Exam practice

A mushroom has no chlorophyll, so it can’t make its own food by photosynthesis. Its mycelium absorbs ready-made food from dead and decaying organic matter such as rotting wood, dung, leaves and straw. An organism that gets its food from dead and decaying matter is called saprophytic, so a mushroom is saprophytic.

Beneficial: many mushrooms are nutritious food, rich in protein, vitamins and minerals and low in fat; some are used as medicine; growing and selling them (and morels, sukuti and pickles) earns money; and in nature they decompose dead matter and return nutrients to the soil.

Harmful: some wild mushrooms are poisonous and can kill people who eat them, and they are hard to tell from edible ones; some fungi also spoil stored food and wood.

Mushrooms are low in fat, sugar and salt and have no cholesterol, while they are rich in fiber, potassium, protein and vitamins. Such food helps keep blood sugar, blood pressure and blood fats under control, and research suggests mushrooms also support the immune system. So they are a healthy food for these patients (along with their medicines, not instead of them).

Some wild mushrooms are poisonous, and some of them look very like edible ones. There is no simple test (color, smell, silver, cooking) that can tell them apart, cooking does not destroy the strongest poisons, and their symptoms may begin only many hours later, after the liver is damaged. Eating an unknown wild mushroom can kill, so only farmed or expertly identified mushrooms should be eaten.

Protein (19–35% of the dry weight, with essential amino acids); vitamins: riboflavin (B₂), niacin (B₃), pantothenic acid (B₅), thiamine (B₁), biotin, folate and a little B₁₂ (and vitamin D after sunlight); minerals: potassium, phosphorus, calcium, copper, iron and selenium; and fiber. They are low in fat and have no cholesterol.

Mushrooms have long been used as medicine in China, Japan and Korea, and Ayurvedic doctors in Nepal advise eating them. Research suggests that eating them regularly supports the immune system and helps people with diabetes, high blood pressure and heart disease, since they are high in fiber and potassium and low in fat, sugar and salt and have no cholesterol. Medicines and health products made from red mushrooms (such as Ganoderma) are taken for asthma, diabetes, cancer, piles and diseases of the airways, though they can only support a doctor’s treatment: no mushroom is a proven cure for these diseases.

Health: dried mushrooms are 19–35% protein (more than rice at 7.5% or wheat at 12.5%), with the amino acids the body needs; they are rich in B vitamins, potassium, phosphorus, iron and copper; they are low in fat and free of cholesterol, so they suit patients with diabetes, high blood pressure and heart disease; and they are used in medicine.

Income: oyster mushrooms grow in about 25 days on cheap straw in a small dark room, so farming them is profitable even for a small family; button mushrooms are grown commercially in the hills; wild morels (guchi chyau) from Jumla fetch very high prices abroad; and sukuti, pickles and ketchup made from mushrooms are sold.

Oyster mushrooms (kanye chyau) are grown on straw: cut clean paddy straw into 1–3 inch pieces, boil it for 15–20 minutes to kill germs, and let it cool and dry until just damp. Fill a plastic bag with 5–6 layers of straw, sprinkling spawn on each layer, press it down, and make 10–12 holes. Keep it in a dark room for about seven days, until white mycelium spreads through it. Then make a few more holes and sprinkle water as needed. Around day 10, cut the plastic so the mushrooms can come out; around day 17, small mushrooms appear; around day 25, pick the grown mushrooms.

Sukuti (dried mushroom) and mushroom powder, pickle (achar), ketchup, chutney and soup; also dishes such as curry, pakoda, omelette and sandwiches; and medicines and health products from red mushrooms.

Wash the mushrooms clean and cut them into small pieces. Dip them briefly in boiling water. Dry them in the sun, over a fire or in an oven: in the sun at over 25 °C or in a machine at 40–45 °C (or, for the best quality, soak them for 16 hours in a solution of 1% potassium bisulphite, 0.2% citric acid, 6% sugar and 3% salt, then dry them at 60–62 °C for 8 hours). When completely dry, pack them airtight and store them in a suitable place; they keep for up to 120 days in a sealed polythene bag.

Mushrooms with these features are often thought to be poisonous: a dull gray or light brown color; white gills; a ring (annulus) on the stipe or a cup (volva) at its base; a bright red color, or a red stipe or pileus; a smooth, shiny pileus that insects have not touched; and a yellow liquid when the pileus is pressed. These are only guesses, not reliable rules: only an expert or a laboratory test can say for sure, so no wild mushroom should be eaten on a guess.

Draw a mushroom as in Figure 3.1, and label the pileus (cap), gills (under the cap), annulus (ring on the stalk), stipe (stalk), mycelium and hyphae (threads in the soil).

1. The mature mushroom’s gills have a hymenium with basidia. In each basidium, a plus and a minus nucleus fuse into a diploid nucleus.
2. It divides by meiosis into four haploid nuclei (two +, two −). Four sterigmata grow on the basidium, one nucleus goes into each, and four basidiospores form.
3. The ripe basidiospores are released and spread by air.
4. In a suitable place, each spore germinates into a primary mycelium with one nucleus per cell.
5. A plus and a minus primary mycelium fuse to form the secondary (dikaryotic) mycelium, with two nuclei per cell.
6. In the right temperature and moisture, the secondary mycelium forms buttons that grow into mature mushrooms, and the cycle repeats.

Draw the cycle as a ring of these stages: mature mushroom → basidiospores → primary mycelium → secondary mycelium → button → mature mushroom.

A. A: pileus, the cap, which carries and shelters the gills. B: gills, which make the basidiospores. C: stipe, the stalk, which holds the pileus up so that the spores can be carried away by the air. D: mycelium (hyphae), which absorbs water and food from the soil.
B. On the gills (B), in their outer layer, the hymenium, on the tips of the basidia.
C. Fruiting body: pileus (A), gills (B) and stipe (C). Mycelium: D.

A. A: basidium; B: paraphysis; C: hymenium; D: sub-hymenium; E: trama.
B. A, the basidium, is fertile: it makes four basidiospores on four sterigmata. B, the paraphysis, is sterile: it makes no spores and only supports and spaces the basidia.
C. A young basidium has two haploid nuclei, one + and one −. They fuse to form a diploid nucleus, which divides by meiosis into four haploid nuclei. Four sterigmata grow at the tip of the basidium; one nucleus moves into each, and a basidiospore forms at the tip of each sterigma.