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AOBPreview published online on October 15, 2004
Annals of Botany, doi:10.1093/aob/mch205
© 2004 by Annals of Botany Company
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Received November 10, 2003
Revised March 17, 2004
Accepted August 11, 2004

Article

Natural Hybridization between a Deciduous (Nothofagus antarctica, Nothofagaceae) and an Evergreen (N. dombeyi) Forest Tree Species: Evidence from Morphological and Isoenzymatic Traits

M. STECCONI 1*, P. MARCHELLI 2, J. PUNTIERI 1, P. PICCA 3, and L. GALLO 4

1 Departamento de Botánica, Centro Regional Universitario Bariloche, Universidad Nacional del Comahue, Quintral 1250, 8400 Bariloche, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
2 Unidad de Genética Forestal, INTA, EEA Bariloche, CC 277, 8400 Bariloche, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
3 Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón II, 4to. piso, Ciudad Universitaria (1428), Buenos Aires, Argentina
4 Unidad de Genética Forestal, INTA, EEA Bariloche, CC 277, 8400 Bariloche, Argentina

* To whom correspondence should be addressed. E-mail: stecconi{at}crub.uncoma.edu.ar.


  Abstract

• Background and Aims Trees with a partial leaf-shedding pattern and other morphological features a priori considered intermediate between those of the deciduous Nothofagus antarctica (G. Forster) Oersted and the evergreen N. dombeyi (Mirb.) Oersted (Nothofagaceae) were found in natural stands. The hybridization between a deciduous and an evergreen species of Nothofagus has not been reported so far in natural communities.

• Methods The putative hybrids and the two presumed parental species were compared using 14 enzyme systems as well as shoot, leaf and reproductive morphology.

• Key Results Six enzyme systems showed good resolution (MDH-B, IDH, SKDH, 6-PGDH, GOT and PGI) and in four of them (PGI, MDH-B, SKDH and 6-PGDH) the putative hybrids showed intermediate zymogram patterns between N. antarctica and N. dombeyi. Both principal coordinates analysis on isozyme data and principal components analysis (PCA) on quantitative morphological traits of shoots and leaves separated both parental species and located the putative hybrids closer to N. antarctica than to N. dombeyi. In the PCA, the number of basal cataphylls and the length : width ratio of leaves were the variables most discriminating among shoots of the three entities. The putative hybrids were intermediate between both species regarding leaf vernation, outline and venation, variation in leaf shape (length/width) with position on the parent shoot and in staminate inflorescence and cupule morphology. For other morphological traits, the putative hybrids resembled one of the parental species or differed from both species (e.g. valve morphology).

• Conclusions Isoenzymatic and morphological data sets support the idea of the hybrid nature (probably F1 generation) of the semi-deciduous trees found. Nothofagus antarctica and N. dombeyi are probably more closely related than previously assumed. The relevance of pollen type in revealing evolutionary relationships between Nothofagus species is supported, and that of leaf-shedding pattern is rejected.

Keywords: Nothofagus antarctica, Nothofagus dombeyi, hybridization, semi-deciduous, isoenzymes, leaf morphology, reproductive morphology, Patagonia.
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