The number of chromosomes of many cultivars and Tulipa species have been counted at PRI. The tulip assortment consists mainly of diploids (2 sets of 12 chromosomes; 2n = 2x = 24), some triploids (mainly Darwinhybrids) and a rare tetraploid (2n = 4x = 48). Since tetraploids are more robust and firm than diploids, research has been carried out to obtain more tetraploids. By making crosses between tetraploids new tetraploids were obtained. Several of these tetraploids were released by PRI in 1974 of which ‘Judith Leyster’ is best known. Other tetraploid cultivars originated from PRI are Zorro, Hunter and Rambo.
Crossing tetraploids with diploids can result in strong growing triploids. Unfortunately, these triploids are mostly sterile and can not be used in further breeding. Tetraploid T. gesneriana cultivars can also be used in combination with diploid T. fosteriana to obtain Darwinhybrids with a better vase life and suitable for early forcing. In 1988, the cultivar ‘World's Favourite’ was released, bred from a tetraploid T. gesneriana seedling (‘Denbola’ x ‘Lustige Witwe’) crossed with a diploid T. fosteriana seedling.
Interspecific hybrids exhibiting characteristics like earliness and resistance against tulip breaking virus and Fusarium and several garden tulips were released by PRI. Some well known cultivars are ‘Beau Monde’, ‘Come Back’, ‘Explosion’, ‘Lefeber's Memory’, ‘Pink Impression, ‘Purple World’ and ‘Spryng’.
Fusarino and Furand are Tulipa gesneriana cultivars selected for their Fusarium- resistance. |