In vitro polyploidisation of tulips (Tulipa gesneriana L.) - Phenotype assessment of tetraploids

In vitro adventitious shoot cultures of three diploid tulip cultivars ('Fringed Black', 'Victor' and Pol-D 32) were treated with antimitotic agents (colchicine 200 mg L-1, oryzalin 5 mg L-1, amiprophos methyl 15 mg L-1 or trifluralin 100 mg L-1) in order to obtain tetraploids. The treatments with colchicine were the most phytotoxic, resulting in the reduction of the survival rate to 50% in 'Fringed Black' and to 0-12.5% in two other cultivars. Among the three tulip cultivars, homogenous polyploids were obtained only for 'Fringed Black' (28 tetraploids and 4 octoploids). Each of the antimitotic agents induced the formation of polyploids, with the highest number for colchicine treatments; in total, 20 polyploids were detected. Phenotype observations were performed in the fifth growing season. Compared to diploids, in tetraploids the percentage of flowering plants was lower and flowering was delayed on average by six days. Mitotic polyploidisation had also negative side effects on leaves and flowers, which in tetraploids were significantly smaller: leaf width reduced by 30%, tepals reduced by 45%. Tepals were more rounded and more fringed in tetraploids. Flower scapes of tetraploids were shorter by 40% but their diameters were slightly larger as compared to diploids. Stomata were longer by 30% and pollen grain diameter was larger by 25% in tetraploids. Tetraploid were fertile, pollen germination was on average 6.3%, whereas in diploids it was 30.3%. Microscopic observation of flower scapes on transverse sections revealed increased cell diameters of the epidermis and the cortex and significant reduction of collenchyma layers in tetraploids, resulting in higher fragility of the scape.