Key Artificial Cultivation Technique by the Naxi Nationality for Dioscorea bulbifera: A Traditional Medicinal and Edible Plant

Genlin YANG, Qinghua LI, Yungui GAO, Zhigang YANG

Forestry Science Institute of Lijiang, Lijiang 674100, China

Abstract Dioscorea bulbifera is a medicinal and edible plant of the Naxi nationality living in Lijiang area, and its tuber as a vegetable has the functions of clearing away heat and detoxification, and its bulbil has the functions of clearing away heat and resolving phlegm, relieving cough and relieving asthma, dispersing the accumulation of evils and detoxification, etc. Related studies have shown that it mainly contains steroids, diterpene lactones, flavonoids, polyphenols, alkaloids and so on, and it can also fight cancer, inhibit bacteria, relieve pain, resist inflammation and so on. There is also related literature about hepatotoxicity after taking it. The key technique of traditional vegetable cultivation in Lijiang area is systematically summarized in this paper for reference in the future cultivation process.

Key words Naxi nationality, Medicinal and edible plant, D. bulbifera, Cultivation technique

1 Introduction

Dioscoreabulbiferais a twining vine in the family Dioscoreaceae, also known as Huangyao (PrimitiveHerbalMedicine), Shancigu (AnIllustratedBookonPlants), Lingyuzi yam (Russian, Latin and Han seed plant names), Lingyushu (GuangzhouFlora,HainanFlora), Huangyaozi (name of herb in Jiangsu, Anhui, Zhejiang, Yunnan and other provinces), and Shancigu (Chuxiong, Yunnan)[1]. It is widely distributed in China, from Henan and southern Gansu to Guangdong and Guangxi, and to Yunnan and Tibet in the west. It has strong adaptability, not only likes shade and dampness, but also needs plenty of sunshine. It can be seen in alpine areas ranging from tens of meters to 2 000 m above sea level. It is often found in river valleys, gullies or forest edges, and sometimes grows in the shade of trees on all sides. It is distributed in Japan, North Korea, India, Myanmar, Oceania and Africa.

2 Herbal research on the traditional consumption of "yellow yam" by the Naxi nationality

The Naxi people living in Lijiang, Yunnan, generally use medicinal plants for stewing and steaming with meat, pay great attention to daily conditioning, and like to prevent diseases and strengthen their health in the form of food cooked with medicinal herbs[2-3]. The medicinal and edible plant "yellow yam" daily consumed by the Naxi people is one of them. Yellow yam, also known as Huangchu among the Naxi people, is a medicinal and edible plant planted by the Naxi nationality living in Qihe Township, Baisha Town, Longpan Township, Shigu Town, Judian Town, Tacheng Township and other townships in Lijiang area. It is regarded as a traditional vegetable to be widely cultivated, its tuber is mainly eaten as a vegetable, and its bulbil is used as a national herbal medicine. In Naxi tradition, during the days of pig killing, Chinese New Year, or other banquets, people always make a dish of stewed ribs with yellow yam, which can not only be used as a vegetable, but also has the role of heat-clearing and detoxification. In the cooking process, it is also so elaborately prepared. In order to remove its own bitterness, you have to peel and cut it into small pieces before stewing, soak it in cold water for about 3 h, and rinse it repeatedly 3-4 times, and then must simmer it with ribs. Naxi tradition believes that its bulbil can not be eaten as vegetables, but it has the effects of clearing heat and resolving phlegm, relieving cough and relieving asthma, dispelling the accumulation of evils and detoxification. It can be used for the treatment of phlegm-heat, cough and asthma, sore throat,etc., and is mainly externally used for the treatment of sores and furuncles. After collecting samples, consulting the relevant literature for comparison, the situation of food and medicine use by the Naxi people was investigated. Through systematic research, the origin of yellow yam, a traditional medicinal and edible plant of Naxi nationality, isD.bulbifera, and there are no reports and records of poisoning as a result of eatingD.bulbiferatuber in Lijiang area.

3 Research progress on chemical constituents and pharmacological effects of D. bulbifera

As a medicinal plant,D.bulbiferahas a long medicinal history and was first published inKaiyuanMateriaMedica. Its medicinal properties and application were first seen inRihuaziMateriaMedicain the early Song Dynasty, and it was first used as a veterinary medicine for the treatment of horse diseases. The effect of detoxification and detumescence has been recorded sinceKaibaoMateriaMedicain the Song Dynasty.D.bulbiferais recorded inSouthernYunnanMateriaMedica: it is cold in nature and tastes bitter.TheCompendiumofMateriaMedicacomprehensively clarifies the efficacy ofD.bulbifera: it can cool the blood and reduce pathogenic fire, eliminate galls and relieve internal heat or fever. As a result, the scope of clinical application ofD.bulbiferais expanded[4].With the deepening of research, it has been reported that the main chemical components are steroids, diterpene lactones, flavonoids, polyphenols, alkaloids and so on, and it has the anticancer, bacteriostatic, analgesic, and anti-inflammatory effects. Clinically, it is mainly used for the treatment of thyroid diseases and cancer, and it is also often used to treat inflammations such as cervicitis, dysentery, asthma, mammary gland hyperplasia and so on[5-6]. Indian people commonly use its plant buds to treat hemorrhoids, dysentery, syphilis and ulcers and other diseases[7]. There are also some reports about hepatotoxicity. Miao Zhengqiu, Cheng Fangetal.[8-9]have reported toxic hepatitis caused byD.bulbifera. Song Yuming, Li Jun, Wang Shaozhen and Wang Jinfeng[10-14]discussed the mechanism and compatibility of liver poisoning.

4 Related reports on artificial cultivation

D.bulbiferais a traditional medicine, and with the in-depth understanding of the chemical composition and activity ofD.bulbifera, it will be used more and more widely and has high economic value. With the decrease of wild resources, artificial cultivation will get more and more attention. Hong Senrong, Yin Minghua, Zhang Zongliangetal.[15-16]have carried out related studies on tissue culture and rapid propagation of virus-free seedlings. Miao Cunming[17]and Sun Wei[18]etal. have carried out studies on artificial cultivation in Fujian and Shenyang, respectively. Relatively speaking, there are few reports on artificial cultivation.

5 Key technique of artificial cultivation

In Lijiang area, there is very mature experience in the traditional cultivation ofD.bulbifera, and many Naxi people cultivate it as a traditional vegetable. Through a systematic summary of the key technologies of artificial cultivation, we aimed to provide technical reference for the next step of artificial cultivation.

5.1 Site selectionD.bulbiferahas strong adaptability, it can grow normally from the Jinsha River valley 1 800 m above sea level to the area 2 400 m above sea level, and the cultivation site was selected with sufficient sunshine, good irrigation conditions and loose and fertile sandy loam. Terraces formed from gentle slopes along contours can also be selected for planting.

5.2 Soil preparation, furrowing and application of base fertilizerAfter the rainfall is reduced in the autumn, the soil was ploughed under to great depth, raked and loosened, and the perennial roots and weeds were picked up and removed, repeated twice. The furrow for planting was 30-40 cm wide, 30 cm or so deep, length depended on growth vigor, and furrow spacing was about 30 cm. A layer of superphosphate or plant ash was spread evenly at the bottom of the furrow. In the areas infested by the grubs, we can properly disinfect the soil or sprinkle a layer of low-toxic insecticides for planting.

5.3 Seed selection and seedling cultivationBulbils with a diameter larger than 5 cm or smaller tubers (usually less than 8 cm in diameter) were generally selected for cultivation ofD.bulbiferaseedlings. For example, if the bulbil diameter was smaller than 5 cm, it needed to be cultivated for one year to form a tuber, then replanted next year, or cultivated continuously for 2 years after planting for harvest. As for the cultivation of seed tuber, the smaller bulbils were selected for cultivation. After soil preparation, 100 cm wide, 15 cm deep furrows were created, calcium superphosphate was applied as base fertilizer, andD.bulbiferabulbil was evenly spread, and covered with soil. It is necessary to carry out daily management including watering and drainage, weeding and so on. After harvesting in autumn and winter, to prevent frost damage and decay, it is necessary to dig deep into the soil for storage and reserve seed for planting.

5.4 PlantingIn Lijiang, it is generally planted at the end of February, and bulbils or tubers with strong growth and no diseases and pests are selected for planting. The plant spacing is about 20 cm, and the row spacing is according to the furrow spacing. First, the bulbils or tubers were placed flat at the bottom of the furrow, putting the buds head up, and then covered with the rotten farm manure or mountain base soil (humus soil formed by the decay of pine needles or broad-leaved trees).The nutritive root is located in the position where the upper vine of the tuber grows, and the rest of the root is fixed, so the base fertilizer was applied by the way of mulching and fertilization, and then the soil was covered evenly.

5.5 Building vine trellisD.bulbiferalikes to have plenty of sunshine, and its vines grow vigorously, so it is necessary to build high trellis for it to climb. To make the support pole strong, we can insert a 2.5 m high oak pole as a climbing support bar every 50 cm along the furrow for planting, and then bind a bamboo pole horizontally every 1 m in height.

5.6 Daily managementAfterD.bulbiferaplanting, it should be watered sufficiently, and before the rainy season comes, it is necessary to observe the soil moisture and water it at the right time. We should get rid of the weeds in time and remove them early. After the seedlings grow, the auxiliary vines were fixed to the trellis for smooth climbing and growth. If the vines have too many bifurcations and are too strong, the branches that are too strong can be properly removed in order to achieve the overall growth balance. After the rainy season, it is necessary to pay attention to drainage and avoid waterlogging. 300 kg/ha compound fertilizer with N∶P∶K proportion of 15∶15∶15 can be applied in rainy season. AfterD.bulbiferagrows vigorously, the general weeds are very difficult to grow, and the occasional weeds can be removed in time.

5.7 Pest controlExcept for occasional aphids, pests rarely occur in the aboveground parts ofD.bulbifera, and grubs are mainly harmful to underground tubers. Soil disinfection and preventive treatment can be carried out before planting. Diseases are mainly downy mildew, ring spot, and timely prevention and control should be adopted if these diseases are found. The prevention and control of diseases and pests as a whole follows the principle of "prevention first, green comprehensive prevention and control", putting an end to the use of prohibited and restricted pesticides.

5.8 HarvestingAt the end of autumn,D.bulbiferacan be harvested after the leaves have gradually fallen and dried up. When harvesting, it is necessary to remove the trellis first, and then pick up the fallen bulbils to prepare for sowing and reserving seed for planting, and then dig for tubers along the furrow for planting. You can carry out overall digging if you want it to go on the market in large quantities. The harvested tubers should not be placed outdoors in winter to avoid freezing and decay. It can be stored in a warm room and covered with fresh pine needles, or stored in a deep cellar. In order to prevent frost damage in winter, those used as vegetables can be kept in the plantation first, without overall digging, and it is necessary to avoid watering the cultivated land, because watering will aggravate the occurrence of frost damage and decay.

6 Conclusions

As a traditional medicinal plant,D.bulbiferahas a high market prospect. With the deepening of the research, more uses will be found. The cultivation ofD.bulbiferahas low cost and places less demands on technology, so it is a kind of medicinal plant worthy of planting and extension. Although the Naxi nationality in Lijiang area has the tradition of eatingD.bulbiferatubers and there is no record and report of poisoning, it does not mean that it has no hepatotoxicity, and the chemical components ofD.bulbiferagrown in different places are also different, so it is not recommended to be eaten and promoted as a vegetable in other areas.