Historical and modern genetics of plant graft hybridization.

Graft hybridization is a type of asexual hybridization in which heritable changes may be induced by grafting. Darwin was the first to put forward the conception of graft hybridization. The existence of graft hybrids has been extensively documented, although there has been a refusal to accept its reality, other than perceiving the phenomenon as involving "simple" chimeras. Graft hybrids can be divided into two categories--chimera graft hybrid (so-called graft chimera) and nonchimera graft hybrid (so-called vegetative hybrid). These differ with respect to grafting methods, characteristics, and mechanisms proposed to underlie the two categories. Graft hybridization is not only a simple and powerful means of plant breeding but also provides striking evidence in favor of Darwin's notions about Pangenesis--a developmental theory of heredity, on the one hand, and a phenomenon that plays a crucial role in revealing the mystery of non-Mendelian inheritance in grafted fruit trees.