Comparative reproductive ability of bigtooth and trembling aspen and their hybrid

Abstract

Populus tremuloides and P. grandidentata hybridize readily in southeastern Michigan, and gene flow may be occurring that could alter the parent populations. The purpose of the study was to compare the reproductive capacity and initial growth of hybrids with that of the parent species. Seed-bearing branches of clones of each taxon were collected in nature, and seeds were obtained for growth comparisons. The hybrid clones were lower than the parents in some reproductive traits and intermediate in others. The hybrid exhibited significantly lower seed production per shoot than the parents although some hybrid clones produced more seeds per shoot than certain parental clones. Seed germination percentage of hybrid clones was significantly lower than that of the parents, although individual hybrids had higher germination percentages than some parental clones. Initial height growth of hybrid progeny was somewhat greater at 4 weeks, but was somewhat less than progeny of both parents at 18 weeks. Although the hybrid exhibited some-what reduced fertility, hybrid clones still are capable of producing thousands of germinable seeds which exhibit no deficiencies in establishment or early growth. Thus, no strong barrier was found to prevent the continuous establishment and persistence of backcrosses; gene flow may occur provided suitable disturbed sites are available for colonization.