Breeding and Cytogenetics in the Genus Tulipa

Tulip (Tulipa) is one of the most important ornamental bulbous plants, which has been cultivated for cut flower, potted plant, garden plant and for landscaping. Species from the different sections display complementary agronomic characteristics and breeding techniques are used to combine desired features. The main goals of modern tulip breeding are the introgression of resistance against Tulip Breaking Virus (TBV), Botrytis tulipae and Fusarium oxysporum (bulb-rot), and also characteristics such as a short forcing period, good flower longevity and new flower colours and flower shapes into the commercial assortment of T. gesneriana. T. gesneriana has been crossed successfully with only 12 out of the approximately 55 tulip species by using conventional breeding methods. Many successful crosses have been made between T. gesneriana cultivars and TBV resistant T. fosteriana cultivars resulting in highly resistant Darwin hybrids tulips. The majority of tulip cultivars are diploid (2n = 2x = 24) however, there have been many attempts to obtain polyploid tulips. The production of tetraploids was described in the late sixties when young ovaries were treated, under pressure, with laughing gas (N2O). In breeding of polyploid tulip laughing gas has also been used to induce 2n gametes. Several new tetraploids were also obtained by making crosses between tetraploid lines. Polyploids have been derived from interploidy crosses between diploid, triploid, and tetraploid cultivars. Several other polyploids have resulted from 2n gametes, spontaneously produced by diploid F1 hybrids. Molecular cytogenetic tools such as FISH and GISH permitted detailed studies of genome composition and chromosome recombination in the progenies of interspecific hybrids. In this context, tulip breeding and the use of cytogenetic techniques for genome analysis of hybrids are discussed