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Genetic and Systematic Studies on Accessions of Lycospersicon from the Galapagos Islands

Charles M. Rick
American Journal of Botany
Vol. 43, No. 9 (Nov., 1956), pp. 687-696
Stable URL: http://www.jstor.org/stable/2438834
Page Count: 10
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Genetic and Systematic Studies on Accessions of Lycospersicon from the Galapagos Islands
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Abstract

Three living accessions of Lycopersicon (LA166, LA292, and LA317) from the Galapagos Islands were studied in respect to their morphology, breeding systems, cytology, compatibility with representatives of all known Lycopersicon species, and inheritance of certain characters in crosses with L. esculentum. The following characteristics are common to all three accessions: (1) extreme genetic uniformity in first and second generations, (2) very high level of self-pollination, (3) 12 pairs of chromosomes similar to those of other collections of Lycopersicon in metaphase morphology, (4) complete failure of crosses with species of the subgenus Eriopersicon (except limited compatibility with L. hirsutum) (LA292 not tested), (5) complete compatibility with L. esculentum and L. pimpinellifolium, and (6) no reduction in viability or fertility (vs. parents) or F1 and F2 hybrids with L. esculentum and B1 to L. esculentum. On the basis of these findings and morphological comparisons all three accessions are construed as members of the subgenus Eulycopersicon. In respect to its morphology LA317 conforms to descriptions of L. cheesmanii f. minor. In consideration of its compatibility relations and morphology, this entity is considered conspecific with L. esculentum and should be returned to its original status as L. esculentum var. minor. LA166 possesses the key characteristics of L. pimpinellifolium but differs from other collections of that species in a number of striking features. LA292 is identified as L. esculentum. It approaches var. cerasiforme in type but differs in several important key characters. Each collection thus deviates in several unique morphological and physiological details from nearest known mainland equivalents. Of these deviating characters, orange fruit color, small seed size, and seed dormancy are possessed in common by LA166 and LA317. Otherwise each trait is found in only one accession, the accessions tending to deviate from each other as much as they do from mainland equivalents. The orange fruit color of LA166 and LA317 is determined by a single gene, which by its very similar phenotype, dominance, and linkage relations is likely identical with B from L. hirsutum. The absence of pedicel joint in LA166 is determined by an incompletely recessive gene j2, which is not allelic with the previously known j1 (j). Other character differences appear to be inherited in multigenic fashion. The results of this study are discussed in relation to the origin of the Galapagos flora.

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