L. pimpinellafolium x Bonner F1 and F2

[frogsleap farm]

My tomato beds are a Septoria hot spot. Despite heavy mulching, removing diseased debri, etc., I have Septoria problems every year. In 2007 I planted L. pimpinellifolium PI 422397, with reported tolerance to Septoria (Barksdale and Stoner, 1978; Poysa and Tu, 1993). It showed considerable tolerance in my garden, but was a real sprawler with typical small currant type fruit. In an adjacent row I had several plants of Bonner (very early, determinate type). This spring I planted ~100 OP seeds from 422397 and found 1 F1 plant. The F1 was erect, compact, very early flowering, with tasty small red cherry fruits. I segregated this tomato plant from the rest of the crowd and collected seed from a couple dozen F1 fruits. In late July I harvested the first F1 fruit, extracted seed and planted 27 F2 plants into a bed where my early tomatos had been decimated by Septoria. I left the infected debri on the soil surface. The F2 plants varied widely in phenotype; growth habit, plant size, flowering date, and Septoria tolerance. All F2 plants showed some Septoria infection, unfortunately I did not include a susceptible check. All but two were frosted before I could harvest fruit.

I'm willing to share some of the limited F2 seed with anyone interested in working on enhanced tolerance to Septoria leafspot. I'm going to try crosses to some L. hirsutum lines this summer as a follow up. I also have selections from various heirloom varieties that show some tolerance.

[goodwin]

I've started working with l. hirsutum because it appears to have good resistance to early blight. That's the scourge here along with curly top. I can't test for septoria resistance. Have a bunch of the lowland strain of l. hirsutum if you need any.

[frogsleap farm]

The Poysa (1993) paper reported results from growth chamber screening for Septoria resistance (tolerance) and listed a handfull of L. hirsutum and L. peruvianum PIs with "high resistance". I've sent in for these as a starter. I've done a lot of hand crossing, though not yet in tomato. I think I read L. hirstum is an obligate outcrosser. A successful F1 will have a lot of negative baggage - this may be a long term experiment.

[goodwin]

Oh, you're saying the genotype of the F2 has to differ because the F1 doesn't self - the infamous gametophytic self incompatibility. Do we know that? Certainly would complicate things.

[frogsleap farm]

I was thinking that the F1 might be easy, because the L. hirsutum parent is self-incompatible. All seed harvested off that parent must be F1. I found this recent reference that shows the F2 will be segregating for self compatibility ... and hopefully Septoria tolerance.

"Sixteen-hundred BC1 plants of a cross between an early blight (EB) susceptible tomato (Lycopersicon esculentum Mill.) breeding line ('NC84173' maternal and recurrent parent) and a resistant accession ('PI126445') of the tomato wild species Lycopersicon hirsutum Humb. and Bonpl. were grown in a field in 1998. This population was segregating (among other traits) for growth habit, self-incompatibility and earliness in maturity." (Foolad and Lin, 2008)

These Penn State researchers were chasing early blight tolerance from L. hirsutum, and found that in analyzing the F2 progeny eb tolerance was a quantitative trait (i.e. controlled by several genes). Not necessarily a bad thing, but it will take longer to introgress multiple genes into a favorable background.

My concern is that there are going to be a lot of undesirable traits in L. hirsutum, including fruit quality. Accumulating the favorable disease resistant gene(s) and simultaneously eliminating the undesirable genes from the wild parent will take several generations and will require looking at a lot of plants, thus my comment about long term experiment.

Sixteen-hundred BC1 plants of a cross between an early blight (EB) susceptible tomato (Lycopersicon esculentum Mill.) breeding line ('NC84173' maternal and recurrent parent) and a resistant accession ('PI126445') of the tomato wild species Lycopersicon hirsutum Humb. and Bonpl. were grown in a field in 1998. This population was segregating (among other traits) for growth habit, self-incompatibility and earliness in maturity.

[goodwin]

It seems like the parents would be hand-crossed with L. esculentum and the F1's selected for successful cross by leaf shape and selfing by flower structure. That's what I was figuring to do, but I'm no botanist. I wonder what else the researchers found? Surely they didn't just drop the project?

[frogsleap farm]

If the L. hirsutum is self incompatible, emasculation shouldn't be necessary, and all seed harvested will be a F1 with esculantum (as long as there aren't any other hirsutum plants around). However I'd welcome comments from anyone who's tried this before. I tried tracking down the researcher, but think he retired.

[frogsleap farm]

Well, a little more reading on interspecific crosses suggests a cross with L. hirsutum requires L esculentum be used as the female parent. There are also incompatibility factors in esculentum x hirstum hybrids leading to poor pollen production, seed fertility and plant fitness - requiring additional backcrossing to esculentum. The new interspecific crosses are now sounding like a greenhouse project .... and a little outside my available time, energy or resources.

[goodwin]

I grew out 3 L. hirsutum plants last year and I would expect nearly all the seed I collected is pure - tiny seed as you know. From what you've said this may be tricky - but I think I'll attempt some deliberate crosses this summer and see what I get. Maybe some other wild species would be easier to work with, though.

[goodwin]

I have 6 hirsutum crosses planted out. They are vigorous - very dense foliage and sprays of blossoms. I'm not sure what to expect from the fruit. I'll test Brix levels and compare disease and insect resistance to standard varieties. There are no signs of premature senescence which is sometimes reported. I also have several other species and early strains going, so it should be an interesting summer.

[frogsleap farm]

This winter/spring I planted out the two early flowering/fruiting F3 families harvested just prior to fall frost, and started another couple of dozen F2 families from the Bonner x L. pimpinellifolium cross. They are segregating widely for the rugose/dwarf characteristic of Bonner, but with almost continuous variation for this dwarf vs regular growth characteristic. What I find most interesting is how early these buggers are - most flowering and setting fruit in my basement growth room well prior to transplanting. In comparison many appear to be much earlier than Stupice. I've kept the best of these in captivity in my sunroom and have made crosses with mid-season beefsteak types as they come into bloom in the nursery.

[frogsleap farm]

A progress report. I had another banner year for Septoria, except for those beds where I used fungicidal control. Although I am seeing some progress in my longer term project in selecting for Septoria tolerance within heirloom types, the S. pimpinellifolium project has been discouraging. Levels of Septoria tolerence in these lines was inferior to other more adapted lines in my Septoria nursery, and the progeny from these "wild crosses" have various minor/major agronomic flaws. I am keeping a couple of very early rugose lines from this cross, but that's a different project. It's interesting that the Cornell SLS project used the same pimpinellifolium PI that I did, though combined this with one or more hirsutum crosses - they are reporting progress on developing resistant/tolerant lines.

[frogsleap farm]

Goodwin - were these crosses you made last year? Was this a difficult cross to make? I've got one of two cross with hirsutum planned for this summer, using the hirsutum plant as the pollen parent.

[goodwin]

No, it got too late in the year and my one attempt didn't take. So I got this seed online and I don't know the cross.
I had a dozen started, but some froze hard. Perhaps they are prone to that, because other nearby plants did not die off. The other wild species and strains I bought from a fellow in Ecuador. I should take some time this weekend and try some crosses and backcrosses. I'll let you know how that goes and post some photos. Been busy getting ready for market.

[goodwin]

Sounds like a good plan - getting two generations in a year would really speed up the process. That's probably what I should do. Not just backcross, but test the viability of the seed and start some F2 to get an idea how it will segregate. I have a greenhouse now so I could continue the project well into the fall. What you have so far is interesting. The plant habit must be controlled by more than one gene or there is incomplete dominance. How about fruit size? Do you think there will be any correlation to plant type?