Authors; CM Ayyub, Saqib Ayyub, M. Muzammil Jahangir, Asad ur Rehman, Saeed Ahmad (IHS, UAF)

The milky mushroom has unique characteristics of high-temperature tolerance during its growth. Cultivation of warm-weather (30-38°C) varieties of edible mushrooms has been scientifically challenging. Milky white mushroom (Calocybe indica) is one of such mushroom varieties, where complete commercial production techniques have been standardized. The first-ever milky white mushroom variety (Calocybe indica) was released from Tamil Nadu Agricultural University, Coimbatore, India in 1998. Over a decade, commercial production of this mushroom variety has assumed greater impetus in the world. The first report on the wild occurrence of Calocybe indica P&C, commonly called “Dhuth chatta”. Its milky white color and robust nature are appealing to consumers. In nature, milky white mushrooms are seen grown on humus-rich soil in agricultural fields or along the roadside in tropical and subtropical areas.

This mushroom is morphologically similar to Agaricus bisporus (button mushroom), it has been quite popular in southern Indian states and slowly getting popular in other countries (China, Malaysia, and Singapore). Small-scale mushroom growers prefer to grow this tropical mushroom due to the following reasons:

  • Ideally suited to a warm humid climate (30-38°C; 80% to 85% humidity).
  • Its longer shelf life without any refrigeration (can be stored for up to 7 days at room temperature).
  • Retains a fresh look and does not turn brown or dark black like that of button mushrooms.
  • Lesser contamination due to competitor molds and insects during crop production under controlled conditions.
  • The infrastructure needed to grow this mushroom is very much affordable and the cost of production is comparatively low, which means industrial production could be attractive.
  • Has a short crop cycle (7-8 wk) and good biological efficiency of 140%.

Spawn and spawning

SUBSTRATES AND SUPPLEMENTS

Sorghum or wheat grains were found to be the best substrates for Calocybe indica spawn production. During the preparation of the spawn culture, these substrates are half cooked in water for about 30 min, and the excess water is usually drained before the grains are slightly air-dried and mixed thoroughly with 2 wt% calcium carbonate. This wet substrate is then transferred to autoclavable polypropylene bags (usually 30 × 12 cm), which should be filled up to 75% volume and sterilized at 1.42 kg/ cm2 pressure for 2 hours.

After cooling to ambient temperature, the bags should be aseptically inoculated with the mushroom mycelia, closed, and incubated at 30°C. After 15 to 20 days of incubation, complete colonization of the substrate by the mushroom mycelia should be observed, meaning that they can be used for culture bed inoculation. The age of spawn is an important factor that influences the flushing pattern and yield of milky white mushrooms. Prolonged storage of spawn reduced productivity and total yield.

A variety of substrates were tested for the cultivation of Calocybe indica but, with limited success. Including soil-sand, soil-sand-maize meal, and soil-sand pulse powder. In soil-sand-meal, primordial fungus appeared in 5-6 weeks, but another 2-3 weeks were required to have a matured well-differentiated fruiting body. Later they develop suitable, low-cost synthetic compost for the production of more fruit bodies. Calocybe indica grows on unsterilized, paddy straw-maize or wheat bran substrate chopped rice straw. Several other lignocellulosic agricultural residues like sunflower stalks and hulled head, jackfruit rind, cotton stalks, waste cotton, sugar cane Bagasse, jute waste, corn cobs, groundnut hulls, coffee/tea waste have also been tried by many workers with limited success. In a separate study, Kumar et al. evaluated 11 different supplements viz., wheat bran, soybean flour, pigeon pea powder, green gram powder, cotton cake, mustard cake, neem cake, and lentil powder. Use 30% maize powder to supplement paddy straw substrate in order to increase mushroom yields.

Milky white mushroom production.

Currently, milky white mushroom farming is done manually. The cultivation process is labor-intensive and fairly energy demanding. The crop production process involves six different steps viz.

  1. Spawn production
  2. Substrate pre-treatment
  3. Mushroom bed preparation,
  4. Cropping room maintenance during spawn run and mushroom production
  5. Harvesting and packaging
  6. Management of spent mushroom substrate

Farmers normally use milled paddy straw as substrate (2-4 cm) The milled straw is soaked in water for 4-5 hr, prior to hot water (80°C) or steaming treatment for 45-60 min. After pre-treatment, the materials are shade-dried to get appropriate moisture conditions (60-70%) before bed preparation. Polypropylene bags (60 × 30 cm) are normally used as containers for bed production and layer spawning with grain spawn is typically the adopted technique. For spawn run, the bags are kept in clean rooms maintained at 25-30°C and 80-85% humidity for 15-20 days. At this stage, steam-treated casing soil is applied on half-cut beds to a depth of 1.5-2.0 cm. The beds are then transferred to cropping rooms (polythene sheet-covered rooms) maintained at 30-35°C, with humidity of higher than 80%. Sufficient natural light should be made available inside the cropping room. Pinheads will appear on the casing surface within a week and the mushrooms attain harvesting maturity in a couple of days. The first flush of mushrooms will normally appear within 24-30 days of bed preparation. Over a period of 40-45 days, mushrooms could be harvested in three to four flushes. Temperature ranges of less than 25°C, degenerated the mushroom growth. Other hindrances to milky mushroom production include over-matured spawn, insect infestations, contaminant fungi, and bacteria due to unhygienic conditions and poor farm maintenance.

Role of growth regulators in crop production

Several growth regulators like indole acetic acid, indole-3-butryic acid, gibberellic acid (GA), and kinetin were tested for their effect on the sporophore size and yield of milky white mushroom. The results clearly indicated that GA at 40 ppm increased the yield of sporophores. The average weight of individual mushrooms was found to be high when GA and kinetin were sprayed. Pileus (cap of mushroom) diameter and its weight were found to be slightly higher in the above treatments, but none of the growth regulators showed a significant influence on the stipe length and its weight. Pani has also reported that spraying GA at 50 ppm at the time of pinhead formation had greatly influenced the size of sporophores and yield of milky white mushrooms.

CHEMICAL COMPOSITION AND NUTRITIONAL VALUE

The six major constituents of mushrooms are water, proteins, carbohydrates, dietary fiber, fat, and ash. The moisture content of mushrooms is usually determined by drying at 105°C in a hot air oven overnight to a constant weight. The difference in weight before and after drying is expressed in terms of percentage. The protein content is determined by Kjeldahl method and the lipids are estimated by the Twisselman method using an extractive solvent like diethyl ether. The lipids in mushrooms include free fatty acids, mono-, di-, and triglycerides, sterols, sterol esters, and phospholipids. The sporophore samples are incubated in a muffle furnace at 500°C to estimate the ash content which normally contains potassium and phosphorous. According to Crisan and Sands, the energy content in mushrooms is influenced by the composition of crude protein, fat, and carbohydrates whose conversion factors are 2.62, 8.37, and 3.50 kcal/g of the individual components, respectively. These conversion factors are slightly lower than the actual conversion factors used for other food ingredients because they are estimated as crude components. Sivaprakasam and Doshi et al, recorded 20.2% protein from the caps of milky white mushrooms (on a dry weight basis). The dietary fiber (fungal cell wall components mostly, chitin-N-acetyl-glycosamine units) and protein contents of milky white mushrooms are higher than button mushrooms but lower than oyster mushrooms. The beta-glycans present in dietary fibers of mushrooms is reported to have a stimulatory effect on the immune system with anti-mutagenic, anticancer, and antitumor activities. Mushrooms are good sources of minerals (Ca, K, Mg, Na, and P), trace elements (Cu, Fe, Mn, and Zn), and sometimes, toxic heavy metals (Cd and Pb) as compared to vegetables.

Medicinal properties of milky mushroom       

 The nutritional quality of mushrooms is influenced by the substrate used, organic supplementation, and other additive effects. Medicinal mushrooms are known to be an abundant source of nutraceuticals that could decrease/reverse the progression of several diseases. One such disease is diabetes mellitus, which is otherwise characterized as hyperglycemia associated with insulin deficiency. A complication of this disease includes hypertension, atherosclerosis, microcirculatory disorder, and changes in large and small blood vessels. Along with medicinal herbs, mushrooms are believed to play an important role in treating diabetic patients without any harmful side effects. Both cold and hot water extracts of milky white mushroom powder were tested for anti-hyperglycemic effects on diabetes-induced rats (using streptozotocin). The rats were orally given mushroom extract for 45 days and tested for insulin and glycosylated hemoglobin levels. The results indicated normal values at the end of treatment.       

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I am working as Assistant Horticulturist (BS-18) at Water Management Research Farm Renala Khurd, before this served as Assistant Professor (IPFP) in Horticulture at the University of Sargodha. I have completed my Ph.D. in 2018 from the Institute of Horticultural Sciences, UAF previously worked as Visiting Lecturer in Horticulture UOS, worked as Research Fellow in ACIAR project on vegetables, and worked as Teaching Assistant in Horticulture UAF. Moreover, Ph.D. IRSIP did in the NC State University, United States.

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