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Article

Evaluation of Corn Stalk as a Substrate to Cultivate King Oyster Mushroom (Pleurotus eryngii)

by
Yuanyuan Zhou
,
Zihao Li
,
Congtao Xu
,
Jinlong Pan
,
Haijun Zhang
,
Qingxiu Hu
and
Yajie Zou
*
Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China
*
Author to whom correspondence should be addressed.
Horticulturae 2023, 9(3), 319; https://doi.org/10.3390/horticulturae9030319
Submission received: 27 January 2023 / Revised: 23 February 2023 / Accepted: 23 February 2023 / Published: 1 March 2023
(This article belongs to the Section Vegetable Production Systems)
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Abstract

:
Corn is widely planted in China, but corn stalks have not been adequately utilized for a long time. Here, the potential of corn stalks to serve as an ingredient in the composition of substrates to cultivate king oyster mushroom (Pleurotus eryngii) was studied. Corn stalks were added to the matrix at a ratio of 10.5%, 21%, or 42% to replace sawdust or sugarcane bagasse in the typical matrix. Analysis of the mycelia growth rate, production days, agronomic traits, and nutrient content confirmed the feasibility of using corn stalk instead of sawdust and bagasse for the cultivation of P. eryngii. The samples grown on Y5 (without sawdust and bagasse) has more crude fiber (8.3%) and polysaccharide (5.05%) content compared to those of the control substrate (7.1% and 4.16%, respectively), moreover, it also conteined more zinc and calcium than others. Therefore, these findings indicate that corn stalks could be used as an alternative to sawdust and sugarcane bagasse for P. eryngii production, which would not only reduce costs and improve food quality, but also improve waste utilisation.

1. Introduction

Major quantities of agricultural byproducts are produced yearly in China. Corn stalk from corn used for human consumption is the most abundant of these byproducts, and approximately 2.64 × 108 t/year are produced [1]. Data from the National Bureau of Statistics of China indicated that 26,077.89 million tons of corn were produced in 2019, which indicated that there were 31,293.468 million tons of dry corn stalks. However, most of these stalks are burned in the field or discarded, which ends up producing excessive amounts of air pollutants, including greenhouse gases [2]. The efficient and comprehensive utilization of corn stalks is a serious concern. Crop residues are commonly utilized as animal feed [3], but the demand has not exceeded the supply. The primary components of corn stalks are similar to those of wood in that they contain hemicellulose, lignin, and cellulose, which render them similar to wood; they serve as nutrients that edible fungi require for cultivation [4]. Edible fungi that have been cultivated on corn stalks include maitake (Grifola frondosa), shiitake (Lentinula edodes), and oyster mushroom (Pleurotus sajor-caju) [5,6,7,8,9,10]. The application of corn stalks to cultivate edible fungi will improve the utilisation of waste, and reduce environmental pollution.
King oyster mushroom (P. eryngii) is both medicinal and edible, and is widespread in central Europe, the Mediterranean, North Africa, and Central Asia [11]. Originally, this species was cultivated in Switzerland and Northern Italy where it is known as cardoncello [12]. It is a highly nutritive, low-calorie food with high-quality proteins, vitamins, and minerals, and this fungus can be used as an important natural source of food and medicine [8,13,14]. The China Edible Fungi Association estimated that 2.05 × 106 tons of P. eryngii were grown in the country in 2021. Consumers are increasingly recognizing it as a functional food due to its bioactive components with potential health promoting effects [15]. Since P. eryngii is in such high demand, it is likely that there will be a continued increase in the commercial production of this fungus.
Lignocellulosic wastes offer an inexpensive organic recycling process that facilitates the cultivation of mushrooms [16]. Recently, a wide variety of substrates have been used to cultivate P. eryngii of which cotton seed hulls, sawdust, soybean meal, and wheat bran [17], sugarcane bagasse [18], chopped rice straw [19], umbrella plant (Cyperus alternifolius) [12], rice husks, wheat straw, peanut meal, sawdust and rice straw [18], corn cobs, sugar beet pulp, and barley straw [20], and other materials [20,21,22]. In China, the main components of the cultivation material for P. eryngii are sawdust and sugarcane bagasse, the rest being cottonseed hulls, corn flour, etc [23,24]. Moreover, sawdust is also the principal substrate for the cultivation of L. edodes and Auricularia auricula. Thus, there is an urgent need to encourage the widespread use of agricultural waste to rapidly develop the industry of cultivating P. eryngii. The wood sawdust resources are restricted by the forest protection policy, and the “contradiction between fungi and forests” is prominent, which has become an important bottleneck that affects the industrial benefits and restricts the sustainable development of this industry. Therefore, it is urgent to develop agricultural and forestry waste resources to replace the traditional cultivation raw materials. However, the chosen raw materials shall be evaluated for their potentially toxic elements bioaccumulation and their possible risk on human health [25].
There is a need to develop and optimize a detailed formula for the substrate of king oyster mushroom to facilitate its practical production on an industrial scale. The aim of this study to was to evaluate corn stalks as potential substrate materials to achieve maximal growth and therefore, high yields of P. eryngii. Moreover, this study also estimated the influence of substrates on the accumulation of mineral elements, which should improve the nutritional composition of P. eryngii fruiting bodies. The results of this study promote the concept of recycling corn stalks, so they can serve as a useful resource to cultivate king oyster mushrooms, while also serving as a favorable alternative to mushroom factories that enable an increase in the production of mushrooms and the subsequent income of growers.

2. Materials and Methods

2.1. Inoculum Source and Spawn Preparation

Pleurotus eryngii strain CCMSSC 003898 was used in this experiment and was obtained from the China Center for Mushroom Spawn Standards and the Control, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences (Beijing, China). The mycelia were grown on potato dextrose agar (PDA, 200 g potato, 20 g dextrose, 24 g agar, and 1 L water). They were grown in the dark at 25 °C in an incubator until most of the plate surfaces were covered with mycelia.

2.2. Substrate Preparation

Broad-leaved wood branches were sourced from Yanqing, Beijing. Sugarcane bagasse was purchased from sugar mills, and the other materials were purchased from a local market. All the materials were less than 0.5 cm in size, so they could be packed into polypropylene bags (17 cm × 35 cm) (Figure S1). Table 1 shows the substrates that were used in this research. CK was added with 21% sawdust and sugarcane bagasse [26,27], Y1 was added with 10.5% sawdust and corn stalks and 21% sugarcane bagasse, Y2 was added with 21% sawdust and 10.5% corn stalks and sugarcane bagasse, Y3 was added with 21% corn stalks and sugarcane bagasse, Y4 was added with 21% corn stalks and sawdust, Y5 was added with 42% corn stalks. All the treatments contained 4.2% of cottonseed hull, 18.4% of ground corncobs, 18.4% of wheat bran, 6.8% of maize powder, 8.4% of soybean meal, 0.8% of calcium hydroxide, and 1% of gypsum. These ingredients were thoroughly dry mixed and then with 65% tap water [28]. The final moisture content was determined by oven-drying the substrate thrice. A total of 1 kg of moistened substrate was placed in polypropylene bags that were 17 cm wide and 35 cm long. Each bag contained 350 g dry weight of substrate, and each treatment had 50 replicates. To inoculate the spawn and provide aeration, each bag had a single vertical hole in its center that was 2 cm in diameter and 18 cm deep. The bags were sealed with vent caps and plastic rings and then autoclaved for 120 min at 121 °C. The sawdust was composted for 6 months in the open air, so that it was weathered before being incorporated. All other ingredients were not pretreated before being added to the substrate. The loss of ignition and Kjeldahl method were used to estimate the contents of carbon (C) and nitrogen (N), respectively. The C:N ratio was established for each substrate as previously described [11].

2.3. Assay for the Growth Rate

The mycelial growth rate were determined on all the combination of substrate using linear growth methods as previously described [29,30]. Each combination of substrate was placed separately in glass tubes that were 320 mm long and 30 mm in diameter with densities of approximately 0.8 g cm−3. A mycelial disk that was 5 mm in diameter was used to inoculate the samples by placing it on top of the tube. Sterile rubber plugs were then used to block the tubes, which were incubated at 25 ± 1 °C. 7, 12, 17, 24 and 31 days after inoculation, respectively, the length of mycelial spread and the growth rate were calculated. The speed at which the mycelial growth extended was assessed by the observed spawn running times (the days for mycelial growth to fill the substrate), which was calculated over the entire growth period with no correction for the length of the lag period. This experiment was assessed in five replicates for each substrate group.

2.4. Spawning and Fruiting Bodies

P. eryngii was cultivated as described by Zhang [30] with minor modifications. The spawn sticks were prepared for the inoculation using polypropylene bags with dimensions of 15 cm × 30 cm × 0.04 cm. The sticks, which were prepared from broadleaf tree wood, were 15 cm long, 0.42 cm thick, and 0.7 cm wide with rough surfaces. The sticks were soaked in 2% calcium hydroxide for 48–72 h until they were completely moistened, and the excess moisture from the sticks was drained. The sticks were coated in a mixture of wheat bran (50%) and maize powder (50%). The sticks were then placed in bags parallel to each other, and the gaps among the sticks were filled with the control described in Section 2.2. The stick spawn were then inoculated into sterilized cultivation bags. The samples were grown for 30–35 d at 24 ± 1 °C in darkness and 60% relative humidity until it was totally covered with mycelia. Cultivation was continued for 5–7 days under the same conditions for the mycelia to physiologically mature. The next step was to transfer the fungi to a mushroom chamber to grow adaptively for 2 d. The conditions of chamber were 20 ± 2 °C and 70–80% relative humidity, and a concentration of CO2 was established as 500–1000 ppm. Afterwards, the mushroom chamber was established of 11–14 °C and a 12 h white light/dark photoperiod at 1500–2000 lux. The relative humidity was approximately 90%, and a CO2 concentration of 1000–2000 ppm was used to induce the differentiation of primordia and the development of fruiting bodies. When the mushrooms were in the young stages, the growth of stipes was promoted by adjusting the conditions to 10–13 °C with a CO2 concentration at 7000–8000 ppm. The agronomic traits of the fruiting bodies were determined using a slide caliper. The diameter and length of the stipe and the diameter of the pileus were measured. One flush of fruiting bodies was generated, harvested, and measured, which was consistent with the commercial cultivation practices for king oyster mushrooms in China. The fructification lasted for 18–20 days. After removing the extreme values, 30 replicates were obtained by weighing the fresh yields of fruiting bodies. The fresh yield of fruiting bodies was divided by the primary dry substrate in each bag to calculate the percentage of biological efficiency (BE) [17].

2.5. Compositional Analysis

Once the fruiting bodies were harvested, different samples were dried to a constant weight at 60 °C in an oven and sealed for storage. The total proteins (%), ash (%), and fats (%) were measured using this powder as previously described [31,32,33,34]. The total soluble sugar content was determined using the sulfuric acid-anthrone colorimetric method [35]. The macro Kjeldahl method was used to measure the crude protein content (N × 4.38) of the mushrooms [36]. Soxhlet extraction (GB5009.6) was used to determine the crude content of fat. The standard procedure GB5009 was used to analyze the content of mineral elements in the fruit bodies, and GB5009.4 was used to measure their ash content. The PONY Testing International Group (Beijing, China) conducted all the test analyses.

2.6. Statistical Analysis

The original data were processed using Microsoft Excel 2021 (Redmond, WA, USA). Differences among the means of groups were assessed using Duncan’s multiple range tests at a 95% confidence level (p < 0.05). SPSS 19.0 (IBM, Inc., Armonk, NY, USA) was used to conduct the statistical analyses and correlation analysis. ChiPlot (https://www.chiplot.online/ accessed on 20 November 2022) was used for heat mapping.

3. Results

3.1. Composition of Corn Stalks

Table 2 shows the composition of holocellulose, including hemicellulose, lignin, and cellulose, of the substrate materials that were used in this study and those reported from previous research [34,35]. The corn stalks had a high content of hemicellulose, with 28.10% cellulose, 34.20% hemicellulose and 21.70% lignin, confirming that its chemical composition is an ideal carbon source to produce Pleurotus [20]. Compared to wood chips, corn straw had a lower cellulose and hemicellulose content (42.12% and 34.55%), while compared to sugarcane bagasse it has a lower cellulose content (36.87%) and a higher hemicellulose content (27.58%). The lignin of corn stalks was higher than that of sawdust and sugarcane bagasse (15.12% and 14.90%, respectively). However, it was estimated that the C:N in the formula (CK, Y1, Y2, Y3, Y4, and Y5) was 21.04:1, 20.68:1, 18.64:1, 20.78:1, 19.95:1 and 19.82:1, respectively.

3.2. Mycelia Growth Rate

The duration of mycelial growth varied significantly under the different treatments as shown in Table 3. The mycelial growth rates of P. eryngii when grown on Y2 and Y1 were 4.34 ± 0.30 mm d−1 and 4.03 ± 0.28 mm d−1, respectively, which were higher than that of the CK, while the growth rate of mycelia when grown on Y3 and Y4 were 3.81 ± 0.15 mm d−1 and 3.67 ± 0.26 mm d−1, respectively, which was slower than that of the traditional culture medium CK. In addition, growth rate of P. eryngii mycelia on Y5 was 3.08 ± 0.14 mm d−1, significantly lower than that of the CK.

3.3. The Morphology and Fruiting Characteristics of P. eryngii

Table 4 shows the morphology and characteristics of the P. eryngii fruiting body grown on different substrates. The days to production of fruiting from Y1, Y2 and Y5 were 21.3, 20.9 and 21.4 days, respectively. The difference with CK (21.0 d) was not significant, but under the conditions of Y3 and Y4, the days to production were 25.5 and 25.6 days, respectively, which were longer than that of the CK. The fruiting body yields of Y1, Y2, Y3 and Y5 were 273.1 ± 42.9 g/bag, 275.5 ± 32.7 g/bag, 270.9 ± 49.9 g/bag, and 265.8 ± 38.5 g/bag, respectively, which did not differ significantly from the traditional substrates of the CK group (275.0 ± 32.8 g/bag). However, Y4 (239.4 ± 39.6 g/bag) was significantly different from the CK group. The biological efficiency (BE) of different substrates ranged from 68.4% to 78.71% (Table 4). Y4 was the only treatment in which the biological efficiency differed significantly from the control group, which owing the lowest BE. The weight of fruiting bodies and BE of the other treatment groups was not significantly different from that of the control group (p > 0.05).
As shown in Figure 1, the morphological characteristics of the king oyster mushroom fruiting bodies grown on Y4 differed significantly from those of the other samples evaluated and was the shortest criterion among all the treatments, which is The ash consistent with the findings of Table 4. The length of fruiting bodies and stipe thickness in the Y1, Y2, Y3 and Y5 treatments were not significantly different compared to CK, but the standard deviations of the results from substrates CK and Y2 were basically the same, while those of Y4 were significantly different compared to CK. The pileus diameters of the Y1, Y4 and Y5 were significantly different compared to CK, but those of Y3 and CK were basically the same. However, this parameter of Y2 was not significantly different compared with the other samples that were evaluated. Findings from the morphological characteristics are directly related to the yield outcome.

3.4. Nutrient Content of the Mushrooms

As shown in Table 5, the nutritional elements in P. eryngii cultured on different substrates varied significantly. The samples grown on CK and 42% corn stalks substrates (Y5) had comparable protein contents, the protein contents of the samples grown on Y2, Y1, Y3 in turn reduced and the protein contents of the mushrooms grown on Y4 were slightly lower than those of CK. Samples grown on substrate Y1 (10.5% corn stalk replaced 10.5% sawdust) had higher fat content and lower levels of crude polysaccharides and ash compared to the control group. The samples which were grown on CK had the highest ash content and then the ash contents of the mushrooms reduced when they were grown on Y5, Y2, Y1, Y3 and Y4 in turn. The contents of crude fiber and polysaccharide were the highest (8.3% and 5.05%, respectively) in the samples grown on substrate Y5 (42% corn stalks substrate that lacked sawdust and sugarcane bagasse). It increased by 16.9% and 21.4% compared to those of the control substrate, respectively (7.1% and 4.16%). The fiber content of the samples grown on the Y2 and Y4 were not significantly different, but the samples on Y2 medium contained two-fold as much polysaccharide as Y4.

3.5. The Mineral Composition of Mushrooms

The evaluation of mushroom fruiting bodies for important minerals is shown in Table 6. There was significant variation in the contents of minerals analyzed in the dried mushroom cultivated on the various treatments. The macronutrient elements analysis showed that there was no significant difference in the Mg, Na, and Ca content between samples cultivated on CK and Y2, however, the samples cultivated on Y5 had the highest Ca content of 110.0 mg kg−1. An analysis of the micronutrient elements showed that fruiting bodies cultivated in Y5 substrates had the highest contents of Zn, Cu and Se, which were significantly different from those of the CK. The fruiting bodies cultivated in Y2 had the highest content of Mn, while the CK had the highest content of Fe. Y2 and Y4 had lower contents of Fe.
The content of heavy metals also been tested to analyze the effect of different substrates on fruiting bodies. The composition of minerals was substantially affected by the different substrates that were used for cultivation. The highest values of copper (Cu), arsenic (As) and cadmium (Cd) were recorded in Y5, while the highest content of lead (Pb) was observed with CK substrate. The selenium (Se) content of fruiting bodies grown on Y3 was the highest. Y4 differed significantly from the other substrates because it resulted in fruiting bodies that had a higher content of mercury (Hg).

4. Discussion

In this study, mycelium growth rates were fastest on Y2 substrates and slowest on Y5 substrates. The quickest mycelial growth of P. eryngii was observed when 10.5% of the corn stalks were replaced with 10.5% sugarcane bagasse. However, with the addition of corn stalks, the mycelial growth rate decreased (Table 3). As shown previously, the growth rate of mycelia correlated with the amount of corn stalks that were supplemented to the substrates used to grow nameko (Pholiota microspore) and L. edodes [4,6]. Therefore, addition of corn stalks within a certain range may have some impact on the growth of mycelia, increase the BE, and shorten the fruiting time of P. eryngii. This study suggests that corn stalks had the largest effect on the mycelial growth rate, which could be consistent with the results of previous research.
In this study, three types of common agricultural residues, including sawdust, sugarcane bagasse, and corn stalks, were used as the primary ingredients. The mushroom species vary in the ideal optimal C:N ratio required for the growth of mycelia and the highest yield [36,37]. Therefore, regulating the C:N ratio in composting similar to that of the control was established in all the treatments, which ranged from 18.64 to 21.04 (Figure 2). The optimal C:N ratio of the medium was shown to be between 20–25, and the growth rate of the P. eryngii did not differ significantly within this interval [38]. In contrast, the results of this study showed that Y2 was the most effective and suitable substrate for the highest mycelial growth rate of P. eryngii when its C:N ratio was 20:1. However, fungi grown on Y5 with a C:N ratio of 20:1 reacted oppositely. This could be also related to the physical structure of substrate because medium containing 10% corn stalks is more permeable. Differences in the mycelial growth of the mushroom could not only depend on the C:N ratio but also on the substrates used.
As shown in Table 3, Y1, Y2, Y3, and Y5 with 10.5%, 21%, or 42% corn stalks were comparably productive compared to the conventional formula that was 21% sawdust and 21% sugarcane bagasse. The only exception was that the lowest yield of mushrooms was observed on 21% of corn stalks that replaced 21% sugarcane bagasse. The yield of mushrooms was not associated with the mycelial growth rate in this study. Our results are typically consistent with those of Lechner [36], who showed that the optimal and highest mycelial growth did not result in the highest yields of mushrooms. These data clearly indicate that the yield of mushrooms is strongly affected by the composition of growth substrate, which is consistent with the findings of previous research [37,38].
Except for the fruiting body from Y4, the agronomic traits of the fruiting body on the other media were not significant (Table 4 and Figure 1). The length of fruiting body ranged from 13.0 to 14.9 cm. With the exception of the replacement of 21% corn stalks with 21% sugarcane bagasse, there were no significant differences in the fruiting body lengths and stipe thickness from the treatment groups. A scatter plot of the agronomic characteristics of fruiting bodies showed that the mushrooms grown from CK, Y2 and Y5 were more homogeneous in their traits, while Y1, Y3 and Y4 were more dispersed. Uniformly sized mushrooms are better suited to uniform collection, thus, reducing the costs of labor (Figure 3). The combination of weight, shape, and color are good criteria to use to evaluate mushrooms [39]. The substrates Y1, Y2, Y3, and Y5 have the potential to serve as excellent media to grow P. eryngii. Corn stalks are rich in lignin, which provides a beneficial source of carbon. An additional factor that makes corn stalks desirable substrates to cultivate P. eryngii mushrooms compared with sawdust is that they are much cheaper. In the Chinese market, the price of corn stalk is $59 per ton; sawdust is $118–133, and sugarcane bagasse is $118–133. Thus, Y5 (42% corn stalks replaced with 21% sugarcane bagasse) is not only inexpensive but also an excellent medium to grow P. eryngii for commercial uses.
A large amount of research has shown that many factors affect the content of protein in mushrooms. These include the type of substrate, its physical and biochemical properties, amounts of nutrients added in the substrates, and the types of nutrients [39,40,41]. The protein content of mushrooms found in this study with the use of corn stalks to supplement the substrate was comparable with the findings of earlier studies [35], while it was not significantly different when 42% corn stalks were supplemented as the substrate compared to CK. Mushrooms have digestible dietary fiber and serve as excellent sources of essential food compounds that are valuable for human nutrition, which include prebiotic and positive health effects, such as anti-cholesterol effects, the promotion of gastrointestinal motility, and immunomodulator properties among others [42]. It appeared that compared to CK, supplementation with 42% corn stalks improved the crude fiber and accumulation of polysaccharides in P. eryngii mushrooms. The higher crude fiber and polysaccharide found in P. eryngii grown with 42% corn stalks suggests the use of corn stalks as a new strategy to produce king oyster mushrooms of superior quality to satisfy the demands of consumers.
Studies have shown that in addition to affecting the mycelial growth and substrate production of edible mushrooms, carbon and nitrogen sources and their ratios also affect the production and accumulation of bioactive substances in edible mushrooms [43,44]. Correlation analysis was used to show the effect of the contents of C and N in the substrate on the rate of mycelial growth and the nutritional quality of the substrate. A heatmap (Figure 4) showed that the C and N contents of the substrates positively correlated with the mycelial growth rate, and the C content had a greater effect on the rate of growth than the N content. Additionally, the contents of C and N of the substrates negatively correlated with the fiber content in the substrate, while the C and N contents of the medium had little relationship with the protein, ash, fat, and polysaccharide contents of the substrate. Elemental C has a greater effect on the proteins in the substrates than elemental N. However, the C and N contents of the medium had less effect on the ash, fat, and polysaccharide contents of the substrates.
The major ingredients in the substrates are key factors that affect the mineral spectrum of the fruiting bodies of edible fungi, and there are significant differences in the uptake of individual elements [45]. Mg was the highest one found in the fruiting bodies, followed by Na, Ca, Zn, Se, Fe, Mn, and Cu (Table 6), which is consistent with our previous experiment of cultivating P. eryngii [46]. These elements were found to occur naturally in the substrate materials, and corncob contained higher levels of several minerals compared to sawdust, such as Cu, Ca, Fe, Mg, P, K, Mn, and Zn, but the contents of Na were lower compared with sawdust [47]. In general, the cultivation of selenium-rich edible mushrooms primarily uses the addition of sodium selenite (Na2SeO3), sodium selenate (Na2SeO4) or selenium dioxide (SeO2) to their culture material at appropriate concentrations. Studies have shown that the mycelia and fruiting bodies of P. eryngii are highly effective at enriching, absorbing, and transforming selenium [48,49,50]. This study observed that the application of corn stalks to replace sugarcane bagasse in the substrate improved the ability of mushroom fruiting bodies to uptake Mg and Se from the substrate. Zinc and selenium play an important role in human growth and development, reproductive heredity, immunity, endocrine and other important physiological processes [51,52]. This study showed that corn stalks in the cultivation substrates could be used to produce mushrooms that are rich in selenium.
An abundance of the toxic heavy metals Pb, As, Cd, and Hg in the mushrooms would lead to progressive toxicity [53]. Pb was the highest mineral in the fruiting bodies, followed by As, Cd, and Hg (Table 6). The content of Pb in the mushrooms ranged from 106.7 μg kg−1 (Y5) to 60.7 μg kg−1 (Y3). The Chinese national standard (GB 2762) stipulated standard limits for Pb, and Hg (<0.1 mg kg−1 dw), As and Cd (<0.5 mg kg−1 dw) in the mushrooms. The harmful heavy metals in all the mushroom samples, including As, Cd, Pb, and Hg, were lower than the levels that are recommended by the food safety standard in China. Previous research revealed that the heavy metals tend to accumulate in the fruiting bodies in parallel with the increase in metals in the substrate [54]. It is important to note that if the corn stalk comes from heavy metal contaminated land, its heavy metal content may exceed the standard. Therefore, corn stalk that is free from excessive heavy metal content can be safely used as a material to cultivate P. eryngii, which will not significantly influence the elemental composition of fruiting bodies. In addition, it preserves their excellent characteristics that include their contents of crude fiber and polysaccharide, thereby amplifying the benefits of formulations of corn stalks.

5. Conclusions

This study confirmed the feasibility of using corn stalks as an ingredient to replace different ratios of sawdust and sugarcane bagasse in the substrates to cultivate P. eryngii. The results showed that the yield of mushrooms grown on 42% corn straw substrate was not significantly different from that of CK, but the crude fibre, polysaccharide and mineral contents of the substrates were higher. Therefore, corn stalks can be used in the commercial cultivation of P. eryngii to reduce the supply of sawdust and sugarcane bagasse. Therefore, it is possible to manage the problem of a reduced supply of matrix components and rising prices. These results indicate a practical method that mushroom growers could use to produce a high yield of P. eryngii. In future studies, the influence of culture medium on the growth rate, protein and fiber content of Pleurotus eryngii should be explored.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/horticulturae9030319/s1, Figure S1: Polypropylene bags with moistened substrate.

Author Contributions

Conceptualization, Y.Z. (Yajie Zou) and Q.H.; methodology, Y.Z. (Yajie Zou); software, H.Z.; validation, Y.Z. (Yuanyuan Zhou) and Z.L.; data curation, C.X. and J.P.; writing—original draft preparation, Y.Z. (Yuanyuan Zhou) and J.P.; writing—review and editing, Y.Z. (Yajie Zou); visualization, Y.Z. (Yuanyuan Zhou) and C.X.; supervision and project administration, Y.Z. (Yajie Zou); project administration and funding acquisition, Y.Z. (Yajie Zou) and Q.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the earmarked fund for CARS20.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Morphological characteristics of the fruiting bodies of P. eryngii from mycelia that were grown on different substrates. CK: treatment with 21% sawdust and sugarcane bagasse. Y1: treatment with 10.5% sawdust and corn stalks and 21% sugarcane bagasse. Y2: treatment with 21% sawdust and 10.5% corn stalks and sugarcane bagasse. Y3: treatment with 21% corn stalks and sugarcane bagasse. Y4: treatment with 21% corn stalks and sawdust. Y5: treatment with 42% corn stalks.
Figure 1. Morphological characteristics of the fruiting bodies of P. eryngii from mycelia that were grown on different substrates. CK: treatment with 21% sawdust and sugarcane bagasse. Y1: treatment with 10.5% sawdust and corn stalks and 21% sugarcane bagasse. Y2: treatment with 21% sawdust and 10.5% corn stalks and sugarcane bagasse. Y3: treatment with 21% corn stalks and sugarcane bagasse. Y4: treatment with 21% corn stalks and sawdust. Y5: treatment with 42% corn stalks.
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Figure 2. Effect of different substrates on the C:N rate and mycelial growth rate of P. eryngii.
Figure 2. Effect of different substrates on the C:N rate and mycelial growth rate of P. eryngii.
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Figure 3. Scatter plot of the agronomic characteristics of fruiting bodies. A (cm): Diameter of the pileus, B (cm): Fruiting body length, C (cm): Stipe thickness.
Figure 3. Scatter plot of the agronomic characteristics of fruiting bodies. A (cm): Diameter of the pileus, B (cm): Fruiting body length, C (cm): Stipe thickness.
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Figure 4. The heatmap depicts the relationship between the contents of C and N of the substrate on the nutritional quality of the substrate and the rate of mycelial growth.
Figure 4. The heatmap depicts the relationship between the contents of C and N of the substrate on the nutritional quality of the substrate and the rate of mycelial growth.
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Table
Table 1. Composition of ingredients for the substrates with different inclusion rates for Pleurotus eryngii cultivation * (g 100 g−1 except for the C:N).
Table 1. Composition of ingredients for the substrates with different inclusion rates for Pleurotus eryngii cultivation * (g 100 g−1 except for the C:N).
SubstrateSawdustSugarcane BagasseCorn StalksNCC:N
CK2121-1.7737.1721.04
Y110.52110.51.7836.8220.78
Y22110.510.51.9736.7719.95
Y3-21211.7937.1720.68
Y421-211.8336.4218.64
Y5--421.7334.2519.82
* Dry matter.
Table
Table 2. Analysis of the lignocellulosic waste used to cultivate Pleurotus eryngii.
Table 2. Analysis of the lignocellulosic waste used to cultivate Pleurotus eryngii.
MaterialCellulose (%)Hemicellulose (%)Lignin (%)
Sugarcane bagasse27.5836.8714.90
Sawdust42.1234.5515.12
Corn stalks34.2028.1021.70
Table
Table 3. Physical characteristics of Pleurotus eryngii when cultivated on different substrates # (mean ± SD, n = 5).
Table 3. Physical characteristics of Pleurotus eryngii when cultivated on different substrates # (mean ± SD, n = 5).
Substrate Growth Rate in the Different Times (mm d−1)Growth Rate (mm d−1)
7 d~12 d12 d~17 d17 d~24 d24 d~31 d
CK4.01 bc3.18 b4.60 a3.92 c3.98 ± 0.18 b
Y14.27 ab3.75 a4.21 b3.88 b4.03 ± 0.28 b
Y24.33 a3.93 a4.73 a4.25 a4.34 ± 0.30 a
Y33.85 c3.27 b4.19 b3.80 b3.81 ± 0.15 c
Y43.44 d3.21 b4.17 b3.65 b3.67 ± 0.26 d
Y53.29 d2.85 d3.23 c2.94 b3.08 ± 0.14 e
# Note: Different lowercase letters denote significant differences in each column (p < 005). CK: treatment with 21% sawdust and sugarcane bagasse. Y1: treatment with 10.5% sawdust and corn stalks and 21% sugarcane bagasse. Y2: treatment with 21% sawdust and 10.5% corn stalks and sugarcane bagasse. Y3: treatment with 21% corn stalks and sugarcane bagasse. Y4: treatment with 21% corn stalks and sawdust. Y5: treatment with 42% corn stalks.
Table
Table 4. Productivity parameters of Pleurotus eryngii when cultivated on different substrates # (mean ± SD, n = 30).
Table 4. Productivity parameters of Pleurotus eryngii when cultivated on different substrates # (mean ± SD, n = 30).
SubstrateDays to
Production (d)		Fruit Body
Yield (g/bag)		Biological
Efficiency (%)		Length of Fruit Body (cm)Thickness of
Stipe (cm)		Diameter of Pileus (cm)
CK21.0 ± 1.2 b275.0 ± 32.8 a78.57 ± 9 a14.5 ± 1.1 ab5.3 ± 0.8 ab6.7 ± 0.8 b
Y121.3 ± 1.7 b273.1 ± 42.9 a78.03 ± 12 a14.7 ± 1.8 a5.6 ± 0.8 a7.2 ± 0.8 a
Y220.9 ± 1.4 c275.5 ± 32.7 a78.71 ± 9 a14.5 ± 1.2 ab5.5 ± 0.8 ab7.0 ± 0.8 ab
Y325.5 ± 1.3 a270.9 ± 49.9 a77.17 ± 14 a14.9 ± 1.4 a5.3 ± 0.7 ab6.6 ± 1.1 b
Y425.6 ± 1.2 a239.4 ± 39.6 b68.40 ± 17 b13.0 ± 1.6 c4.6 ± 0.9 c7.3 ± 0.9 a
Y521.4 ± 1.1 b265.8 ± 38.5 a75.94 ± 11 a14.1 ± 1.6 b5.1 ± 0.7 b7.1 ± 1.2 a
# Note: Different lowercase letters denote significant differences in each column (p < 0.05). CK: treatment with 21% sawdust and sugarcane bagasse. Y1: treatment with 10.5% sawdust and corn stalks and 21% sugarcane bagasse. Y2: treatment with 21% sawdust and 10.5% corn stalks and sugarcane bagasse. Y3: treatment with 21% corn stalks and sugarcane bagasse. Y4: treatment with 21% corn stalks and sawdust. Y5: treatment with 42% corn stalks.
Table
Table 5. Nutritional value of Pleurotus eryngii when cultivated on different substrates # (g 100 g−1, mean ± SD, n = 3).
Table 5. Nutritional value of Pleurotus eryngii when cultivated on different substrates # (g 100 g−1, mean ± SD, n = 3).
SubstrateProteinAshFiberFatPolysaccharide
CK20.74 ± 0.17 a6.47 ± 0.03 a7.10 ± 0.09 cd1.07 ± 0.03 d4.16 ± 0.01 b
Y119.06 ± 0.03 c5.62 ± 0.14 d6.71 ± 0.24 d2.14 ± 0.04 a2.40 ± 0.13 e
Y219.76 ± 0.14 b6.00 ± 0.04 c7.72 ± 0.22 b1.02 ± 0.01 e4.10 ± 0.01 c
Y318.30 ± 0.19 d5.14 ± 0.02 e7.05 ± 0.23 cd0.92 ± 0.01 f2.70 ± 0.09 d
Y417.56 ± 0.31 e5.22 ± 0.09 e7.28 ± 0.35 bc1.29 ± 0.01 c2.05 ± 0.04 f
Y520.41 ± 0.17 a6.19 ± 0.06 b8.30 ± 0.27 a1.42 ± 0.04 b5.05 ± 0.21 a
# Note: Different lowercase letters denote significant differences in each row (p < 0.05). CK: treatment with 21% sawdust and sugarcane bagasse. Y1: treatment with 10.5% sawdust and corn stalks and 21% sugarcane bagasse. Y2: treatment with 21% sawdust and 10.5% corn stalks and sugarcane bagasse. Y3: treatment with 21% corn stalks and sugarcane bagasse. Y4: treatment with 21% corn stalks and sawdust. Y5: treatment with 42% corn stalks.
Table
Table 6. Element content in Pleurotus eryngii when grown on different substrates # (mean ± SD, n = 3).
Table 6. Element content in Pleurotus eryngii when grown on different substrates # (mean ± SD, n = 3).
ElementsCKY1Y2Y3Y4Y5
Mg (mg kg−1)Macronutrient elements1020 ± 17 a951 ± 8 b1008 ± 13 a1013 ± 23 a879 ± 27 c1003 ± 22 a
Na (mg kg−1)284.3 ± 8.7 a245.3 ± 5.0 b290.0 ± 4.6 a147.3 ± 4.0 d163.3 ± 6.8 c129.0 ± 3.6 e
Ca (mg kg−1)95.6 ± 2.8 b66.9 ± 2.6 d96.3 ± 2.7 b68.8 ± 3.1 d78.2 ± 3.0 c110.0 ± 4.4 a
Zn (mg kg−1)Micronutrient elements71.3 ± 1.2 b64.9 ± 1.1 c70.3 ± 1.6 b60.8 ± 1.6 d59.9 ± 0.1 d81.9 ± 1.2 a
Fe (mg kg−1)40.1 ± 1.0 a31.4 ± 0.4 d30.2 ± 0.6 de33.5 ± 1.5 c28.5 ± 1.2 e37.3 ± 0.5 b
Mn (mg kg−1)6.59 ± 0.15 b5.78 ± 0.22 c7.04 ± 0.30 a6.12 ± 0.20 c5.96 ± 0.21 c6.92 ± 0.27 ab
Cu (mg kg−1)3.30 ± 0.28 b3.05 ± 0.07 bc3.13 ± 0.09 b2.73 ± 0.17c3.23 ± 0.19 b3.91 ± 0.19 a
Se (μg kg−1)54.3 ± 1.2 bc53.0 ± 2.6 bc55.7 ± 1.5 b68.0 ± 1.0 a52.7 ± 1.5 c66.3 ± 0.6 a
As (μg kg−1)Heavy metals69.1 ± 4.8 d80.1 ± 2.3 c89.4 ± 307 b76.5 ± 5.4 c58.1 ± 4.8 e98.8 ± 2.9 a
Pb (μg kg−1)130.0 ± 10.0 a86.0 ± 4.4 c72.0 ± 3.6 de60.7 ± 4.5 e79.3 ± 4.6 cd106.7 ± 11.5 b
Cd (μg kg−1)41.0 ± 2.8 bc34.5 ± 0.8 d41.9 ± 2.2 b37.3 ± 2.4 cd33.8 ± 3.0 d66.3 ± 1.2 a
Hg (μg kg−1)7.41 ± 0.62 c6.21 ± 0.31 d5.89 ± 0.43 d9.03 ± 0.17 b10.25 ± 0.93 a5.49 ± 0.42 d
# Note: Different lowercase letters denote significant differences in each column (p < 0.05). CK: treatment with 21% sawdust and sugarcane bagasse. Y1: treatment with 10.5% sawdust and corn stalks and 21% sugarcane bagasse. Y2: treatment with 21% sawdust and 10.5% corn stalks and sugarcane bagasse. Y3: treatment with 21% corn stalks and sugarcane bagasse. Y4: treatment with 21% corn stalks and sawdust. Y5: treatment with 42% corn stalks.
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Zhou, Y.; Li, Z.; Xu, C.; Pan, J.; Zhang, H.; Hu, Q.; Zou, Y. Evaluation of Corn Stalk as a Substrate to Cultivate King Oyster Mushroom (Pleurotus eryngii). Horticulturae 2023, 9, 319. https://doi.org/10.3390/horticulturae9030319

AMA Style

Zhou Y, Li Z, Xu C, Pan J, Zhang H, Hu Q, Zou Y. Evaluation of Corn Stalk as a Substrate to Cultivate King Oyster Mushroom (Pleurotus eryngii). Horticulturae. 2023; 9(3):319. https://doi.org/10.3390/horticulturae9030319

Chicago/Turabian Style

Zhou, Yuanyuan, Zihao Li, Congtao Xu, Jinlong Pan, Haijun Zhang, Qingxiu Hu, and Yajie Zou. 2023. "Evaluation of Corn Stalk as a Substrate to Cultivate King Oyster Mushroom (Pleurotus eryngii)" Horticulturae 9, no. 3: 319. https://doi.org/10.3390/horticulturae9030319

APA Style

Zhou, Y., Li, Z., Xu, C., Pan, J., Zhang, H., Hu, Q., & Zou, Y. (2023). Evaluation of Corn Stalk as a Substrate to Cultivate King Oyster Mushroom (Pleurotus eryngii). Horticulturae, 9(3), 319. https://doi.org/10.3390/horticulturae9030319

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