Interspecific hybridization, gene transfer and the development of resistance to the broomrape race F in Spain

Abstract

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 abortion. The chromosome homology between genomes of wild species and cultivated sunflower is high, and the meiotic chromosome pairing of wild diploid x cultivated F1is reasonably good, except for the multivalent formation, bridges, and fragments due to translocation and inversion differences. Chromosomal doubling by colchicine treatment substantially increases the F1 fertility, improves backcrossing success, and leads to the production of amphiploids. The amphiploids have restored fertility and can be maintained by sib-pollination, and will serve as a bridge for gene transfer. Using this approach, we successfully transferred genes resistant to the new broomrape race F, which attacks all the cultivated sunflower in Spain. Inheritance studies suggest a single dominant gene provides resistance.