WERA089 – March 11 and 12, 2009 – Tucson, AZ (v 4-7-09)Pg 1 of 22
WERA089 Agenda
Potato Virus Diseases Control
March 11-12, 2009
Radisson Suites Hotel Tucson Airport, Tucson, AZ
Chair: Steven Marquardt, Nebraska Potato Certification Association
Vice-chair: Stewart Gray, USDA-ARS
Secretary: Jeff McMorran, OSU
Administrative Advisor: Dr. Greg Bohach, University of Idaho, Moscow, ID
1) Call to Order - 8:10 AM. Registration fee to be assessed tomorrow. Jeff M. passed around a pre-prepared signup sheet, based on past attendance. Those present were asked to check off their names and to cross off the names on list of those folks no longer active in committee. He also passed around a printout of the NIN roster, noting that the contact for several of those listed was out-of-date. Roster at: Members should check and update this information.
2) Introductions - For those present see attached list (at end of minutes)
3) Approval of Agenda – No formal additions.
4) Correction/Approval of 2008 Minutes – one correction, for Idaho Report, Doug Boze should replace Greg Boze. Approved (I/II - Dan Hane/Doug Boze).
5) Report o Western Association of Ag Experiment Station Directors (WAAESD) Administrative Advisor (Dr. Greg Bohach) – Mid-term Impact Statement will need to be prepared. This year is of special significance because it is a WAAESD review year. A fairly routine procedure, but of importance because it ensures the continued existence and funding for the project. Awards for the committee in 2008 included the regional ‘WAAESD Outstanding Multidisciplinary Research Award’. Certificates given to each member listed on the official roster (NIMSS System). Group did not get the national award but Greg encourages the group to apply again this year and feels the group stands a good chance to achieve this award. It includes national recognition, attendance at the national award meeting, and financial incentives to the group to fund guest speakers (etc). There is a very short turn around time to get this going.
6) Report of Seed Certification Personnel
Oregon – Jeff McMorran reported it was a relatively ‘average’ year for Oregon in terms of acreage and disease levels observed in field and winter grow-outs. Growers struggled to find a replacement for the Alberta seed sources they had planned to plant but were not available due to the nematode situation. Alberta seed has become an increasingly important source of clean seed for Oregon growers. Varieties grown continued to diversify away from Russet Norkotah and Russet Burbank into several of the PVMI and Colorado varieties, but no replacement for Shepody was available.
Idaho – Doug Boze passed out a handout entitled “Summary of Winter Test Plots 2002-2008”. Mosaic was stable in 2009 with a decrease in the number of ineligible lots. Rob Davidson felt the Idaho data showed that the seed programs were, by and large, working to keep virus down, though some failures still occur (as with R. Norkotah). Question (Rob D.): Was the decrease in ineligible lots related to reduction in R. Norkotah lots? In Colorado they found that growers of R. Norkotah lots (and other ‘latent varieties’) had virus problems in all their varieties and when they quit growing R. Norkotah, PVY issues slowly went down, thus showing that these types of varieties should not be in the system! A (D. Boze): RN definitely a factor in management of mosaic in Idaho, PVY/PVA ELISA testing of all WGO lots is likely helping. No visual assessment is made of the lots, so any strains not giving + ELISA reaction would be missed. Q: Is PVA a problem? A (Phil N.): Essentially all Mosaics were PVY not PVA, there are a few ‘pockets’ of PVA in Idaho but PVA does not seem to spread like PVY. Jonathan W. noted that basically ‘you have to buy PVA’ in the seed to get it.
A discussion on the differences between PVY and PVA followed. Data has shown that infection rates for PVY and PVA were 80% vs. 20% in similar field environments. Thus reduced plant-to-plant transmission may be involved. Steve M. pointed out that some PVA strainscan be very virulent, as described in Slack’s paper in the 1990s. Jorge (?) noted that if PVA sometimes kills the host plants, that may actually reduce plant-to-plant spread in the field. The host range of PVA is also narrower than PVY, thus reducing the amount of over-wintering host plant sources of PVA. Jorge A. pointed out that the aphid vectors are also different for these two virusesas well as their preferred host plants.
Phil Hamm asked ifShepody was still considered a problem in regards to PVY management (yes). He noted cases in Oregon where Russet Burbank and Shepody fields with the same virus levels in the beginning of the season (and similar aphid exposure), were radically different at the end of the season, with mosaic levels in Shepody much greater than in R. Burbank. This has lead him to believe that the virus actually increases faster in Shepody than in RB plants.
Q (Mike T to Doug B.): Do you follow the ineligible lots to see how they perform relative to eligible lots then next season? No. Mike noted that anything over 0.5% should not be planted as seed. Q: (Phil H.) Are there areas in Idaho with more mosaic problems than others? A: Yes, Doug noted that there are seed control districts, and that most of the ‘problem areas’ are outside these control districts.
Phil H. asked if there have there been any PLRV issues in the seed lotsin general? No, little PLRV was observed by any of the Agency present in 2008.
Nina Z. asked about the Idaho’s ELISA program, was this for summer lots? A: No just the WGO, where leaves from all 400 emerged plants (Idaho’s standard lot size) are bulked by 5 and tested. In the summer program, all plants scored for mosaic are flagged, sampled, and tested for PVY and PVA also. Initially Idaho did a comparative test between visual and ELISA testing of the WGO and, based on the results, switched over to an ELISA only system. Overall Idaho has been pleased with the ELISA only system for PVY/PVA in the WGO.
Steve M. asked what the basis of the 400-tuber standard sample size in Idaho was. A (Doug B/Phil N.): The switch was somewhat imposed as a cost saving measure but was also based on work done by RE Lund and Mike Sun in 1985 (“Sample size determination for seed potato certification” Am. Pot. J. (62) 347:353) that showed little benefit in determining the accuracy of the % virus in the lots above the 400 tuber level. Steve M. pointed out that thisconclusion assumeda truly random sample, which is may not be the case for very large acreage lots if only 400 tubers are taken. Larger WGO lot sizes may better represent the entire lot (i.e. be more ‘random’). In Idaho, they felt the cost saving of the 400-tuber standard lots size outweighed the potential drawbacks of not having a larger sample size. The concept of “A” and “B” samples for the WGO as also discussed (A=primary sample, B=backup sample in case of challenges on the results of the A sample). Kent S. pointed out that this system has worked well in solving grower challenge ‘issues’ in Colorado, and that in general the B sample results confirmed the results of the A samples.
Colorado – Kent Sather presented slides showing the acreage change of several states from 1995 to 2008. Most were down (ND, WI, MI, ID) some were up (CO) some about the same (MT). Gary Franc asked if this downward trend means supply is down (short) or need is down; are adjustments needed? A: (Rob D.) Part of the reason acreage is down is that many of the ‘poor growers’ who produced rejected lots are no longer in the system, thus meaning that more of the acreages entered are accepted. (less ‘lost lots’). Thus now, in Colorado anyway, they have fewer growers and less acreage, but more ‘serious/better growers’. An increase in seed yields over time has also help offset acreage loss. Colorado does not have a Seed Law (yet), but will soon. Nebraska and Wisconsin are also in the process of implementing a state seed law (i.e. requiring all potato acreage to be planted with certified seed). All other potato seed states have seed laws in place. Phil N. noted that Idaho has a seed law, but it is not well enforced, and some folks still ‘get burned’ planting uncertified seed. Although the initial seed laws were put in place to help control Bacterial Ring Rot, it was felt by the group that such ‘certified seed only’ requirements also help keep PVY under control (albeit to a lesser degree than BRR). Phil N. noted that no system is perfect but the primary issue is that ‘what is sold needs to be controlled’, not necessarily what is kept on the farm and not sold..
Kent also showed a slide on acres entered vs. acres accepted 1975-2005. There was a steady increase in acres entered.Three periods of high rejections were noted: (1) late 1970 where PLRV rejections predominated; (2) early 1980 where Bacterial Ring Rot was a problem; and (3) 2000 to 2008 with rejections rising due to PVY. He also pointed out the years Russet Norkotah was introduced was not the year PVY issues stated, it took several years for the PVY inoculum to build up and cause general wide-spread problems. The BRR problem was caused when a commercial warehouse was used to store seed and exposed several seed lots to BRR, resulting in a very aggressive push by certification and the industry to control this disease in seed lots (‘many stars in the book’). Development of good and fast test methods for this disease, implementation of the flush through system, and use of tissue culture, has created the overall control of BRR in Colorado (as else ware). The move from many small farms to fewer and larger operations has also helped.
Q (Jeff Mc): What are the Russet Norkotah acreages being replaced with? A (Kent/Rob D.): Many of the new PVMI varieties (Canela Russet, Classic Russet, Blazer Russet). Any early variety with good grade out and that have PVY resistance (but showing good PVY symptom expression) are potentials. Kent was particularly impressed with Classic Russet noting a case where a late-planted, late-harvested lot (which made it prone to getting PVY) ended up with very little mosaic in the WGO. Jonathan W. noted that Classic Russet is the perfect variety for PVY control because it has good resistance and good symptom expression allowing PVY to be rogued when present. Dan Hane noted that Shepody is still an issue in PVY management because, as of yet, there is no good replacement for this very early processor.
Colorado is still only a PVYo state, though PVYo5 strain (that gives a positive to PVYn antisera) is causing problems with shipments to Mexico (see Alex’s report below). PVYn may be present but is not at all widespread. Alex noted that any program that only uses monoclonals for PVY-ELISA detection could select for this problem. Phil Hamm asked if certification agencies are routinely doing PVY strain surveys. A (group): No, because this PVY strain identification is not part of states standards, and most programs are based on visual mosaic (i.e. they only need to be sure the ‘mosaic’ is viral caused, not which strain causes it). Above all, there is not yet available and affordable diagnostic test that differentiates all occurring strains.
Mike Thornton asked if the Late Blight quarantine in Colorado has worked to limit this disease in Colorado. A: Yes, it seems to have worked. There are a few incidences but no blowups. Organic growers in areas of commercial potato sprayed for Late Blight have seen less LB in their tomato crops, which Rob Davidson felt was due to a reduction of LB spores in the area.
Montana - Nina Zidack reported that her official year began in October, but she had spent part of the summer visiting growers in Montana. No PLRV was observed in 2008. The Winter Grow-out results pretty much mirrored the summer readings, with just a few downgrades or rejections. Russet Norkotah is still a problem for some growers in regards to PVY. Keeping levels below 2% can be challenging for these growers (no surprises). They do have one grower who has never had a PVY + in his Norkotah lots, he lives in an area with very severe winter weather, so this might help. Q: What is the tolerance for PVY in the Montana WGO. A: The WGO levels are for the grower’s information only, they can advise the grower, but not reject lots based on the WGO level. They do have a 0.5% Mosaic limit for re-certification.
Nebraska – Steve Marquerdt reported this was a good year for Nebraska lots, with few rejected. Nothing new to report.They note that mosaic occurred in previously ‘clean’ seed lots while grown near wild plum and chokecherry trees that occurs in hedgerows.
Washington – Andy Jensen was present but had nothing to report.
North Dakota – (this was given by Nick David on Thursday) – N. Dakota and Minn. had a very wet spring and summer, resulting in much of the crop not being harvested this year. WGO results of 373 lots from ND and MN showed 80% of lots entered were eligible for recertification, 60% had no detectable virus. ND has very few Russet Norkotah so PVY is not as big of an issue in this state as other areas. PMTV is present, but not a problem. MN has not had a major problem with TRV. It is in 4 regions of the state but low volume applications of Vydate 4 times in the early season 3 weeks apart are effective in controlling the nematode vector. Discussion on how the depth of penetration affectsthe efficacy of Oxamyl in control of stubby-root nematode followed. It was noted that the nematodes follow the roots, so if the previous crop was a deep-rooted crop like corn, the Oxamyl would only be effective if it reached fairly deep into the soil.
Othello and Hermiston Commercial Seed Lot Plots - Phil Hamm reported on strains studies done at the Othello and Hermiston Commercial Seed Lot Plots that showed most mosaic found were PVYo, though some PVYno, PVYn, and PVYntn was also present. Owners of these lots were notified. Incidence of PVYno was down. Alex pointed out that in France the reverse is true, that there was more PVYn than PVYo. Another report on the Othello Seed lot trials was given by Mark Pavek (see below).
7) Virus Discussion Sessions
a) PVY (many reports)
Interactions between PVY and Rhizoctonia - Phil N. presented slides showing a study done in Idaho in 2007 and 2008 (NOT A RIGOROUS TRIAL) suggesting a link between incidence of PVY and Rhizoctonia in the field. Fields with high PVY also had high Rhizoc. Study data compared PVY levels with yield produced, indicating a 1.5 cwt reduction for each 1% PVY. Data showed fields of ‘low’ mosaic vs. high (>50%) had yields of 411 vs. 300 cwt; with US#1 yields of 260 vs. 160 cwt. Most PVY + plants also had Rhizoc. Individual plants with and without PVY were dug and the roots were examined for Rhizoc; 81% of the Mosaic plants had Rhizoc while only 12% of the ‘healthy’ plants had Rhizoc. Was yield reduction due to PVY or Rhizoc? Are PVY infected plants more susceptible to Rhizoc, or are Rhizoc infected plants more susceptible to acquiring PVY? Q: Had the plants with PVY acquired the Rhizoc the previous year and thus the affect was not purely seasonal (i.e. plants with PVY die down early, acquire Rhizoc and then it shows up in year 2? A: Maybe, but the previous year field was out of potatoes 8 years so shouldn’t have much Rhizoc. More RIGOROUS study in the future may answer these questions. Jonathan W. noted that in his plots the PVY infected plants were more severely eaten by Colorado Potato Beetles than the non-infected plants, whether this is because the beetles are attracted to higher sugar levels in the infected plants, or just that the feeding action reduced re-growth rates of the plants was not known. Rob Davidson noted that there are many cases in Colorado when a grower challenges a mosaic call, saying its ‘just Rhizoctonia’ (based on above ground symptom expression), but lab test have confirmed the presence of PVY. He also pointed out that, under Colorado conditions, the 1.5 cwt per 1% PVY rule does not hold out, fields with essentially 100% PVY that were only yielding about 7-9% less than comparable ‘clean’ fields, perhaps just a ‘Colorado effect’. Phil N. said that both PVY and PVA vary in regards to being ‘current season’ or ‘tuber perpetuated’ with CS infection only reducing yield significantly if they occur early in the season.
PVYo5 Problem in Shipments to Mexico – Alex K. reported on work involving export shipment of potatoes to Mexico in which loads were being rejected at the border for having PVYn. Further investigation showed that the virus PVYo5 was involved, not PVYn. PVYo5 reacts as “+” to PVYn ELISA tests that use 1F5 antisera, which is the NAPPO required test for PVYn detection of such shipments. All load of tubers being shipped to Mexico must be tested using the 1F5 antisera and it is causing unnecessary rejections. Thus the rules need to be changed to allow for the use of other antisera, or PCR, so these loads will not be held back. The original 1F5 antiserum came from Peter Ellis and is a monoclonal. Extensive testing using indicator hosts, tuber inoculations, and isozyme analysis, has shown that PVYo5 is a strain of PVYo by all accounts and does not pose any risk to the Mexican potato industry. Only the serology is different, and is based on a single nucleotide difference. Survey work has also shown that PVYo5 is widely spread across the US, showing that 10-16% of the PVYo detections are actually PVYo5, perhaps as high as 25% in Colorado. Alex showed a slide of 4 ELISA plates demonstrating the possible erroneous PVYn finds, and how they could be correctly identified using different antisera. Of course the NAPPO rules will have to be changed to allow this protocol to be used. It was not known if the Mexican authorities are likely to accept this change.