How to identify contaminant fungi in edible mushroom cultivation? Simple identification methods to share

During the cultivation of edible mushrooms, various harmful organisms and abiotic disturbances often occur. Mushroom growers all consider contaminant fungi to be a major enemy in production, and they must be recognized and prevented in advance, with targeted control, in order to ensure a good harvest.

1. Competitive contaminant fungi are mainly some saprophytic fungi that compete with edible mushrooms for nutrients, water and oxygen in the substrate, especially in the early stages of cultivation management when they are more likely to invade the mushroom blocks, secrete toxins, and inhibit the expansion and spread of the edible mushroom mycelium.

2. Infectious and non-infectious diseases. Infectious diseases include fungal, bacterial and nematode diseases, etc., all of which can infect the edible mushroom body, causing mycelial shrinkage and fruiting body rot. Non-infectious diseases are mainly physiological disorders caused by some unsuitable physical and chemical factors, such as nutrient deficiency, water supply imbalance, excessively high or low temperature, excessively strong or insufficient sunlight, and poisoning caused by harmful substances.

Competitive contaminant fungi include Penicillium, Trichoderma, Aspergillus, Neurospora, Mucor and Rhizopus, etc. During cultivation, they can be identified from three aspects: the color, odor and antagonistic line of the contaminant fungi.

Identification by color: different microorganisms have different colors, especially the common molds, which have conidia of different colors; this is a simple way to distinguish them. The common Penicillium is blue-green and is the most frequently occurring filamentous fungus; it can grow at 25°C and above. The mycelium is white at first, gradually maturing and producing green spores. It is mainly caused by lax operation during inoculation or overly wet cotton plugs, and is most likely to occur when cultured in a high-humidity, unventilated environment. Trichoderma is green, initially appearing as white patches, then gradually producing green spores; the center of the mushroom block is dark green, gradually becoming lighter outward, with white edges. It mostly occurs in slightly acidic environments and grows rapidly at 25°C and above. Aspergillus is similar to Penicillium, white at first, becoming black, yellow or green as it matures, and growing rapidly at around 28°C. Rhizopus starts as gray-white spider-like mycelium, then produces black sporangia; its reproductive capacity is very strong, and it propagates over the entire medium. It mostly occurs when air humidity is high, water content in the substrate is high, and ventilation is poor. Mucor mycelium is white and relatively long, some reaching 3-10 cm, with sparse colonies, and is easy to distinguish from edible mushrooms; the mycelium grows relatively fast and mostly grows under conditions of high temperature, high humidity and poor ventilation. Neurospora has loose, relatively long, white mycelium, with conidiophores branching dichotomously; the conidia are single-celled, spherical and in chains, red or pink, and often occur on starchy substrates such as corn and corn cobs. Neurospora often occurs on the cotton plugs in spawn bottles during spawn production, or on the substrate, especially under high temperature and high humidity conditions above 30°C, where it occurs fastest. Other common bacteria do not have mycelial structures and generally appear as a thick liquid on the surface of the substrate.

Identification by odor: oyster mushroom mycelium generally has a mushroom fragrance or almond fragrance. Various contaminant fungi each have their own odors, mostly appearing sour, foul, moldy and ammoniacal; molds mostly have similar moldy odors, while yeasts mostly appear sour and foul-smelling. Other ammonia-producing bacteria mostly appear as ammonia water odor.

Identification by the antagonistic line on the surface of the substrate: during the growth of oyster mushroom mycelium and contaminant fungi, at the junction of the two kinds of mycelium, a pure white line often appears, like a boundary line on a map; this line is called the antagonistic line. Through this line and conditions such as the inoculation site, color and odor, one can identify which side is oyster mushroom mycelium and which side is contaminant fungi, and what type of contaminant fungus has occurred.