My wild tomato breeding project

[joseph]

I had 4 successful crosses this year using LA1777, Solanum habrochaites, as a pollen donor to domestic tomatoes.

As far as I can tell attempted crosses with species from the peruvianum complex were not successful.

I have once cluster of fruit that may have seeds in it from an attempted cross between S. habrochaites and S. corneliomulleri. I should plant some of them this winter to see if any obvious hybrids show up.

[StrongPlant]

Originally Posted by FredB

I've tried several of these crosses over the last decade or so, and I can summarize my experiences.

Solanum pimpinellifolium. The domestic tomato probably originated from S. pim. or a close relative, and this cross is very easy. The F1 between S. lycopersicum and S. pim. is sweeter than either parent, and many of the supersweet cherry tomatoes probably have S. pim. in their ancestry.

S. galapagense. This is a relative of S. pim. with tiny yellow fruit. It is also easy to cross with S. lycopersicum. The F1 is sweet but has a bad off-taste that it gets from its S. gal. parent. You can find F2 and F3 plants that are still sweet but lack the off-taste, but I haven't fully succeeding in stabilizing a line.

S. cheesmaniae. Another yellow one from the Galapagos Islands. Easy to cross, but in my experience the F1 lacks the sweet taste you get with S. pim. or S. gal.

S. habrochaites. This is from another sub-group of the tomato family, and it is difficult to cross with S. lycopersicum. I have had one successful cross out of about 30 tries. The rootstocks bred by Syngenta all seem to be S. habro. If you let a rootstock plant grow instead of using it as a rootstock, you get a huge vine with fuzzy leaves and a distinctive smell. The plants are completely resistant to Septoria and some varieties are also resistant to early blight, as well as being resistant to just about every known root and stem disease. The fruits are about 3/4" and stay hard and green. Oddly enough, crossing green-fruited habrochaites with pink-fruited Brandywine resulted in orange fruit, an interesting example of what geneticists called epistasis (when you get a particular trait with a combination of two genes but not with either one separately). Apparently habrochaites is missing one of the genes on the pathway to orange pigment, and Brandywine is missing a different gene, but when you cross them the F1 has all the necessary genes and can make orange pigment.

S. peruvianum. Difficult. I had one apparently successful hybridization, but the F1 plants all seemed to be sterile as both male and female parents. One of the genes for blue fruit comes from peruvianum, so it must be possible to do this cross, but so far it is beyond my skill.

Fred

Interesting,have you tried crosses between the wild species themselves?

[FredB]

Originally Posted by StrongPlant

Interesting,have you tried crosses between the wild species themselves?

No, I haven't. S. habrochaites and S. peruvianum are in the same sub-group, so they might cross. Both have very large showy flowers. Both have hard green fruit, and I suspect that crossing one rock with another rock will produce a third rock, but you never know.

[Keen101]

Originally Posted by TheLoud

I just wanted to clarify this general point about interspecific hybrids, although I don't have any information about these species in particular. It's true that reproductive isolation defines species. However, that barrier to crossing can take many different forms. There can be a geographic barrier between two populations that prevents any pollen from getting from one population to the other. The two populations can live in different habitats, or bloom at different times, or be pollinated by different vectors. All of these barriers to hybridization are very easy to overcome by a hobbyist.

There are other barriers that are harder to overcome, that require the massive effort and fancy equipment mentioned above. The barrier between species might be that fruit don't set, or abort early, or seeds don't sprout, or seedlings are weak and die young, or hybrids are vigorous but sterile, like mules. Try the crosses in both directions, because sometimes one works better than the other.

I agree with this statement. I suspect many inter-specific hybrids are easier than some people believe. Joseph has an interesting population of squash that seems to fit this idea.

Though i want to mention that here in Colorado there is a farm that has a population of mules that are able to breed with each other and produce offspring. So just because most mismatched gene number crosses produce sterile offspring does not mean that they all do. If one is patient enough i suspect many of those crosses could be viable as well. It's more a matter of statistics rather than possibility.

[Keen101]

Originally Posted by FredB

Oddly enough, crossing green-fruited habrochaites with pink-fruited Brandywine resulted in orange fruit, an interesting example of what geneticists called epistasis (when you get a particular trait with a combination of two genes but not with either one separately). Apparently habrochaites is missing one of the genes on the pathway to orange pigment, and Brandywine is missing a different gene, but when you cross them the F1 has all the necessary genes and can make orange pigment

Nice. A cool cross to be sure. In peas this is really apparent when you cross a pink flowered vine with a white flowered vine. The result is a plant that has bicolor-purple flowers that neither parent have. In the pea example the gene A is the (dominant) gene that controls Anthocyanin (or color) expression. The pink flowered vine has at least one if not two copies of this "master switch" that allows it to have colored flowers, but must lack another dominant gene elsewhere as the flowers are pink instead of the wild bi-color purple. The white flowered plant has the bi-color gene hidden but since it has two recessive copies of the little "a" gene it has it's "master switch" turned off. So the expression of specific color is epistatic to the A "master switch" gene. Some call this a throwback phenomenon as you can suddenly see traits that have been hidden for generations suddenly show up seemingly out of nowhere.

Interestingly enough Darwin saw this happen when he bred pidgeons. He just didn't fully know what was going on. In his case he bred a white pidgeon with another white pidgeon (that had black tail feathers) and in his F1 generation he got a BLUE pidgeon. One had the master switch color gene but lacked another, the other had the blue gene but lacked the master switch.

[goodwin]

I have several lines still going. They include a very early PL dwarf hirsutum cross, several stable L.chmielewski crosses, and one using LA1777 that is not only edible, but pretty good. It is orange. I sold a number of the dwarf plants at the market last spring and people said they did well.
Below is a photo of the LA1777 cross at F4. The fruit of earlier generations was more brown and russeted. There is some concentric cracking in wet weather, but it is quite cold-tolerant. The foliage still has that odd mushroom aroma.
Lee

[FredB]

Does your F4 have resistance to leaf diseases? LA1777 is supposed to be resistant to late blight, and I have seen resistance to septoria leaf spot and early blight in some of the habrochaites hybrids that are used as rootstocks.

[Keiththibodeaux]

If you really want to go wild, I have some Maná-cubiu (Solanum sessiliflorum) seeds sent straight to me from a friend in Manaus, Brazil.

[goodwin]

Hi Fred,

We had a wet 2015 season and this line is definitely resistant to late blight. There was resistance to early blight as well, but not across the board. I don't know about septoria, which we haven't seen here yet.
I'm not sure about the genetics, either. However, I think it is not the result of a major gene as we see in some hybrid varieties, but a more general resistance. There were heirlooms with resistance to earlier races, but not against what is showing up now. Matt's Wild is an exception, as you may know.

Lee

[Fusion_power]

S. habrochaites and S. peruvianum are in the same sub-group

S. chmielewskii, S. habrochaites, S. neorickii, and S. pennelli are in the group that can make 1 way crosses to domestic tomato. S. Chilense and S. Peruvianum are genetically further away and do not cross with domestic tomato except with embryo rescue. The reason is because of differences in formation of endosperm. Study a domestic tomato seed will show a relatively large endosperm, roughly three times as large as for wild species. This difference is the primary reason Peruvianum won't cross with Lycopersicum. I'll note one exception which is with S. Arcanum. Under some circumstances S. Arcanum will cross to domestic tomato and produce viable seed.

Including Solanum lycopersicum, there are currently 13 species recognized in Solanum section Lycopersicon. Three of these species—S. cheesmaniae, S. galapagense, and S. pimpinellifolium—are fully cross compatible with domestic tomato. Four more species—S. chmielewskii, S. habrochaites, S. neorickii, and S. pennelli—can be readily crossed with domestic tomato, with some limitations. Five species—S. arcanum, S. chilense, S. corneliomulleri, S. huaylasense, and S. peruvianum—can be crossed with domestic tomato with difficulty and usually require embryo rescue to produce viable plants.

[goodwin]

Hi Darrel,
That's a good summary. I grew what was supposed to be a peruvianum cross a number of years ago which came to me from a fellow in Ecuador.
It was some sort of interspecies cross and a monster plant. I used it as a parent for the Bosque Green Cherry.
Maybe I should see if I still have that seed and try it again.
Lee

[FredB]

Originally Posted by goodwin

Hi Fred,

We had a wet 2015 season and this line is definitely resistant to late blight. There was resistance to early blight as well, but not across the board. I don't know about septoria, which we haven't seen here yet.
I'm not sure about the genetics, either. However, I think it is not the result of a major gene as we see in some hybrid varieties, but a more general resistance. There were heirlooms with resistance to earlier races, but not against what is showing up now. Matt's Wild is an exception, as you may know.

Lee

Every habrochaites rootstock that I tried seemed to be completely resistant to Septoria, so it may be a common property of all S. habrochaites lines. I think there is a good chance your interspecies hybrid will also be resistant.

[Fusion_power]

Septoria Resistande: it may be a common property of all S. habrochaites lines.

Most Habrochaites are susceptible to septoria to varying degrees. A few Habrochaites lines are highly resistant. The resistance often seen in rootstocks is from rampant growth together with high alkyl production. It won't hold up under heavy fruit production in a typical edible tomato genetic background. LA2175 has a high degree of genetic resistance that is transferable to domestic tomato. It just takes a lot of generations of growing plants to eliminate most of the genetic drag from Habrochaites.

[Keen101]

I'd be interested in seeds for any wild progeny or hybrids with wild tomatoes, especially these hard to cross or one-way crosses. I've already got seed for S. cheesmaniae and S. galapagense. But some of these other species sound interesting.

Also has anyone found novel new recombinations by crossing two wild species together? For fun i might try crossing S. galapagense with S. pimpinellifolium.

[Keen101]

Yesterday i had two S. galapagense seedlings pop up. Today there are a total of TEN! I guess they were just a bit late in germinating.

Out of the 6 or so S. Cheesmanaie three seem to have dark anthocyanin stems, the others do not. One has very dark stems. Too early to see if there are any antho stems on this batch of S. galapagense seedlings, though i think i used this as my "test batch" because they don't and it wouldn't be as big a loss if these ones all died or failed to germinate.