Sunday, July 12, 2015

Crosses Between Cherry and Beefsteak Tomatoes

Whether a new cross is designed to be a F1 hybrid, which is sold as such commercially, or a breeding start for a program to develop new inbred/O.P. lines, selection of parents is critical.   Most breeders will select parents that complement each other, so that in the F1 (or F8) generation you capture the best characteristics of each parent.

We have now made and tested several dozen crosses between beefsteak and cherry types – hoping to capture some of the exquisite taste of the best cherries (think Sungold) in a larger fruited type.  We have also used early fruiting cherries to get earlier maturity in these hybrids and hybrid-derived Fx progeny.

There are some general patterns that we find interesting:

In crosses between smaller x larger fruit, the fruit size in the F1 generation will be much smaller than the mid-parent mean.  My tomato friend Bill Jeffers told me many years ago that fruit size in hybrids could be estimated using the mean of the square root of the fruit weight of the parents – for example (1oz x 9oz) –-> (√1 + √9)/2=2oz fruit wt for the F1.  I’ve found this to be a pretty good rule of thumb.
   
     In the F2 generation we have found almost the whole range of variation in fruit size, but heavily skewed toward smaller fruit.  The frequency distribution typically looks something like this: 



In this example, again the parents were a 1oz cherry and a 9oz medium beefsteak.  You need to look at a lot of F2 plants to find one that comes close to capturing the size of the large fruited parent.

The frequency distribution for maturity (i.e. earliness in fruit set) is similarly skewed toward the early parent, but in these F2 populations earliness and fruit size are negatively correlated – generally small fruited types are early, larger fruited types are later.   Thankfully we have been able to get earlier large fruited types by selecting primarily for size in the F2 and then for size and earliness in the F3 – again using large populations in both generations.


Our "go-to" cherry parent - derived from Sungold
Much of our recent crossing involves commercial hybrids (e.g. Bella Rosa, Mountain Merit, Panzer and Tasti-Lee) with exceptional disease resistance as the large fruited parent and very flavorful striped cherries as the small fruited parent, so we are also selecting in the F2 and F3 for flavor, stripes, plant health and fruit quality.  So far we are making progress on all fronts.  

Fruit from F5 line derived from cherry x beefsteak cross


10 comments:

  1. Interesting to read this great article indeed because I have known many great and new things from you. Thanks a lot one more time.
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  2. This is really interesting to me. This year I bought some plants that were labeled as 'low acid beefsteak' from a local. They grew up into small dark striped fruits similar to your photo above but smaller and paler, it is pink with pale green thin stripes. One has the beefsteak U double shape to it, but still very small. I am keeping some seed and might experiment in the future.

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  4. This formula doesn't look to be correct. It may have given you the same result as your actual results from the field, but let's look at another example.

    I have a 25oz tomato i grow every year. I would like to increase the size of one of my other varieties, a 9oz tomato. Using your formula let's see what my F1 weight would be.

    ✓(25oz)+✓(9oz) = 8oz
    8oz/2 = 4oz

    So my F1 would be smaller than my smallest parent, by a large margin? I don't believe it would. I haven't proven it false in the field, but this doesn't align with the statement you made either.

    Using your numbers, a better formula would be something like this.

    (9oz * 10%) + 1oz = ~2oz
    With 27% of the fruit at this weight of 2oz (12/44 = 27).

    Using this formal with my fruit sizes, i get.

    (25oz * 10%) + 9oz = 11.5oz.

    This is more reasonable i think. Now to test it

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    Replies
    1. Hi Robert. Good point. My comment was specific to crosses between cherries and larger fruited types - as you point out this formula may not apply to crosses between plants in other fruit size categories. I do believe that regardless of fruit size of the parents, the fruit size of the F1 will be skewed toward that of the smaller fruited parent - but there may not be general equation that predicts this accurately.

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  5. An even better formula that could scale better would be.
    [(25oz * 10%) + (9oz * 190%)] / 2 = 9.8oz

    More to test i suppose.

    This would also depend on how you rounded your scale measurements. Your numbers yield 1.4oz with this formula.

    Only field testing will test tell

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  6. Final option i can think up, and honestly the one i feel is most correct.

    [((larger - smaller) / larger) + 1] * smaller

    (((25-9)/25)+1)*9=14.76

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  7. This is really interesting. Last year i grew beefsteak beside cherries. I would have swore one of the cherry plants grew way bigger tomatoes than i expected, this is probably why. They were unbelievable too, bursting with juice. Like giant cherry tomatoes that pop when biting into them.

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  8. I mean i lost the tag thing that says what type of tomatoes now i think of it, i'm not sure exactly what happened but i swear they were supposed to be cherry tomatoes.

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  9. Yeah, i just double-checked and had 2 cherry tomato plants but only 1 produced Cherie's and the other was mid-size and bursting with flavour, best tomato i ever had.

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