Oyster Mushroom - Pleurotus Ostreatus

Scientific Name: Pleurotus Ostreatus
Common Name: Oyster mushroom

The prototypic Oyster mushroom, Pleurotus ostreatus has long been a favorite of mushroom hunters, especially in the spring time in lowland, hardwood forests. A prolific producer on a wide array of substrates, strains of this species are plentiful and easy to grow. Enjoying a worldwide reputation, specimens of extraordinary size have been collected from the wild. For instance, in the fall of 1998 near the north coast of Sicily, Salvatore Terracina, a farmer, collected a P. ostreatus nearly 8 ft. in circumference, 20 inches thick, and weighing 42 lbs.! For the prepared and strute cultivator, cloning this monster could have resulted in an extraordinarily productive strain.

Mycelial Characteristics: Whitish, longitudinally radical, soon becoming cottony, and in age forming a thick, tenacious mycelial mat. Aged mycelium often secretes yellowish to orangish droplets of a metabolite which is a toxin to nematodes. This metabolite deserves greater study.

Microscopic Features: This mushroom produces white, to slightly lilac, to lilac grey spores.

Suggested Agar Culture Media: Malt Yeast Peptone Agar (MYPA), Potato Dextrose Yeast Agar (PDYA), Oatmeal Yeast Agar (OMYA), or Dogfood Agar (DFA). Optimal growth seen at pH 5.5-6.5.

Spawn Media: Rye, wheat, milo, sorghum, corn, and millet. Sawdust spawn in not needed for indoor cultivation methods. However, sawdust spawn is ideal in the inoculation of stumps and logs in outdoor settings.

Substrates for Fruiting: A wide array of agricultural and forest waste products can be used, including but not limited: straw (wheat, rye, oat, rice, and barley straw); corn stalks, sugar cane bagasse; coffee pulp; banana waste; cotton waste and cottonseed hulls; hardwood sawdusts; pater by-products; soybean waste; palm oil by-products; agave waste; and even the pulp remaining from tequila production! The pH at make-up can vary between 6.0-8.0 but should fall to an optimum of 5.0 at fruiting for maximum biomass production.

Martinez et al. reported yields of 132% biological efficiency (4 flushes) from coffee pulp that was fermented for 5 days, pasteurized, and inoculated with wheat grain spawn. Further, they found residual caffeine from the spent substrate was reduced by more than 90%. (Caffeine represents a signigicant toxic waste to streams in coffee growing regions of the world). Martinez-Carrera validated the results with yields in excess of 100% biological efficiency in the same substrate adn presented the first model for utilizing this abundant waste product.

Platt published studies on the utility of cotton straw as a substrate for this mushroom. Their yields average 600-700 grams per kilogram of dry cotton straw, in other words 60-70% biological efficiency.

Yield Potentials: 75-200% biological efficiency, greatly affected by teh size of teh fruitbodies harvested, and the number of flushes orchestrated.

---Growth Parameters---

Spawn Run:

Incubation Temperature: 75* F (24* C)
Relative Humidity: 85-95%
Duration: 12-21 days
CO2: 5000-20,000 ppm
Fresh Air Exchanges: 1 per hour
Light Requirements: n/a
Primordia Formation:

Initiation Temperature: 50-60* F (10-15.6* C)
Relative Humidity: 95-100%
Duration: 3-5 days
CO2: <1000 ppm
Fresh Air Exchanges: 4-8 per hour
Light Requirements: 100-1500 lux
Fruitbody Development:

Temperature: 60-70* F (10-21* C)
Relative Humidity: 85-90%
Duration: 4-7 days
CO2: <1000 ppm
Fresh Air Exchanges: 4-8 per hour
Light Requirements: 1000-1500 lux
Cropping Cycle:

3-4 crops, 7-14 days apart, over 45-55 days.
Comments: The Oyster mushrooms are the easiest to grow. Disadvantages of their cultivation are in their short shelf life, post harvest, and the health problems posed by the prolific spore load generated within the confines of the growing room.

Cold and warm weather strains of this mushroom are widely in use. The above described temperatures for initiating P. ostreatus are based on cold weather strains. Strains evolving in warm geographical niches behave more in accordance with the parameters outlined for Pleurotus pulmonarius.

Pleurotus ostreatus is an extraordinarily interesting mushroom from many viewpoints. Highly tolerant and responsive to carbon dioxide levels, Zadrazil noted that mycelial growth peaks at 280,000 ppm or 28% CO2. Unless CO2 levels are reduced to less than 1000 ppm (.01%), noticeable malformations of teh fruitbidies occur: typically long stems and small caps. In fact, the cap-to-stem ratio is an accurate measurement of atmospheric carbon dioxide levels in the growing room and is used as a visual cue by Oyster cultivators for increasing air exchange.

This mushroom species is also super-sensitive to light levels. In low light, a similar effect to that seen under elevated carbon dioxide conditions is induced. When exposed to high light levels, pigmentation of the cap is usually enhanced. Blue strains become bluer. Brown capped strains become a richer brown. Similar results are also seen at lower end temperatures give constant light conditions.

Thorn and Barron first noted that P. ostreatus exudes a metabolite toxic to nematodes. As the nematode lies stunned, the mycelium soon invades through one of its orifices, quickly consuming the internal organs. From an evolutionary viewpoint, this is remarkable that a saprophytic mushroom can become predatory to an animal in its quest for new sources of nitrogen. This may well explain why nematodes have never been reported as a pathogen in Oyster mushroom cultivation whereas their occurrence in the cultivation of the Button Mushroom (Agaricus brunnescens) is economically devastating and commonplace.

(Information taken from Growing Gourmet and Medicinal Mushrooms, Paul Stamets)