• Tom Brain

The case for Pleurotus parsonsiae - The Velvet Oyster

Updated: Jun 15, 2021

Recently a new mushroom has hit the growing circles in New Zealand, it’s the endemic species of Oyster mushroom, known as Pleurotus parsonsiae, or Velvet oyster.

A mushroom belonging to the same clade as Pleurotus djamor, or better known as the Pink Oyster, it’s a delicate mushroom with semi firm brown flesh that enjoys growing on a wood based substrate, being saprotrophic. The cap is convex, the stipe is bare, and the spore print is a bright white, almost like snow.

Here at Oak and Spore we purchased the culture to conduct some trials and grow for local markets. Our methods are not scientific, rather we are growing to observe it in comparison to other commercial species to get an overall feel for its suitability as a commercial species. We compared it to Pleurotus pulmonarius, the Phoenix Oyster.

Pleurotus parsonsiae was inoculated onto 200kg of a substrate known as masters mix, which is 50/50 woodchip and soy hulls. It was inoculated using 1.5% wheat spawn and allowed to incubate at 21 degrees for 3-4 weeks. Compared to the commercial Pleurotus pulmonarius strain the Pluerotus parsonsiae colonised about 20% slower.

Holes were cut into the bags and they were placed into fruiting condition in a controlled environment. Humidity was kept between 95%-99% humidity to stimulate primordia formation, and the temperature was kept between 14-18 degrees. CO2 was kept at 650 ppm or lower at all times. Humidity was dropped back to between 85%-90% after primordia formation.

Primordia formation was slightly slower that the commercial Pleurotus pulmonarius, with primordia forming for the Pluerotus parsonsiae after about 3-5 days, and the Pleurotus pulmonarius after 2-3 days. primordia clusters appears to show large amounts of small pins, but would later develop into a few dominant fruit bodies.

The fruit body development was also slower that the phoenix, but the fruit body it produces shows a consistent form and quality.

Higher heats produced a lighter coloured mushroom, with a noticeable increase in quality when the mushroom was produced at lower temperatures, around 14 degrees, over higher temperatures around 18. This increase in quality at a lower temperature seems to be a trait shares across a lot of oyster mushrooms, potentially excluding Pink Oyster as they are a topical mushroom and enjoy the heat. A lower heat caused a darker cap with a more vibrant color.

The Pluerotus parsonsiae has little in the way of identifiable stem for each cap, and the base of the cap seems to grow into the next cap. This is a major factor in deciding suitability of the mushroom as is prevents singular mushrooms being taken from high yielding crops. The crop would have to be taken as one giant mushroom rather than being cut into it’s components of several smaller mushrooms. If trying to separate it into small amounts the mushroom would tear and become unmarketable.

pleurotus parsonsiae mushroom
Red circles noting areas where a lack of stem is prevalent. Causing the mushroom growing as one large fruit body, not many individual fruiting bodies as what is desired in a commercial species of oyster mushroom. .

pleurotus parsonsiae mushroom
Pleurotus parsonsiae showing no signs of a visible stem. It's spore load can also be seen.

The spore load from the Pleurotus Parsonsiae is incredibly high. It’s easily the highest spore load of any mushroom we have grown at our facility by a considerable margin. The spores are a milky white and form a layer under the mushroom between the gills and the substrate or between the gills and the mushroom below. Because the mushroom is generally lacking a defined stem it means the spores get caught and build up. This build up in biological matter forms a breeding ground for potential contamination, and our mushrooms showed contamination on the spores under the mushrooms. We have grown Oysters for a long time and we have never had a Trichoderma infection in Oysters, until we grew Pluerotus parsonsiae where the Trichoderma would infect the spores.

Pleurotus parsonsiae spore load
The spore load seen under the Pleurotus parsonsiae, showing signs of contamination

As the mushroom gets older is gets incredibly moist, this trait can also be seen with the Pink oysters where they will often turn into a wet mess when stored at 1 degree. When the temperature of Pleurotus Parsonsiae was crashed to 1 degree for storage it seemed to slow the effects of the moisture egressing from the flesh, but it was still noticeable as the days went on.

It seemed to have a reasonable shelf life, matching that of Phoenix Oyster. Phoenix oyster tends to dry out, with Pleurotus Parsonsiae doing the opposite and getting soggier as time went on.

The fruit bodies were not weighed, so a base biological efficiency for masters mix could not be ascertained, but observations showed a first flush that produced a few number of very large mushrooms, often attached to accompanying mushrooms. Second flush was extremely poor, with following flushes unable to be completed as the spore load it drops would contaminate and the bags would have to be removed from the fruiting chamber.

Contamination was a serious issue. The spore load would sit between any gap it could find, and the naturally wetness of the mushroom meant that contamination in these areas was rife. Bags would often have to be removed from the fruiting chamber early to prevent the spread of contamination. Some contamination would also be hidden until the mushrooms were harvested as which point you could see the contamination hidden under the fruit bodies.

pleurotus parsonsiae contamination
Contamination of the spores after the mushroom body was harvested

To sum it up the Pleurotus parsonsiae is an interesting mushroom, not suitable for commercial cultivation until the species can be selectively bred to remove the undesirable traits and increase traits it’s not showing. It would benefit from smaller fruit bodies, a severe decrease in spore load, elongated stem and a separation of fruit bodies, and an increased biological efficiency through easier consecutive flushes.

We have stopped growing the Pleurotus parsonsiae as it’s simply not economically viable and the extreme spore load means we have to work overtime to clean our facility. The mushrooms are unable to be picked and packaged in a reliable manner, and the biological efficiency simply just isn't good enough.

If you are going to grow this mushroom we recommend not growing it indoors where you live, the spore load will be extremely bad for the health of your lungs. Oak and Spore contacted Landcare Research in New Zealand to discuss it's potential to cross breed with the introduced species of Pleurotus djamor. Landcare Research told us that there is no evidence that cross breeding can or has happened, but they assumed it would be possible as they are part of the same species complex. Landcare Research also referred us to a report showing zero inter-fertility between Pleurotus parsonsiae and Phoenix Oyster(1). Small scale growers like the option to grow NZ mushroom cultures(2), and they are gaining in popularity. (1) https://www.jstor.org/stable/3760923?seq=1#page_scan_tab_contents (2) https://www.sporeshift.co.nz/post/mushroom-growing-nz-nz-cultures

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