Identification and Control of Several Common Diseases of Edible Fungi

I. Causes of Malformed Mushrooms and How to Avoid Them

Malformed mushrooms lower product grade and may even lose their commercial value, affecting the economic returns of cultivation; this problem is widespread. Common malformed mushrooms include: caps tightly clasped and not opening, appearing "fist-shaped"; long, thick, fat stipes with small caps, appearing "vase-shaped"; sunken caps with cracked, outwardly rolled edges, appearing "broken-bowl-shaped"; narrow, elongated caps, appearing "ox-tongue-shaped"; freckled cap surfaces, appearing "pockmarked"; swollen, protruding tumors in the center of the cap, appearing "bulging-belly-shaped"; two caps spreading side by side with stipes tightly joined, appearing "butterfly-shaped"; caps crooked and uneven, appearing "wavy-edged"; round, wrapped caps with tightly contracted gills, appearing "bald-headed"; longitudinal cracks and fissures on the cap surface, appearing "flower-mushroom-shaped"; several mushrooms growing together, appearing "lotus-shaped"; in addition there are also shrunken mushroom forms, yellowed and discolored mushroom forms, and so on. The occurrence of malformed mushrooms stems ultimately from a mismatch between the cultivation environment conditions and the physiological and biochemical requirements of Bai Ling mushroom (Pleurotus nebrodensis). The key lies in poor coordination of temperature, humidity, light and air during the fruiting period, and operational errors in management techniques, and so on. A detailed analysis follows, along with corresponding methods to avoid the occurrence of malformed mushrooms.

1. Unreasonable house and shed structure

Many of the existing Bai Ling mushroom cultivation sites (indoor mushroom houses and outdoor mushroom sheds) are crudely built with unreasonable structures. Some mushroom houses have doors and windows on only one side, and some have vents opened in the upper half of the wall, so that indoor air does not circulate; some plastic greenhouses have vents on both sides, but the vents all face the two ends of the mushroom wall; and some, although they have vents, never open them in order to keep warm. Because the air in the shed does not circulate, severe oxygen deficiency results, causing the aerobic Bai Ling mushroom to become malformed. An ideal mushroom shed should face south from a north-facing orientation, or face east from a west-facing orientation. From the standpoint of heat retention and ventilation, the cultivation house or shed should not be too large; usually a rectangular shed holding 3000 bags (15 x 8 x 2.2 m) or 5000 bags (25 x 8 x 2.2 m) is suitable. Vents should be set at the lower part of both long sides, built of brick with a 24 x 24 cm opening, one every 1 m, with the openings on the two lateral sides at the same height, which favors air convection. The doors and films at both ends of the mushroom shed should be able to open and close, favoring longitudinal air convection; the shed roof should use anti-drip film plus straw curtains or a shade net.

2. Improper stacking of the mushroom wall

The manifestations: bags are brought into the shed and stacked too high, 10 bags to a stack, exceeding 1 m; some mushroom walls have sticky mud filled between them, which is not breathable; some are watered insufficiently after filling with soil and are on the dry side; some mushroom walls are stacked too densely with no soil filled in between; and some, when building the wall, cut the film at the bag ends incorrectly, cutting only 1/3 of the inward-facing part, too little, while instead cutting the film at the outward-facing end, leaving the mycelium exposed to the air without moisture retention. These conditions inevitably inhibit the growth and development of the fruiting bodies. For example, in the north, when bags are stacked into walls and the soil between bags has insufficient water, and when heating and primordium induction begin in deep winter with little water and a dry bias, the water content inside the bags is instead absorbed by the filling soil, dehydrating the mycelium, and malformed mushrooms with unopened or shrunken caps inevitably appear;

while sticky mud becomes compacted and has poor breathability, cannot regulate the mycelium, and instead hinders normal physiological reproduction.

In mushroom-growing areas north of the Yangtze River, bag walling is the carrier for Bai Ling mushroom fruiting, and it includes both the bags and the filling soil. The purpose of filling soil is to use the organic matter in the soil and at the same time to regulate temperature and humidity. At low temperatures the soil can retain warmth, and when the temperature is high it dissipates heat; this is a casing-soil cultivation mechanism and is also a current model for outdoor shed cultivation of Bai Ling mushroom. To achieve timely fruiting and good mushrooms, based on the large-scale production practice in Guangshui City in northern Hubei, the "five musts" must be met: (1) Timing must be accurate: after the bags are physiologically mature, this is usually completed in early to mid-December, so as to shift into primordium induction; (2) Wall stacking must be stable: bags are stacked 6-7 layers, in a sloped form, wide at the bottom and narrow at the top, with a bottom width of 120 cm, top width of 80 cm, and wall length of 280 cm as suitable; the working aisles between mushroom walls are 60-80 cm apart; (3) Film cutting must be appropriate: the purpose of cutting the film at the inward-facing end of the bag is to let the mycelium connect with the filling soil, and cutting off 2/3 is suitable; when stacking the wall, 2 bags are placed side by side, 4-5 cm apart; the outward-facing end leaves 1.5-2 cm uncut, and the film must not be cut there, serving to protect and enclose the fruiting body; (4) Filling soil must be good: clay is suitable for building the wall, but the soil filled between bags should be clay plus sandy loam, mixed with 1% lime and 0.5% compound fertilizer to make nutrient soil; it is used in two parts, one part mixed with water into a muddy state for building the bags, and one part dry-mixed as filling for the gaps and grooves between bags, after which water is applied; (5) Air holes must be made: after filling the top of the mushroom wall with 3 cm of soil, use mud to form a water-storage rim about 10 cm deep, and every 40-50 cm make a hole 3 cm wide, deep down to a position 2-3 bags from the bottom of the mushroom wall, serving both as an air vent and for irrigation.

3. Congenital nutritional deficiencies

There are 4 manifestations: (1) The raw and auxiliary materials in the formula, cottonseed hulls and wheat bran, are aged, damp and moldy, with nutrients degraded; moreover, the amount of wheat bran, the nitrogen-containing substance in the formula, is on the low side, so there is no adverse reaction in the early stage of mycelial growth, but by the fruiting stage it cannot meet requirements; (2) the culture medium becomes sour and spoiled; (3) water in the bags evaporates and the mycelium dehydrates. These belong to congenital malnutrition, so the mushrooms produced have thin caps, wavy edges, or unopened caps and a yellowish rather than white color, and other variant forms.

The culture material is the medium for the growth and development of Bai Ling mushroom fruiting bodies, and the quality of the substrate is closely related to how many and how good the mushrooms are. To produce more high-quality mushrooms, the "four musts" must be met: (1) Raw materials must be fresh and free of mold, and sun-dried before use for sterilization; (2) The formula must be reasonable; here 2 formulas are introduced: cottonseed hulls 87%, wheat bran 8%, corn flour 2%, lime powder 3%; a formula based mainly on sawdust: broadleaf tree sawdust 80%, wheat bran 15%, corn flour 3%, lime powder 2%. Water content about 60%, pH 7-8.5. (3) Additives must be controlled: the additives commonly used in mixing are gypsum powder or lime powder; besides supplying calcium, both mainly serve to regulate pH. Gypsum powder, namely calcium sulfate, is slightly acidic and is used to buffer alkalinity; lime powder is light calcium carbonate, is alkaline, and is used to prevent pH from becoming too acidic. The culture medium of Bai Ling mushroom

requires a pH of 7-8.5, which is on the alkaline side. In addition, bag making takes place in late autumn when temperatures are high, so to prevent the culture medium from becoming sour and spoiled, lime powder is preferable. According to green food requirements, additives in the formula must not exceed 5%; (4) Fermentation must be controlled: mechanism fermentation uses beneficial microorganisms to naturally catalyze and decompose the culture medium, thereby improving the physical and chemical properties of the substrate, increasing effective nutrients, favoring mycelial absorption, promoting the conversion of as much of the effective components of the culture material as possible into fruiting bodies, and helping to increase yield. During fermentation, 0.3% fermentation agent may be added, the fermentation time is 7 days, and after turning the pile 3 times it is transferred to bagging, sterilization, cooling and inoculation.

4. Inaccurate control of the expected fruiting period

Often, because the cultivator is eager for mushrooms, the mycelium is forced into artificial primordium induction before it is physiologically mature, resulting in premature fruiting and malformation.

Bai Ling mushroom requires "a hundred days of mycelial growth, and primordia appear in a single morning." For this reason, the "three standards" for physiological maturity of the mycelium must be controlled: (1) Mycelial age: cumulative mycelial growth time of 90 days from the inoculation date; (2) Appearance: the surface mycelium on the bag surface is deep white in color; (3) Substrate feel: firm and hard to the touch, slightly elastic, with a "peng" sound when tapped; reaching this standard indicates physiological maturity, and at this time bringing the bags into the shed, arranging them, and building the wall is most suitable.

5. Primordium induction techniques not in place

After the mycelium is physiologically mature, it still needs 10-15 days of low-temperature stimulation at 0-13 degC, and during this period it also needs 5-7 days of temperature-difference stimulation above 10 degC, before the primordia can be induced to differentiate into mushroom buds. This is a distinctive characteristic of Bai Ling mushroom. Cultivators often fail to control this unique species trait, with insufficient low-temperature mycelial resting period and insufficient temperature-difference stimulation, so the physiological and biochemical requirements of the fruiting period are not coordinated, causing fruiting body development to be inhibited and deformed. Some mushroom growers, when bringing bags into the shed for primordium induction in early December, neglect ventilation in order to keep warm, resulting in severe oxygen deficiency in the shed; as a result, what is induced is entirely "fist mushrooms" with stipes up to 20 cm long and caps tightly clasped and not opening. Low-temperature, variable-temperature primordium induction must meet the "four coordinations": (1) Open the mouth to increase oxygen: untie the bag mouth, loosen and twist the bag opening to let a tiny amount of air into the bag, but the bag mouth must not be fully opened, to prevent the mycelium from drying out; (2) Scratch the mycelium to wake it up: according to experience in Xinjiang and the production areas of Beijing and Hebei, after opening the bag mouth, use a small iron rake to scrape away the original spawn block and the surrounding 3.5 cm of aged mycelial skin inside the bag, but do not scratch other parts. Scratching the mycelium favors early emergence of primordia and positions the fruiting point at the center; (3) Alternate dry and wet: on sunny days use a sprayer to spray atomized water in the shed space, with relative humidity required at 85%; at night lift the shed-side covering film to cool naturally, forming dry and wet stimulation; (4) Introduce scattered light: during the fruiting stage, the straw curtains on the shed roof should be thinned by day, with spacing of 6-10 cm, letting sunlight in. The suitable light intensity is 500-600 Lx, but direct light must be avoided, lest water evaporate, primordia shrink, or the mushroom body crack into flower-mushroom patterns.

6. Thinning of mushroom buds not taken seriously

Some people, seeing mushroom buds clustered together, are delighted as if a windfall had come, and although they know the buds are too dense, they cannot bear to pick them off. Because bud thinning is neglected, the fruiting bodies crowd each other, and thus butterfly shapes appear, and lateral

elongated ox-tongue shapes, hunchback mushrooms and other variant forms emerge.

Bud thinning can ensure product shape and quality, and is one of the important technical steps in cultivation management. The specific "four requirements": (1) Keep an appropriate number of buds: usually keep 1-2 per bag, at most no more than 3. More than that disperses nutrients, the mushroom body is not thick and fleshy, and quality instead declines; (2) Select buds accurately: use silver-white color and upright mushroom body as the standard, select the superior and remove the inferior, keep the large and remove the small, keep the strong and remove the weak, and thin where dense; (3) Handle carefully: use a sharp knife to cut off excess young buds, without injuring the retained mushroom bodies and mycelium; (4) Protect buds after thinning: after thinning, the bag mouth film should be pulled straight and slightly twisted to retain warmth and moisture. Maintain temperature at 13-18 degC, not below 8 degC and not above 20 degC; spatial relative humidity 85%-90%. The working aisles between mushroom walls should have shallow water storage for moisture retention; and vents should be opened to keep the air in the shed fresh; at the same time introduce light and raise temperature to promote young bud development.

7. Poor management during the fruiting period

After mushroom buds emerge, they gradually differentiate into fruiting bodies. During the fruiting period, poor regulation of temperature, light and air often leads to deformed fruiting body development, lateral growth, hunchback, sunken cap surfaces, freckled pockmarked faces, color changes, and delayed harvesting with oversized mushroom bodies that do not meet grade standards.

During the fruiting period, management must achieve the "three coordinations": (1) Coordinate heating with oxygen retention: the fruiting period falls in the twelfth lunar month when north winds blow and the climate is cold, and fruiting requires an optimum temperature of 13-18 degC. In northern production areas, besides introducing light and covering with film to keep warm by day, at night one may burn outside the shed and let steam into the shed to raise the temperature. But note that ventilation must not be neglected, lest oxygen deficiency deform the mushroom bodies; (2) Coordinate humidification with ventilation: during the fruiting period the spatial relative humidity required is 85%-95%, and in the cold winter when it is dry, atomized water must be sprayed in the space to increase humidity; at the same time combine this with ventilation, and by no means spray closed-door water or excessive water, lest the shed become oxygen-deficient, or water droplets fall on the mushroom surface and cause water to collect on the cap, rotting it into a pockmarked face. (3) Coordinate light introduction with moisture retention: the fruiting period requires scattered light of 500-600 Lx. The straw curtains on the shed roof should be opened 6-10 cm apart to let sunlight into the shed, creating an environment of "three parts sun, seven parts shade." But light must by no means be too strong, lest it cause water evaporation and cracking of the mushroom body. Therefore, on sunny days the working aisles between mushroom walls in the shed should maintain shallow water storage, so that after light enters the shed, water vapor rises and increases spatial humidity; morning and evening one may spray the space to increase humidity, but by no means spray onto the fruiting bodies, lest mushrooms rot or the caps turn yellow.