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Bias in Inheritance of Chloroplast DNA and Mechanisms of Hybridization between Wind- And Insect-Pollinated Eupatorium (Asteraceae)

Victoria I. Sullivan, Joseph Neigel and Bomao Miao
American Journal of Botany
Vol. 78, No. 5 (May, 1991), pp. 695-705
Stable URL: http://www.jstor.org/stable/2445090
Page Count: 11
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Bias in Inheritance of Chloroplast DNA and Mechanisms of Hybridization between Wind- And Insect-Pollinated Eupatorium (Asteraceae)
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Abstract

Hybrids of the wind-pollinated E capillifolium and the insect-pollinated E. serotinum were found to occur in the Coastal Plain of Louisiana, Mississippi, and southern Arkansas and on the Piedmont in three locations. Interspecific cross-pollination occurs when wind causes the flexible flowering branches of E. capillifolium to whisk over the stiff upright branches of E. serotinum plants. Interspecific pollen was found to be captured by E. serotinum more effectively than by E. capillifolium. However, analysis of cpDNA of natural field hybrids indicated that most were maternally descended from E. capillifolium This latter bias can be explained by the far greater number of flowers, and thus greater seed producing capacity, of E. capillifolium relative to E. serotinum. Morphological variability observed among field hybrids suggests that backcrossing has occurred; however, field hybrids and progeny grown from field hybrid achenes generally had low pollen stainability, irregular meiosis, and reduced achene set. Furthermore, field hybrids were found to have a chromosome number of 2n = 20, like the parental species, whereas progeny grown from field hybrids had deficiencies and duplications of chromosome numbers. Because these chromosome number deviations were not seen in field hybrids it is logical to suggest that either they are F1s, or that strong selective forces in the field eliminated the progeny of hybrids with deficiencies and duplications.

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