Topic: Blight resistant tomato varieties

[galina]

Has Tom Wagner done a cross to incorporate PH2 and PH3 resistances? 

[Jayb]

Yes, I think he has incorporated in quite a few of his lines, but how far along any of the lines are I don't know. Skykomish I believe is one, although so far the segregates I've grown haven't been particularly resistant, but not too say that other siblings aren't brilliant. I think Real Seeds may have some seeds.

Skykomish (NWS 2012, 2013, 2014. TWS 2013) Tom's description and picture from New world Seeds, "A beautiful bicolor fruit of yellow/orange/red with a flavor out of this world...and near 100% late blight resistance. Â One of my better creations.... 4 inch fruits of reveled colors. 

[Jayb]

Thompson and Morgan are selling Mountain Magic F1 another Late Blight resistant variety, again with PH2 and PH3 genes. Bred by Randy Gardner in the US it was made available there I think in 2011. Good to see seeds have finally been offered here too.

[Ellen K]

I've read this thread with interest but I'm not a biologist so still need help please ....

Q1: Is every seed in any tomato genetically identical to all the others in the same single fruit?

Q2: For something like Crimson Crush, how many tomatoes would you have to take for seed to have say a 90% probability of one being from the 1/16th group that has inherited both the PH2 and PH3 genes?

Thanks
Baffled of Loughborough

Edited to add: Is it really only 1/16th of the population that has both genes from its parents?  Oh you guys, I haven't had enough coffee yet to get my head around this.

** back to drawing on bits of paper **

[laurieuk]

There are a lot of comments in "Bargains galore" mainly concerned with Crimson Crush. free plants.

[galina]

I've read this thread with interest but I'm not a biologist so still need help please ....

Q1: Is every seed in any tomato genetically identical to all the others in the same single fruit?

Q2: For something like Crimson Crush, how many tomatoes would you have to take for seed to have say a 90% probability of one being from the 1/16th group that has inherited both the PH2 and PH3 genes?

Thanks
Baffled of Loughborough

Edited to add: Is it really only 1/16th of the population that has both genes from its parents?  Oh you guys, I haven't had enough coffee yet to get my head around this.

** back to drawing on bits of paper **

Apparently both resistance genes are dominant, because they have a code name starting with a capital letter.  What happens after that, I'm not so sure.  We can assume in most cases that tomatoes are self pollinated and not crossed (which is the exception and I think we can ignore in this case).  I would appreciate a simple explanation as well, please.   

[goodlife]

I can only add my penny's worth if what I've experienced myself...so scientific answers from me.

All seeds in any non-hybrid tomatoes should be identical...providing the flower is self pollinated...or pollinated by same variety.
It is the hybridisation that throws things into different category.
We know that F1 don't come true to type from seed...even if it is self-pollinated...the fruit from those seed can show any mixture of trait's from its parentage.
In past I've trialled this and I've ended up with VERY similar fruit..but not quite. There might be duller shine for the skin...there might be different amount of divisions inside the fruit...the size or shape might be slightly different....etc. BUT..what seeds I've harvested from few particular F1 plants...all the 1st generation plants that I grew, they were all same, though there was subtle differences to the parent plant. I've even ended up with fruit that looked almost identical to the original hybrid but when 'proper' hybrid plant and one that comes from self pollinated seeds from same variety were grown side by side...receiving same care...the fruit from the 1st generation did actually taste better!!!!
I've crossed 1st generation hybrid with 'heritage' type....getting 3 different type of fruit from the seeds from same tomato... I suppose that's the result of  3 parent genes in work..
I love to play with  'seeds' that come from F1 plants and I've never ever ended anything that was tasting or looking horrid or even disappointing.
Every year I trial few toms from supermarket and if something is even half decent tasting...I just might save few seeds from them and usually ending up with similar looking fruit that will taste much better when they are lovingly grown in my own GH Though when the seeds come from 'commercial' varieties, the plants usually do tend to grow 'sky high'...luckily my GH is able to accommodate fair bit of growth, and rest can grow out of window  But I can't see general supermarket toms being all from F1 source...it would cost them too much money..?!

[Ellen K]

OK, I tried to remember the trees that Silverleaf and Galina were drawing at the A4A get together last year - here goes:

Each parent has one copy of the PH2 and one of PH3.  And they are separate right?  So its genetic contribution to the progeny is one of 4 possibilities: PH2 + PH3, PH2 only, PH3 only or nothing.  Same with the other parent.  So you can draw a 4 by 4 grid (that's where the 16 comes from), with those 4 possibilities on each axis.  So one lucky offspring ends up with 2 copies of each gene (YAY!!).  But another 8 end up with at least one copy of each gene which gives then the same resistance as the parent because its a dominant gene.  Then 6 end up with just one type of gene, though they may have 2 of the same one.  And one ends up with none.

Of course, I might have gone miles down the wrong track here  .

[Ellen K]

And you don't need many tomatoes to do this because 9 out of 16 of the F2s are at least as good as the original F1s.

 

But it does assume self pollination.

And you can't tell which ones you've got until they've made a plant.

Ooooooo - you know, this dehybridisation business can't be easy.

[galina]

And you don't need many tomatoes to do this because 9 out of 16 of the F2s are at least as good as the original F1s.

 

But it does assume self pollination.

And you can't tell which ones you've got until they've made a plant.

Ooooooo - you know, this dehybridisation business can't be easy.

This works if tomatoes (like peas) are diploids.  Not sure whether they are.  Tried to google and it mentions that they could be either diploid or triploid.  And I don't know how or whether this would affect the outcome.

[Robert_Brenchley]

All the seeds from an F1 will be almost identical because there's very little genetic diversity in the parents, but it's probably safe to assume there will be at least a little. They're not clones. The same goes for any tomato, F1 or otherwise, since they're inbreeders. Every variety is likely to be descended from a single common parent. The  only exception would be a plant which had crossed, whether deliberately or otherwise.

[galina]

All the seeds from an F1 will be almost identical because there's very little genetic diversity in the parents, but it's probably safe to assume there will be at least a little. They're not clones. The same goes for any tomato, F1 or otherwise, since they're inbreeders. Every variety is likely to be descended from a single common parent. The  only exception would be a plant which had crossed, whether deliberately or otherwise.

Don't think they will be almost identical.  Seeds from an F1 are the F2 generation and this generally is the generation that expresses the most diversity.

And we don't know the parents, apart from one being a resistant tomato from the USA and the other a resistant tomato from the UK.  Not sure how similar they looked and tasted as tomatoes.
 

[Jayb]

I've found Kieth Mueller's site very helpful http://kdcomm.net/~tomato/gene/genes.html   http://kdcomm.net/~tomato/gene/genes2.html

I think looking for two dominate genes is going to be very difficult, particularly as they aren't readily visible in the same way as if you were looking for a black or cherry fruited tomato.

A stable self pollinated tomato variety will give identical plants from saved seed.

Two stable parents crossed together will give identical F1 plants from saved seed. Only in the second generation (F2) of plants will differences be seen, sometimes these differences might be minimal if say the two parents are both cordon, black fruited cherry tomatoes with regular type leaves. But if a black fruited beefsteak with potato leaves is crossed with a yellow pear shaped regular leaved tomato then very much more variation will be seen.

If either parent is not stable and then crossed, this still gives F1 seeds but they are not identical and behave more like f2's in the variation seen in the first generation.

[amphibian]

I've read this thread with interest but I'm not a biologist so still need help please ....

Q1: Is every seed in any tomato genetically identical to all the others in the same single fruit?

Yes and no - in a non-hybrid tomato, that has self pollinated, all the seeds should be genetically identical unless a random mutation has occurred.

All F1 seeds in a packet are identical genetically, but the fruit on the plants grown from those seeds will have great diversity between seeds, even taken from the same fruit.

Q2: For something like Crimson Crush, how many tomatoes would you have to take for seed to have say a 90% probability of one being from the 1/16th group that has inherited both the PH2 and PH3 genes?

15 plants would render a 94% chance of recovering at least one plant of the desired genotype.

Edited to add: Is it really only 1/16th of the population that has both genes from its parents?  Oh you guys, I haven't had enough coffee yet to get my head around this.

** back to drawing on bits of paper **

The 1/16th is based on the genes Ph2 and Ph3 having incomplete dominance. That is where a plant that is homozygous for the genes has a greater degree of resistance than one that is heterozygous at the same loci.

The F1 being heterozygous is not as resistant as some of its potential offspring a selfing of the f1 would only produce 1/16th of offspring that are homozygous at both loci.

This would all be so simple if we were dealing with normal simple dominance. Because of the incomplete dominance the progeny will have varying degrees of resistance depending as some will be homozygous at one loci but not the other.

[Ellen K]

^^ thank you, I am beginning to understand this now.  It's a lot of work but you do get to eat nice tomatoes.

I think I will try the clone approach first, if the CC plants do well - overwintering cuttings. 

Suddenly the seeds seem good value.

 

[amphibian]

I have fruit set on my first trusses, plants are doing very well even in this chilly weather.

The first fruit look like they're going to be fairly large, but the first tomato on a plant is often a multi-lobed mutant.

I have five plants all together, three large ones and two freebie ones from Dobies which are still very small.

[amphibian]

I've done a little punnet square to illustrate what we may see when attempting to dehybridise crimson crush, if indeed it is a hybrid.



In this diagram A represent Ph2 and B Ph3. Because Ph2 and Ph3 have incomplete dominance we should see 9 genotypes (phenotypes being the same as genotype in this case) at these loci - of course we may see all manner of other segregation and there is the danger the magic AABB may be a spitter.

Each genotype will have varying resistance from AABB having the best to aabb having none. The positive thing is that genotypes AABB, AABb, and AaBB - 5/16ths have better resistance than the F1 and 9/16ths have better or the same as the F1.

Where things get tricky is that depending on when and which strain of blight appears in a given season AAbb and aaBB may show better resistance than AaBb, AABb or AaBB while actually being less desirable. Given this it's going to be important not to rogue any variety showing any resistance too soon. Otherwise an AAbb may be kept over a AaBB only for the AAbb to die completely later in the season where an AaBB would have kept going.

Dehybridising to a AABB may best be achieved by maintaining lines for many season and rouging whole lines once varying resistance becomes apparent - the danger here is discovering years later you never had an AABB line in the first place.

Ultimately my aim would be, through crossing, to produce an AABB cultivar that can be then used to transfer the genes to any variety through recurrent back crossing.

[goodlife]

 
 
 
 
 
 
 

All clear now! 

[amphibian]

All this said and done I don't quite get the hype being generated by dobies/suttons - Skykomish is already homozygous for Ph2 and Ph3, so unless there is more to it than their literature claims Crimson Crush is not a first and would be less resistant than Skykomish.

I suppose Skykomish can be used as a good control plant to compare degrees of resistance and see if more is at play in Crimson Crush.

[Silverleaf]

Does Skykomish taste any good?