Cytogenetics and potential of haploidy in forest tree genetics and improvement

Abstract

In recent years, haploids produced in vitro and their subsequent doubled haploids have become an important source of homozygous lines for hybrid breeding in crop plants. Homozygous lines have also been produced traditionally by continuous inbreeding. However, this approach is time consuming and impractical for forest trees because of long generation cycles and inbreeding depression. By making use of haploid induction in vitro, with a subsequent doubling of chromosome number, pure lines can in theory be obtained and incorporated in breeding programs for genetic improvement (Winton and Stettler, 1974). Hybrid breeding is an interesting alternative in forest tree improvement, especially for fast-growing species such as poplar, aspen, birch, and willow. Through the process of haploidization in vitro most individuals carrying detrimental recessive genes will be eliminated and hence it may be expected that the surviving plants are of high genetic quality. Haploids are also ideal for somatic hybridization, for genome mapping, for use in resistance breeding, mutation selection and as recipients for foreign genes.