Growing for Late Blight resistance?

[jayb]

If I sow selfed seed from a Late Blight resistant variety, Sarpo Mira as an example, can the same level of LB be passed on and if it can, what percentage of offspring might show these traits?

I’m hoping to do a couple of grow outs next year of seed from resistant varieties (UK blight strains) and maybe a couple of crossed varieties. I’m supposing selecting for foliage resistance will be fairly self-evident and I’m fairly sure L. Blight will oblige by wiping out any plants not resistant. What else should I be thinking about or looking for?

[stevecrouse]

One of the more LB resistant varieties that I have grown is Juliette.

[jayb]

Excellent
Sadly L.Blight infected Juliette here, nasty big splodges on the leaves and spores underneath.

[stevecrouse]

That is surprising.
Probably a different strain of blight.
The year I grew them and had late blight, they were in the middle of other varities that were infected and they showed very little damage, mostly to the flowers and flower stems.

BTW, I'm getting ready to harvest the progeny of the ones you sent me a couple of years back.
Thanks again.

[sweetquietplace]

When I harvested my potatoes this year, it was still early and I thought I would try for a second crop using the various potatoes (odds and ends) that looked like they were interested in sprouting. Starting about the first of September (still hot and humid as heck) I noticed spots on the leaves of about half of the plants. About half of those died quickly, mainly the little ones. As the conditions cooled and drier air moved in, the remaining spotted plants put on new green growth and started flowering. The variety that came through without a spot or problem of ANY sort was Mt. St. Helens. Looks as fresh as the variety did in May. There another good one too, but I won't know what it is until I dig it.

[Tom Wagner]

Sárpo Mira open pollinated TPS will throw a fair number of good blight resistant lines for me. Some crosses to poor lines still give me a few clones to work with. Crossing to locally adapted resistant lines gives me the best performance. I suspect a Sárpo Mira x Mt. St. Helens seedling would do well.

Juliette would not do well here...the parents (Nicola and Hansa) don't have the track record either.

As just about anything that seems to have promise...a break down of the resistance is to be expected. One must have a revolving group of perhaps a hundred clones, inter-mating them each year...grow out seedlings for screening and late planting of same clones to get an early batch of clean tubers to keep and a late batch for identifying the best clones. It would be better not to keep the tubers from heavily infested potato patches for replanting purposes. The level of tuber resistance is not always the same as foliage tolerance.

Many lines have a regrowth potential after being hit, those however tend to be late maturing.

I have been at this late blight thing for so long with tomatoes and potatoes, you would think there would be a commercial interest. Sadly, no.

Maybe if the readership on this forum keep at it ....maybe some outside interest will show up.

[jayb]

Sept 28, 2014 4:03:38 GMT -8 sweetquietplace said:

The variety that came through without a spot or problem of ANY sort was Mt. St. Helens. Looks as fresh as the variety did in May. There another good one too, but I won't know what it is until I dig it.

I'm glad you are getting good results with Mt St Helens, look forward to hearing about the other one too.

[jayb]

Scary numbers for me Tom!
Much to think about thank you.

[nathanp]

One must have a revolving group of perhaps a hundred clones, inter-mating them each year...grow out seedlings for screening and late planting of same clones to get an early batch of clean tubers to keep and a late batch for identifying the best clones. It would be better not to keep the tubers from heavily infested potato patches for replanting purposes. The level of tuber resistance is not always the same as foliage tolerance.

This strikes me as the most practical strategic plan I have seen laid out. With annual goals for those whose who are interested in their own breeding efforts at maintaining late blight resistance.

If 100 clones are necessary, the next logical questions would be:

1 how many TPS plants should be started, annually, prior to screening?
2 how many TPS plants should be phased into the 100 clones on an annual basis after screening?

[Tom Wagner]

To associate me with practical strategic planning as regards to breeding for Late Blight resistance is laughable.
I am neither practical nor strategic in my planning as it were. I plunder along with the idea that there is safety in numbers much to the bane of my cooperators. Innately, I use the template of probability and statistics to screen my materials for whatever value I attribute to the potato clones. Late Blight imposes on me to the point that I have to live with it or cease breeding potatoes. The literature is rampant with valuable and sometimes obsolete references to potato clones with purported blight tolerance, etc. I try to maintain a number of internationally recognized clones that fair quite well in their country of origin and also perform well here against LB. There is an attrition of those clones of those clones if they fail to respond well to LB and or if they succumb to virus buildup making them useless for breeding.

I replace clones quite often due to virus and access new or old tried clones from tissue culture or small tuber samples of virus free potatoes.

There is something about saving the best ten percent of of previously grown name varieties and adding one hundred clean clones to the mix. If the potatoes are planted in soil that has lots of volunteer potatoes and lots of tomatoes planted nearby in areas known to blight up regularly, one can see the flowers succumb to blight and fail to set fruit. If the blight hits early enough that eliminates them from further breeding and or setting OP berries. Having lots of TPS seedlings in the area that have parental histories of blight resistance allows one to mix them up in the breeding and the healthy seedlings and tuber lines are then available for pollen collection, flower pollination, and natural sources for wind/insect transferred crossing.

I suspect one should start with a thousand TPS seedlings in order to reduce them down to the best one hundred combining LB resistance with agronomic traits desired. Replanting those tubers the next spring are often reduced due to storage features, flavor, or berry setting ability. I tend to favor berry setting as a necessary requisite to adding to my favorite 100 clones to use in a LB breeding block. I need selfers as much as I need natural crossers and hybrids I make myself. Doubling up whatever alleles in a vertical and horizontal resistance package is extremely important.

I phase out clones sometimes at the rate of 99% or more. I can't maintain as many as I would like. I place much importance to new seedlings. If a new seedling tuber gets planted out the next season that may be the last time...as I rarely maintain a tuber line from established international clones or from my own creations very long. I often go back to TPS of five to ten years ago to build up that genetic stock in order to keep the breeding work fluid. I don't rely on just current year tolerance of blight to dictate my screening. By having lines that trace back to specific years for tolerance and retrying them in a mix of clones for breeding I think I keep the diversity vibrant for my purposes.

Providing TPS to my customers with lots of variation coupled with LB resistance, I hope it keeps the interest alive. Accidental successes are as important as planned successes. As incompetent as I think I am, likewise many in the professional potato world think too....my limited success is nevertheless valuable to someone.

[DarJones]

That would run into inbreeding depression after about 30 generations. Add an input of new lines from outside sources and the problem will be avoided.

The approach of using large numbers is the safest approach from a long term perspective. It is susceptible to over-reliance on R-Genes instead of stacking multiple low impact but cumulative resistances. R-Genes are rapidly overcome by blight. Sarpo Mira has 5 stacked genes conveying excellent tolerance. It would be a good parent if crossed to resistant lines carrying diverse genes for tolerance.

A disciplined strategic approach to breeding is the best approach. The Sarpo lines are a result of such a program.

In the end, some form of marker assisted selection will win the race for late blight tolerance.

Sarpo Mira qualitative R genes include R3a, R3b, R4, and the newly identified Rpi-Smira1. The qualitative resistances matched responses to avirulence (AVR)3a, AVR3b, AVR4, and AVRSmira1 RXLR effectors and were overcome by particular P. infestans strains. The quantitative resistance was determined to be conferred by a novel gene, Rpi-Smira2.

apsjournals.apsnet.org/doi/pdf/10.1094/MPMI-01-12-0010-R

[nathanp]

Valuable wisdom there from both of you.

[jayb]

Awesome, thank you both.
Much is over my head but I now have a starting point.

Excellent link Snicheringbear

[marches]

If you do two crosses with a resistant parent and non-resistant parent then select resistant offspring and then cross the resistant offspring you will have a higher chance of carrying more resistance genes over.

I plan to do (Sarpo Mira x Estima) x (Tollocan x Accord) - crosses like that, but you could also do things like (Sarpo Mira x Estima) x (Sarpo Mira x Estima) or Sarpo Mira x (Sarpo Mira x Estima), although presumably the more inbred the varieties are the more runts you'll get (is that way with grapes, but I'm not sure with potatoes as they're usually tetraploids).

Nice to see other UK breeders on here anyway.
I'm trying to develop blight resistant varieties that could have widespread appeal and perhaps be sold in supermarkets.
So conventional flavours, good storing qualities, good cooking qualities and ease of cultivation alongside resistance.
Sarpo Mira is known among gardeners but people often complain about its cooking qualities, so there is work to do to get quality in alongside the resistance.
If one of my varieties were to become popular even among just gardeners I'd be happy.

I also breed grapes - am working towards early, resistant, quality seedless table grapes for less than favourable climates such as ours and much of Northern Europe.
Taters are quicker to breed though and usually produce something edible in an year or so even if not worthy of release unlike grapes and are one of our staple crops.

[DarJones]

Sarpo Mira X Accord would be the most interesting. I'll let you figure out why.