Hybridization in Betula Alleghaniensis Britt. and B. Lenta L.: A Comparative Analysis of Controlled Crosses
Abstract:Progenies of the crosses B. lenta X lenta, B. alleghaniensis X alleghaniensis, and B. lenta X alleghaniensis, at age 27, were compared using 47 morphological characters of leaves, fruit, bark, and pollen. Stepwise discriminant analysis indicated that number of cilia of bracts of fruiting catkins, length of bark exfoliation, and pollen diameter, in that order, gave the best separation of three taxa. B. lenta (2n = 28) was distinguished from B. alleghaniensis (2n = 84) and the hybrid by cilia alone. B. alleghaniensis and the hybrid were not completely separated until all three characters were considered. Principal components analysis using 25 morphological characters, and hybrid indices based on 47 characters, also indicated that the F1 hybrid was more similar to B. alleghaniensis than to B. lenta. Analyses based on leaf characters revealed considerable overlap between the hybrid and both parent taxa. Pollen abortion of the hybrid was low (3.3 percent) and not significantly different from B. alleghaniensis. Average height and diameter of the hybrid were significantly less than the parent taxa. Germination of open-pollinated seeds from the hybrids was only 10 percent. It was concluded that reduced vigor of F1 hybrids and low germination rates are postzygotic barriers strong enough to preclude or significantly reduce successive generation hybridization and gene flow between B. lenta and B. alleghaniensis in natural habitats. Forest Sci. 17:415-424.
Document Type: Journal Article
Affiliations: Research Associate and Professor of Forestry at the School of Natural Resources, University of Michigan, Ann Arbor 48104
Publication date: 1971-12-01
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