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Journal Article

Cytogenetic Studies on the Origin of Tagetes patula. I. Meiosis and Morphology of Diploid and Allotetraploid T. erecta x T. tenuifolia

Joseph W. Towner
American Journal of Botany
Vol. 48, No. 9 (Oct., 1961), pp. 743-751
Stable URL: http://www.jstor.org/stable/2439647
Page Count: 9

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Topics: Hybridity, Plants, Species, Chromosomes, Diploidy, Achenes, Pollen, Meiosis, Ploidies, Florets
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Cytogenetic Studies on the Origin of Tagetes patula. I. Meiosis and Morphology of Diploid and Allotetraploid T. erecta x T. tenuifolia
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Abstract

Cytological and morphological evidence is presented to show that Tagetes patula L. is an allotetraploid species (2n = 48) which probably originated by hybridization between the diploids T. erecta L. and T. tenuifolia Cav., or species closely related to them. The putative parent species are separated by strong reproductive isolation barriers, and controlled crosses between them yielded very few good seed. Most of the hybrid seedlings died before reproductive age, and the few survivors were sterile and extremely weak. At meiosis in the diploid hybrid, bivalent frequency per cell was 0-11 and averaged 4.4. Although 43.6% of the quartet stage consisted of restitution dyads, pollen was essentially all non-viable and seed set was less than 1%. A true-breeding, fertile, allotetraploid T. erecta-tenuifolia was synthesized by colchicine-doubling of the chromosome number of the F1 hybrid. In the synthetic allotetraploid, average chromosomal association was 23.97 bivalents plus 0.05 univalents, and 97.4% of MI cells had 24 bivalents; there were no multivalents, bridges, or fragments. Tagetes erecta-tenuifolia showed a striking morphological similarity to T. patula. Both the natural and synthetic allotetraploids were intermediate between T. erecta and T. tenuifolia for nearly every character. Of 10 species of Tagetes whose chromosome numbers are known, 5 are tetraploid (2n = 48).

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