Review on the Research Progress of Dictyophora rubrovolvata

Senlin ZHU　Ling TANG　Rende YANG　Bangxi ZHANG

AbstractDictyophora rubrovolvata has beautiful shape， good taste and high nutritional value， and has anti-oxidation， anti-tumor， hypoglycemic and other effects. In this review， the biological characteristics， nutritive chemical composition， polysaccharide extraction and functions， cultivation and pest control of D. rubrovolvata were intensively discussed and summarized， and the future research direction was also prospected. This study aims to provide future recommendations for the research of D. rubrovolvata and then promote the development of D. rubrovolvata industry.

Key wordsDictyophora rubrovolvata; Biological characteristics; Nutritional chemical composition; Extraction and function of polysaccharide; Cultivation; Plant diseases and insect pests

Bamboo fungus mostly parasitizes on the roots of withered bamboo[1]. There are 12 species of bamboo fungus reported， mainly distributed in China， India， Sri Lanka， Africa， Australia， North America， South America and the East and West Indies. There are 7 species of bamboo fungus distributed in China， including Dictyophora indusiata， Dictyophora duplicata， Dictyophora multicolor， Dictyophora cinnabarina， Dictyophora merulina， Dictyophora rubrovolvata， and Dictyophora echinovolvata， of which D. rubrovolvata， and D. echinovolvata were named by Chinese scholars[2]. The new species of D. rubrovolvata was jointly named and published by Zang et al. in 1976. It belongs to Basidiomycotina， Gasteromycetes， Phallales， Phallenaceae， Dictyophora[3]. D. indusiata is a model species of Dictyophora.

D. rubrovolvata is mainly produced in Guizhou and Yunnan， and it was first successfully cultivated in Zhijin County， Guizhou Province. "Zhijin bamboo fungus" was approved as a national geographic logo product in September 2010， and has been cultivated on a large scale at present， becoming the most distinctive and advantageous edible fungus industry in Guizhou Province. In the past five years， the retail price of D. rubrovolvata was basically stable， and the price of fresh products was about 100-150 yuan/kg， while that of dry products was 760-1 200 yuan/kg. The yield of dry products is 1 350-2 700 kg/hm2， and the net profit can reach 0.285 million-0.72 million yuan/hm2， so it has a high economic value. D. rubrovolvata is not only brittle and delicious， but also has a high nutritional value. Studies show that it is rich in various biologically active substances such as amino acids， inorganic salts， polysaccharides and vitamins. Among them， polysaccharides in the bamboo fungus have anti-oxidation[4]， anti-tumor[5] and other effects， and have great potential development value. At present， the reports of D. rubrovolvata mainly focus on cultivation technology research， and the study of nutritional active components and functions， etc. In this paper， the research status of D. rubrovolvata was summarized to provide reference for its follow-up research and promote the vigorous development of D. rubrovolvata industry.

Biological Characteristics of D. rubrovolvata

Morphological characteristics of the fruiting body

Before the the fruiting body of D. rubrovolvata is opened， it is called button or egg， purple-red， oval， and connected with rhizobacterial cord at the base[6]. The mature fruiting body consists of four parts： pileus， stipe， indusium and volva. The pileus is bell-shaped and white， with a flat and perforated， and there are irregular concave grids on the surface[7]. Dark green viscous spores are attached to the grids， and basidiospores are long oval or oval， with smooth， colorless and transparent walls[8]. The stipe is spongy cylindrical， white and hollow， brittle and easy to fold; it is generally 7-20 cm in length， and the maximum is up to 27 cm[9]. After the fruiting body matures， the inner fungus unfolds and droops from the fungal cap， which is shaped like a skirt， so it is called the indusium. The indusium is a white mesh， which is an important basis for distinguishing Phallus from Dictyophora. The volva wraps the base of the stipe， is oval or bowl-shaped， membranous， and purple-red[10-11].

Nutrient conditions for mycelium growth

In the wild state， D. rubrovolvata mainly absorbs nutrients from the rotten withered bamboo roots and bamboo stakes to grow. Wang Yun[12] studied the physiology of the wood rot of bamboo fungus， and found that both D. rubrovolvata and D. indusiata had the ability to decompose cellulose， hemicellulose and lignin. During the culture period of 80 d， the degradation of lignin by mycelia was greater than that of hemicellulose and cellulose. Therefore， they believe that bamboo fungus is a wood-rot fungus， which may be a white-rot fungus among wood-rot fungi. In production， the cultivation substrate of D. rubrovolvata generally uses wood chips and crop straws as carbon sources and wheat bran or rice bran as nitrogen sources.

D. rubrovolvata can use monosaccharides， disaccharides and polysaccharides as carbon sources. The research of Huang et al.[10] showed that the mycelium of D. rubrovolvata can better utilize D-fructose， D-glucose， mannose， and sucrose as carbon sources for growth， while DL-malic acid， D-galactose， rhamnose， lactose， oxalic acid， salicylic acid， tannin， and succinic acid can not be used as carbon sources. In terms of nitrogen sources， ammonium salts such as ammonium chloride， ammonium nitrate and ammonium sulfate can be well used， and organic nitrogen sources such as ammonium tartrate and beef extract can also be used， but potassium nitrate， sodium nitrate， yeast extract and L-methionine are used as nitrogen sources for growth. In addition， Gong et al.[13] found that glucose was the most suitable and fast-acting carbon source for the growth of the mycelium of D. rubrovolvata， and fructose was the most suitable slow-acting carbon source; the most suitable fast-acting nitrogen source was peptone， and the most suitable slow-acting nitrogen source was ammonium sulfate; adding an appropriate amount of zinc sulfate， bamboo leaf juice， vitamin B6 and IAA to the medium can significantly promote the germination and growth of the mycelium， and the optimum carbon-nitrogen ratio was 23∶1. Whether the carbon-nitrogen ratio is appropriate will directly affect the growth time and yield of D. rubrovolvata. The suitable carbon-nitrogen ratio of the bacterial culture material is （20-25）∶1， and the suitable carbon-nitrogen ratio of the culture material is （60-70）∶1. If the nitrogen source is too low， the yield will be affected. If the nitrogen source is too high， the mycelium will grow excessively， which will affect the differentiation of primordia and lead to the reduction of fruiting[14].

Hao[15] optimized the liquid submerged culture system of D. rubrovolvata， and determined that the optimum carbon source， nitrogen source and inorganic salt were sucrose， corn meal and magnesium sulfate through a single factor experiment. Increasing the amount of inoculum within a certain concentration range can reduce the volume of mycelial balls and increase the number of mycelial balls. Liu et al.[16] also optimized the fermentation conditions and formulations of the liquid strains of D. rubrovolvata， and the results show that the most easily absorbed carbon sources during the liquid fermentation of D. rubrovolvata were wheat flour and corn flour， while sodium cellulose， galactose， and pine needles were poorly absorbed. The most easily absorbed nitrogen sources for the test were peptone and yeast extract， which were weak in urea absorption.

Environmental conditions for mycelium growth

D. rubrovolvata is a typical mesophilic aerobic bacterium. The growth temperature of mycelium is 5-35 ℃. When temperature is higher than 35 ℃ or lower than 5 ℃， the mycelium stops growing. The suitable growth temperature of mycelium is 20-25 ℃， and the optimum growth temperature is 25 ℃. The suitable growth temperature of the fruiting body is 18-24 ℃， and the optimum growth temperature is 22 ℃. If temperature exceeds 28 ℃， the fruiting body grows slowly and weakly; it stops growing when it is higher than 35 ℃[17]. In the growth stage of mycelium， the water content of the mother culture medium is 100%-340%， and the most suitable content is 220%. The water content of the original and cultivated species medium is 60%-70%， and the optimum air humidity is 81%[7]. The suitable air humidity in the primordium formation stage is 85%-95%， and the air humidity in the growth and development stage of the fruiting body  is 75%-85%[14]. The study of Gong Guanglu et al.[13] show that D. rubrovolvata could grow well in a slightly acidic environment， and the suitable pH for mycelium growth was 5.5-6.5; when the pH was lower than 4.5， the mycelium was difficult to germinate or even die; as the pH was 10， the mycelium could also germinate， but it was easy to kink into mycelium bundles; the optimum pH for mycelial growth was 6.0， and the germination time and growth rate were the maximum， up to 1.7 d and 0.94 mm/d， respectively. They also compared the growth of D. rubrovolvata mycelium under full light， full darkness， and natural light sources， and found that the germination time （0.23 d） and growth rate （0.78 mm/d） of mycelium under full darkness were significantly faster than the germination time （7.67 d） and the growth rate （0.40 mm/d） of mycelium under full light conditions， indicating that the growth of D. rubrovolvata mycelium did not require light， and light will inhibit its growth. When light intensity is above 3 000 lx， the mycelium is easy to age and turns pink， and a certain amount of scattered light is required in the primordium growth and development stage. D. rubrovolvata is an aerobic bacteria and has a high demand for oxygen. Therefore， attention should be paid to ventilation during the cultivation process. The suitable CO2 concentration for mycelium growth is 0.03%-0.33% （w/w， mass percentage）， and the most concentration is 0.13%[10].

Analysis of Nutritional Chemical Composition

D. rubrovolvata has a unique flavor， crisp and tender. Zou et al.[18] isolated and identified 108 volatile substances from the extracts of D. rubrovolvata， including aldehydes， ketones， alcohols， phenols， esters， acids， hydrocarbons， and heterocycles. It is speculated that aldehydes， ketones， alcohols and heterocycles are the main contributors to the aroma of D. rubrovolvata， and these substances give it unique flavor. Hang et al.[19] identified 82 volatile constituents in D. rubrovolvata， including 11 aldehydes， 10 ketones， 6 alcohols， 2 hydroxybenzenes， 9 esters， 19 acids， 14 hydrocarbons and 11 other compounds by gas chromatography-mass spectrometry. Liang[20] also identified a total of 91 and 96 volatile substances from various parts of the fruiting body and embryo of D. rubrovolvata， among which the relative content of alcohols was relatively high， ranging from 23.15% to 46.73%; compared with the fruiting body， the volatile substances in various parts of embryo were more abundant， so the flavor of embryo was better.

D. rubrovolvata is not only fragrant and delicious， but also has high nutritional value. Rao et al.[21] determined the nutrient components of D. rubrovolvata， and the results show that its water content was 89.86%， and the total amount of free amino acids per 100 g of fresh product was 308.780 mg. Among them， the content of glutamic acid was the highest， up to 133.576 mg， and the content of glycine was the lowest， only 1.462 mg， while the content of alanine was 29.598 mg. The contents of other components such as soluble protein， flavonoids， vitamin C， and total sugar were 181.05， 22.5， 106.77， and 285.59 mg/100 g， respectively. Liang et al.[22] studied the nutrient components of various parts of the fruiting body and embryo of D. rubrovolvata， and found that the nutritional components of the fruiting body and embryo were significantly different， with low fat （0.40%-1.52%） and high protein （13.89%-27.66%）. In the fruiting body， the content of polyphenols， flavonoids and vitamin B2 in the volva was the highest， up to 2.43 mg GAE/g， 1.95 mg/g and 1.04 μg/g， respectively; the content of triterpenes in the indusium （stip） was the highest， up to 6.59 g/100 g; the content of protein in the pileus was the highest， which was 27.66 g/100 g; the content of polysaccharide in the pileus and volva were 14.19 and 11.48 g/100 g， respectively. Among the three parts of the embryo， the content of polysaccharide in the indusium （stip） was the highest （21.47 g/100 g）， and the other components were most abundant in the volva; the content of polysaccharide in the three parts of the embryo was higher than the corresponding parts of the fruiting body. In the various parts of the fruit-body and embryo of D. rubrovolvata， there were complete amino acid species， and the total free amino acid content was 5.13-18.18 mg/g. The content of glutamic acid was the highest， up to 1.34-4.86 mg/g. The contents of polysaccharide and vitamin B2 in the embryo were 2.06 and 1.25 times that of the fruit-body respectively， and the differences in the other ingredients were small， indicating that the embryo had higher edible value than the fruiting body.

The volva of D. rubrovolvata is a high-quality protein resource. The content of crude protein in dry products is 26.74%， of which true protein accounts for 91.14% of the crude protein; the content of albumin is significantly higher than other edible fungi， accounting for about 69.52% of the crude protein; the content of essential amino acids is high， and the score of amino acid is 105[23]. Moreover， the content of protein in the volva of D. rubrovolvata （26.74%） is much higher than that of the pileus （15.55%）， and albumin had the highest content in the volva and pileus， accounting for 69.52% and 27.91% of the total protein， respectively[24]. However， when eating the fruiting body， we usually only take the pileus， stipe， and indusium， and the nutrition of the volva cannot be utilized at all， and the loss rate of nutrients is 16.41%-38.93%[20]. Therefore， the waste volva has high potential utilization value and can be developed and utilized as high-quality plant alkali protein resources. In addition， D. rubrovolvata is also rich in various mineral elements， such as K， Fe， Mg， Ca， Na， Mn， Zn， Cu， Cd， Se， Cr， As， Pb and Hg， etc. The types of inorganic elements contained in the stipe and indusium， pileus， and volva are similar， but the contents are different. Sun et al.[25] found that the content of Se， K and Cd in the stipe and indusium of D. rubrovolvata was the highest， and the content of other elements was the highest in the volva. Among them， the content of elements Fe and Se was very rich， and the content of Se far exceeded the local standard of selenium-rich agricultural products （0.15-1.00 mg/kg）. Se is a recognized anti-cancer trace element. The content of Se in the three parts of D. rubrovolvata was 1.21-1.90 mg/kg， indicating that D. rubrovolvata had a strong enrichment effect on Se. However， it is worth noting that in this study， except for the content of Hg， the content of other heavy metal elements Pb， Cd， As and Cr exceeded the standard， and the content of Cd even was 16 times of the limit standard. It shows that it also had a strong ability to enrich heavy metals， which may be related to the contamination of soil samples by heavy metals. Therefore， the content of heavy metals in the cultivation environment must be strictly controlled during the cultivation of D. rubrovolvata. Li et al.[26] also pointed out that macroelements K and Mg are rich in D. rubrovolvata， followed by the content of Ca and Na; the enrichment ability of different mineral elements was different， and it had a strong enrichment ability for Se and K. In the future， the selenium-rich products of D. rubrovolvata can be developed and utilized to improve their market competitiveness.

Extraction and Functions of Polysaccharide

Extraction methods of polysaccharide

Edible fungus polysaccharide is an important biologically active substance， which has the functions of enhancing immunity， anti-tumor， anti-oxidation， lowering blood sugar， lowering blood lipid and slowing down aging. It has become a hot spot in the field of edible fungi research. The content of polysaccharide in D. rubrovolvata is relatively high， and polysaccharide is mainly composed of galactose， glucose， mannose and xylose[27-29]. The extraction methods and functions of polysaccharide have been reported.

The main methods of extracting polysaccharide from D. rubrovolvata are water extraction and alcohol precipitation， ultrasonic-assisted method and compound enzyme method. Zhuang et al.[28] found that the optimal conditions for the hot water extraction of polysaccharide from the pileus of D. rubrovolvata are as follows： the ratio of solid to liquid is 1∶25 （g∶ml）， extraction temperature 85 ℃， and the extraction time 2.5 h. Under this condition， the polysaccharide yield was 8.25%. Xu[30] found that the material-liquid ratio of 1∶20 （g∶ml）， the temperature of 90 ℃， the extraction time of 2 h， and the ethanol concentration of 70% were the best conditions for the extraction of polysaccharide by water extraction and alcohol precipitation from D. rubrovolvata. Under this condition， the content of polysaccharide was 8.25% in thepileus， 8.97% in the stipe， and 10.89% in the volva， and all had antioxidant activity， among which the volva polysaccharide had the strongest antioxidant activity in vitro. Zhang et al.[31] optimized the extraction process of polysaccharide from D. rubrovolvata by response surface method， and the optimal conditions were obtained as follows： the ratio of solid to liquid was 1∶31， and the extraction temperature was 75 ℃; the extraction time was 3.5 h， and the extraction was performed twice. The extraction rate can reach 12.05%.

Teng et al.[32] used the ultrasonic-assisted method to extract polysaccharide from D. rubrovolvata， and the optimal extraction process parameters are as follows： the solid-liquid ratio was 1∶20 （g∶ml）; the ultrasonic power was 480 W， and the ultrasonic time was 35 min; the extraction was performed twice. The extraction rate of polysaccharide was （14.55±0.16）%， and polysaccharide content was （60.33±1.53）%. The purity of polysaccharide was effectively improved by membrane separation technology. Gong et al.[33] optimized the ultrasonic detection process of total sugar in the mycelium of D. rubrovolvata by response surface method， and the results show that when the solid-liquid ratio was 11∶1 （g∶ml）， the amplitude was 41%， the ultrasonic treatment was performed for 22 min， and the ultrasonic opening time was 2.7 s， the extraction rate was 1.18%.

Ye[34] also used the compound enzyme method to extract the water-soluble polysaccharide from D. rubrovolvata， and the optimal extraction conditions were optimized as follows： the enzyme concentration was 1.5%， pH=4.5， and enzymatic hydrolysis was conducted for 120 min at 50 ℃; the extraction rate was 7.98%. In addition， she also compared different methods for deproteinization of D. rubrovolvata， and the results show that the papain method had the best effect， and the optimal deproteinization conditions are as follows： papain concentration 4%， enzymatic hydrolysis temperature 55 ℃， enzymatic hydrolysis time 3 h， and enzymatic hydrolysis pH 6.0. Under these conditions， the removal rate of protein was 77.97%， and the loss rate of polysaccharide was 19.31%[35].

It can be seen that the extraction rate of polysaccharide from D. rubrovolvata is the highest by the ultrasonic-assisted method; the papain method for deproteinization has high protein removal rate and low polysaccharide loss rate. This method is simple in process and low in cost， and is worthy of popularization and application.

Functions of active ingredients

The polysaccharide of D. rubrovolvata also has many functions， and it is its main active ingredient. Studies have shown that the polysaccharide of D. rubrovolvata has strong antioxidant activity. Ye[36] found that the polysaccharide of D. rubrovolvata had a strong scavenging effect on hydroxyl radicals and superoxide anion radicals， and IC50 values were 0.51 and 0.83 mg/ml， respectively， indicating that it had obvious antioxidant activity in vitro. Wang et al.[37] also pointed out that the polysaccharide of D. rubrovolvata had a scavenging effect on DPPH free radicals， hydroxyl free radicals and superoxide anion free radicals， and the half scavenging rate （EC50） was 1.468， 2.580 and 2.330， respectively; oxidative activity was slightly stronger than BHT， but its scavenging ability was not as strong as that of Vc. Cai et al.[38] also developed a compound polysaccharide beverage made from D. rubrovolvata， and the optimal formula is as follows： the polysaccharide of D. rubrovolvata 2 mg/ml， the polysaccharide of Disporum cantoniense （Lour.） Merr. 12.6 mg/ml， citrus juice 60 ml， sucrose 3%， and citric acid 0.01%. The beverage also had strong antioxidant activity.

In addition， the polysaccharide of D. rubrovolvata also has anti-fatigue， hypoxia tolerance， anti-aging and hypoglycemic effects， but the hypoglycemic effect is not obvious[39-40]. Ye et al. found that the polysaccharide of D. rubrovolvata could induce the apoptosis of mouse ascites tumor S180 cells， and its stipe aqueous extract could protect the mouse liver from being induced by hydrogen tetrachloride， indicating that it had anti-tumor and liver protection effects[41-42]. Yan et al.[43] also proved that the polysaccharide of D. rubrovolvata had a protective effect on alcoholic liver injury in rats. Therefore， the polysaccharide of D. rubrovolvata has strong medicinal value and is worthy of further development and utilization.

Cultivation and Pest Control

Cultivation of D. rubrovolvata

Wild D. rubrovolvata grows mostly in the southwest region， and is famous in Zhijin， Guizhou. It likes moderate-to-low temperature climate and acidic soil matrix. It is more common in autumn， and grows singly or in groups on yuba sticks or bamboo roots[44]. D. rubrovolvata can grow in a shady and humid environment. It should be planted in an area with an altitude of 500-1 000 m. High-altitude areas has good ventilation， cool climate in summer， large fog and high relative humidity， which can avoid the damage to mycelium and fruiting body in high-temperature and dry season. In low-altitude areas， off-season cultivation should be adopted. In southern areas， it should be cultivated from February to June or September to November. In northern areas， it can be flexibly arranged according to different climatic conditions[45-46].

The raw materials for the cultivation of D. rubrovolvata are widely sourced， such as bamboo stems， bamboo leaves， bamboo stalks and bamboo chips， most broad-leaved trees， as well as various crop straws， wheat bran， rice bran， etc. Among them， the cultivation effect of the mixture of broad-leaved trees and bamboo branches and leaves is better. In the cultivation and production of D. rubrovolvata in Guizhou， the most outstanding variety is Zhijin D. rubrovolvata No. 1， also known as "Jinsun No. 1".

The current cultivation mainly uses solid strains， and the seed production cycle is long. It takes more than half a year from the mother strain to the cultivar. The production of the mother strain takes 20-30 d， and the production of the original strain takes 30-80 d， while that of the cultivar needs 70-90 d; it takes 50-80 d from sowing to germinative growth， and the embryo becomes mature after 30-36 d[45，47-48]. The use of liquid strains can significantly shorten the strain production cycle， with consistent bacterial age and high strain activity. It takes 15-25 d for the first-level liquid strain culture and 7-8 d for the second-level liquid strain cultute[49]. However， the preparation of liquid strains requires high technical means， and the requirements for instruments and the environment are relatively strict， otherwise it is easy to contaminate them and cause heavy losses， so it needs to be continuously explored and improved.

There are various cultivation methods of D. rubrovolvata. In the early days， spore liquid was used for direct cultivation. For isntance， Ji et al.[47] washed the spores with water to make a suspension， and sprayed it in the bamboo forest to make it grow naturally; the fruit body can be harvested in the second or third year， and they also used indoor box planting and outdoor furrow planting with success. Then Lu[50] adopted segment wood and indoor substitute material cultivation， and also successfully harvested fruiting bodies. In general， it can be divided into fermented raw meal cultivation and clinker cultivation according to cultivation materials， bag， frame， pot and casserole cultivation according to the carrier[51-52]， indoor field cultivation， indoor shelf-type three-dimensional cultivation， shade field cultivation， and wild field cultivation under forest according to cultivation sites[48，53-54]. At present， bacteria stick field cultivation and layered three-dimensional cultivation in production.

The cultivation process mainly includes strain selection and preparation， site selection， cultivation material preparation， sowing， soil covering， fungus management， fruiting management， harvesting and processing， etc. In the cultivation process， the key is to pay attention to the selection of strains， the selection of sites， humidity management， ventilation， and pest control. First of all， it is necessary to choose strains with a strong mycelium and a slightly purple-red surface， and the age is 3-4 months; the mycelium of other parts is white and has no mildew， no yellow water flow， no pollution spots or pests， no drying up， and no detachment[55]. Secondly， the site should have loose and fertile soil， be close to water sources， have convenient irrigation and drainage， short sunshine time， shady and humid space， and acidic soil （pH is around 6.5）[56-57]. The last is scientific management. During the whole management process， temperature should be kept at 20-28 ℃. In the early stage of mycelium development， soil humidity should be controlled at 60%-65%， and air humidity should be 60%-70%. In the middle stage of embryo formation， temperature should be controlled at 22-28 ℃; soil humidity should be kept at 60%-70%， no more than 75%; air humidity should be above 90%. In the later growth and development period of bamboo fungus， temperature should not exceed 28 ℃. When temperature exceeds 28 ℃， water should be sprinkled in time to cool down to avoid burning the embryo. Air relative humidity should be kept at about 80%. If the humidity is too high， mildew and diseases will occur on the embryo. During the whole management process， attention should be paid to ventilation， and light should be kept in a weak state[58-60]. In addition， after opening the umbrella and spreading the skirt， D. rubrovolvata is very easy to self-dissolve. It must be harvested in time to avoid affecting the properties of the product and causing unnecessary losses.

Pest control

The common pests of D. rubrovolvata are mites and slugs. The mites can be sprayed with special acaricides such as 70% Mante 200-time solution or 2.5% Tianwangxing 2 000-time solution. The slugs can be sprayed with fenitrothion or 50% salt water and 5% cresol soap solution in the place where it appears for drip killing[44]. The main environmental diseases are caused by  myxomycete and soot bacteria. The myxomycete disease occurs on the bare soil or covered straw on the bamboo fungus. Initially， it can be sprayed with carbendazim， thiophanate-methyl， bleaching powder or copper sulfate. The soot bacteria disease mainly occurs on the surface of the overlying soil layer， and mainly damages the mycelium of bamboo fungus. In the early stage， phenolic acid or formaldehyde can be sprayed on the diseased place[57]. The compound antibacterial （insect） adhesive prepared by Lian[61] has a certain trapping and killing effect on diseases and insect pests during the cultivation of D. rubrovolvata， which is a supplement to the pest control method.

In addition， the rot disease of fungus eggs is one of the most serious diseases in the cultivation process of D. rubrovolvata. Once it occurs， it cannot be controlled by any pesticide. As a result， fungus eggs will discharge pus and become shriveled and moldy， which will seriously affect the development of D. rubrovolvata industry. Pan et al.[62] found that the disease mainly occurred in the egg formation stage of D. rubrovolvata， and it was the most likely to cause egg disease when the temperature of the mushroom shed exceeded 35 ℃ and the relative air humidity exceeded 85% for more than 8 h. Studies have shown that bacteria and fungi are not the cause of the disease， while high temperature and high humidity are the key to inducing the rotten skin of the egg. In a high-temperature and high-humidity environment， the eggs are damaged， with loe immune function， and the bacteria take the opportunity to infect them， so that rot plaques appear[63]. Later， due to fungal infection， secondary diseases are caused， which is the key reason for the occurrence of rot disease[64]. Through separation， purification and identification， Li et al.[65] found that in the later stage of the rot disease of D. rubrovolvata， the secondary disease was mainly caused by the infection of Trichoderma fungi， which was also the main reason for the large-scale production reduction or no harvest of D. rubrovolvata after the occurrence of the rot disease. Chen et al.[66] also proposed that the causative bacterium of the rot disease of D. rubrovolvata was Trichoderma koningiopsis， which was validated by Koch's Law， and this is the first report in the world. Therefore， it is necessary to avoid long-term high temperature and high humidity to reduce the occurrence of rot disease， and keep the environment clean to reduce the growth of Trichoderma in the surrounding environment and the secondary damage in the later stage of the rot disease.

Outlook

In recent years， the research on D. rubrovolvata has gradually become popular. More and more farmers have begun to cultivate D. rubrovolvata especially as a characteristic edible fungus in Guizhou. Many researchers have studied its basic biological characteristics， cultivation characteristics， nutritional components， active ingredients and functions， diseases and insect pests and new varieties of breeding， and have achieved good results. At the same time， there are some difficulties and restrictive factors， which restricts the development of D. rubrovolvata industry.

First of all， the mycelium of D. rubrovolvata grows very slowly， and it takes more than a month to cultivate the mother strain alone. In addition to the production of the original strain and cultivated strain， the entire strain production cycle will take more than half a year， which greatly increases the cost of cultivation. Therefore， it is urgent to optimize its medium and find an optimal formula to promote the rapid growth of the mycelium of D. rubrovolvata. Secondly， the cultivation of D. rubrovolvata mainly uses solid strains， which leads to problems such as low survival rate of strains， slow growth of mycelium， and long bacterial age. The growth cycle of solid strains is long， which often leads to the fact that the lower mycelium is not full but the upper mycelium has aged and cannot be used. Liquid strains can greatly shorten the production cycle of strains， and reduce production costs. Moreover， the growth and development and bacterial age of liquid strains are consistent， so the harvest time of the fruit body is more concentrated， which is convenient for unified management and processing. At present， the cultivation technology of liquid strains of D. rubrovolvata needs to be improved further. In addition， in the breeding of D. rubrovolvata strains， it is mainly to carry out selective breeding， namely obtaining excellent strains by comparing and screening mycelial growth characteristics， stress resistance， disease resistance， agronomic traits or other excellent traits， etc. However， hybrid breeding has not been reported yet. Hybrid breeding can well retain the excellent traits of the parents and is also an important way to obtain excellent strains. Finally， there is a lack of research on the mating system， life history， and genetic information of D. rubrovolvata. Strengthening basic research can promote the prosperity and development of D. rubrovolvata industry.

The artificial cultivation of D. rubrovolvata has started in the 1980s， while research in other aspects has basically started in the 21 century， and has only attracted much attention in recent years. Its development has gone through a long period of time， and some progress has been made. Generally speaking， the basic research is still relatively weak， and there is a lot of research on industrial cultivation， but a relatively standardized cultivation method has not been formulated. Although large-scale artificial cultivation can be conducted currently， the management technology is not mature enough. In this paper， expansion research and innovative research are conducted on the basis of the predecessors， so as to promote the faster and better development of D. rubrovolvata industry.

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