Effects of Light Time, Light Intensity and Light Color on the Growth and Quality of Cordyceps militaris

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1. College of Agriculture, Yulin Normal University, Yulin 537000, China; 2. Guangxi Zhuangrentang Biotechnology Co., Ltd., Nanning 530000, China

Abstract Cordyceps militaris, which is a precious edible fungus, contains effective ingredients such as cordycepin and adenosine, and can treat a variety of diseases. However, light has the greatest effect on the growth of C. militaris in the process of artificial cultivation. In this study, the effects of light time, light intensity and light color on the growth, physiology, yield and quality of C. militaris were discussed to provide reference for the efficient artificial cultivation of C. militaris.

Key words Light time, Light intensity, Light color, Cordyceps militaris, Quality

1 Introduction

Cordycepsmilitaris, which is a precious edible fungus, mainly contains a variety of active ingredients such as cordycepin, adenosine, cordyceps polysaccharide, cordycemic acid and ergosterol. Relevant research shows thatCordycepshas effects of resisting tumor, inhibiting leukemia, enhancing immunity, enhancing sexual function, and inhibiting the clotting of human platelets.C.militarisis one of several available species in the genusCordyceps, and it is also one of the species that can be produced on a large scale at present. The growth and development ofC.militarisand the production of metabolites are affected by many factors. Among the factors, light, as an important environmental factor, has an important impact on the growth, development and active ingredients ofC.militaris.

2 Effects of Light on the Growth and Physiological Properties of Cordyceps militaris

2.1 Effects of light intensity on the growth and physiological properties ofCordycepsmilitaris

2.1.1Mycelium coloring. Mycelium coloring is the key toC.militariscultivation, and appropriate light intensity can promote mycelium coloring. The shortening of coloring time and deepening of mycelium are conducive to the high yield and carotenoid accumulation of stroma[1]. In the cultivation and management ofC.militaris, the coloring condition of mycelium can be used as an important reference index, and appropriate light intensity can be adjusted at the coloring stage to promote the occurrence of coloring.

2.1.2Light intensity affects the growth ofCordycepsmilitaris. 7-13 d afterC.militarisis inoculated, light intensity can be adjusted to 248 lx, which is conducive to stroma coloring; 14-34 d after inoculation, when light intensity is maintained at about 300 lx, the stroma grows fastest. As light intensity is 300 lx, the inflection point ofC.militarisgrowth curve appears on the 35th day after inoculation, which is 3 d earlier than 150 lx[2]. Therefore, 35 d after inoculation, light intensity is reduced to about 150 lx to maintain the growth ofC.militaris. It can be seen that in the cultivation and management ofC.militaris, it is necessary to adjust light intensity in good time.

2.1.3Light intensity influences the metabolism ofCordycepsmilitaris. Appropriate light intensity can promote the decomposition and utilization of nutrient components in culture medium by mycelium cells ofC.militaris. When light intensity exceeds 500 lx, the utilization rate of substrate significantly reduces. Properly increasing light intensity helps the accumulation of cordycepin. As light intensity is 75 and 650 lx, stroma matures slowly, and cordycepin is secreted less extracellularly, so the content of cordycepin in the stroma is higher than that of substrate; at other levels of light intensity, cordycepin is secreted more extracellularly, and its content is not much different in the stroma and substrate[3]. Adenosine is a primary metabolite, and its content in the stroma is much higher than that of substrate. It can be seen that light intensity is an important way to regulate the metabolism ofC.militaris.

2.1.4Light intensity affects on the activity of antioxidant enzymes. The activity of SOD and CAT and MDA content are closely related to the duration of stress. In the early stage of growth, light stress causes the accumulation of reactive oxygen and increase the activity of antioxidant enzymes[4]. AsC.militarisadapts to stress, antioxidant enzymes gradually remove harmful reactive oxygen, and cell membrane lipid peroxidation weakens. When light intensity is 150 lx, the activity of SOD and CAT and MDA content are lower, indicating that the stress caused by appropriate light intensity is weaker, which is beneficial to the growth ofC.militaris.

2.2 Effects of light time on the growth and physiological properties ofCordycepsmilitaris

2.2.1Mycelium coloring. Reasonable light-dark alternation can promote mycelium coloring. When light time is 7.95 h/d, mycelium color is the darkest. Too short or too long light time will affect mycelium coloring. When light time is shortened to less than 4 h/d, aerial mycelium is strong and dense, the coloring time of mycelium is delayed, and the degree of coloring is weakened. Therefore, in the stage of mycelial coloring, light time must be sufficient.

2.2.2Proper light time can increase cordycepin content. When light time was 8 h/d, the content of cordycepin in the stroma and matrix is the highest, up to 4.41 and 8.48 mg/g, respectively. As light time is 8 h/d, the content of cordycepin is higher than 2 h/d, which indicates that proper extension of light time can promote the synthesis of cordycepin.

2.2.3Light time affects the activity of antioxidant enzymes. Immediately after the differentiation of the stroma, the activity of SOD and CAT increases with the continuing of light stress, and the reactive oxygen that is harmful to cells are removed. On 29th day after inoculation, the activity of SOD and CAT decreases with the adaptation to stress. After the stroma is mature, it can be harvested later to increase the activity of antioxidant enzymes and then slow the senescence of the stroma[6].

2.3 Effects of light color on the growth and physiological properties ofCordycepsmilitaris

2.3.1Blue light promotes the synthesis ofCordycepsmilitarispigments. Suitable light color is the key to the mycelium coloring ofC.militaris. Carotenoid content in the stroma is the highest under white light, followed by blue light and green light, while red light and yellow light are not conducive to pigment synthesis[7]. Among various light colors, blue light plays a major role in promoting the accumulation of carotenoids, followed by green light, and the two may interact, so pigment content under white light is higher than that of single light. Appropriate light color not only promotes pigment synthesis, but also correlates with the morphology of the stroma.

2.3.2Light color affects the synthesis of cordycepin and adenosine. Blue light and red light can promote cordycepin synthesis, and the effect of blue light is more obvious. The content of cordycepin in the stroma ias highest under blue light, reaching 5.61 mg/g, followed by red light, and the content of adenosine is highest in the stroma under red light[8]. Blue light and red light may interact in promoting cordycepin synthesis. To increase the content of cordycepin and adenosine, appropriate amounts of blue and red light can be used.

2.3.3Light color affects the activity of antioxidant enzymes. MDA content inC.militarisis low in the early stage of growth. With the accumulation of active oxygen caused by light wave stress, the activity of SOD and CAT increases to remove peroxidation products and slow the damage to membrane lipids. Under yellow light stress, the activity of CAT is higher, and MDA content increases significantly 29 d after inoculation, indicating that yellow light can cause stress on the growth ofC.militaris[9].

2.3.4Light color affects amylase activity. The activity of α-amylase and total enzyme is low when the stroma is newly differentiated. 29 days after inoculation, as the growth ofC.militarisstroma accelerates, its metabolic capacity increases, and the activity of α-amylase and β-amylase increases, which promotes the decomposition and absorption of starch and other nutrients in the culture medium by mycelia[10]. After the stroma matures, amylase activity decreases, and the ability of mycelia to break down starch decreases. Under green light, the activity of a-amylase and total enzyme in the stroma is higher, indicating that green light is beneficial to the increase of amylase activity , which promotes the degradation and utilization of starch by mycelia.

3 Effects of Light on the Yield and Morphology of Cordyceps militaris

3.1 Effects of light intensity on the yield and morphology ofCordycepsmilitarisAppropriate light intensity can significantly increase the yield of the stroma. Too high or low light intensity will lead to a reduction in the yield ofC.militaris. At the same time, it can increase the length of the stroma. When light intensity exceeds 500 lx, the stroma differentiates later, grows slowly, and becomes short. When the light intensity of the culture environment is 279 lx, the density of the stroma is the largest. Light plays a major role in the synthesis of carotenoids, and unsuitable light intensity will cause a decrease in the content of carotenoid in the stroma[10]. Therefore, in the three-dimensional cultivation ofC.militaris, it is necessary to reasonably arrange light to minimize the difference of light intensity above and below a cultivation frame.

3.2 Effects of light time on the yield and morphology ofCordycepsmilitaris

3.2.1Light time affects the yield ofCordycepsmilitaris. When light time was 8.65 h/d, the biological efficiency ofC.militarisis the highest, up to 89.06%. Too short light time will lead to a decrease in the yield ofC.militaris. When light time is shortened to 2 h/d, the yield of the stroma will decrease significantly, which is 10.76% lower than that under 8 h/d. In order to increase the yield of the stroma, light time should be sufficient.

3.2.2Light time affects the growth ofCordycepsmilitarisstroma. 7-13 d after inoculation, light time should be 7.95 h/d to promote mycelium coloring. 14-25 d after inoculation, light time should be about 6 h/d to promote the differentiation and rapid growth of the stroma. 26-44 d after inoculation, when light time is about 8 h/d, and the stroma grows faster. 45 d after inoculation, light time is shortened to about 6 h/d to promote continuous growth ofC.militaris[11].

3.3 Effects of light color on the yield and morphology ofCordycepsmilitaris

3.3.1Green light is the key to an increase in the yield ofCordycepsmilitaris. Green light has the greatest effect on an increase in the yield ofC.militarisstroma, with a biological efficiency of 96.64%, followed by white light and blue light. Green light and blue light may have an interaction in the increase of stroma yield. In cultivation management, in order to increase the yield ofC.militarisstroma, an appropriate amount of green light can be used.

3.3.2Light color affects the morphology and density of the stroma. There is a big difference in the effects of different light colors on the morphology ofC.militarisstroma. Under green light, the length of the stroma is much longer than that of other treatments. Under red light and yellow light, the stroma differentiates later, becomes short, and increases in diameter. Moreover, the top of the stroma is difficult to swell, and the maturity time is not easy to judge. Its cultivation cycle is much longer than that under white light. Under white light, the density of the stroma is the highest, reaching 0.037 4 a/mm2. Under red light and yellow light, the stromata are more solitary, and the density is extremely low.

4 Conclusions

In conclusion,C.militarisis affected to varying degrees by light intensity, light time, and light color. In the cultivation and management ofC.militaris, it is necessary to adjust light intensity in good time. In the stage of mycelium coloring, light time must be sufficient. Appropriate amounts of blue and red light are helpful in increasing the content of cordycepin and adenosine, while green light can enhance the activity of amylase and promote the decomposition and utilization of starch by mycelia. In order to increase the yield of the stroma, light time should be sufficient. When artificial three-dimensional cultivation is adopted, light should be arranged reasonably to minimize the difference of light intensity above and below a cultivation frame.