Hybrid vigor in tomatoes

[joseph]

"Brandywine From Croatia" in my garden a few days ago... Showing the two different leaf types. The sad thing about these tomatoes, is that if they actually manage to produce fruit in my garden, I won't know if they are Brandywine tomatoes because Brandywines don't mature in my garden so there is no point trying to grow them... [An exception was made this year for a specific cultivar for a breeding project.]

[travis]

Let's get back on subject. The OP subject is interesting. Is there more to discuss in that regard?

[joseph]

About 5 years ago a study* in Pakistan found hybrid vigor of up to 47% for total yield of fruit in tomatoes. But that was in specific crosses. Other crosses showed as much as 50% reduction in yield. So the specific combining ability of the two parent lines is an important consideration when making crosses in tomatoes. Willy-nilly crosses might yield more fruit or less.

Most of the tested crosses ripened fruit sooner, by 1% to 10% so on an 80 day tomato that would make a difference of 1 to 8 days. Hmmm. That might be useful in my short-season garden.


*[Pak. J. Bot., 41(3): 1107-1116, 2009.GENETIC ANALYSIS TO IDENTIFY SUITABLE PARENTS FOR HYBRID SEED PRODUCTION IN TOMATO (LYCOPERSICON ESCULENTUMMILL.)
MUHAMMAD YUSSOUF SALEEM, MUHAMMAD ASGHAR, MUHAMMAD AHSANUL HAQ, TARIQ RAFIQUE, ATIF KAMRAN AND ASIF ALI KHAN]

[frogsleap farm]

In other crops it has been clearly demonstrated that a successful hybrid breeding program requires early screening of inbred lines for general combining ability (i.e. suitability as a parent generally with common testers) followed by more intensive screening for specific combining ability (i.e. finding the "perfect" hybrid parent combo that optimizes hybrid vigor and associated phenotype). As was pointed out in this thread by Joseph and Tom, it will be a rare cross that optimizes hybrid vigor (fruit yield and flavor) and that either one is very lucky, or that a large number of combinations are tested. I am guessing that Sungold/SunSugar were the result of testing countless hybrid combinations.

To Carolyn's point, a commercial F1 hybrid may have parents that are closely related, so that the F2 progeny do not appear to segregate significantly for obvious traits. They may however be segregating for disease/nematode resistance (non-obvious unless the pest is present). In a hybrid that expresses traits controlled by recessive alleles (e.g. gf, gs, y, t, etc.) both parents would need to contain the recessive allele there would be no segregation for these obvious phenotypic traits in the F2. The hybrid seed would still meet the legal requirements for "hybrid".

[Fusion_power]

Fred, grow a S. Habrochaites plant beside a Sungold plant. They will smell almost identical. I have not seen this odor in any of the other wild species. This is why I suspect Sungold is derived from a S. Habrochaites cross.

Carolyn, as Frogleap noted, an F1 hybrid may not appear to segregate from visible traits, but it may still be an F1 that is segregating for traits that are not easily visible. Disease tolerance particularly would not necessarily be visible, but would segregate into a range of types in the F2. Take Big Beef as an example. I've grown it and I've grown F2 seedlings derived from it. There is clear evidence that it is segregating for disease tolerance in the F2.

[PaulF]

Pardon my question. I am not into tomato breeding but the topic is very interesting as much of it as I can understand. Is breeding for disease tolerance more of a southern thing? Having only grown in the upper midwest, disease problems are not particularly prevalent. Are the tolerances meant for the larger scale and commercial growers rather than the backyard gardener?

I can understand finding a tomato that produces earlier fruit for short season areas and trying to find a flavorful fruit. That would be for the more northerly areas. Here where the season is just long enough, a couple of weeks doesn't matter. When frost happens my good tasting healthy plants succumb and that is OK. Just trying to figure out the lure of you breeders' interest.

[frogsleap farm]

I've assumed the Sungold's "wild" heritage was from S.chmielewskii http://link.springer.com/article/10....0220895#page-2, though this assumes Sungold's unique flavor and high soluble solids traces to the "sucr" mutation leading to sucrose accumulation. I know that similar loss of function mutations for this gene have been found in other species, but in this example we know the novel allele was introgressed into tomato. Dar's comparison of foliage scent has me rethinking my assumptions though. The mystery around Sungold (and SunSugar) pedigree has intrigued me for years. They have a very unique and complex flavor that appeals to almost everyone. I don't understand the genetic basis for this yet, but it is heritable and appears to co-segregate with the unique foliage scent of these varieties.

[Fusion_power]

Frogleap, I strongly suspect that sucr is not involved in Sungold. From what I have seen, it appears to accumulate large amounts of fructose and glucose, about 60/40 split. The sucr gene causes accumulation of sucrose by blocking the action of invertase which converts sucrose into simple sugars.

I have plants of LA4104 in my garden this year and plan to make a few crosses with it. You might look up the background to see why it is interesting.

[ChrisK]

Where did you get your sugar analysis done?

Originally Posted by Fusion_power

Frogleap, I strongly suspect that sucr is not involved in Sungold. From what I have seen, it appears to accumulate large amounts of fructose and glucose, about 60/40 split. The sucr gene causes accumulation of sucrose by blocking the action of invertase which converts sucrose into simple sugars.

I have plants of LA4104 in my garden this year and plan to make a few crosses with it. You might look up the background to see why it is interesting.

[Fusion_power]

I let my tastebuds do the test. Sungold affects my tastebuds about the same as gallberry honey and gallberry honey tests out at 60% fructose 40% glucose with less than 2% other sugars.

[joseph]

Originally Posted by PaulF

Is breeding for disease tolerance more of a southern thing? Having only grown in the upper midwest, disease problems are not particularly prevalent. Are the tolerances meant for the larger scale and commercial growers rather than the backyard gardener?

I don't breed for resistance to specific pests or diseases... But I grow nearly all of my own tomato seed, so if a family group is not resistant to the diseases and pests in my garden then it is less likely to produce fruit, and less likely to be saved as seed for next year.

As examples: This year there is one variety of tomato that is being vigorously attacked by flea beetles. (It was also very susceptible last year). It is a wonderful short-season tomato that does well in cold weather, but if it can't handle the flea beetles it won't be allowed to stay long-term in my garden.

A few years ago I trialed one plant each of a hundred varieties. One plant was covered with Colorado Potato Beetles every time I observed the patch. It got chopped out.

Whenever I trial a lot of tomatoes from far away there are always a few that turn yellow and wither away: I presume from micro-organisms. So it's chop, chop, chop even though culling is mostly pointless since they are self-eliminating.

While Blossom End Rot is not a disease, some varieties of tomatoes are much more susceptible. Those varieties are not allowed to continue living on my farm.

[bower]

Such an interesting thread, and many thanks to Tom for pointing out "combining ability", which is an excellent search term as well as being a key concept, I'd never heard of before.

There are reports of heterosis or "combining ability" for many different traits besides yield and earliness, including brix% (http://www.idosi.org/mejsr/mejsr2%283-4%29/9.pdf ) and other fruit quality traits like ascorbic acid and total soluble solids, as well as plant traits like salt tolerance, and heat tolerance (http://journal.ashspublications.org/content/116/5/906.full.pdf ) to name a couple.

[maf]

I am a bit late to this thread, but I thought I would reply as it chimed with many of the thoughts I have had on the merits of F1 hybrid tomatoes that can be bred for flavor rather than the usual commercial considerations.

In addition to the hybrid vigor, which is noticeable but variable depending on how well the parents play together, there are many other traits that can only be reliably captured in an F1 cross between two stable lines. (In other words, a trait that is only expressed in the heterozygous state, which would be 100% of the F1's but only 50% or less in subsequent generations.) The rin gene is the classic example of this type of expression in the commercial tomato field with almost every tomato sold in supermarkets being heterozygous for rin. But there are many other characteristics that are only available in the heterozygous state; for example the exact color of an F1 cross may turn out to be impossible to stabilse in a true breeding line.

Some lines express improved flavor in the F1, others not so much. As mentioned earlier in the thread some varieties have a better combining ability than others, and some just don't work well together.

I have discussed this subject with Mark (Frogsleap) a couple of years ago and have touched on it with Travis too. I really think there could be a niche market for specialist flavor oriented F1 hybrids, but a good name is needed to differentiate them from commercial F1 hybrids. My suggestion is: "Boutique hybrid" or "Boutique F1".