Breeding and culture of Lilium longiflorum

3.1. Introduction

The acreage of Lilium longiflorum in the Netherlands has increased during the last twelve years more than tenfold, covering last year 1996 more than 200 hectares. The Netherlands now produce their own L. longiflorum bulbs and are no longer dependent on bulbs imported from Japan. Fifteen years ago, problems with this lily indicated the need to give the highest priority to breeding research on this species (Van Tuyl. 1979a). The aims of this research project were attained in 1985 and the project was concluded with the release of suitable material to the Dutch growers (Van Tuyl, 1985b, 1988).

This chapter gives an account of what was undertaken within the scope of this research: study tours to America, Japan, and Israel, introduction of material, extensive trials, development of a scale propagation method, studies on the effects of heat treatment of the bulb, and on differences in sensitivity to summer sprouting, genetic research, the selection methods and the release of plant material.

3.2 Origin and breeding history

The most southern Japanese Islands located at the 27th parallel (same latitude as Cairo, Egypt) with an almost tropical climate, form the original geographic center of L. longiflorum (Van Tuyl, 1981). For more than 100 years Japan has grown L. longiflorum bulbs there for export to Europe and the United States where they are used as cut flowers and as pot plants. Because of disease problems, the outbreak of World War II, and the introduction of new cultivars in the United States, the export of Japanese bulbs to America decreased markedly. The United States produce now already for more than 50 years their own bulbs along the west coast (Van Tuyl, 1979b, 1980). The leading cultivars are 'Ace' and 'Nellie White', which are grown exclusively to be brought into flower at Easter as pot lilies (Easter lily).

At Oregon State University, Dr. A.N. Roberts worked on the physiology and breeding of the Easter lily for more than 25 years (Roberts et al., 1985). Twenty selections from this program were introduced in 1978 and have been tested at the former IVT; one of these, 'White American' (Bonthuis-Van Aken & Van Tuyl, 1984, Matsuo & Van Tuyl, 1984, 1986; Van Tuyl, 1982, 1985a) was released in the Netherlands in 1981.

In Japan for more than 100 years bulbs of L. longiflorum are grown (Kobayashi, 1969). A comparison between the bulb production in the Netherlands and Japan was made by Matsuo (1986). In Japan the breeding of L. longiflorum has also started (Kobayashi, 1969; Van Tuyl, 1981). To my opinion breeding in Japan was scarcely export-orientated.

In a third country Israel, Herut Yahel at the Volcani Center, has been working for 20 years to initiate a L. longiflorum culture for the purpose of exporting bulbs (De Jong & Van Tuyl, 1985). Ten years ago, cultivation was started with two of Yahel's cultivars, 'Osnat' and 'Shovav'. In Israel attention was given to suitability for year around glasshouse culture in western Europe. Therefore Dutch growers tested the material that was introduced and 'Osnat' is grown now in the Netherlands as 'Snow Queen' with an acreage of 125 ha in 1996.

3.3. Vegetative propagation

One of the problems in growing L. longiflorum under the relatively cool conditions in the Netherlands is the lack of vigor and the premature sprouting of the daughter bulbs. To investigate this, it was first of all necessary to develop a scale propagation method adapted to conditions in the Netherlands. To this end the temperature effects on scale propagation as observed in 'Enchantment' and other Asiatic hybrids were investigated for L. longiflorum. The research yielded interesting results. A high initial temperature for a long period together with a relatively short cold period produced the highest bulb yield. This could be explained by the fact that all bulbs sprout with no 'sleepers' and most produce stems (bolt) (Van Tuyl, 1983). The scale propagation method, which has been used for ten years as a standard in the research, comprises 12 weeks at 26 °C, four weeks at 17°C, four weeks at 5 °C, after which planting out in the field takes place around mid-April. In this manner, the bulbs grow in the warmest months of the year, from June through September. The developed method was investigated for other lily cultivars as well and advised to the Dutch growers (Boontjes et al. 1984; Hendriks, 1988).

In selection, bolting has played an important role, because bulb yields increase when more stems are formed. Yild weights of more than 75 selections originating from 30 g of scales at planting are presented (Van Tuyl, 1985b,1988). Apparently the final yield weight is not determined by the number of bulblets arising from these 30 g scales but by the number of stems. Thus the multiplication factor of L. longiflorum can easily be 50-100 per year. In an experiment with 'Gelria', it was shown that when the larger scales (over 2 gr.) are broken into four parts this factor can be increased still more.

3.4. Heat treatment of bulbs

The optimal cold period (necessary to satisfy the vernalization requirement) of a L. longiflorum bulb at a temperature of 0-6°C is about six weeks. Under field conditions in the Netherlands some vernalization already takes place during the summer growth period. A heat treatment (25-30°C) directly after lifting the bulbs, when they still are sufficiently at rest, influences the forcing results: the forcing period becomes longer, the plants grow longer and the number of flowers increases (Van Tuyl, 1982). Research on 'White American' has shown that devernalization can also occur with bulbs that have already had a long cold period (Bonthuis-Van Aken & Van Tuyl, 1984). It was found that devernalization increased with higher temperatures.

3.5. Summer sprouting

Summer sprouting, the premature sprouting of the daughter bulb during the bulb growth stage, is caused by a long period of low temperature during the growing season. For many L. longiflorum types 14 0C appears to be a critical temperature; a longer period at or below this temperature leads to premature sprouting. It was found that cultivars such as 'Arai' (synonym for 'Georgia') and its virus-free selection, 'White Europe', are highly sensitive to summer sprouting. Consequently growers looked for cultivars that have a lower critical temperature or can tolerate a longer period with temperatures close to 14°C without summer sprouting occurring. In field trials and at low temperature in the controlled conditions of the phytotron (14°C), genetically divers material was investigated for sensitivity to summer sprouting (Van Tuyl, 1985a). It was found that 'Mount Everest' and 'Saeki' are hardly sensitive, while 'White American' and the selection from 'Indian Summer' are little sensitive to summer sprouting in combination with excellent bulb growth characters. In contrast, 'White Europe', with excellent flower forcing characters, is highly sensitive to summer sprouting.

3.8. Release of the material

Following the release in 1981 of 'White American", a selection originating from Oregon State University, in 1983 'Gelria', (a counter part of 'Georgia' = 'Arai 5') came available to growers. Also in 1983, 13 selections were released for further testing to various breeding firms. To conclude the L. longiflorum project another three named selections, 'Albivetta', 'Longivetta' and 'Blancivetta' as well as 16 unnamed clones were released to the lily nurseries in the Netherlands in 1985 en 1986. Meanwhile several of these selections are propagated commercially on a large scale and named f.e. 'White Horn', 'White Ideal', 'White Saphire', 'White Palermo', 'White Paradise', 'Evert van Benthem'. The active L. longiflorum breeders in the Netherlands are J. van Riet (of 'World Bulbs', Koewacht en Breezand) and J. Boon (Venhuizen).

After concluding the L. longiflorum breeding project, more attention was given to techniques to overcome barriers in interspecific hybridization. In that research L. longiflorum also played an important role as well (see Chapter 4).

3.9. Conclusions

Considering the results of the research in the Netherlands compared to developments of Lilium longiflorum in America, Japan and Israel, it can be concluded that we were able to set up a successful local production of L. longiflorum bulbs. Commercial propagation of released material has taken place by many growers resulting in a large increase of the acreage of L. longiflorum the last few years.