Yanrong BAI1, Yalian JIANG

1. Kunming University, Kunming 650213, China; 2. Flower Research Institute, Yunnan Academy of Agricultural Sciences, Kunming 650214, China

Abstract Lucetta, a cultivar of Eustoma grandiflorum (Raf.) Shinners, was subjected to treatments of different light intensities (100%, 85%, 70% and 55% of natural light intensity) and different light durations (10-h natural lighting, 12-h natural lighting, 12-h natural lighting+2-h LED lighting, 12-h natural lighting+4-h LED lighting), and then its plant height, crown width, stem thickness, stalk thickness, total flower number, flowering period and growth situation were analyzed. The results show that E. grandiflorum (Raf.) Shinners is sensitive to the changes in light intensity. Under 85% of natural light intensity (40 000-50 000 lux), E. grandiflorum (Raf.) Shinners grew faster, bloomed earlier with more flowers, and was taller, thicker, more robust, higher in yield, larger in pedicel length, and better in cut flower quality, without rosette phenomenon. Long-term exposure to low-intensity light would led to slow growth, thin stalk, delayed flowering, low yield and reduced cut flower quality in E. grandiflorum (Raf.) Shinners. The illumination duration of more than 12 h could promote the differentiation of flower buds, increase the plant height, increase the length of pedicels of E. grandiflorum (Raf.) Shinners. Extending the light duration by 2-4 h at night, that is, 14-16 h of illumination was the most ideal illumination time for the growth of E. grandiflorum (Raf.) Shinners. A longer photoperiod could promote the growth and bring forward the blooming of E. grandiflorum (Raf.) Shinners. The longer the illumination time, the higher the plant. The optimum illumination time was between 14 and 16 h. When the illumination duration was shorter than 12 h, the growth of E. grandiflorum (Raf.) Shinners was retarded, and its flowering was also delayed.

Key words Illumination, Eustoma grandiflorum (Raf.) Shinners, Cut flower, Growth and development, Quality

1 Introduction

Eustomagrandiflorum(Raf.) Shinners (Gentianaceae) is a perennial plant, with height of 30-100 cm. Leaves are opposite, broadly elliptic to lanceolate, sessile, slightly clasped at the base, and blue-green on the surface[1]. Pistils and stamens are conspicuous. Sepals are narrowly lanceolate. Petals are tiling, monopetalous or bipetalous. Flowers are rich in color, with monochromatic and complex colors.E.grandiflorum(Raf.) Shinners is native to the limestone area between the southern United States and Mexico. Modern cultivation ofE.grandiflorum(Raf.) Shinners arose from Japan. Commercial cultivation began in the 1960s. Cut flowers ofE.grandiflorum(Raf.) Shinners are beautiful, colorful and gorgeous. They are more resistant to storage and transportation, with a long vase life.E.grandiflorum(Raf.) Shinners is popular among the market as a cut flower variety. It has broad market prospects in Europe, America, Japan and Taiwan, China, is one of the most popular types of cut flowers in the world and has a very broad application prospect[2].

At present, there are few studies on temperature, light, water and fertilizer during the cultivation process ofE.grandiflorum(Raf.) Shinners, let alone study on light conditions. The suitable temperature for the growth ofE.grandiflorum(Raf.) Shinners is 15-28℃. The night temperature cannot be lower than 12℃. When the temperature in winter is below 5℃ or the temperature in summer is above 30℃, the plants will cluster, leading to the appearance of rosette phenomenon; and the flowering will fail or be delayed.E.grandiflorum(Raf.) Shinners can adapt to low temperature of 0℃ for a short time. Wu Yuanyuan[3]believes that the optimum light intensity forE.grandiflorum(Raf.) Shinners is 40 000 lux, and generally, the light duration of 16 h is the most ideal. He Jiatao and Fu Xiuzhi[4]found thatE.grandiflorum(Raf.) Shinners is not tolerant to waterlogging, so in the cultivation, attention should be paid to prevent water accumulation in the soil; however, insufficient watering would cause the plants to grow into clusters, affecting normal flowering; and therefore, the soil should be kept in a slightly moist and dry state, and the amount of irrigation should be increased as pedicels begin to extend. There are many problems in the production process of cut flowers ofE.grandiflorum(Raf.) Shinners, such as greatly declined quality and high mortality, and most of them are caused by the improper adjustment of temperature, light, water and fertilizer during the cultivation process. In this paper, the appropriate lighting parameters for the growth and development of cut flowers ofE.grandiflorum(Raf.) Shinners were explored to provide a basis for production.

2 Materials and methods

2.1 MaterialsA total of 80 pots ofE.grandiflorum(Raf.) Shinners (Lucetta) seedlings were selected. The other materials used included sunshade net, black-out fabric, photometer, vernier caliper and LED lamps (1 600 lux/lamp).

2.2 Methods

2.2.1Different light intensity treatments. The 80 pots of seedlings were randomly divided into four groups, and subjected to treatments of different light intensities (100%, 85%, 75% and 55% of natural light intensity) using shading materials of different light transmittance. The four zones were independent to each other, and managed according to the conventional method. The plant height, crown width and stalk thickness of theE.grandiflorum(Raf.) Shinners plants were measured with vernier caliper, and their growth was observed and recorded 0, 2, 4, 6, 8, 10 and 12 weeks after the field planting, respectively. The length of the pedicel of the first flower was measured and recorded. The total number of flower pubs per plant was counted.

2.2.2Different light duration treatments. The 80 pots of seedlings were randomly divided into four groups, and subjected to treatments of different light durations (10-h illumination, 12-h illumination, 14-h illumination and 16-h illumination). In the treatment of 10-h illumination, theE.grandiflorum(Raf.) Shinners plants were shaded with black-out fabric after 10 h of daylight per day; in the treatment of 12-h illumination, theE.grandiflorum(Raf.) Shinners plants were subjected to the natural lighting duration; in the treatment of 14-h illumination, theE.grandiflorum(Raf.) Shinners plants were exposed to 10 h of natural lighting and 2 h of LED lighting; and in the treatment of 16-h illumination, theE.grandiflorum(Raf.) Shinners plants were exposed to 10 h of natural lighting and 4 h of LED lighting. The management method was consistent. The plant height, crown width and stalk thickness of theE.grandiflorum(Raf.) Shinners plants were measured with vernier caliper, and their growth was observed and recorded 0, 2, 4, 6, 8, 10 and 12 weeks after the field planting, respectively. The length of the pedicel of the first flower was measured and recorded. The total number of flower pubs per plant was counted.

3 Results and analysis

3.1 Effects of different light intensity on growth and development of cut flowers ofE.grandiflorum(Raf.) Shinners

3.1.1Effect of different light intensity on plant height ofE.grandiflorum(Raf.) Shinners. As shown in Table 1, theE.grandiflorum(Raf.) Shinners plants grew fastest and were tallest under 85% and 70% of natural light intensity, followed by those under 100% of natural light intensity, and under 55% of natural light intensity, theE.grandiflorum(Raf.) Shinners plants grew extremely slowly and were generally shorter than normal plants.

Within 12 weeks after field planting, the increase in plant height ofE.grandiflorum(Raf.) Shinners under 70% of natural light intensity was greatest, followed by the increase under 85% of natural light intensity which differed insignificantly with that under 100% of natural light intensity, and the increase in plant height ofE.grandiflorum(Raf.) Shinners under 55% of natural light intensity was the smallest which differed significantly with those under the other light intensities.

Table 1 Growth of plant height of Eustoma grandiflorum (Raf.) Shinners after field planting under different light intensity cm

3.1.2Effects of different light intensity on crown width ofE.grandiflorum(Raf.) Shinners. As shown in Table 2, there was no significant difference in growth rate of crown width ofE.grandiflorum(Raf.) Shinners between 85% and 100% of natural light intensity. The average crown width of theE.grandiflorum(Raf.) Shinners plants growing under 75% of natural light intensity was smaller, and the growth rate was slower. The crown width of theE.grandiflorum(Raf.) Shinners plants growing under 55% of natural light intensity was the smallest, and the growth rate was the slowest. Within 12 weeks after filed planting, the increase in crown width ofE.grandiflorum(Raf.) Shinners differed insignificantly between 85% and 100% of natural light intensity, and the increase in crown width ofE.grandiflorum(Raf.) Shinners growing under 80% of natural light intensity was greater. As the light intensity decreased since 85% of natural light intensity, the increase in crown width ofE.grandiflorum(Raf.) Shinners reduced.

Table 2 Growth of crown width of Eustoma grandiflorum (Raf.) Shinners after field planting under different light intensity cm

3.1.3Effects of different light intensity on stalk growth ofE.grandiflorum(Raf.) Shinners. As shown in Table 3, the grow rate of stalk thickness ofE.grandiflorum(Raf.) Shinners was highest under 100% of natural light intensity, followed by that under 85% of natural light intensity, and the growth rate under 55% of natural light intensity was smallest. Overall, as the light intensity decreased, the stalk thickness and its growth rate both decreased. The analysis results show that the increase in stalk thickness ofE.grandiflorum(Raf.) Shinners was negatively correlated with light intensity.

3.1.4Effects of different light intensity on pedicel length and total flower number ofE.grandiflorum(Raf.) Shinners. As shown in Table 4, the number of flower buds inE.grandiflorum(Raf.) Shinners growing under 85% of natural light intensity was the largest, followed by that under 100% of natural light intensity, and the total number of flower buds inE.grandiflorum(Raf.) Shinners growing under 55% of natural light intensity was the smallest. The pedicel length ofE.grandiflorum(Raf.) Shinners growing under 70% of natural light intensity was the largest, and it differed insignificantly with that under 85% of natural light intensity. When the light intensity was increased or reduced, the pedicel length reduced. TheE.grandiflorum(Raf.) Shinners plants growing under 100% and 85% of natural light intensity bloomed earliest, while those under 55% of natural light intensity bloomed latest. Under 85% of natural light intensity, one plant died; and under 55% of natural light intensity, two plants grew into clusters.

Table 3 Growth of stalk thickness of Eustoma grandiflorum (Raf.) Shinners after field planting under different light intensity cm

Table 4 Pedicel length and flower number in Eustoma grandiflorum (Raf.) Shinners under different light intensity

3.2 Effects of different light duration on growth and development of cut flowers ofE.grandiflorum(Raf.) Shinners

3.2.1Effects of different light duration on plant height ofE.grandiflorum(Raf.) Shinners. As shown in Table 5, there was no significant difference in growth rate ofE.grandiflorum(Raf.) Shinners between 14-h and 16-h illumination. The growth rates of theE.grandiflorum(Raf.) Shinners plants in the 14-h and 16-h illumination zones were higher than those in the other treatments. The growth rate of theE.grandiflorum(Raf.) Shinners plants in the 10-h illumination zone was the lowest, and they were shorter, followed by those in the 12-h illumination zone. The analysis results show that the increase in plant height ofE.grandiflorum(Raf.) Shinners was positively correlated with illumination duration. The increase in plant height ofE.grandiflorum(Raf.) Shinners in the 16-h illumination zone was the largest, and that in the 10-h illumination zone was the smallest.

Table 5 Growth of plant height of Eustoma grandiflorum (Raf.) Shinners after field planting under different lighting duration cm

3.2.2Effects of different light duration on crown growth ofE.grandiflorum(Raf.) Shinners. As shown in Table 6, the growth rate of crown width ofE.grandiflorum(Raf.) Shinners in the 14-h illumination zone was the highest, followed by that in the 16-h illumination zone, and in the 10-h illumination zone, the crown width of theE.grandiflorum(Raf.) Shinners plants grew most slowly, and it was smaller than that of normal plants and had big differences compared with those of other treatments. The analysis results show that the increase in crown width ofE.grandiflorum(Raf.) Shinners in the 12-h illumination zone was the largest, there was no big difference in increase in crown width ofE.grandiflorum(Raf.) Shinners between 14-h and 16-h illumination zones, and the increase in crown width ofE.grandiflorum(Raf.) Shinners in the 10-h illumination zone was the smallest.

Table 6 Growth of crown width of Eustoma grandiflorum (Raf.) Shinners after field planting under different lighting duration cm

3.2.3Effects of different light duration on stalk growth ofE.grandiflorum(Raf.) Shinners. As shown in Table 7, the growth rates of stalk thickness ofE.grandiflorum(Raf.) Shinners in the 14-h and 16-h illumination zones were basically the same, and they were higher than those of the other treatments, followed by that in the 12-h illumination zone, and the growth rate of stalk thickness ofE.grandiflorum(Raf.) Shinners in the 10-h illumination zone was the lowest. The analysis results show that the increase in stalk thickness ofE.grandiflorum(Raf.) Shinners in the 14-h illumination zone was the largest, followed by that in the 16-h illumination zone, and the increase in stalk thickness ofE.grandiflorum(Raf.) Shinners in the 10-h illumination zone was the smallest. The increase in stalk thickness ofE.grandiflorum(Raf.) Shinners expanded as the lighting duration increased from 10 to 14 h, and the opposite was true after the lighting duration was extended longer than 16 h.

Table 7 Growth of stalk thickness of Eustoma grandiflorum (Raf.) Shinners after field planting under different lighting duration cm

3.2.4Effects of different light duration on pedicel length and total flower number ofE.grandiflorum(Raf.) Shinners. As shown in Table 8, the total flower number and pedicel length ofE.grandiflorum(Raf.) Shinners in the 14-h illumination zone were the largest, followed by those in the 16-h illumination zone, and the total flower number and pedicel length ofE.grandiflorum(Raf.) Shinners in the 10-h illumination zone were the smallest. Plant clusters appeared in the 10-h and 14-h illumination zones. Plant death occurred in the 12-h illumination zone, but the proportion was not large, and had no significant effect on the experiment. TheE.grandiflorum(Raf.) Shinners plants in the 14-h and 16-h illumination zones began to bloom earlier, all in the 8th week, followed by those in the 12-h illumination zone, and theE.grandiflorum(Raf.) Shinners plants in the 10-h illumination zone began to bloom latest, in the 10th week.

Table 8 Pedicel length and flower number in Eustoma grandiflorum (Raf.) Shinners under different lighting duration

4 Conclusions

The comprehensive results show thatE.grandiflorum(Raf.) Shinners is sensitive to the changes in light intensity. The optimal light intensity was 85% of natural light intensity. Under the light intensity of 40 000-50 000 lux,E.grandiflorum(Raf.) Shinners grew faster, bloomed earlier with more flowers, and was taller, thicker, more robust, higher in yield, larger in pedicel length, and better in cut flower quality, without rosette phenomenon. Long-term exposure to low-intensity light would led to slow growth, thin stalk, delayed flowering, low yield and reduced cut flower quality inE.grandiflorum(Raf.) Shinners. The illumination duration of more than 12 h could promote the differentiation of flower buds, increase the plant height, increase the length of pedicels ofE.grandiflorum(Raf.) Shinners. Extending the light duration by 2-4 h at night, that is, 14-16 h of illumination was the most ideal illumination time for the growth ofE.grandiflorum(Raf.) Shinners. A longer photoperiod could promote the growth and bring forward the blooming ofE.grandiflorum(Raf.) Shinners. The longer the illumination time, the higher the plant. The optimum illumination time was between 14 and 16 h. When the illumination duration was shorter than 12 h, the growth ofE.grandiflorum(Raf.) Shinners was retarded, and its flowering was also delayed.

5 Discussion

The experimental results show that theE.grandiflorum(Raf.) Shinners plants under 85% and 70% of natural light intensity grew fastest and were tallest, followed by those under 100% of natural light intensity, and theE.grandiflorum(Raf.) Shinners plants under 55% of natural light intensity were weak and thin. Through comprehensive comparison, it could be concluded that the optimal light intensity was 80% of natural light intensity, under which the plants ofE.grandiflorum(Raf.) Shinners grew more robust. If the illumination is too strong, the plant will be dwarfed, and if it is too weak, the plant will grow in vain. Under 80% of natural light intensity, there were more flower buds inE.grandiflorum(Raf.) Shinners, and its pedicels were longer and cut flowers were better.

Through shading and light-supplementing treatment, it could be seen thatE.grandiflorum(Raf.) Shinners is very sensitive to photoperiod[6]. When the lighting duration was longer than 12 h, the plants bloomed earlier. When the lighting duration was shorter than 12 h, the blooming of the plants was delayed and even failed. When the lighting duration ranged from 14 to 16 h, the plants grew most robust, with more flower buds and longer pedicels. Wang Limian[7-8]concluded that the optimal photoperiod forE.grandiflorum(Raf.) Shinners was 16 h. In this study, the differences in growth and flowering period ofE.grandiflorum(Raf.) Shinners were not significant between the lighting durations of 14 h and 16 h. Under the lighting duration of 14 h,E.grandiflorum(Raf.) Shinners showed more flower buds and longer pedicels[9-11]. Under the lighting duration of 16 h,E.grandiflorum(Raf.) Shinners showed larger crown width and stalk thickness. From the perspective of cost, it is more satisfactory to supplement 2 h of lighting in the cultivation ofE.grandiflorum(Raf.) Shinners, improving the yield and quality of cut flowers while saving cost.

The experimental results suggest thatE.grandiflorum(Raf.) Shinners was sensitive to changes in light intensity, and the optimal light intensity was 85% of natural light intensity (40 000-50 000 lux), under whichE.grandiflorum(Raf.) Shinners grew faster, bloomed earlier with more flower buds, and was taller, thicker, more robust, higher in yield, larger in pedicel length and better in cut flower quality[12-13]. Long-term exposure to low-intensity light would led to slow growth, thin stalk, delayed flowering, low yield and reduced cut flower quality inE.grandiflorum(Raf.) Shinners.

A longer photoperiod could promote the growth and bring forward the blooming ofE.grandiflorum(Raf.) Shinners. The longer the illumination time, the higher the plant[14-16]. The optimum illumination time was between 14 h and 16 h. Long-term exposure to the environment with lighting duration less than 12 h would make the growth ofE.grandiflorum(Raf.) Shinners retarded and flowering delayed.