Maataloustieteellinen Aikakauskirja Vol. 56: 9—22, 1984 � Experiments on the cultivation of dandelion for salad use.l Study of cultivation methods and their influence on yield and sensory quality TAINA KUUSI 1, KIRSTI HÄRDH 2 and HELENA KANON 3 ' Technical Research Centre ofFinland, Food Research Laboratory, SF-02150 ESPOO 15, Finland 2 Department of Horticulture, University of Helsinki, SF-00710 HELSINKI 71. Finland Abstract. Cultivation of mild-tasting dandelion types for salad use has been studied as one part of an investigation aimed at evaluation the possible uses of dandelion. Eleven Finnish agamospecies were compared with two middle-European varieties, ’Vollherziger, verbesserter’ and ’Vert de Montmagny’ in regard to preferred methods of cultivation as well as to yield level and quality properties. Further, suitability and effects of the culturing methods were studied, the main variables being level of fertilization and use of various coverings to bleach the ro- settes. Of the cultivation properties, particularly the earliness, flowering, winter hardiness, vigour of growth and resistance against diseases and pests were considered. The yields in spring varied between about 50 and 150kg/are. When growth was in light the bitterness of all the agamospecies and varieties studied was only slight and when effective covering was used bitterness was insignificant. The sensory quality varied somewhat depend- ing on the agamospecies or variety and method of cultivation, being at best very good and at worst satisfactory. In the conditions studied, the higher level of fertilization was too high. The single black film, the black fibre cloth and thick bark humus layer were all suitable coverings. Though they decreased the yield (at least when calculated as dry matter), the cover- ings improved the taste and texture of the rosettes. With film and fibre cloth, rosettes were somewhat more greenish and yields better than with bark humus. The humus also made the rosettes more succulent and crisp, so that the texture was improved. This method is laborious, however, and better suited for home gardening than commercial cultivation. Of the agamospecies and varieties studied, the best for cultivation in light were Taraxa- cum hemicyclum, T. lanyphyllum, ’Vollherziger verbesserter’ and ’Vert de Montmagny. For cultivation under covering the best were ’Vert de Montmagny’, T. hemicyclum and T. pal- lidipes. Index words: dandelion, salad greens, cultivation methods, agamospecies, fertilization, bleaching, yield, sensory quality, bitterness 9 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=WAlrVtAZPy6Mi3z9.cNafE_OZ2bmzv_XPcBEX-g.o4iodTgBOox4LXXO23hHVEbWxpZtuQqQqWlj3iHrT_K_2D3hrnNywHYxX81i5XoSjA45NzAd0LrCHHNQTdAbOkyrVZ0W3hOJDdbtEsH_qNWBy0WyJ143Wmff6DjDUQqrgN0G0ZIe_uap7d9MwtvojwJvTyxBTuG8bDV5l6pUGHk7L75IQgeQMEdwmkwDZLdHqmjdLq4_DejLZx34KVk 10 Introduction The possibility of utilizing the dandelion has been studied since 1977 by a group of re- searchers, originally from the Food Research Laboratory of the Technical Research Centre of Finland and the Department of Botany at the University of Turku, and later further from the Department of Horticulture at the University of Helsinki. The aim has been to investigate the various possible uses of the dandelion, which flourishes throughout Fin- land. At the start of the study, 157 samples of Finnish dandelions were removed to the Botanical Garden of the University of Tur- ku. These samples were identified and found to represent 69 different agamospecies. The botanical, cytological and genetic properties of the agamospecies were studied in Tur- ku by Rousi and his co-workers (1984, in press), while the degree of bitterness was in- vestigated by sensory methods at the Food Research Laboratory. The bitterness is an in- teresting property: if dandelion is used for taste-giving purposes e.g. in drinks, strong bitterness is an advantage, whereas if it is used as a salad ingredient, the bitterness should be minimal. The bitterness properties will be discussed in a forthcoming paper. The possibility of cultivating the dandelion commercially has been studied since 1980. On the basis of thebitterness tests, those aga- mospecies most promising for cultivation as a salad green were selected for further inves- tigation. The most important properties for such use are mild taste, and vigorous growth as a basis for sufficient yields. Winter-hardi- ness, resistance against diseases and pests, general sensory properties and nutritive value are important as well, but about these was little knowledge when the experiments were begun. Elsewhere in the world, particularly in the Unites States and France, dandelion has been cultivated for salad use, and information is available on methods of cultivation (see the review by Kanon 1982). The dandelion has apparently not been cultivated for food in Finland, though it was once experimentally grown for its rubber content (Suomela 1950). One important cultivation method for salad dandelion involves bleaching the ro- settes. In this respect it was of interest to ex- periment with some new methods of horti- culture, such as covering the plants with black polyethylene film, black fibre cloth, or layers of bark humus, instead of using the rather laborious methods suggested in the literature. The cultivation experiments were designed and carried out at the Department of Horticulture, and the Food Research La- boratory performed the sensory analyses and evaluations of bitterness. These results are reported in this paper, and the nutritive value and intrinsic quality properties such as ni- trate content are reported in part II which follows (Kuusi, Härdh and Kanon 1984 pp. 23—31). Full details on the cultivation experiments can be found in the pro gradu work of Ka- non (1982). Experiments concerning the winter-forcing of salad dandelion will be re- ported at a later date. Material and methods Material. The material consisted of 11 Finnish agamospecies, selected from the 69 agamospecies primarily on the basis of their mild taste (= low degree of bitterness) and vigorous growth. For comparison, two for- eign cultivars were included in the experi- ments: ‘Vollherziger, verbesserter’ Mauser of Swiss origin, and ‘Vert de Montmagny’ Vilmorin of French origin. The seeds of the Finnish agamospecies were collected in 1978 and 1979 from the experimental cultures in the Botanical Garden of the University of Turku, and stored at + 5°C. The seeds of the foreign cultivars were obtained commercial- ly. The agamospecies and varieties are listed in the tables. Design of the cultivation experiments: Two main experiments were performed: 1) comparison of the different agamospecies and varieties and evaluation of bleaching with black film, and 2) comparison of two levels of fertilization and of different me- thods of covering. The experimental method was that of split plots with four replications. Cultivation methods: The seedlings were grown in a glasshouse, where mean tempera- ture was 20°C and humidity 71 % (8 o cl.). Seeds were sown in April in sxB cm peat pots (FP 620), filled with light, medium po- rosity, medium fertilized peat (St-400 B 2), two seeds per pot. The seeds were covered with a 0.5 cm layer of sand and protected against evaporation with colourless film until after germination. Later, the less advanced seedling was removed from each pot. In the first experiment comparing the agamospecies and varieties the glasshouse cultivation was continued for 6 Vi weeks, in the second, fer- tilization and covering experiment for nearly 6 weeks. In the second experiment the variety used throughout was ‘Vert de Montmagny’. Planting outdoors took place the end of May. Planting distance was 20 cm and distance between the rows 50 cm. Care of the cultures included mechanical weeding and weeding by hand. The flower stalks and buds were removed every week. During long periods of dry weather irrigation was applied, four times approximately 15 mm each time. Fertilization and use of coverings. The ex- perimental field was inclined slightly toward the northwest, the soil type was medium-hu- mus fine sand. The area had been ploughed the previous autumn. Before basic fertiliza- tion the nutrient level was according to anal- ysis (by Viljavuuspalvelu Oy) the following: for Gardens Y I* was applied, in the second experiment either 8 or 16 kg/are of the same mixture. In the second experiment an ad- ditional 1 or 2 kg/are calcium nitrate (Ca(NO 3)2 , 15.5 °?o N) was applied in April before laying of the covering. The nutrient status of the soil was checked in the second spring before the beginning of growth and after harvesting. The coverings used were bark humus (bark humus of Kirkniemi, lime added and basic fertilizing done), black polyethylene film (thickness 0.05 mm), and black slitted »Fi- bertex» cloth. The bark humus was applied 1) before planting of the seedlings outdoors, as a layer 2.5-cm thick, or 2) after the plants had withered in November, as a 5-cm thick winter covering, or 3) in addition to 2), at the end of April as a further layer of 5 cm. In this last case the covering was intended for bleaching of the rosettes. The other cover- ings to bleach the rosettes were similarly applied at the end of April, when the upper- most 10 cm of the surface of the earth was unfrozen and the dandelions had begun to grow. The black film was supported by ar- ches ca. 50-cm high in the first experiment, while in the second experiment the covering had no support. The fibre cloth was similarly unsupported. The edges of both the film and fibre cloth were anchored with earth. In one part of the covering experiment the black film was applied double; when single, the bleaching was insufficient. When the temperature rose too high the film and fibre cloth coverings were opened to allow ventila- tion. Observations in the field during the Conduct- Exchangeable Exchangeable Easily soluble Water soluble Nitrate ance pH Ca mg/l K mg/1 P mg/1 B mg/l NO,-N mg/l 1.7 7.1 1900 280 50 1 < 10 Basic fertilization was carried out before planting the seedlings outdoors. In the first experiment 10 kg/are of Fertilizer Mixture * composition, %: Main nutrients N-P-K = 10-4-17 (P 2 Os , K2 (D), B 0.15, Cu 0.4, Mn 0.7, Mg 2.5, Mo 0.02, Zn 0.03, Fe 0.1 11 growing season. The viability of the plants was checked after transfer to the field in June and at the end of the growth season in September, the winter hardiness at harvest in the spring. The start of flowering was noted during the first summer and the flower stalks were counted every week. In spring the rosettes were inspected for flower buds. The earliness of withering was checked at the end of the season, and the earliness of sprouting at the end of April, where this was not prevented by the coverings. Numerical scales were used to register the differences. The diseases and pests occurring were identified at the Departments of Plant Pa- thology and Agricultural and Forest Zoology of the University of Helsinki. The damage was followed and the degree assessed using a numerical scale (0—4) weekly or every other week. In the first experiment harvesting took place the second spring between May 18 and 22, in the second experiment on May 19 and 20. The rosettes were cut ca 1 cm below ground level to keep the rosettes intact. Withered leaves were removed and the ro- settes stored at + I—2°C, wrapped in plastic pouches. Yields were determined by weighing the harvested and cleaned rosettes and calculated as kg/are. Weighing was carried out in spring and in August of the first year. The sensory evaluation was done accord- ing to established principles (see e.g. Ame- rine et al. 1965). Evaluation was performed on the day of harvest by 8 to 12 trained pan- elists. The point scale of Karlsruhe, I—9,1 —9, Fig. I. The form for the sensory evaluation of salad dandelion 12 was used (see Paulus et ai. 1969) with se- parate points given for appearance and col- our, texture, smell and taste. Appearance, colour and smell were evaluated from whole rosettes, texture and taste from leaves that had been shredded without removal of the vein and served as such. (Fig. 1 shows the evaluation form.) Bitterness was evaluated from extracts pre- pared immediately after harvesting from the replicate leaf samples. Thus, 18 g leaves was homogenized in 100 ml distilled water with a Bamix for 2 min., after which the homoge- nate was boiled for 2 min., cooled, filtered and diluted to 100 ml with distilled water. The degree of bitterness was evaluated by 5 trained panelists using a numerical scale between 0 and 6, where bitterness value 3 ( = medium) was fixed with a quinine stand- ard of strength 0.0015 % quinine in distilled water. (Fig. 2 shows the evaluation form.) Results Observations in the field. The earliness of growth in the second year was evaluated at the end of April using a numerical scale o—3.0—3. (Fig. 3). The agamospecies Taraxacum alatum, T. ekmanii and T. hjeltii were the earliest, with the foreign varieties closely be- hind. A similar order was observed at har- vest. Fig. 2. Form for the evaluation of bitterness Fig. 3. Earliness of sprouting 29 Apr. 1981. Scale o—3 0 = growth not yet begun 1 = viability of the terminal bud observed 2 = rosette consists of thickened nerves almost without lamina 3 = rosette shows large lamina 13 Since flowering lessens the nutrient re- serves and removal of the flowers occasions extra work, it would be optimal if the plants did not flower in the first growing season. Further, dandelions may then be transferred to undesired places. The earliest to flower was T. hjeltii, followed by T. alatum, T. amplum and T. aculeatum in July—August. The others began to flower at the end of Sep- tember of not at all. Figure 4 shows the trend for flowering during the first year. In the fol- lowing spring the rosettes were harvested be- fore flowering, but in all cases flower buds were present. Use of covering to bleach the rosettes delayed the flowering for one or two weeks. The extent of withering was checked at the end of the growing season, 6 Nov. 1980 (Fig. 5). By that time, the early agamospecies T. hjeltii was already fully withered. The figure makes clear the considerable variation in the withering of the different agamospecies and varieties. The winter hardiness was checked after the winter and it was noted that, in all, 6.7 °Jo of the plants perished during the win- ter. In this respect, however, there were no systematic differences between the agamo- species and varieties. Plant diseases: The following were the most important diseases observed: Sphaerothecafuliginea (Schlecht ex Fn.) Poll, (powdery mildew) Puccinia taraxaci (Rebent.) Plowr., 0, 11/I (dandelion rust) Ramularia taraxaci Karst., (dandelion leaf spot) and Botrytis cinerea Pers. (grey mould). The diseases were most conspicuous from mid-August until the end of September, but in spring they did not harm the rosettes to be harvested. Figure 6 shows the susceptibility of the different agamospecies and varieties to these diseases. Among pests, the insects Delia floralis Wied. (turnip root fly), Mamestra brassicae L. (cabbage moth) and Meligethes aeneus F. (pollen beetle) were observed, while ticks and aphids were not. Larvae of the turnip root fly damaged the roots of T. ekmanii in July, but two thirds of the plants recovered by forming a new root. The larvae of cabbage moth damaged the receptacles irregularly in Fig. 4. Number of flowers of different agamospecies and varieties during the first year of growth Fig. 5. Earliness of withering of different agamospecies and varieties. 6 Nov. 1980. Scale o—2 0 = rosette unwithered 1 = rosette partly withered 2 = rosette fully withered 14 'Vert de Montmagny late summer. Pollen beetles appeared abun- dantly at the end of August but did not cause damage. In addition, damage by voles to leaves and roots was noticed in late autumn, and 16 plants were destroyed (1.9 %). The yield results are shown in Table 1. Average yields of the foreign varieties were mostly somewhat higher than those of the Finnish agamospecies, though individual yields of some of the latter were at the same level. The fresh weights were higher in late summer than in spring in many cases. How- ever, salad dandelion is typically harvested in spring, and thus the higher yield in late sum- mer would ordinarily not be utilized. The influence of darkness is clear-cut: yields tend to be much lower in darkness. The higher level of fertilization did not increase the yield. Of the coverings, the bark humus systematically decreased the yield, and the black film and fibre cloth increased it. The results of the sensory evaluations in Table 2 show slightly higher averages for the foreign varieties than the domestic agamo- species. For cultivations in light, the scores of taste and texture are generally lower than the scores for colour, appearance and smell. Bleaching systematically improved the scores, in particular taste and texture, and to some extent colour. Some of the Finnish agamo- species have scores as high as the foreign va- rieties, although the latter show a clearer superiority when bleached. The scores for the two fertilization levels are very similar: fertilization had no influ- ence on the sensory properties. In contrast, Fig. 6. Susceptibility of different agamospecies and varieties to diseases (the greatest degree of infection during the first season of growth). Scale o—4 0 = no infection 3 = strong infection 1 = weak infection 4 = very strong » 2 = medium » 15 16 Table 1. Yields of different dandelion agamospecies and varieties (fresh weight of the rosette, g, and yield calcula- ted as kg/a), and the effect of the different methods of cultivation. YIELDS OF DIFFERENT AGAMOSPECIES AND VARIETIES Agamospecies Yield, weight of rosette, g Yield, kg/a or vanety Spring 1981 Summer 1980 Spring 1981 In light In darkness In light In light In darkness Taraxacum aculeatum 107 83 155 107 81 T. alatum 108 72 60 106 60 T. amplum 102 97 118 96 78 T. ancistrolobum 86 61 51 81 55 T. ekmanii 85 68 93 75 54 T. hemicyclum 127 115 169 127 106 T. hjellii 103 78 72 66 70 T. pallidipes 109 107 166 96 92 T. piceatum 90 79 116 77 79 T. sublaeticolor 69 67 124 69 61 T. lanyphyllum 123 53 272 111 43 'Vollherziger' 106 58 120 106 51 'Vert de Montmagny' 129 111 172 116 101 Averages: Finnish 101 80 127 92 78 Foreign 118 85 146 111 76 All 103 81 130 95 72 EFFECT OF DIFFERENT METHODS OF CULTIVATION (VARIETY 'VERT DE MONTMAGNY') Covering Yield, weight of rosette, g Yield, kg/a Fertilizing level Fertilizing level 1x 2x 1 x 2x No covering 118 108 118 97 Bark humus 2.5 cm 81 88 62 79 Bark humus 5 cm 92 81 90 80 Bark humus 5 + 5 cm 94 75 92 70 Black film 155 144 147 86 Black film and bark humus 5 cm 119 110 116 104 Black fibre cloth 146 132 139 125 Average 115 105 109 92 covering improved the sensory properties if definite bleaching was obtained. Of the bark humus coverings only the 10cm covering was effective in this way. The results of the bitterness tests are shown in Table 3. In this respect the different agamospecies and varieties varied markedly, even though all had been selected for their mild taste. The range of values was widest in the late summer when the bitterness was also greatest. The foreign varieties tend to be more bitter than the Finnish agamospecies. However, the bitterness is low in all: on the scale used here, 3 represents medium bitter- ness, and in the spring dandelions all scores were below this, varying between 1.3 and 3.0 when cultured in light and between 0.8 and 2.0 when cultured in darkness. Salad dande- lion is not ordinarily harvested in late sum- mer when the bitterness is greater. Table 2. Results of the sensory evaluation of leaves of different dandelion agamospecies and varieties, and the ef- fect of different methods of cultivation SENSORY PROPERTIES OF DIFFERENT AGAMOSPECIES AND VARIETIES. I: IN LIGHT Agamospecies or variety Colour Appearance Texture Smell Taste Sum of points Taraxacum aculealum 6.6 6.7 5.7 6.7 5.3 31.0 T. alatum 7.0 7.2 6.8 7.2 5.9 34.1 7". amplum 6.7 7.1 6.3 6.7 5.8 32.6 T. ancistrolobum 6.4 6.6 5.4 6.5 5.0 29.7 7". ekmanii 6.6 6.7 6.0 7.0 5.4 31.7 T. hemicyclum 6.9 7.2 6.7 7.2 6.1 34.1 T. hjeltii 6.7 7.0 5.6 6.8 5.7 31.8 T. pallidipes 6.5 6.1 5.6 7.1 5.8 31.1 T. piceatum 6.0 6.1 5.2 6.8 ' 4.9 29.0 7". sublaeticolor 6.8 7.4 6.0 7.3 5.1 32.6 T. lanyphyllum 6.5 6.8 5.6 7.4 5.3 31.6 'Vollherziger' 7.0 7.6 6.4 7.3 5.9 34.1 'Vert de Montmagny' 6.5 6.5 5.9 7.0 5.9 31.8 Averages: Finnish 6.6 6.8 5.9 7.0 5.5 31.8 Foreign 6.8 7.1 6.2 7.2 5.9 33.0 All 6.6 6.8 5.9 7.0 5.5 31.9 II: IN DARKNESS Taraxacum aculealum 7.2 5.8 7.4 6.8 7.6 34.8 T. aialum 7.8 6.5 7.5 7.4 7.1 36.3 T. amplum 1.1 6.0 7.4 7.0 7.9 36.0 T. ancistrolobum 7.3 6.8 7.2 7.4 7.0 35.7 T. ekmanii 7.8 7.4 7.1 7.4 7.6 37.3 T. hemicyclum 7.6 7.2 7.3 7.3 7.0 36.4 T. hjeltii 7.8 7.6 7.6 6.3 7.3 36.5 T. pallidipes 7.8 7.5 7.4 6.8 7.1 36.5 T. picealum 7.4 7.0 7.3 7.3 7.2 36.2 T. sublaeticolor 7.4 7.4 7.4 7.1 6.5 35.8 T. lanyphyllum 6.9 6.9 7.2 7.5 7.2 35.7 'Vollherziger' 8.3 8.0 8.0 7.6 8.0 39.9 'Vert de Montmagny' 7.6 7.6 8.1 7.7 7.8 38.8 Averages: Finnish 7.5 6.9 7.3 7.1 7.2 36.1 Foreign 8.0 7.8 8.1 7.7 7.9 39.4 All 7.6 7.1 7.5 7.2 7.3 36.6 EFFECT OF THE DIFFERENT METHODS OF CULTIVATION (VARIETY 'VERT DE MONTMAGNY') Covering and fertilizing Colour Appearance Texture Smell Taste Sum of level points Fertilizing level I x No covering 6.2 6.5 6.4 7.1 6.1 32.3 Bark humus 2.5 cm 6.1 6.5 6.2 7.1 5.8 31.9 Bark humus 5 cm 6.0 6.4 6.4 7.2 6.0 32.0 Bark humus 5 + 5 cm 6.4 6.3 6.8 6.7 7.2 33.7 Black film 7.1 5.9 7.6 6.0 7.4 33.9 Black film and bark humus 5 cm 7.1 7.5 7.1 7.0 7.2 36.2 Black fibre cloth 8.1 7.5 7.9 6.6 7.5 37.5 Averages 6.7 6.7 6.9 6.8 6.7 33.9 Fertilizing level 2 x No covering 6.1 6.5 6.5 7.0 6.2 32.4 Bark humus 2.5 cm 5.9 6.5 6.7 6.9 6.0 32.0 Bark humus 5 cm 5.8 6.0 6.6 7.0 6.5 32.0 Bark humus 5 + 5 cm 6.0 5.8 6.5 6.0 7.3 31.5 Black film 7.3 6.9 7.8 6.7 7.7 36.4 Black film and bark humus 5 cm 7.0 6.9 7.4 6.7 7.3 35.3 Black fibre cloth 8.1 7.2 7.8 5.9 7.5 36.4 Averages 6.6 6.5 7.0 6.6 6.9 33.7 Influence of fertilizing level: No covering lx 5.8 6.0 6.1 7.1 5.2 30.1 2x 6.0 6.0 6.1 7.1 4.7 29.9 Black fibre cloth lx 8.1 8.1 7.4 7.5 6.2 37.3 2x 8.1 7.9 7.7 7.3 6.8 37.7 Table 3. Bitterness of leaves of different dandelion agamospecies and varieties, and the effect of different methods of cultivation (scale o—6) BITTERNESS OF THE DIFFERENT AGAMOSPECIES AND VARIETIES Agamospecies or variety In light In darkness Spring 1981 Summer 1980 Spring 1981 Taraxacum aculealum 2.3 4.7 0.8 T. alatum 1.4 3.2 2.0 T. amplum 3.0 5.0 1.3 T. ancistroloburn 1.8 4.8 T. ekmanii 1.3 3.0 T. hemicyclum 1.9 2.6 1.3 T. hjeltii 2.4 2.8 T. pallidipes 1.9 4.5 T. picealum 1.5 3.2 T. sublaelicolor 2.6 4.9 0.9 T. tanyphyllum 1.6 2.9 0.8 'Vollherziger' 2.4 4.8 1.2 'Vert de Montmagny' 2.1 4.1 1.4 Averages: Finnish 2.0 3.8 1.2 Foreign 2.3 4.5 1.3 All 2.0 3.9 1.2 EFFECT OF DIFFERENT METHODS OF CULTIVATION (VARIETY 'VERT DE MONTMAGNY') Covering Fertilizing level lx 2x No covering 1.6 1.6 Bark humus 2.5 cm 1.5 1.8 Bark humus 5 cm 1.8 1.6 Bark humus 5 + 5 cm 1.3 0.8 Black film 0.9 0.4 Black film and bark humus 5 cm 2.8 0.3 Black fibre cloth 0.9 1.0 Averages 1.5 1.1 The level of fertilization has no clear-cut influence on the degree of bitterness, but covering clearly decreased the bitterness if bleaching was obtained. A thin layer of bark humus was not sufficient for this effect. Discussion Among the properties studied here, the most important for the future use of the dan- delion as a salad green are yield, sensory qua- lity and degree of bitterness. Certain proper- ties of cultivation will have to be taken into account as well. In the following the results are evaluated from the point of view of such use. The yields of the different agamospecies and varieties varied widely, with Taraxacum hemicyclum and ‘Vert de Montmagny’ grown in light performing best. The level of yield corresponded to that obtained in East Germany (see Hahn & Mildnerl962), but was lower than the yield considered good in the United States (Sackett 1975). The weights of the rosettes were greater in late summer of the first year than at harvest- time, the following spring, but the sensory quality and nutritive value were essentially better in spring. It may be added that salad dandelion is more reasonably harvested in the spring, when other salad greens are un- available or expensive. Although the dandelions were harvested by cutting below the upper end of the root, all except T. hjeltii regenerated new rosettes about one month after the harvesting, which offers the possibility of increasing the yield. The features of regeneration have been stud- ied further in experiments to be reported se- parately. The sensory quality was in general either satisfactory or good, and the best agamospe- cies and varieties, such as T. hemicyclum and ‘Vollherziger, verbesserter’ were good even without bleaching. In the spring harvest the differences in the sensory quality were only slight. The bitterness varied somewhat between the different agamospecies and varieties, being clearly less in spring than in late sum- mer, in agreement with the results of Huttu- nen (1981). There was no correlation between the degree of bitterness and the in- tensity of the green colour of the leaves, typi- cal for agamospecies, nor between bitterness and the presence or absence of red colour of the middle vein or the type of lobes in the leaves (see also Huttunen 1981). Such char- acteristics can therefore offer no guidance when wild dandelions are being collected. In the dandelions studied here the bitterness was consistently slight, as intended. Of the cultivation properties, earliness would be an advantage. In the spring of the second year, growth was sufficient from the middle of May (though that year the spring season was two weeks later than usual). The earliest agamospecies was T. hjeltii, which comes from northern Finland. The differ- ence in time of harvesting was at most one week, the latest species being T. ancistrolo- bum, T. tanyphyllum and T. pallidipes. Hot weather may well diminish the differences in earliness, and thus this property may not be very important. The period of proper harvesting is compa- ratively short, since immediately the rosette of leaves has reached the desired size, the flower stalks begin to lengthen and bitterness rapidly increases. This period could be somewhat prolonged by growing several aga- mospecies or varieties differing in earliness. The differences in flowering were conspic- uous: during the first growing season only a good third of the samples flowered. Where the flowers are not needed, it would be best to select species that do not flower during the first summer. No definite differences were noticed in winter hardiness: all species studied were suf- ficiently resistant. The winter of the experi- ment, it may be added, was less favourable than average. Pests, except perhaps voles, are not a threat to dandelion cultivation. Three main fungus diseases were observed, of which par- 19 ticularly powdery mildew could become harmful. Rust and leaf spot were also of im- portance, although they occurred mostly in late autumn. Grey mould was insignificant. The diseases do not influence the quality of the rosettes to be harvested in spring, but as general factors weakening the plants they may decrease the yield. Of the cultivation methods, a higher level of fertilization did not increase the yield in the conditions studied. Only when bark hu- mus was applied during the growing season, causing a need for more fertilizer, did the higher level of fertilization give better yield than the lower. The results do not exclude the possibility that the optimal level may be higher or lower than the lower level used here. Bleaching by covering with black film sig- nificantly decreased the yield in the first ex- periment. In the second experiment, where the different coverings were compared, the yields for plants under film and fibre cloth were greater than for uncovered plants, while covering with bark humus diminished the yield. The results may be connected with the temperature effects of the different cover- ings. However, when the yield was calculated as dry matter, the yield was always lower when coverings were used, in agreement with earlier results (Wassink 1965). Use of coverings delayed the beginning of flowering, but the harvest period was not thereby longer, since under film and fibre cloth the rosettes may become too long, and when bark humus covering is used, harvest- ing must be done before the leaves penetrate the layer. Bleaching virtually eliminated all bitter- ness and thereby improved the sensory quali- ty, particularly taste. But also texture was improved: the bleached rosettes were succu- lent and crisp, and particularly when bark humus covering was used, the base of the pe- tiole was pleasingly fleshy. Certainly the 10-cm layer of bark humus was not suffi- cient; it would be better to apply at least a 20-cm thickness, given the length of the leaves and the fact that in darkness the ro- settes assume a more vertical position than when growing in light. Comparison of the different methods of covering showed that the double black film was too tight, causing damage to the ro- settes. If it was applied single, the bleaching effectiviness was somewhat less than that of the fibre cloth. Where bark humus was used growth was a little delayed, because the cov- ering had to be laid in spring on the cold, still frozen earth, which then warmed up more slowly. Further, the bark humus covering caused a decrease in yield. The decision to cover, as well as the type of covering, depends on the kind of crop desired. Unbleached the yield is greater, ro- settes are pale green, and there is slightly more bitterness. Fibre cloth gives a crop of somewhat better quality, but it is more ex- pensive than black film. A thick layer of bark humus gives the best texture of the ro- settes, but application is laborious and the method is thus more suitable for home gar- dening than commercial cultivation. In addi- tion, with bark humus covering the fertilizer level must be increased. In comparing the merits of the different agamospecies and varieties, each of the pro- perties studied must be taken into account and its importance weighed. If yield, sensory properties and mild taste, as well as resist- ance against diseases and pests are consi- dered to be most important, and only half as much weight is placed on earliness, flowering properties, ability of regeneration and amounts of vitamin C and soluble solids, then the most suitable lines for culture with- out bleaching are T. hemicyclum and T. ta- nyphyllum, and the two foreign cultivars ‘Vollherziger verbesserter’ and ‘Vert de Montmagny’. With bleaching the most suit- able are ‘Vert de Montmagny’, T. hemicyc- lum and T. pallidipes. Of the Finnish aga- mospecies the most suitable is thus T. hemi- cyclum, where the growth of rosettes is vig- orous, the yield high and taste mild, and where the sensory properties are as good 20 unbleached as bleached, and the yield is not significantly lowered by bleaching. This aga- mospecies is early in growth and does not form flowers at all during the first summer. As disadvantages, a medium susceptibility to both Sphaerotheca (powdery mildew) and Puccinia (rust) as well as also Ramularia (leaf spot) must be mentioned. In all, the experiments showed that dande- lion is well suited for outdoor cultivation in Finland. The harvest is exceptionally early, yield is abundant, bitterness is only slight and sensory properties are good. Results are influenced by the cultivation methods; in particular the use of coverings gives a crisper texture. The possibilities of perennial culture and breeding and the problems of seed pro- duction are topics remaining to be investi- gated. Acknowledgements. The authors are indebted to Dr. Karin Autio for the measurements of bitterness, to the panelists of the Food Research laboratory for the sen- sory tests and to the Departments of Plant Pathology and Agricultural and Forest Zoology for the identifica- tions of plant diseases and pests. Financial support has been provided by the Juho Vainio Säätiö. References Amerine, M.A., Pangborn, R.M. & Roessler, E.B. 1965. Principles of sensory evaluation of food. 602 pp. Academic Press, New York and London. Hahn, P. & Mildner, E. 1962. Neue Gemiise- und Arzneipflanzensorten, die 1962 in die Sortenliste der DDR aufgenoramen wurden. Lowenzahn. Deut. Gar- tenb. 9: 213—214. Huttunen, H. 1981. Viljelykokeessa olevien 71 Taraxacum-pikkulajin fenologisista, morfologisista ja kemiallisista ominaisuuksista sekä lisääntymista- vasta. Pro gradu -tutkielma. Turun yliopiston biolo- gian laitos. 69 pp. Kanon, H. 1982. Salaattivoikukka. Pro gradu -tut- kielma. Helsingin yliopiston puutarhatieteen laitos. 128 pp. Kuusi, T., Hardh, K. & Kanon, H. 1984. Experiments on the cultivation of dandelion for salad use. 11. The nutritive value and intrinsic quality of dandelion leaves. J. Agric. Sci Finl. 56: 23—31. Paulus, K., Gutschmidt, J. & Fricker, A. 1969. Karls- ruher Bewertungsscheme Entwicklung, Anwend- barkeit, Modifikationen. Lebensmittel-Wissenschaft u. Technol. 2 (6): 132—139. Rousi, A., Huttunen, H. & Hyrkäs-Lyytikäinen, K. 1984. Chromosomes and reproductive behaviour of Finnish Taraxacum agamospecies. Nordic Journal of Botany (in press). Sackett, C. 1975. Dandelions. Fruit & vegetable facts & pointers. Mimeogr. 7 pp. (Available United Fresh Fruit and Vegetable Association, Washington, USA). Wassink, E.C. 1965. Some introductory notes on Tara- xacum officinale L. as an experimental plant for morphogenetic and production research. Meded. Landb. hogesch, Wageningen, Nederl. 65, 16. 15 pp. Ms received January 9, 1984 21 SELOSTUS Tutkimuksia salaattivoikukan viljelystä. I Viljelymenetelmät ja niiden vaikutus satoon ja aistinvaraiseen laatuun Taina Kuusi 1, Kirsti Härdh 2 ja Helena Kanon 2 1 Valtion teknillinen tutkimuskeskus. Elintarvikelaboratorio, SF-02150 Espoo 15 Puularhalieleen laitos, Helsingin yliopisto, SF-007W Helsinki 71 Voikukan hyötykäyttöä selvittävän tutkimuskokonai- suuden osana on tutkittu miedonmakuisten voikukka- kantojen viljelyä salaattitarkoituksiin. Tutkimuksessa verrattiin keskenään 11 kotimaista pikkulajia ja kahta keski-eurooppalaista kantaa, ‘Vollherziger, verbesser- ter’ ja ‘Vert de Montmagny’, sekä viljelyominaisuuksien että satomäärän ja laadun kannalta. Edelleen selvitettiin viljelymenetelmien soveltuvuutta sekä vaikutuksia, muuttujina lannoitustaso sekä erilaisten kaiteiden käyt- tö ruusukkeiden vaalentamiseksi. Viljelyominaisuuksis- ta kiinnitettiin huomiota erityisesti aikaisuuteen, kukin- taan, talvenkestävyyteen ja elinkelpoisuuteen sekä tau- tien ja tuholaisten kestävyyteen. Tulokset osoittivat, että kevätsadon määrä vaihteli ra- joissa 50—150 kg/a. Kaikilla tutkituilla kannoilla kitke- ryys oli vähäinen myös ilman vaalentamista, ja vaalenta- malla se jäi merkityksettömäksi. Aistinvarainen laatu vaihteli tyydyttävästä erittäin hyvään riippuen kannasta ja viljelymenetelmästä. Vallinneessa ravinnetilanteessa todettiin korkeampi lannoitustaso liian korkeaksi. Kokeilluista vaalennuskatteista todettiin soveltuviksi yksinkertainen musta muovikalvo, musta kuitukangas ja paksu kuorihumuskate. Katteiden todettiin kylläkin vähentävän satoa (kuiva-aineeksi laskettuna), mutta pa- rantavan makua jarakennetta. Muovia tai kuitukangas- ta käytettäessä saadaan hiukan vihertävämpiä ruusuk- keita ja enemmän satoa kuin kuorihumuskatteella. Vii- memainittua käytettäessä ovat ruusukkeet mehevämpiä ja rapeampia. Menetelmä soveltuu kuitenkin työläyten- sä vuoksi paremmin kotipuutarhoihin kuin kaupalliseen viljelyyn. Tutkituista kannoista soveltuvat vaalentamatta viljel- täviksi parhaiten T. hemicyclum, T. lanyphyllum, ‘Voll- herziger, verbesserter’ ja ‘Vert de Montmagny’, vaalen- tamalla viljeltäviksi taas ‘Vert de Montmagny’, T. hemi- cyclum ja T. pallidipes. 22