Tulip breeding at PRI - The Lilium information page

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PRI STRAATHOF & EIKELBOOM TULIP BREEDING AT PRI Pre-selection based on forcing Forcing for cut flower production is the most important quality for tulip breeders. This will be obvious from the following production figures. Approximately 50 per cent of the bulb growing acreage in the Netherlands is planted with 20 cultivars which are all suitable for forcing. Furthermore, the ten most important cut flower cultivars account for approximately 50 per cent of the tulip cut flower production in the Netherlands. Research on pre-selection showed that the juvenile seedlings which sprout and die early in comparison with the other juvenile seedlings can be forced as the earliest flowering ones at the adult bulb stage. This knowledge is rarely used by the hybridizers in their breeding programmes because of the administrative effort needed. Besides earliness, other characteristics such as stem length (lower and upper internode), firmness of leaves and stem, leaf position and leaf number, flower size, bud presentation and the proportion between flower and leaves are also important. Consequently, in practical breeding, seedling populations consisting of bulbs large enough to initiate a flower are all forced and judged for the characteristics mentioned above. This strategy means that many seedlings have to be cultivated for at least five years but in the end will not pass the selection criteria. In 1978 and 1979, plant material obtained from the pre-selection research was released by PRI to the breeding companies. The cultivars ‘Debutante’ and ‘Silver Dollar’ are the best known results at present, they also have a long vase life. Shortening of the juvenile period Besides pre-selection, another approach to speed up tulip breeding is shortening of the juvenile period. By cultivation in greenhouses and storage in climate rooms with standardised conditions the growth cycle could be reduced from one year to eight months. In two years, three growth cycles could be obtained. Despite additional lightning, however, the seedling bulbs from the greenhouse with three cycles of cultivation were not larger than the bulbs from outside with only two cycles of cultivation. Nowadays, by applying optimal field and storage conditions it is possible to shorten the juvenile period from 4-5 years to 3-4 years. Flower colour and flower shape The tulip derived its fame mainly from its diversity in flower colour and flower shape. Almost all consumer wants can be fulfilled by exploring this diversity. Biochemical analyses of 2
PRI STRAATHOF & EIKELBOOM TULIP BREEDING AT PRI flower pigments and crossing experiments were carried out to obtain more knowledge about the inheritance of flower colour and flower shape. Inheritance of flower colour Flower colour is determined by the composition and proportion of different flower colour pigments. Colour pigments have been determined from approximately 500 modern and older cultivars and Tulipa species. Yellow flowers contain only carotenoids, while orange flowers contain at least carotenoids and cyanidin. Red flowers contain cyanidin and mostly also pelargonidin and purple flowers contain a combination of cyanidin and delphinidin. Pink flowers contain the largest variation in flower colour pigments but the level is mostly lower compared to the other colours. White flowers contain almost no colour pigments. From approximately 1000 seedlings obtained from 21 populations the flower colour was compared with the flower pigment composition. In addition to single-coloured tulips there are also multi-coloured tulips e.g. pink-red and purple-red. Flowers with approximately the same colour differed in the flower pigment composition and flowers with approximately identical flower pigment composition differed in flower colour. Furthermore, in several seedlings flower pigments were found which were not present in either of the parents. Consequently, it is generally not possible to predict the flower colour of the progeny on the basis of the flower pigment composition of the parents. For example, a yellow x yellow cross can result in some red seedlings. Inheritance of flower shape Crosses were made between lily-flowered, double-flowered, edge-coloured, single-coloured and base-coloured cultivars to study the inheritance of flower shape and other flower characteristics. As with the inheritance of flower colours, prediction of the inheritance of flower shapes in relation to that of their parents appeared to be difficult. The lily-flowered cultivar ‘Dyanito’ combined with a non lily-flowered cultivar gave almost no pure lily-flowered seedlings. Populations with T. accuminata as a parent, however, gave many beautiful lily-flowered seedlings. The cultivars ‘Novired’ and ‘Talbion’ were released from this programme by PRI. The double-flowered tulip ‘Abodement’ gave hardly any pure double-flowered seedlings. Cultivars are known, however, which pass on this characteristic much better. Crosses between edged-coloured cultivars gave high percentages of edged-coloured seedlings and when combined together with non-edged cultivars the offspring resulted in approximately 50 per cent of edged-coloured seedlings. 3
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