Growing characteristics of midrange hybrids

General characteristics:

The midrange hybrid strains are the result of a long breeding work started with the crosses of U1 and U3 type hybrid lines. As a U1 type heritage these new hybrids have compact tissue, excellent shelf life, attractive, well-shaped fruit bodies. The U3 type parents gave them the easy pinning feature and good performance under various circumstances. Combining these advantageous parental traits these midrange hybrids:

• are less sensitive to shortages of compost and growing method, in contrast to large hybrids, and adapt well to a wide range of growing conditions;
• grow faster, more agressively than large hybrids do and produce mushrooms several days earlier;
• have fruit bodies with excellent texture and shape, size of which can be influenced by carefully monitored growing conditions; therefore these strains can produce mushrooms both for fresh market and for processing.

• humidity: 68-71%
• total N: 2-2.4%
• pH: 7.1-7.5
• ammonia: less than 3 ppm

The recommended spawning rate is 8-10 l spawn per ton of pasteurized compost. After filling in a formerly disinfected growing room the upper layer of compost can be inoculated additionally with a few grains of spawn. The bags then should be covered with nylon or paper to prevent compost from drying out. The compost temperature should be maintained between 26 and 28 °C during spawn run. Daily checks of compost temperature is required to avoid exceeding 30 °C. In case of possible overheating the compost can be cooled by lowering the air temperature and/or by watering the building's floor. During spawn run the CO₂ level should be kept above 3000 ppm with 95-98% relative humidity. The spawn run is finished in 14-16 days normally depending on the quantity of spawn used, the bed temperature and the quality of compost.

Casing

For excellent achievements good quality casing is necessary characterized by the followings:
- high peat content (90-100%) assuring adequate structure;
- pH: 7.3-7.5
- good adsorbent and water-holding capabilities
- free from pests and diseases.

The casing soil should be disinfected - depending on the applied growing technique - with 2-2.5% solution of formaline 2-3 days prior or immediately after use. The casing layer must be spread out evenly on the compost 5-6 cm thickly. After casing the compost temperature should maintained at 24-26 °C with 95-98% relative humidity and 3000 ppm or higher CO₂ level. It's advised to keep casing soil temperature at 22-23 °C until ruffling in order to provide adequate conditions for the mycelium to colonize the peat.

Watering until ruffling

After the formaline treatment the bags should be sprinkled with insecticid and pesticid solutions. On the 4th day after casing the filling up of casing soil with water can be started. It is important to apply rather small portions (1-1.5 l/m²) at one time to prevent watering the compost through the casing soil. Until ruffling 5-12 l of water ought be added this way for every square meter depending on the relative humidity, the quality of the casing soil, the growing intensity of the mycelium and on the air and bed temperatures. The mycelium's development, the structure and humidity of casing layer must be checked every day. The gained information can be useful for choosing the right time of ruffling and for solving problems in the future.

Ruffling

Ruffling means breaking up of the casing soil, distribution and mixing of colonized and untouched parts by hand or by tools. It normally takes place on the 8th day after casing, when the mycelium has grown throughout the lower half or 2/3 of casing soil. The proper time of ruffling is influenced by the technology of cultivation, the depth and other features of peat layer, and the air and bed temperatures. (Growers applying Casing Inoculum or CAC-ing, don't have to ruffle.)

The main purpose of ruffling is:
- thorough distribution of the mycelium in order to gain even pinhead-formation;
- elimination of anaerob parts created by waterings, improving the structure of casing soil.

The casing layer must be ruffled deeply and thoroughly to promote evenly developed primordia. If rather large mushrooms are needed, one should ruffle only the upper half of the peat. The surface of the loosened, mixed and carefully spread casing soil has to remain rough to provide a suitable microenvironment for primordia. Since no watering should occur after ruffling until pea-size mushrooms, it is extremely important to maintain high (95-98%) relative humidity and CO₂ level exceeding 3000 ppm. Therefore no fresh air is required in the first 2-3 days after ruffling. The air temperature is best to be kept at 21-22 °C not allowing compost temperature reaching 28 °C or more.

Flushing

The midrange hybrids should be flushed when the mycelium is evenly spread throughout the casing layer and is visible on the surface but not aerial. It usually occurs a week after ruffling. The intensity of flushing determines the number and size of fruit bodies. If larger mushrooms are needed, the compost temperature should lowered slowly in 4-5 days to 19-20 °C with 17-18 °C air temperature. In order to pick more, but smaller mushrooms (ex. for processing), the compost should be cooled down quickly to 18-19 °C in two days with 15-16 °C air temperature. Meantime the CO2 concentration and the relative humidity must be lowered gradually also to 1000-1500 ppm and to 90%. Extreme care must be taken when lowering the RH to avoid the damage of pinheads due to too much ventilation. After pinning the compost temperature can be brought back up to 21 °C with 1200-1500 ppm CO₂ level and 85-90% relative humidity.

Cropping

The number of fruit bodies is influenced by the air to bed temperature ratio, the relative humidity, the ventilation etc.. In the cropping period these strains require 85-90% relative humidity and 17-18 °C air temperature. A significant difference between air and bed temperatures is advantageous for cropping, therefore the compost temperature should not be lower than 20-21 °C. The CO₂ concentration must not exceed 1500 ppm. When pinheads are approximately 1 cm, the cap and stipe ought to be the same diameter. If the cap is smaller than the base, there is insufficient ventilation, thus high CO₂ level. If the cap is larger than the stipe, then there is too much ventilation.

The watering can be started when the mushrooms are pea-size (0.5-1 cm). The amount of water applied depends on the followings:
- water holding capabilities of casing soil
- environmental factors (relative humidity, ventilation, temperature etc.)
- phase of applied growing method.
It is recommended to sprinkle 1 l of water per each kg of the expected yield of the forthcoming flush. Rather small amounts should be watered at one time and the fruit bodies' surface has to be allowed to dry off in a couple of hours. Free water on the mushrooms supports bacterial infections. The watering must be finished a day before picking in order to improve the shelf life of fruit bodies.

Appearing of the first flush can be expected 35-40 days after spawning depending on the applied cultivation technology. Using phase III compost, the first break can be picked as early as 20-25 days after filling in and casing of the fully colonized compost. In the last days of the flush, when ¾ of the crop expected in the first flush have been picked, the watering can be started for the next break. Using poor quality peat with relatively small water adsorbent feature, the casing soil should be watered more frequently even during flushes. This must be done always after pickings, paying great attention to proper quantity.

It is advantageous to rise the compost temperature at the end of the flush. If it is not feasible with 17-18 °C air, the air temperature can be risen up to 21-22 °C with intensive ventilation until the compost temperature reaches 21 °C. Then the air must be cooled back to 18 °C and there should be only a minimal air movement. Due to this technique the temperature difference between air and compost increases, which need to be maintained for several days.
The flushes usually follow each other with a week delay. Cultivating midrange hybrids it is not uncommon to have significant yield between breaks, although it is advisable to pick these mushrooms at small size otherwise the forthcoming flush can be weakened.
The performance of these hybrids is influenced primarily by the grower itself, however it can be stated in general, that under adequate circumstances (good quality compost, professional knowledge) these strains are capable of producing high yields often exceeding 25 kg on phase II compost. A significant, 15-20 % increase can be gained by the application of phase III compost with a further 10-15% increase using supplements.