mushrooms

In broad sense, “mushroom is a macro fungus with a distinctive fruiting body, which
can be either epigeous or hypogeous and large enough to be seen with naked eye and
to be picked by hand” [1]. It is perhaps the most well-known and documented edible
forest product [2]. Mushrooms have been widely used as foods [3, 4] and very often
as delicious and nutritious foods [5]. Approximately 14,000 described species of the
1.5 million fungi estimated in the world produce fruiting bodies that are large enough
to be considered as mushrooms [6]. Mushrooms belong to basidiomycetes and
ascomycetes with a cell cycle including the formation of sexual spores and have
two growth phases, i.e., the vegetative phase (mycelia) and the reproductive phase
(fruit bodies). The fungal spores are located in a special structure called the basidium
(for Basidiomycetes) or the ascus (for Ascomycetes). The mushroom continues its
life cycle in three key stages. viz., vegetative growth, reproductive growth, and spore
production by fruit bodies of the mushrooms (Fig. 1).
Fungi lack the most important feature of plants, i.e., the ability to use energy from
the sun directly through chlorophyll. Thus, fungi depend on other organisms for
food, absorbing nutrients from the organic material in which they live. The living
body of the fungus is mycelium made out of a tiny web of threads (or filaments)
called hyphae. Hyphae absorb digestive products, penetrating the substrate to some
extent. Under specific conditions, sexually compatible hyphae will fuse and start to
form spores. The larger spore-producing structures are considered as mushrooms.
The spores released from the gills again germinate and develop to form hyphae,
which is the main mode of fungal vegetative growth. The mushroom produces
several million spores in its life, and this life cycle is repeated each time the spores
germinate to form the mycelium. Mycelial growth is generally coupled with
increased enzyme production and respiration.

Global Trends of Mushroom Cultivation
Mushrooms are the common components in folk medicine, especially in Africa, the
Middle East, China, and Japan since ages. Earlier, edible mushrooms were only
harvested wild and were difficult to domesticate and cultivate. Collection from wild
woodlands is still important in the world and particularly in southern Asia [7, 8] and
other developing countries [9]. Mushrooms such as Auricularia, Flammulina, and
Lentinula were most likely cultivated for the first time around the year 600–800 AD
in China and other Asian countries [10]. Their cultivation at large scale started only
at the beginning of the twentieth century when pure cultures of mushroom were
prepared from spore and tissue. As the amount of wild mushrooms shrink from both

the degraded environment and natural resources and more costly labor, cultivated
mushrooms would not only provide food security but also sustainable and more
nutritious diets [5]. The commercial production of edible mushrooms represents
the unique exploitation of a microbial technology for the bioconversion of agricultural, industrial, forestry, and household wastes into nutritious food (mushrooms).
Mushrooms have the capacity to breakdown the lignin and utilize it as a food source,
thus exposing the underlying cellulose and hemicellulose for food use by other
organisms. Thus, mushroom cultivation represents a very basic natural process of
fungal decay.
With the world’s increasing population and its decrease in per capita arable land,
along with rapid urbanization and industrialization, climate change, and a demand
for quality and functional foods, it will be necessary to focus on secondary agriculture and novel crops, such as mushrooms. Mushroom cultivation could also be an
important part of sustainable agriculture and forestry. Huge quantities of wide
varieties of organic waste are generated from agriculture, forestry, and food processing. The impacts of the mushroom business on livelihoods and poverty reduction are significant and widespread. Mushroom cultivation does not require a lot of
land, significant capital investment, but is a viable and attractive activity for both
rural farmers and semi-urban dwellers. Mushroom cultivation strengthens the livelihood of poor and marginal farmers by generating constant farm income and
reduces the vulnerability to poverty. The scale of cultivation can be large or small
based on the capital and labor availability. It can be cultivated on a part-time basis
with little maintenance. Indirectly, mushroom cultivation also provides opportunities
for improving the sustainability of small farming systems through the recycling of
organic matter, which can be used as a growing substrate and then returned to the
land as fertilizer. There are hundreds of identified species of fungi which have made
a significant contribution to human food and medicine. The total number of

described fungi of all kinds is currently 110,000 species [11] of which 16,000 (15%)
species are mushrooms [11–13]. Out of these, more than 3000 species from 231 genera are regarded as prime edible mushrooms [13–15] of which only about 200 are
experimentally grown, 100 economically cultivated, around 60 commercially cultivated, and more than 10 produced on an industrial scale in many countries [16].
Approximately 700 mushroom species out of the known 16,000 are considered to be
safe and have medicinal properties [13]. The number of poisonous mushrooms
approximates 500 species. The most acceptable varieties among the cultivated
types are Agaricus bisporus (button mushroom), Pleurotus spp. (oyster mushroom),
Lentinus edodes (Shiitake), and Volvariella spp. (paddy straw mushrooms). In the
second half of the twentieth century, there were rapid changes in rate of growth of
mushroom production and number of species like shiitake, oyster mushrooms, and
wood ear mushroom, and Flammulina were brought under commercial cultivation.
By the end of the twentieth century, the share of button mushroom in total world
production was less than 40%, which in next 10 years became around 30%. Presently
shiitake, oyster, wood ear, and button mushrooms contribute 22%, 19%, 18%, and
15%, respectively in terms of total mushroom production in the world [17]. The
contribution of medicinal mushrooms in world trade has also increased over last few
decades.
Mushroom farming is today being practiced in more than 100 countries, and its
production is increasing at an annual rate of 6–7%. Cultivated mushrooms have now
become popular all over the world. In 1999, the world production of cultivated
edible mushrooms was estimated to be >7 million tons, showing a steady increase
over the last two decades. China is the largest producer, consumer, and exporter of
mushrooms in the world, followed by the United States and the Netherlands
(Table 1). In China, mushroom is the 6th important crop in the country as far as
revenue generation for the nation is concerned. Mushroom production in China in
2010 was 21,524,473 t [18]. The last few decades have witnessed a sharp rise in
diversification in number of mushroom species that have been cultivated, world
mushroom production, commercialization accompanied with mechanization, and in
many cases automation. Mushroom cultivation and its processing have been beneficial to millions of people in China, India, and other developing countries in terms of
financial, social, and health improvement. The global mushroom industry has
expanded very rapidly in the last two decades by the addition of newer types of
mushrooms for commercial cultivation. In addition, cultivation and development of
mushroom industries have positively impacted on economic growth, and this impact
of mushroom cultivation and mushroom derivatives and products on human welfare
in the twenty-first century can be considered globally as a “nongreen revolution.”