Pleurotus eryngii and P. nebrodensis: from the wild to commercial production.
Pleurotus eryngii differs from other members of the genus Pleurotus because it grows as a facultative biotroph on the roots and underground portions of the stem of certain plants (Zervakis et al. 2001a). The species name "eryngii" is derived from such a host-mushroom relationship. Pleurotus eryngii is found in association with Eryngium campestre and other species of the Umbelliferae and Compositae families. Pleurotus nebrodensis (=P eryngii var. nebrodensis) develops in association with species of the genera Diplotaenia, Opopanax and Cachrys. Pleurotus nebrodensis can be found during the spring (April through May) in the mountains of Modonie, a region of the Nebrodi mountain range (northeast of Sicily, Italy) (Boisselier-Dubayle and Baudoin 1986; Cailleux and Joly 1987; Zervakis et al. 2001b). In China, P. nebrodensis is found in association with Ferula sinkiangensis (Zhang et al. 2005). Other varieties of P. eryngii also have been described including: ferulae, elaeoselini and hadamardii (Venturella et al. 2000; Zervakis et al. 2001b). Therefore, P. eryngii is commonly referred to as a species-complex or as "Pleurotus of the Umbellifers." Controversy regarding the placement of varietal or species levels of the members of this group still remains.
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Geographical Distribution Of Wild Pleurotus eryngii
The P. eryngii species-complex occurs naturally in subtropical regions of the Mediterranean basin, Central and Southern Europe, Ukraine, North Africa, Central and Western Asia and Iran. Pleurotus eryngii (Fig. 1) is found in arid pastures, on limestone and silicaceous soils at 0-1,500 meters in elevation (Cailleux and loly 1987). Pleurotus nebrodensis (Fig. 2) is found in the subalpine zones of Europe and Asia between 1,200 and 2,000 meters (Boisselier-Dubayle and Baudoin 1986; Zervakis et al. 2001b). Pleurotus eryngii is not found in America.
Pleurotus eryngii Consumption, Production & Marketing
Pleurotus eryngii (= P. eryngii var. eryngii) is known by several common names such as King Oyster (United States), Cardoncello or Cardarello (Italy) and Xing bao gu (China) among others. Presently, Japan, China, South Korea and Italy are the major producers of this mushroom. In the U.S., commercial production of this species began in 2000. By 2004, 85 tons were produced in the country (Royse et al. 2005). In China, P. eryngii production in 2001 was 21,000 t and increased to 114,000 t by 2003 (Chang 2005). Fresh King Oyster mushrooms are commercialized in packages (over-wrapped trays) or in bulk (Fig. 3). They also may be sold as dried slices or as powder. China producers sell the mushroom boiled, brined and packed in plastic bags or cans. The demand for the Cardarello in Italy exceeds 2,000 t per year (Oei 2006). Wild mushrooms are collected and sold fresh in the local markets in some European countries such as Spain and Italy.
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The retail price of the King Oyster varies considerably among countries. In the U.S., fresh mushrooms may cost up to $16/kg. The price dramatically increases to $38.70/kg when labeled as an organic product. In Italy, wild/fresh mushrooms may cost up to $9/kg during the growing season and more than $13/kg at the end of the season. In Germany, the retail price of the organic product is $27 to $34/kg and the wholesale price is around $16/kg. When sold dry, the King Oyster may fetch prices of up to $62/kg in the U.S. (Oei 2006 and Kynast pers. comun). Cultivated strains of P. eryngii vary enormously in their morphology and the consumer preferences are quite diverse in different countries. For example, in Spain light caps are ideal (Fig. 5a), while in Italy dark caps are most preferred (Fig. 5d). In China, consumers like wide stipes and small caps (Fig. 5b) and in North America, Korea and Japan, wide stipes and caps are more frequently favored (Fig. 5c).
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Pleurotus nebrodensis Consumption, Production & Marketing
Inzenga, who first described P. nebrodensis in 1863, referred to this species as "the most delicious mushroom of the Sicilian mycological flora" (Venturella 2006). This mushroom traditionally has been collected and locally consumed. However, since 2006, it was considered a critically endangered species by the IUCN (World Conservation Union) and was included on the red list of threatened species. Pleurotus nebrodensis is rarely found in nature, and in fact, it is estimated that only 250 basidiomata reach maturity every year in the north of Sicily. Due to its scarcity, the price of this mushroom collected from the wild ranges from $68 to $95/kg in Italy (Venturella 2006).
Pleurotus nebrodensis in China is known by the common name Bailinggu (white sanctity mushroom), Baiaweiwo and Tuolibianzhong among others (Shen et al. 2005). It is commercially produced in China and Poland, where the wholesale prices for exportation of the fresh product fluctuates from $10 to $12/kg. Conversely, the wholesale price within China may be as low as $2 to $3/kg; still, it is one of the highest priced mushrooms. The retail price of P. nebrodensis in China is approximately $5/kg while P. eryngii may cost $3 to $4/kg. Processed P. nebrodensis is sold in cans and jars (Fig. 4b) or as frozen slices. Chinese commercial strains often are divided in two morphological groups: palmate or funnel-shaped. The former group has become the preferred commercial cultivar since 1995 (Zhang et al. 2005). The mushrooms are commercially classified into five grades. Grade A represents the highest quality, where the mushrooms are white or ivory, have a smooth and spotless surface, thick caps (2.5 cm) and weigh 125 to 200 g. On the other hand, grade E, the lowest quality, comprises mushrooms with twisted or malformed caps and long stipes (Shen et al. 2005).
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Three cultivation methods are generally used to produce P. eryngii and P. nebrodensis: bags, bottles and outdoors. A fourth method consists of placing a casing layer on the colonized substrate; this method is mostly used to produce P. eryngii.
Pleurotus eryngii: The bag system mainly is used in Europe and China. Polypropylene or polyethylene bags (0.5-3 kg substrate/bag) with filter patches are used as the cultivation containers (Fig. 6). The substrate formulation varies considerably although cottonseed hulls, sawdust, wheat straw and dried beet residues are among the most popular ingredients (Tan et al. 2005; Rodriguez Estrada and Royse 2007). Bags are filled with moistened substrate at approximately 1/2 to 2/3 of their capacity. The substrate is sterilized for at least one hour at 121[degrees]C, cooled and then inoculated with grain spawn. Incubation is carried out at 23 to 25[degrees]C for 21 to 28 days, depending on the substrate volume. To induce pining, the colonized substrate is exposed to a mild cold shock that is achieved by lowering the temperature to 18-21[degrees]C. Once the primordia are formed and reach 1 to 3 cm in height, the bags are opened and the plastic folded to the sides (Fig. 7). Mature mushrooms (Fig. 8) develop within 6 to 7 days after primordial formation. Usually, only one flush is obtained by this method.
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Pleurotus nebrodensis: In China, this species is cultivated mainly on cottonseed hulls, sawdust or maize cobs (Tan et al. 2005). Autoclavable plastic bags of 500 g capacity with or without filter caps are normally used. The substrate is inoculated at both ends of the bag so that spawn run time is shortened compared to substrate inoculated at only one end (Kang 2004). According to Tan et al. (2005), optimum spawn run temperature is 25 to 28[degrees]C for 22 days. After that period is completed, the temperature should be maintained below 25[degrees]C to avoid an excessive mycelial growth. To induce pining, the temperature should be dropped to 10-15[degrees]C for 10-15 days (Tan et al. 2005). Kang (2004) reports that colonized substrate contained in bags is placed in a cold room where the temperature is close to 0[degrees]C to induce pin formation. Basidiocarp development requires temperatures of 12-15[degrees]C. Only one flush and one mushroom per bag are obtained.
Pleurotus eryngii: Casing is utilized by growers in China and Italy when P. eryngii is grown in non-controlled environments. The purpose of the casing overlay is to prevent desiccation of the substrate once the bags are opened (Oei 2006). The substrate composition and preparation is very similar to the standard bag system. After the substrate is colonized, the casing layer (in Italy, sandy or common soil watered to field capacity is used as casing material) is placed on the substrate (1.5 to 3 cm). In Italy, fructification temperatures range from 7 to 20[degrees]C. Up to 3 flushes may be obtained with two to three weeks between the peak of each flush (Oei 2006). A variation of this system is practiced on Chinese mushroom farms. The plastic bags are completely removed from the substrate after 6 to 10 days of colonization and then the blocks are placed in beds and covered with casing soil. In some cases, growers in China may case colonized blocks that have been harvested for one break in the regular bag system. This allows them to obtain a second flush of mushrooms from the same block (Tan et al. 2005).
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Pleurotus eryngii: The bottle system is used by many growers in Japan, South Korea, China and in some modern production facilities in the U.S. and Canada. The substrate is contained in polypropylene bottles of 850-1050 ml capacity. This system is highly mechanized, with exception of the harvesting process that is performed manually (Fig. 10). Aged sawdust and cottonseed hulls may be the main basal ingredients. The substrates are mixed and the moisture content is adjusted to 60 percent. Sixteen bottles are arranged in plastic trays, filled and capped at the same time. Sterilization is carried out at 121[degrees]C for 1-4 hours. The substrate is cooled overnight at room temperature and then inoculated with grain spawn. In South Korea and Canada, inoculation with liquid spawn has become popular. Spawn run lasts from 28 to 35 days at 16-24[degrees]C. After colonization, the lids are removed and the top layer (1-2 mm) of the colonized substrate is removed mechanically in order to induce a uniform fructification. This process is called "scratching" or "kinkaki" in Japanese. The bottles are covered with a perforated plastic film that is removed when the pins reach approximately 1 cm in length. Usually, several pins are formed but only 3 to 4 develop to marketable-sized mushrooms. The relative humidity for primordia formation is maintained at 95 percent and lowered to 85-90 percent when the basidiomata develop. A single flush is obtained when the bottle system is used. See Rodriguez Estrada and Royse (2005) for a more detailed description of P. eryngii cultivation in bottles.
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Outdoor cultivation of P. eryngii is practiced on farms that do not have controlled environments. The mycelium is grown at 25[degrees]C on a pasteurized substrate (4 kg) contained in polypropylene bags. After colonization, the substrate is removed from the bags, placed in trenches dug into the ground and then cased with soil (2-3 cm depth). Metal frames are placed over the trenches and then covered with black shade cloth. Irrigation is carried out periodically (Zervakis and Venturella 2002).
As expected, outdoor cultivation is seasonal. However, proper management may help avoid long breaks between production cycles associated with climate changes during different seasons. For example, a mushroom farm "Terramia" located in southern Italy has devised a method to produce P. eryngii at different altitudes. Production in the spring is carried out in the mountaineer zone at 1000 m (Dolomitas Lucanas). While production in the autumn and winter are carried out at the Murgia Materana and Metapontino (sea level), respectively. This strategy allows growers to harvest mushrooms from September to July (Folino 2007).
Although domestication of P. eryngii and P. nebrodensis is relatively recent, their production and consumption have expanded rapidly. Obvious culinary (flavor and texture) and medicinal properties make these species excellent candidates for cultivation.
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Alma E. Rodriguez Estrada
Daniel J. Royse
Dept. of Plant Pathology
Penn State University
University Park, PA 16802
Presented at the 49th Mushroom Industry Conference at Penn State University
University Park, PA
June 11, 2007
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|Title Annotation:||specialty mushrooms|
|Author:||Estrada, Alma E. Rodriguez; Royse, Daniel J.|
|Date:||Feb 1, 2008|
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