a popular commercial variety. ELISA and PCR were employed to find out what viruses were involved. Jonathan Whitworth contributed some work to this project in 2003 and 2004. The samples were positive for Potato Virus S and no other common viruses were detected. Interestingly, nearly 80% of the Defender lots and 50% of the Ranger Russet, Russet Burbank and Shepody were positive for PVS. While Defender displayed severe reaction to PVS infection, all other cultivars showed very mild or no symptoms at all. Most were asymptomatic. The tubers were collected thanks to Mark Pavek in the seedlot trial and then grown in the greenhouse to confirm tuber infection. The symptoms persisted, most were symptomless, some with symptoms, but again all plants tested positive for PVS with PCR. Defender symptoms could be described as a hypersensitive response. The analyzed virus is a typical carlavirus. The sequence data achieved so far will be used to generate new RNA and reinfect Defender plants to prove that it is the sequence causing the necrotic symptoms. Hopefully changes can be made in the RNA genome and determinants that are responsible for this differential host response in Defender can be found. Sequences related to the Defender isolate in the Genbank, show that the closest one is reported from Germany. Purification of the virus is in progress and, of course, the ultimate test would be to make an infectious clone. It was noted that parentage of Defender involves a Polish cultivar. These symptoms are reminiscent of Colletotrichum spp. PVS is usually benign. 50% of all Norkotahs and Shepodys are positive for PVS, with very few symptoms. Stacey Gieck (Oregon State University). PMTV and powdery scab (Sss) survey. PMTV is vectored by Spongospora subterranea f. sp. subterranea, the causal agent of powdery scab, and was 1st reported in the United States in 2003 by Lambert et al. (Plant Disease 87:872) from samples collected in Maine. Since then PMTV has been reported by Xu et al. (Plant Disease 88:363-367) from tubers entering Canada from the US but the states were not identified. However reports from APHIS identified nine states. Given the way the Canadian samples were taken, PMTV likely is widespread but obviously not causing symptoms. The objectives of the study were to confirm the occurrence of PMTV, determine similarities /differences in isolates from different geographical areas that might help explain, if the virus is widespread as suggested why internal tuber symptoms have not been widely found. The methods to determine the presence of PMTV were two-fold; one, test tubers with internal symptoms and or powdery scab sent to the laboratory for diagnostic services and, two, bait soil using tobacco where the roots become infected with powdery scab and then PMTV if present. Samples were tested by RT-PCR for PMTV using Crosslin primers targeting the coat protein region of the RNA3 and powdery scab. Tubers positive for PMTV have been confirmed from 4 states. Soil samples have confirmed PMTV from most of those states. Jim Crosslin will look at sequence comparisons of different isolates. Jonathan asserts that PMTV is A2: regulated quarantine pest: present, but under official control. NAPPO: non regulated pest. Purpose is to study and understand the pathogen. Not seeing symptoms of any consequence. Gary Secor (North Dakota State University) reported on Zebra Chip (ZC). 3 different synonyms: US=Zebra Chip, Mexico=papa manchada (stained), Guatemala=papa rayada (striped). Update: 20-30 scientists involving plant pathologists and entomologists are now working on this project. Almost $500,000 from many sources: FritoLay, Sabritas, growers, USPB, NPC, USDA-ARS.. Some of this work has been done by Joe Munyaneza. Scientists are looking at the cause, spread, source, and control. It appears to be spreading not only in the US (CA, NM, TX, CO, KS, southwestern states) but in Mexico, and Central America. It is not in the seed-producing states, neither in Florida or Missouri. The disease is detected based just on symptoms. This is the leading cause for rejection of potatoes for processing into chips and tablestock because of the impact on quality. The disease has been seen since 1995 but really in earnest since 2000. Foliar symptoms are similar to purple top wilt symptoms and include: twisted stems, stunted plants bushy in appearance with a little yellow or purple in the top growth, severe wilt of stems, broken nodes and axillary buds, swollen nodes, and the zigzag appearance. Wilting, often scorching on the leaf edges. There may be brown vascular discoloration and plants could be killed by infection. Underground symptoms include collapsed stolons, lenticel proliferation of the underground stem (indicating some water relations problems), a remarkable pink, sunken stolon attachment like a pink belly button, brown discoloration of the medullary rays throughout the entire length of the tuber (this symptom differentiates the disease from all the other diseases), and affected plants are susceptible to secondary infections by Fusarium and/or Erwinia. The infection causes browning of chips when potatoes are processed. Sugars accumulate and caramelize at high temperatures. We call it zebra chip because of the light and dark streaks. Stems are discolored internally (vascular elements). All the processing and tablestock varieties we have looked at in Mexico, Guatemala and Texas are susceptible. Occurrence has been as high as 70% of affected plants in the field in Mexico and Guatemala. In the US (TX) we usually see from 2 to 5 % in the field. We have not seen an immune variety yet. European varieties, Alpha, Yukon Gold, Red LaSoda, Russet Norkotah, all Frito-Lay (FL) varieties, public chipping varieties all are susceptible. ZC has become the leading cause for rejection of chipping potatoes not only for FL but for the local chippers as well. It is the leading cause for tablestock rejection in Mexico. Experiments in Guatemala covering rows with insect proof cloth seem to prevent infection. This probably indicates an airborne vector. Insect scouting has been extensive. We usually see symptoms by 75 days after planting. 30 to 45 days after planting is probably the time of infection. But we think infection occurs early in the season. The only insect associated with ZC at this time is the psyllid, Bactericera cockerelli (Sulc). Psyllids have been recorded from Guatemala all the way up to Alberta Canada and back as far as the 1920s. We don't know if it's toxin or not. Reversion of symptoms was seen in Guatemala spraying tetracycline in fields. When they stop spraying, the symptoms come back. They did find it in the seed production area of Baja California for the first time in 2006. It appears to be independent of seed source. Affected eyes produce really weak plants. We don't know the epidemiological importance of affected seed. It was seen in 2005 in volunteer Red LaSodas in Texas. Eliminated: all the soilborne pathogens (rhizoc., nematodes, etc.), and viruses (PCR tests all negative). All tubers from affected plants show symptoms, but occasionally a plant where a few tubers don't have symptoms can be found. It is graft-transmissible producing typical symptoms in the greenhouse for multiple generations. Therefore, toxin and physiological disorders can be eliminated as the cause. Xyllela is not a cause of this disease even though it may be present. Many phytoplasmas have been found associated with this disease. We do not have a control in the field except insecticides. Admire at planting and Oberon (new insecticide for psyllid nymphs and whiteflies from Bayer) in the field: this is a new push from growers. We have not found psyllid yellows with this ZC tuber symptom. Scanning and transmission EM reveals good populations of bacteria in phloem. It looks a lot like a proteobacteria present in a disease on sugar beets or strawberries. They have now cut back on the cause to focus on control. ZC is limited to the SW possibly because that is the range of the vector. Solke deBoer tested for viroids and it's negative. Some testing of psyllids and sharpshooters was done but nothing definitive. Jim Crosslin (USDA-ARS, Prosser) presented more Zebra Chip information gathered last year with Joe Munyaneza covering trials. Sequentially grafting experiments (transmitted 3 times into potatoes from plants from Pearsall, TX) were conducted. He saw symptoms consistent with psyllid yellows or ZC with the severe scorch. However, after 3 transmissions he had contamination and had to throw out. Psyllids were originating from Dalhart, TX. All psyllid colonies identified in Beltsville. After slicing, the tuber necrosis appears before your eyes. The symptoms can be reversed if the psyllids are killed before a certain point. On tomatoes in CA, their economic threshold for psyllids is 3 nymphs feeding for a week. Frito first saw this in 1994 in Mexico. Hoba production is new in that McAllen TX area. They have found that an overwintering host is wolfberry (solanaceous tree). The psyllids are all positive for Carsonella (endosymbiont), but they don't think that's a factor. Wolfberry is in Pearsall, Weslaco and McAllen, unknown if its in Dalhart. It is still unknown if we're looking at toxemia or some unknown pathogen. The grafting experiments suggest that there may be a pathogen present. It has been reported that there are fields full of psyllids without ZC and fields with no psyllids that have ZC. There may be some other factors involved. No inclusion body data. IM Lee has done a fair amount of EM work but inconclusive. Two psyllid biotypes are known in the US and 1 more in Guatemala. Phil Hamm (Oregon State University) talked about the further understanding of the Corky Ringspot Disease. The symptomatic tuber arcs are diagnostic but smaller spots can be confused with AMV, TSWV, PMTV, PVYNTN or N:O and Internal Brown Spot (IBS). Aerial field infrared photos show open areas with bare soil, and some not well populated with plants. The plants are not dead but poor growth. Distortion on these plants, irregular sprouting, and multiple stems before emerging, were the symptoms observed. Herbicide damage was suspected. The plants with yellowed leaves were thought to be AMV but tested negative, then noticed chevrons. In another field in Pasco WA: areas very poorly populated with plants. There were distorted plants but no foliar symptoms. Grower used a Vydate program and got him by. Symptomology will give a little bit of an impression it might be rhizoc. Tested nematodes and did find them viruliferous. TRV typically has 2 particles. In potato leaves, they found both particles only once. In roots both particles were found most of the time. Confirming virus presence is not practical with ELISA as it loses its coat protein. Now we use the PCR technique. Roots have both RNA1 and 2 but leaves with RNA1 only. In greenhouse studies, only one was ELISA positive. Tubers usually only have RNA 1, too. (Crosslin: in about ten years, approximately 50% of TRV-positive tubers have only RNA1s.) Methamsodium and Telone II is the program to use at present. TRV and the nematodes have wide host ranges, but the 2 don't mix with weed-free alfalfa. Controls for CRS: don't grow potatoes, rotate with weed-free alfalfa, preplant Telone II the fall before, and in-furrow Vydate at planting to control TRV in potatoes. The nematode spreads TRV so early in the season that you can't control it if you don't have Vydate in furrow. Symptom only reported in Colorado about 10 years ago by Pete Thomas. Need to relate nematodes to early feeding symptoms and number of the viruliferous nematodes related to those early symptoms. Incidence seems to be increasing. Actually, it looks like PMTV with nice chevrons but when they were sent to us they were TRV.

Title: Identifying the components of the tuber necrotic complex. Issue: Identifying the various components of the tuber necrotic complex and developing new molecular diagnostic tools for diagnosis and separation methods and protocols have been accomplished for detection and diagnosis of a heterogeneous group of viruses with overlapping symptoms; 3 different vectors require 3 different control strategies. Diagnostics are limited to scope of the diagnostician's experience without being able to definitively identify pathogen/s. Improperly diagnosed diseases probably have been allowed to be in the system without knowledge. Improved diagnostic tools should help growers make better informed decision leaving less risk to an unknown factor. What has been done: The Canadian quality assurance program uses recommendations from the WERA089 group and also modified primers for detection of PVY strains allowing commercial labs to reliably detect these pathogens, without which the program could not exist. Labs are now able to check for these pathogens providing assurance of quality seed to and empowering the industry receiving this seed to effectively take the appropriate control measures if a pathogen is present. Impact: Improved diagnostic tools will allow heightened confidence in the diagnoses of viruses when high seed volumes move interstate for recertification and for commercial planting as well. Internal necrosis due to PVY cannot be used for planting commercial potatoes, the PVY survey and the Canadian quality assurance survey will provide information about the health status of the seed. New patented tools presented at the meeting (FRITN assay) may be useful to reliably identify necrosis factors of the PVY strains and perhaps levels of infection in seedlots, regions or environments associated with specific cultivar/virus strain combinations in a given environment. Funding sources: State potato commissions, Hatch, National Potato Council (NPC), National Potato Board (NPB), numerous potato growers. Title: Effect of vectors and alternate inoculum sources in the epidemiology of viruses and the PVY complex. Issue: Identifying the various components of the potato viral pathosystem and studying complex intricate interactions between the components with special emphasis on alternate vector reservoirs and inoculum sources and their role in the epidemiology of viruses. The objective of this work is to identify the additional inoculum sources and determine the role of these sources in the epidemiology of the viral diseases. Preferences of vectors for infected plants and weed hosts suggest a possible enhancement of pathogen spread in field. Laboratory studies show that the fecundity of the potato and green peach aphids may be significantly higher on mixed-infected plants than on singly-infected plants or non-infected plants. What has been done: Numerous alternate hosts that serve as vector and virus reservoirs have been identified. The importance of the involvement of the alternate host, hairy nightshade in aphid vector epidemiology of PLRV and PVY is becoming apparent. Impact: The importance of managing the alternate hosts is strictly recommended to be a part of any devised virus management plan primarily by collaborating with state commodity commissions, agricultural departments and seed certification agencies. Recommendations for nightshade control have been developed and published. Funding sources: State potato commissions, Hatch, National Potato Council (NPC), National Potato Board (NPB), numerous potato growers.

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