STRAIN SELECTION
Figure 1. Strain not only strongly influences the productivity of mushrooms, but also the aesthetic appearance and quality of the mushrooms produced.
Similar to plant varieties, strain selection can have a defining influence on mushroom production. In the US, there are not many spawn companies that offer a latitude of named shiitake strains that are specific to forest-cultivated systems. As of 2023, there were two known companies producing more than two or three strains for production on logs. There are several spawn companies that offer a latitude shiitake strains for indoor production, but these have not been evaluated for their performance in forest-cultivated systems.
In general though, shiitake strains are divided into three types (also see Table 1):
wide range
warm weather
cold weather
Table 1. The generalized fruiting seasonality of the three different shiitake strain types. Green-colored bands indicate the seasonality spontaneous fruiting (i.e. no forced fruiting) while blue-colored bands indicate the seasonality of forced fruitings.
There are some spawn companies that sell unnamed strains for forest cultivation that are otherwise only “named” by their type. As the type names suggest, strain type largely relates to the time of year that the strain is expected to fruit based on average temperatures, with wide range strains being considered to be the most versatile. Wide range strains also often are reported to have the shortest spawn run times, while warm-weather strains (and cold-weather strains) may typically have longer spawn run times. Wide range strains will generally produce in mid-summer but may be less productive than warm weather strains. Warm weather strains can also alternatively be thought of as “late season” strains because they will also produce in the fall but are less likely to in the spring than wide range strains. There is also a difference in type regarding how fruiting is initiated. Fruiting in wide-range strains and warm weather strains are responsive to “forced-fruiting” by immersing logs in water typically for anywhere between 6-24 hours, whereas cold weather strains do not, but rather fruit more spontaneously in response to the onset a range of cold weather temperatures that occur in spring and/or fall.
In Japan, much of the shiitake production on logs (including hybrid log/hoophouse-grown shiitake) often excludes the bulk of the summer season, because average temperatures can be too high, and summer is also the wettest season of the year, which degrades shiitake quality if grown outdoors. Because of these seasonal patterns, all types of shiitake may be used, with warm-weather strains being more oriented to fresh market production (often using shaded hoophouses), and cold-weather strains being more oriented to outdoor production for dry shiitake markets; wide-range strains may be used in either production system.
Figure 2. Wide-range and warm-weather strains both respond to forced fruiting that is initiated by immersing shiitake bolts in water for up to 24 hours. Forced fruiting can be game-changing for reliable harvests, quality control and bolt moisture maintenance. This warm-weather strain ‘Night velvet’ also has a distinctive aesthetic quality that some markets may value, especially more traditional Asian markets.
Forced-fruiting and producing for market with wide-range and warm-weather strains in the PNW:
At least one named wide-range, warm-weather and cold-weather shiitake strain that has been trialed in the PNW as of 2023 (‘West wind’, ‘Night velvet’ and ‘Miss happiness’, respectively). More wide-range and warm-weather strains are going be evaluated by Extension in the PNW beginning in 2024. West of the Cascades in the PNW, our seasonal temperature and precipitation patterns and fresh-market production orients us more towards late-spring > summer > early fall production of shiitake using wide-range strains and warm-weather strains. Although it may seem counterintuitive, summer is the more ideal growing season for shiitake for market in the PNW because it’s less likely to be raining, and is when forced-fruiting works best. Forced-fruiting is a key asset to producing shiitake for market- predictable harvest timings are efficient, and, importantly, the soakings from forced fruiting helps to maintain critical log moisture levels throughout each dry summer season. Wide-range strains often a favorable choice for production in spring, summer and fall, but some growers may choose to “mix and match” using both wide-range and warm-weather strains so that your chances of having sufficient yields early (better yield from wide-range strains) and mid-season (better yield from warm-weather strains) are higher. Warm-weather strains good options for producing for market in the PNW because of the high temperatures we can get in summer. Although generally domestic markets for shiitake are unlikely to be as discerning about shiitake quality and appearance as asian markets can be, appearance and quality will hold a degree of value to your markets nonetheless. Strains selection is one way of managing mushroom appearance and quality (see Figures 1 & 2) in addition to other management factors.
Figure 3. Some of the major downsides of using cold-weather strains in the PNW relate to quality control. Fruiting is sporadic, so it is easy to miss, and often lacks uniformity as shown in (A) where one mushroom is clearly overripe, and another is clearly underripe. Fruiting of cold-weather strains also often occurs during the rainy season (B), which would necessitate a coordinated effort to avert the quality degradation that occurs from from rain on mushrooms.
Downsides of commercial production with cold-weather strains in the PNW:
Although mushrooms produced in colder weather generally are considered higher quality because the slower growth rates tend to produce a more dense mushroom, there are considerable downsides for cold-weather strains in a commercial production context in the PNW. Cold-weather strains often fruit during the rainy season in the PNW, which degrades shiitake quality. Also, because fruiting is spontaneous this makes it is easy to miss optimal harvest timings, especially if fruiting is spread out over several weeks. We’ve also frequently observed highly variable yields, and high instances without production with cold-weather strains. Spawn run times have been up to three years in the PNW because of our dry summers, and the lack of moisture-replenishing soakings that would otherwise occur with logs that are being forced-fruited. Slow spawn in cold weather strains run has also allowed some logs to be colonized by other competing fungi (Trametes).
Other strain selection considerations:
Spawn run time is an important factor to consider along with other strain characteristics. It determines how soon you will be able to begin to produce mushrooms after inoculation, and how competitive the shiitake fungus is against other competing fungi. The shorter spawn run times that are associated with wide-range strains adds to their versatility.
Besides information from Extension research on strains, spawn suppliers that are well aquainted with thier strains a should also be able to provide descriptions of strains characteristics that can help with strain choice and long-term production plans. Also be aware that spawn suppliers are often shipping spawn to growers all during the same time of year, which can delay the shipping time. This can be particularly true for more popular strains that appeal to a wider range of growers (commercial producers, hobbyists, & beginners). Be sure to account for this in your planning.