Stoeva, P. Overcoming unilateral incompatibility of Solanum pennellii. (submitted by C. Daskaloff)
Overcoming the unilateral incompatibility of S. pennellii is of particular importance for studying cytoplasm
cytoplasmic-nuclear relations between pennellii cytoplasm and the genomes of species of Lycopersicon. In this
respect in the two successful crosses S. pennellii x L. hirsutum f. glabratum and S. pennellii (tetraploid) x L.
peruvianum (diploid), no cytoplasmic-nuclear interactions were observed.
Breaking the unilateral incompatibility of S. pennellii was accomplished in two ways: a) by a bridge hybrid
containing cytoplasm of S. pennellii and genetic material from both S. pennellii and L. esculentum; b) by using as a
bridge the hybrid proposed by Martin (TGC 16) of S. pennellii x L. hirsutum f. glabratum. Realization of the second
hybrid was easier, but it was less successful as a bridge because the genetic material from f. glabratum impedes
the crossing with species of the subgenus Eulycopersicon. When species of the latter subgenus are used as male
parents, the only successful cross was BC1-P2 (S. pennellii x L. hirsutum f. glabratum) x L. pimpinellifolium. For this
reason we concentrated on the first bridge hybrid, which was obtained in the following way. Flower buds of S.
pennellii (LA716 Atico) were pollinated with F2 and BC1-P2 hybrid plants of the cross L. esculentum x S. pennellii.
Seven plants were grown whose hybrid character was determined by the changed pedicel ratio. These plants were
used as female parents in crosses with different varieties of L. esculentum and different generations (F1, BC1-P1,
BC2-P2) of the esculentum-pennellii cross. Such crosses succeeded only with the F1 as pollen parent. Thus the
bridge hybrid had the constitution S. pennellii (Atico) x F2 (or BC1-P2) x F1 x F1. It was crossed as female parent
with: L. esculentum (3 varieties), L. cheesmanii var. typicum, L. cheesmanii var. minor, and L. pimpinellifolium. Fruit
set was 10.26-16.67% per pollinated bud. The hybrid plants of all of the crosses showed high (seed) fertility and low
pollen sterility (5-52%; mean = 22%).
Tanksley, S. D., and C. M. Rick Prospects for the use of isozymes for legal purposes in tomato breeding.
Isozymes and other protein markers are now being used to identify for legal purposes specific cultivars in a
number of crop species. Allozymes (isozymes encoded by different alleles at the same locus) can be distinguished
without ambiguity by simple electrophoretic techniques. They can thereby be utilized as unequivocal markers of
varieties in place of morphological characters, which are often subject to environmental influence. The question has
naturally arisen about the potential use of such enzyme markers for direct identification of tomato cultivars. In our
laboratory, variation in the tomato and its close relatives has been studied, utilizing more than ten different enzyme
systems, accounting for more than 30 loci. The results are not encouraging for those hoping to find existing
differences between cvs. For the most part, all U. S. and European cultivars examined are indistinguishable
electrophoretically. The exceptions are most nematode-resistant cvs. (derived from L. peruvianum) which carry Aps-
11, several British forcing cvs. which have Est-11 (probably derived from L. pimpinellifolium in breeding for leaf mold
resistance), and Stone, John Baer, Marmande, and several other older Euopean cvs. which are fixed for Prx-47. The
remaining ones -- the great majority -- share the same zymotype for all tested electrophoretic loci. Although our
sample of enzymes does not by any means exhaust the full reportoire of systems amenable to electrophoresis, the
results should be indicative of the lack of such variation in modern cultivars. We are therefore pessimistic about the
prospect of utilizing existing allozymic differences for legal purposes.
In light of this situation, one might consider introducing specific molecular markers into given cvs. Cultivars,
land races, and closely related species from Ecuador-Peru contain a wealth of allozymes not found in any modern
cvs. Thus, in addition to the aforementioned Est-11 and Prx-47 found in North Temperate cvs., Adh-11 , Got-11 , Prx-
42 , and Prx-71 are available in certain Andean cvs. These alleles would have greater appeal to the breeder than
those requiring wider crosses with other species. A cultivar into which one of these alleles has been introduced
would be distinguishable from all others solely on the basis of this one genetic character. An additional advantage of
such allozymic differences is that they have never been observed to exert any
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