© 1998 Heron Publishing—Victoria, Canada
Developmental factors responsible for heterosis in aspen hybrids (Populus tremuloides × P. tremula
Bailian Li (1), Glenn T. Howe (2) and Rongling Wu (1)
1. Department of Forestry, North Carolina State University, Raleigh, NC 27695-8002, USA / 2. Department of Forest Resources, University of Minnesota, St. Paul, MN 55108, USA / Received September 10, 1996
Summary
Juvenile growth and bud set phenology were analyzed to study the biological basis of heterosis (hybrid vigor) in interspecific
hybrids of Populus tremuloides Michx. (T) and P. tremula L. (Ta). Growth, measured as seedling volume index, was significantly higher for each of the two reciprocal interspecific
crosses, T × Ta and Ta × T, than for the T × T intraspecific cross. Broad-sense heritabilities were 2–6 times larger than
narrow-sense heritabilities for growth and shoot components in the T × T intraspecific cross, suggesting an important role
for dominance or overdominance in aspen growth. Previous genetic analyses have indicated that hybrid vigor may be the result
of overdominance at several key loci each with an allele inherited from each of parental species. Internode length and leaf
number contributed substantially to the heterosis of stem volume, but their effects on heterosis differed between the T ×
Ta and Ta × T hybrids. In T × Ta seedlings, heterosis of stem volume was attributed to a high diameter growth rate, whereas
in Ta × T seedlings heterosis of stem volume was probably the result of delayed bud set resulting in a longer duration of
height growth. In addition to internode number and length and leaf number, other morphological or physiological components
might affect heterosis, for example, extended leaf retention.
Keywords:
bud set, dominance, growth, heritability, interspecific cross, intraspecific cross, overdominance.
