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Selection for Reproductive Isolation between Two Populations of Maize, Zea mays L.
Vol. 23, No. 4 (Dec., 1969), pp. 534-547
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2406851
Page Count: 14
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A selection experiment to develop reproductive isolation intraspecifically was conducted with maize, Zea mays L. Two populations, a white flint and a yellow sweet maize having different recessive marker genes, were employed. The two populations were planted mixed in the same field, and at harvest all intercrossed kernels could be readily detected since they expressed the two dominant genes. Intracrossed (homogamic) kernels from the ears having the lowest degree of intercrossing (heterogamic) were saved for planting the next generation. The procedure was followed for six generations. A considerable degree of isolation was obtained. Starting from 35.8% and 46.7% intercrossing respectively for the original populations of white flint and yellow sweet maize, after six generations of selection for isolation, the cycleV populations showed a very low per cent of intercrossing--4.9% and 3.4% The progress on a per year basis in decreasing the per cent of intercrossing was 5.9% for the white flint and 8.6% for the yellow sweet maize. The character proved to be easily selected, and thus the realized heritability values were 45.0% and 47.2% respectively for the white flint and for the yellow sweet maize. The mechanisms involved in the isolations were investigated. The data show that the number of days from planting to flowering was probably the main factor. Although the two original populations flowered at the same time, the cycle-IV populations have a difference of 1 week. The white flint became about 5 days earlier and the yellow sweet about 2 days later. Controlled pollinations using pollen mixtures indicated also that the cycle-IV white flint may have gametophyte genes that favor the fertilization from pollen of its own type, against pollen from the other population. The experiment showed that effective reproductive isolation could be obtained through selection in very few generations.
Evolution © 1969 Society for the Study of Evolution