SUMMARY

The 49 North American wild Helianthus species have long survived extreme environments and possess resistance or tolerance genes to salt, drought, insects, diseases, as well as cytoplasmic male-sterility and fertility restoration, and are valuable genetic resources for sunflower improvement. Gene transfer from wild species into cultivated background depends on the success of interspecific hybridization, F1 fertility, chromosome pairing for genetic recombination, efficient screening methods, and sufficient progenies for selection. Most wild annual species x sunflower crosses produce F1 seeds and can be backcrossed easily. For the more difficult perennial x sunflower crosses where hybrid seed set is rare, a two-step embryo culture technique has been established for rescuing immature interspecific embryos prior to abor-tion. The chromosome homology between genomes of wild species and culti-vated sunflower is high, and the meiotic chromosome pairing of wild diploid x cultivated F1 is reasonably good, except for the multivalent formation, bridges, and fragments due to translocation and inversion differences. Chromosoma