HVX - Highlights from Keynote address by Dr Ben Lockhart

[paul_in_mn]

Passing along some information from Dr Lockhart's HVX presentation, slides and discussion. Dr Lockhart stated that everything he is presenting should be questioned about how results were obtained since some common believed wisdoms had recently been found incorrect - example item #5 below.

What general lesson were learned from this research project:

1 HVX can be spread from infected to healthy hostas on contaminated tools during normal cutting/pruning of plants.

2 Thorough cleaning of tools with household detergent or 10% bleach or 70% alcohol eliminates contamination virus and prevents HVX spread on tools.

3 HVX was not spread by contaminated knife during division of hosta crowns. This suggest that spread by this means may be significantly less frequent than by cutting tools.

4 The chance of spread of HVX on tools is significantly higher in the spring when plants are vegetatively active than after flowering when plants are approaching senescence.

5 HVX can be spread through soil when healthy hostas are replanted in soil containing HVX-infected residual plant debris. -Hostas (2 of 20) planted in soil from which HVX-infected plant had been removed became infect with the virus. - This method of virus spread was not previously reported for potexviruses, and was totally unexpected.

6 To obtain reliable results hostas used in tests of HVX transmission should be followed through two full growing seasons.

Other comment during presentation - they exposed 20 hostas to infection and none became infected - this led to observation that time of exposure and how exposed may affect infection rates. i.e. after flowering and into fall is less likely to get infected.

Dr. Lockhart during QA period - stated that a cut to leaf and later (for example after 15 min) exposure to HVX virus at injury point would not infect the healthy plant - as the leaf would quickly heal and seal off that entry point. HVX needs to get below outer membrane of a leaf to transmit through sap.

I asked afterward directly - a question that had been raised on the Hosta Forums - If a plant became infected and root zones might be in common with other hosta and since he stated that transmission of HVX is less likely late in season is it better to delay removal till late fall or possibly using Roundup and leaving in place. His feeling was that immediate removal of plant and soil was best, and that he would not use roundup for fear of killing adjacent plant.

The only clear conclusion that came from the study was that there was much we don't know and that previous results may need to be retested in light of what was learned about timing of exposure in particular.

From Presentation -
What new questions do these results raise?
A more detailed investigation of HVX spread in soil including:
-How long does HVX remain infective in plant debris in soil?
-How much HVX infected residue is needed for soil contamination?
-Does infection occur through crowns, roots, or both?
-Does the tyoe if cutting tool affect virus transmission during crown division?

Some other questions of interest:
1. Can hostas recover from HVX infection?
-'Stained Glass' and 'Xanadu Paisley': No sysmptons or HVX detected in previously HVX-positive plants.

2. Can HVX be spread between plants during post-harvest washing in commercial operations?

3. Do we need to revisit previous results about HVX susceptibility in different hosta varieties?

4. Do we need to revisit previous results about the range of plants infected by HVX?


I tried to recap best as I could what was presented - it was just over a week ago so most is still in there.

I hope others attending will add their observations and recollections as well.

[Chris_W]

Thanks for sharing this info Paul. I sure wish that Dr. Lockhart could have elaborated more. Some of the results are not surprising at all, but others are, and a lot of this will be misconstrued so badly that it may not really help that much.

For example, I wish he could help to clarify what "Thorough" means when it comes to cleaning. MANY people swore that dipping tools in bleach water was enough, but to me that was always crazy. Heck, can you imagine if we washed dishes that way? I think that it comes down to what I've been saying for years - the goal is to get rid of the plant sap, and from his new info it doesn't really matter so much WHAT you use, just clean things really good I guess.

In the past I prescribed growing hostas at least one season and testing at the end of that growing season. On two occasions in 2005 we had plants that tested negative but later showed symptoms and tested positive the following year. So now I'll be telling people that instead of a ONE year quarantine on suspected plants (ie Dutch imports) there should be a TWO year quarantine.

Other than the surprising results that some HVX residue remains in the soil, the rest is about what we've been saying. But instead of spending more money on research I wish the AHS would commit to educating people. Oh well, I'll keep working at that effort myself.

Thanks again!

Chris

[Noreaster]

Yes, thanks for sharing, Paul.

I still am not sure how I understand how remaining bits of plant debris can infect a new hosta planted in that spot. I thought it had to be sap to sap contact. So the old roots would have to have open wounds pumping sap which then must come into contact with an open wound on the root of the new hosta. It just seems so unlikely.

[Chris_W]

Hi,

I agree, the transmission this way is unlikely since basically his study showed it moved 4% of the time. But it is still a risk since the virus remains active for so long and the percentage might go up over time. When new roots are growing I've seen them get stuck to the sides of pots or get stuck to potting soil, plus I've seen roots fuse together. There must be something about the mechanism of how roots grow or about how they take up nutrients from the soil that makes them susceptible this way.

[Noreaster]

Hi,

plus I've seen roots fuse together. There must be something about the mechanism of how roots grow or about how they take up nutrients from the soil that makes them susceptible this way.

And that is the scary part. I always worry about those co-mingling roots in a bed, even though it's not *supposed* to be a concern (based on the old info, anyway). Ugh.

[renaldo75]

One thing that he kept saying was that some of the results were entirely surprising.

Why would cutting/pruning foliage be a significant cause of spread, but not cutting crown/roots with an infected 'knife' - ??

I don't think that made sense to anyone in the room including Dr. Lockhart.

But this was just the 1st round of testing. There will be at least one more to see if the same things occur.
And to further test things that weren't done in the 1st round.

[jgh]

I think the finding about the early season / late season transmission is interesting. If I understand the growth pattern, in simple terms, hostas put most of their energy into producing above the ground until they flower, then they switch into below-the-ground primacy getting prepared for the following year.

So it could be related to the amount of sap rising in early season... or it could be that more rapid growth in the roots in late season gives them more resistance to taking in the virus...

In any case, I think it has real implications for hygiene. Even though Dr. Lockhart answered in the negative, I think one might really consider putting off digging virused plants for disposal until fall. I'm thinking of one of the tour gardens where the owner had two virused plants pointed out to him. The two are side by side... but overlapping with two other plants, one of which is a Striptease showing no signs of virus.

These are all large... six year in the same spot. If he digs those hostas right now, the root balls of at least four large hostas are totally overlapping. And those overlap with others. I think if it was up to me, knowing no further cross-infection is likely to happen if I wait a few weeks, I'd probably wait a month or so, let everything bloom... then remove the plants. Might also be a good place to use a couple of strips on the nearby plants - given the history, there is probably a good chance the Striptease brought the virus into the bed in the first place...

Anyway, seems like little risk to wait a couple/few weeks, and some potential benefits...

[eastwood2007]

I have wondered, in dealing with infected plants in the garden, if it would be better to first remove the SURROUNDING plants?

If the roots of surrounding plants tear when removing them they tear while being torn AWAY from the infected ones? That way the torn infected roots won't be coming in contact with healthy plants. Then the infected ones could be removed and perhaps soil removed also and replaced in that area?

[paul_in_mn]

Chris -

Dr Lockhart seemed very open to the idea of contacting him with questions.

Here's a link to his page at U of Minnesota with email and phone - I don't want to list here or spam bots may grab.

http://www.virology.umn.edu/investigato ... /home.html

[JoshS]

Much of this has already been covered, but...

At the AHS National Hosta Convention last month in Minnesota, Dr. Lockhart gave the keynote speech on his most current research. This research was sponsored by the AHS and on behalf of Rob Mortko (American Hosta Society Vice President, Genus Hosta), I am posting the following...


Key takeaways from the most recent HVX research include:

-- There are no hosta cultivars that are more (or less) resistant to HVX as had been previously reported. Hosta exposed to HVX while actively growing will likely become infected. However infecting a healthy hosta with HVX in the fall is very difficult as it is approaching dormancy. This would imply that hosta division would be better undertaken in the fall rather than in the spring.

-- HVX is spread by sap via cutting tools. Dishwashing detergent, 70% alcohol or a 10% solution of household bleach (1 part bleach and 9 parts water) are all effective in cleaning and disinfecting cutting tools. However simply dipping the tool in the solution is not sufficient. Thorough scrubbing is required.

-- After removing an HVX infected plant, a healthy hosta planted in the same location can be infected up to two years later. (Note that two years was the duration of this research project.) No one was more surprised by this finding than Dr. Lockhart. Previously the general recommendation was to allow 4 to 6 weeks after removing a virused hosta before replanting. Based on this research another hosta should not be replanted in the same location.

This research was funded entirely by interested individuals, local and regional hosta societies, and hosta growers on behalf of the American Hosta Society. The research findings beg answers to new questions. As a result, it is intent of the AHS to embark on a second phase of HVX research. Individuals, local and regional hosta societies, and hosta growers are requested to consider a generous contribution to this project. More information (including a printable pamphlet of the research findings) is available on the AHS web site:

http://www.americanhostasociety.org/HostaVirusX.html

[jobranch]

Most of my recent hosta purchases have been potted and sunk in the ground mostly because I have had a problem with voles. But, a related benefit is that at least I feel a lot better about the risk of spreading HVX with sinking potted hostas. I gave a hosta to a friend a few weeks back and it was no trouble to pull the pot out of the ground with no worries about the root. I have purchased most of my hostas a little at a time at local places and there is always the risk of HVX. Would not this eliminate the root fusing, etc. kind of problem? Is there something else I should consider? I guess some root material could have been left behind from them growing through weep holes.

[Chris_W]

Hi Jeff,

I think that having them in pots sure would minimize the risk. And really makes it easy if you ever had to get rid of one!

Thanks for the info Josh. I'm a bit shocked that we are talking about 2+ additional years of research. That is a lot of money that could have gone to educating growers, retailers, agriculture inspectors, and the general public. If we could just convince all of the sellers and growers to adopt a ZERO TOLERANCE policy we could get a much bigger start on eliminating this problem. And I'm already seeing people start to use the latest research findings as a way to downplay the severity of the situation.

Things are getting worse and I fear that we missed the chance to stop this 4 or 5 years ago when it started to show up