Ah that’s a good point! Do regular gardeners have an easy time saving seed from multiple heirloom varieties keeping them differentiated? If so, perhaps my worries are exaggerated.
Indeed. There’s a paper on using SC pennellii LA0716 to cross with peruvianum, and by coincidence before I read that paper I tried using the same accession to cross with a bunch of peruvianum accessions. I’ll update here on the forum if I get successful crosses.
Yes I read that … if I remember correctly, there are SC and SI populations within the same species that are mutually incompatible. Makes you wonder about the definition of ‘species’! It is after all a conceptual box, made up by speculating creatures.
I read about SI mechanisms starting up at a specific stage in flower development, such that it may be possible to cross domestic to some SI species/accessions if you use a flower 5 days before it opens. I tried this only a couple of times, one I saw didn’t work, the other must be hidden somewhere in my ‘jungle’ and I guess I’ll see sooner or later if it worked. Tough to work on such small flowers, I should make more attempts I guess but so many things to do!
Also here’s a chart on how far pollen went in various tests:
Source:
‘TESTING THE SI × SC RULE- POLLEN–PISTIL INTERACTIONS IN INTERSPECIFIC CROSSES BETWEEN MEMBERS OF THE TOMATO CLADE ( SOLANUM SECTION LYCOPERSICON , SOLANACEAE)’ - YOU SOON BAEK et al - 2015
Due to that consideration I tried many arcanum and peruvianum cross attempts with some pimps, in case the shorter style helped. Just 1 peruvianum accession, and 2 (and likely their cross) accessions of arcanum. Yet to harvest their fruits though turns out crossing those with domestics and wildings gave fruit in several cases, but… is it the endosperm… not formed in almost all cases. So for those it might not be a style length issue to worry about. I’m now growing 3 wilding x arcanum seedlings (or what is hopefully so anyway), from 2 different wildings. I didn’t do tests myself, I used mix pollen for selfing, but it seems those arcanum are said to be (likely?) facultative-SC.
I also just opened up attempts to cross those with Columbianum, which is a Columbian landrace of domestics supposed to be able to act as a bridge to peruvianum. No proper seeds for the peruvianum attempt, but full load of seeds for the arcanum. Which actually makes me suspicious… but I guess I’ll see when I grow some out.
It may also be possible to cut styles to make them shorter. Some suggest using walnut oil on the end of the cut to hold the pollen - water would make the pollen explode. I don’t know if anyone has actually had success with this method though. I made a few attempts - there are so many hanging labels in my ‘jungle’ that I only check them when fruits are ready to harvest, so no update yet as to whether any of those worked. Though I did not make enough attempts to give the method a fair trial.
I like dendrograms. Kind of allows us to see where on that lake shore of Joseph’s each accession lies (well, to some degree anyway) rather than just having the species concepts as boxes not knowing the relations between them:
These charts are interesting too, using mitochondrial DNA and other methods to see relationships and evolutionary trajectory:
Source: TAXONOMY OF WILD TOMATOES AND THEIR RELATIVES (SOLANUM SECT. LYCOPERSICOIDES, SECT. JUGLANDIFOLIA, SECT. LYCOPERSICON; SOLANACEAE) Iris E. Peralta - 2008
Here’s a chart that I made for my own reference, which makes it easy to see which species are more closely related, and whether they’re SI or SC:
In case anyone’s interested, here’s that book’s take on the species concept:
SPECIES CONCEPT
Our goal for this study is to apply a phylogenetic concept and classification to sections and series, and a more pragmatic, practical concept incorporating a wide variety of data to species. Sections Lycopersicon, Lycopersicoides, and Juglandifolia, and the informal “Lycopersicon” species group are unambiguously monophyletic. The “Arcanum,” “Eriopersicon,” and “Neolycopersicon” species groups may be monophyletic, but there are ambiguities in various data sets regarding these.
Ultimately, all large-scale monographs rely on morphological characters to provide identifications for the many specimens needing determinations, but species concepts may also be influenced by molecular, ecological, and crossing relationships, despite inherent potential conflicts between biological and phylogenetic concepts. Our decisions relied on clear morphological discontinuities to define the easily distinguished species S. habrochaites, S. lycopersicoides, S. pennellii, and S. sitiens. The following closely related species are generally easy to distinguish but sometimes intergrade: 1) S. lycopersicum, S. pimpinellifolium, 2) S. cheesmaniae, S. galapagense (sometimes also with introduced S. pimpinellifolium), 3) S. arcanum, S. chmielewskii, S. neorickii, 4) S. corneliomulleri, S. peruvianum, 5) S. chilense, S. huaylasense. Specific characters used for recognition are detailed with each species description and in the keys. Potential reasons for variability and intergradation are recent divergence and hybridization. Despite the variability in tomato species, our decision to recognize the four segregants of S. peruvianum s.l. (Peralta et al. 2005) is based on a pragmatic combination of phylogeny and morphology, and reflects evolving, recognizable entities within the complex.
We do not recognize taxa below the species level, most notably the small-fruited tomatoes known to many as “var. cerasiforme.” The name “cerasiforme” has been used to refer to putatively wild forms of S. lycopersicum that have been regarded as progenitors of the cultivated tomato (although see Frary et al., 2000, and Nesbitt & Tanksley, 2002). It is impossible to distinguish wild from cultivated forms using herbarium specimens, and we regard many specimens labeled as “var. cerasiforme” to be possible revertants from cultivation (i.e., feral plants) or possible hybrids of wild and weedy taxa. Many cultivar names have been proposed (often not validly published, see Appendix 1) as formal taxa following the principles laid out in the International Code of Botanical Nomenclature (McNeill et al. 2006, and earlier editions), but cultivars would be more usefully named using The International Code of Nomenclature of Cultivated Plants (Spooner et al. 2003; Brickell et al. 2004). In addition to species groups, we distinguish four weakly defined morphotypes within S. arcanum that show discrete geographic ranges but exhibit so much overlap of character states, especially in leaf morphology, that consistent assignment of any given specimen to a morphotype can be difficult in the absence of geographical data.
And here’s a section some of you might find useful:
BREEDING SYSTEMS AND INTERSPECIFIC HYBRIDIZATION
Mating systems in wild tomato species vary from allogamous self-incompatible to facultative allogamous and self-compatible, to autogamous and self-compatible (Rick 1963, 1979, 1982b, 1986b; Table 1). The self-incompatibility system in tomatoes is gametophytic and controlled by a single, multiallelic S locus (Tanksley & Loaiza-Figueroa 1985).
The self-incompatibility system has shown strong relationships with the degree of outcrossing, allelic diversity, floral display, and degree of stigma exsertion in wild tomatoes. Rick (1982b) investigated the genetic bases of self-compatibility, self-incompatibility, and flower characters by studying interspecific hybrids between the self-compatible (SC) S. pimpinellifolium, used as recurrent parent, and the two self-incompatible (SI) species S. habrochaites and S. pennellii. He postulated that three independent genetic phases, most probably regulated by different unlinked genes or gene complexes, are essential for successful functioning of the self-incompatibility system. These genes are operating on: 1) prevention of self-fertilization, 2) changes in the flower structures to ensure cross-pollination, and 3) development of secondary flower characters to attract pollinators. He concluded that the evolution of the mating system in wild tomatoes proceeded from self-incompatibility, as the ancestral condition, to self-compatibility, and probably never reversed to self-incompatibility. Changes from self-incompatibility to selfcompatibility are expected to arise frequently and independently (Rick 1982b). This trend has been found in S. habrochaites and S. pennellii; both species have self-incompatible and self-compatible populations. The self-incompatible populations occupy the center of their species geographic distributions, and have higher genetic variation, larger flower parts, and exserted stigmas. Self-compatible populations occur toward the northern and southern edges of the ranges of S. habrochaites and S. pennellii, have less genetic variation, smaller flower parts, and little or no stigma exsertion (Rick et al. 1979; Rick & Tanksley 1981). The change from self-incompatibly to self-compatibility has been reported in only one population of S. peruvianum (Rick 1986b).
In the self-compatible species, the extent of outcrossing and genetic variation is also related to floral display and degree of stigma exsertion. Within S. pimpinellifolium, the most northern and southern populations at the margins of the species range are highly autogamous with little or no genetic variation, have small flower parts, and little or no stigma exsertion, while the centrally located facultative allogamous populations have higher genetic variation, larger corollas, and marked stigma exsertion (Rick et al. 1977). A comparison of different genotypes of S. pimpinellifolium in experimental plots in Peru showed that different outcrossing rates could be largely attributed to differences in floral characters, especially the level of stigma exsertion, rather than to differences in numbers and types of pollinators (Rick et al. 1978). Smaller flower size in selfing forms of S. pimpinellifolium is due largely to variations in the growing time of individual flowers, with the larger outcrossed flowers growing (i.e., remaining open) for longer time periods than the smaller, selfing flowers (Georgiady & Lord 2002). Four QTLs (total anther length, anther sterile apical appendage length, style length, and flowers per inflorescence) cause major phenotypic variance (Georgiady et al. 2002). Early floral stages showed no significant differences; thus, the difference in size in these flower size transitions can be attributed to a simple heterochronic change in growth (Georgiady & Lord 2002). Chen and Tanksley (2004) have suggested that a locus on chromosome 2 is largely responsible for stigma length, and that the tightly linked genes in this compound locus represent a co-adapted gene complex controlling mating behavior.
Two self-compatible sister species, S. chmielewskii and S. neorickii, illustrate another example of changes in flower characters associated with outcrossing and genetic variation. Solanum neorickii is exclusively autogamous, has low intra-populational genetic variation, small flowers, and stigmas included in the anther tube. In contrast, the facultative allogamous S. chmielewskii exhibits higher levels of heterozygosity, larger flower parts, and exserted stigmas. Rick et al. (1976) postulated that S. neorickii evolved from S. chmielewskii. All populations of S. chilense are self-incompatible. The species in the outgroup sections S. lycopersicoides, S. sitiens, S. ochranthum, and S. juglandifolium, are exclusively self-incompatible.
The Endosperm Balance Number (EBN) crossability phenomenon was analyzed for Rick’s two wild tomato complexes by Ehlenfeldt and Hanneman (1992). The EBN hypothesis (Johnston et al. 1980; Ortiz & Ehlenfeldt 1992; Hanneman 1994) postulates that in the absence of stylar barriers, the success or failure of a cross is determined primarily by a 2:1 maternal to paternal balance in the endosperm, independent of ploidy. The EBN data supported the hypothesis of two intra-fertile groups as proposed by Rick (1979). Rick’s “Esculentum” complex showed uniformity of EBN values, which can be compared to the 2×(1EBN) species in potato. On the other hand, the “Peruvianum” complex showed variable values for EBN, but most comparable to 2×(2EBN) potato species (Ehlenfeldt & Hanneman 1992). These authors hypothesized that Rick’s “Esculentum” and “Peruvianum” complexes are separated by a system analogous to the 2×(1EBN) S. commersonii Dunal and 2×(2EBN) S. chacoense Bitter crossability groups. This putative isolating mechanism may restrict or suppress gene flow among sympatric populations (Ehlenfeldt & Hanneman 1992), and may play a role in the reproductive isolation in tomatoes, such as the S. arcanum assemblages in northern Peru.
In the paper I mentioned above, ‘TESTING THE SI × SC RULE- POLLEN–PISTIL INTERACTIONS…’, there are some nice images. For example:
And:
