Spawn Maintenance

A desirable mycelial culture is pure — free of contaminants and of sectoring of other abnormalities. Contaminants include other fungi, bacteria, or insects growing on or infesting the culture media along with the desired mycelial culture. When a culture is first obtained, it should be transferred several times to fresh media to check for any form of contamination (Figure 10).

Figure 10. Pure culture of mushroom mycelium growing on an agar plate.

Sectoring is any type of mycelial growth that differs in appearance, growth rate, color, or in any other way from the typical appearance of a given strain. Sectoring is often observed as a more rapidly growing area near the leading edge of growth, exhibiting a different growth habit from the rest of the culture. Other abnormalities that might appear in a culture are fluffy, aerial mycelia, thick or rubbery textures, and color changes such as browning or darkening of the mycelium. Sectors of other change in vegetative growth could affect the productivity of the culture. Therefore, recognizing and avoiding propagation of abnormal mycelia to agar and further spawn production is very important.

There is no in vitro test to determine a stock culture’s validity. A series of cropping trials must be conducted on the mycelial stock culture to determine a culture line’s value. Mushroom yield, size, color, cap shape, and any other desired quality or growth factors are selected and then compared for each culture line.

Many commercially prepared spawn strains are available to commercial and noncommercial growers. All commercially grown strains are pure culture of edible, fresh mushrooms; some may vary in texture and growing requirements. Mushroom spawn is produced in several different strains or isolates. Hybrid White is a smooth-cap, highyield, excellent processing strain. Hybrid Off-White has a cap that is slightly scaly on first break and is a preferred fresh-market strain, and Brown (Portabella, Crimini) produces a chocolate-brown, mature mushroom that is fleshy and has a strong, mature flavor.

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