Disease resistance testing
 

I've been doing some reading and thinking on this subject for a while. I have relatively little disease pressure currently, but want to include planning for it in some of my breeding projects.

Marker testing 100's of plant tissue samples is out of the question. I don't have the equipment and grad students to do it, or a budget based on the idea of a future profit from my projects.

Large scale field planting in areas with disease pressure seems to be a common option, selecting plants that appear to have resistance that way. But that takes a while and a lot of space and assumes that the plants are uniformly exposed to the disease you're trying to select for resistance to. Sounds like a lot of work, a lot of time and rolling the dice.

I've read some articles where individual leaves where exposed to isolated strains of the disease in question in a growth chamber and the plants that provide leaves which appear to be infected are culled and the remainder allowed to fruit for further selection.

This kind of approach seems most likely to work for the independant breeder to me. My current thinking, using something where I would be looking for disease resistance is to start several hundred seedlings of a candidate line in cell packs. Once they're at about a 4 week size place them in an isolation chamber where I can maintain a fairly high humidity built from left over polycarb pieces from my greenhouse project. Blend samples of infected plant material with distilled water and spray the seedlings, then observe for a couple of weeks. What lives goes forward.

Not exactly cutting edge, but I think it should work. It would be a bit haphazard compared to using DNA testing or innoculating plants with isolated strains of a disease causing agent, but you could cheaply and easily test 100's of F2's this way.

Anyone have an opinion?

Check with Fusion Power.I remember reading that he was/or is involved with disease testing in some field trials.

be careful what you ask for...diseases are really good at escaping. It is also unlawful to transport pathogens around. Seedlings also sometimes do not display the same resistance levels as mature plants for all pathogens. best to find partners already inflicted...then it's easy to see. just my two cents.
-d

The one I'm thinking of in particular is Septoria, which I do see occassionally here so transporting pathogens isn't an issue.

The difference in resistance between seedlings and mature plants is something I was curious about, otherwise it would be seem odd that a similar screening process wasn't already being commonly used.

The problem is that septoria tolerance is at vanishingly low levels in all known genetic stocks. Do a few searches and you will find one of the best articles about screening for septoria tolerance from Scielo in Brazil. Known tolerance to septoria is polygenic and based on very small additive effects from about a dozen genes.

You must grow your plants disease free. This usually means inside a greenhouse with very careful screening for pathogens. Then you have to expose the seedlings in a controlled fashion to a specific strain of the disease organism. This must be done without exposing the primary plant to the disease ergo the use of detached leaf assay. Once tolerance has been found, then use the specific plants as parents in crosses to combine other desirable traits and/or to stabilize the disease tolerance.


DarJones

Thanks for the pointer to the article, I'll see if I can find and read it today.

I have not found much on the pedigree of Iron Lady, which is what I was considering as a source. I'm hoping there is some binding between those dozen genes, otherwise it's worse than a one in a million chance of developing a stable parent line.

My thought was that I could extract seeds from the first fruits of a couple of Iron Lady plants started early and do the testing with those F2's this year. Hopefully some variation of this idea is feasible, even if it's using detached leaves. While I could plant out a few hundred, seeing as how seeing actual infection is a hit or miss occurance I don't know that it would be an effective way to screen here.

I am assuming this article is the one you were referring to?

Resistance to Septoria lycopersici in Solanum (Section Lycopersicon) species and in progenies of S. lycopersicum × S. peruvianum in Sci. Agric. (Piracicaba, Braz.), v.67, n.3, p.334-341, May/June 2010

Has anyone seen a pedigree for Iron Lady? I found some information about the program at Cornell that I believe was involved in developing one of the parents, but no specifics.

Do a search for "Poysa, Wu, Septoria" and you will find some info about the program that developed the septoria tolerant lines that were used at Cornell.

DarJones

134 pages, I think I found my bedtime reading for a few days. Thanks!

[QUOTE=Fusion_power;328575]Do a search for "Poysa, Wu, Septoria" and you will find some info about the program that developed the septoria tolerant lines that were used at Cornell.

DarJones[/QUOTE]

I think Poysa, in an earlier article, also describes a seedling assay. We are going to try this next winter on progeny from crosses with Iron Lady. The trick is in culturing the pathogen, the method and stage of innoculation and then providing ideal conditions for disease development - all in the literature and not that complicated. Culturing the pathogen requires sterile technique, but you may be able to use ground up infected tissue. I've successfully used both methods on other crop species.

Yes, they inoculated seedlings at 35 days, kept them in high humidity for 36 hours then examined them after another 15 days in the greenhouse.

I've got a friend who is a micro biologist who can probably help with sterile culture should I decide to go that far.

Looks like this will work as far as I can see.

[QUOTE=marktutt;328657]Yes, they inoculated seedlings at 35 days, kept them in high humidity for 36 hours then examined them after another 15 days in the greenhouse.

I've got a friend who is a micro biologist who can probably help with sterile culture should I decide to go that far.

Looks like this will work as far as I can see.[/QUOTE]

My wife is a plant pathologist and she's pledged to culture Septoria for me this summer. I'm not sure if there are restrictions on shipping Septoria cultures from MN to WI, but if not we can send you a plate to start with.

[QUOTE=frogsleap farm;328891]My wife is a plant pathologist and she's pledged to culture Septoria for me this summer. I'm not sure if there are restrictions on shipping Septoria cultures from MN to WI, but if not we can send you a plate to start with.[/QUOTE]

And at the words Microbiologist and "sending a plate" this retired Microbiologist's eyes and ears perked up.

Ever since Dr. Tom Zitter, an excellent tomato pathologist at Cornell wanted me to spray Early Blight on my plants out side in the tomato field, I've wondered about testing for the common foliage diseases.

OK, I can see spraying young seedlings inside in high humid conditions to get the fungal spores of Septoria to infect, but I can't see what that tells you since the upper leaf epidermis thickens as the plants mature and no seasons are the same as to where plants are grown, AM dews, rain, weather, as in airborne transmission and all the other variables.

If it were me, and it's not, I would prefer to see such experiments done at different plant ages of the same variety in an open field situation. Which I think would bear more on reality than any inside growing.

Mark, do you remember when Randy Gardner contacted me and asked about setting up a Septoria kind of study group and Bill Jeffers referred you to me and it turns out that you and Randy had know each other in past times?.

I don't think anything came of that proposed study group, but since the two fungal foliage pathogens S. alternaria and Septoria Leaf Spot are the most common world wide, it certainly would be a big step forward if some tolerance gene(s) could be discovered, and I mean strong tolerance,not weak tolerance.

Carolyn

I am rooting for you Mark. I would totally pay for strong Septoria tolerance.
Marsha

[QUOTE=carolyn137;328921]And at the words Microbiologist and "sending a plate" this retired Microbiologist's eyes and ears perked up.

Ever since Dr. Tom Zitter, an excellent tomato pathologist at Cornell wanted me to spray Early Blight on my plants out side in the tomato field, I've wondered about testing for the common foliage diseases.

OK, I can see spraying young seedlings inside in high humid conditions to get the fungal spores of Septoria to infect, but I can't see what that tells you since the upper leaf epidermis thickens as the plants mature and no seasons are the same as to where plants are grown, AM dews, rain, weather, as in airborne transmission and all the other variables.

If it were me, and it's not, I would prefer to see such experiments done at different plant ages of the same variety in an open field situation. Which I think would bear more on reality than any inside growing.

Mark, do you remember when Randy Gardner contacted me and asked about setting up a Septoria kind of study group and Bill Jeffers referred you to me and it turns out that you and Randy had know each other in past times?.

I don't think anything came of that proposed study group, but since the two fungal foliage pathogens S. alternaria and Septoria Leaf Spot are the most common world wide, it certainly would be a big step forward if some tolerance gene(s) could be discovered, and I mean strong tolerance,not weak tolerance.

Carolyn[/QUOTE]

The hero in this story is Dr. Vaino Poysa, a tomato breeder at AgCanada (now retired) who made crosses to both L. hirsutum and L. peruvianum accessions and screened progeny for Septoria resistance using the seedling screening protocol referenced earlier in this post. This "resistant" material sat around for a long time before being picked up by Dr Munchler at Cornell - from which she developed Iron Lady. I'm interested in making crosses to Iron Lady and doing a seedling pre-screen before going to my 2014 breeding nursery - which is a reliable Septoria hot bed. Unfortunately the resistance reported in Iron Lady is only effective at low innoculum loads in the field - but it appears to be the best we have so far.