Survival, Growth, and Fertility of Carpinus Hybrids

Abstract

Parents Ht Stem diam Female Male Survivalz (m) (cm)y The need for a wider choice of small trees maturing at 10 to 13 m in height and capable of enduring the stressful environments of urban landscapes prompted my interest in the hornbeams (Carpinus). The first control-pollinated hybrids in Carpinus were made in 1973 and 1974 (Santamour, 1978). The chromosome numbers of the individuals used as parents were C. betulus L. (2n = 8x = 64), C. japonica Blume (2n = 2x = 16), C. orientalis Mill. (2n = 2x =16), C. tschonoskii Maxim. (2n = 4x = 32). True hybrids, verified by chromosome counts, were obtained from C. orientalis x C. tschonoskii (2n = 3x = 24), C. betulus x C. orientalis and reciprocal (2n = 5x = 40), and C. betulus x C. tchonoskii (2n = 6x = 48). No interspecific hybrids were obtained from crosses of C. japonica with the other three species. Sargent (1896) recognized two botanical sections in Carpinus, with C. japonica being classified in Sect. Distegocarpus and the other species in Sect. Eucarpinus (= Sect. Carpinus). Self-pollinations were made in all four parental species, but intraspecific crosses were limited to three species because I had only one plant of C. orientalis. Seed set from selfing was extremely low, indicating a high degree of self-incompatibility in these species. Only in C. betulus were the selfed seedlings vigorous enough to grow to outplanting size in 2 to 3 years. Also, in C. betulus, two different intraspecific crosses gave about the same seed set, but only one cross produced seedlings. The loss of several hybrid seedlings severely limited the numbers of plants available