Paddy straw mushroom (Volvariella volvacea), commonly known as the straw mushroom, or the Chinese mushroom, belongs to the family Pluteaceae (Kotl. & Pouz) of the Basidiomycetes (Singer, 1961). It is an edible mushroom of tropics and subtropics, and first cultivated in China in 1822 (Chang, 1969). Initially, this mushroom was known as “Nanhua mushroom” after the name of Nanhua Temple in Northern Guangdong Province in China. In the beginning, paddy straw mushroom was cultivated by Buddhist monks for their table, however, by 1875 it was sent is presumed that cultivation of this mushroom begun before the 18th century, almost 300 years ago (Chang, 1977).
Around 1932 to 1935, this mushroom was introduced into the Philippines, Malaysia and other South Asian countries by Chinese (Baker, 1934; Chang, 1974).Paddy straw mushroom is also known as “warm mushroom” as it grows at relatively high temperature. It is a fast growing mushroom, and under favourable growing conditions, total crop cycle is completed with in 4-5 weeks time.
This mushroom can use a wide range of cellulosic materials and the C: N ratio needed is 40 to 60, quite high in comparison to other cultivated mushrooms. It can be grown quite quickly and easily on uncomposted substrates such as paddy straw and cotton waste or other cellulosic organic waste materials (Ahlawat & 2005). It has been considered as one of the easiest mushrooms to cultivate.
Paddy straw mushroom was first cultivated in India in1940. However, its systematic cultivation was first attempted in 1943. Presently this mushroom is more popular in coastal states like Orissa, Andhra Pradesh, Tamil Nadu, Kerala and West Bengal. However, it can also be cultivated in most of the states, where an agroclimatic conditions suit and Agro waste is available in plenty.
Life Cycle and Genetics of Breeding System
In contrast to green plants, most mushroom species are haploid, and diploid phase is normally transient and restricted to the basidium. Paddy straw mushroom has a distinction from other mushrooms. Being homothallic species, the individual uninucleate haploid self-fertile spores germinate to produce mycelia and completes the life cycle without the need of a mating type factor. Clamp connections are absent in Volvariella spp. In V.
In V. volvacea, the hyphal cells are multinucleate, clamp connections are absent, and basidiospore receives only one nucleus each following meiosis. Wide variation exists in growth rate and other characteristics of single spore mycelia. It is still difficult to call this mushroom as primary homothallic as the research carried out by different workers has given different explanations behind the existence of self-fertility among the majority of the basidiospores and non-existence in minority of the basidiospores.
The fruiting body of the paddy straw mushroom is divided into six different developmental stages viz., pinhead, tiny button, button, egg, elongation and mature stage. Each has its morphology and anatomy.
1. Pinhead stage: The pinhead stage is of the size of a pinhead in which the veil is spotlessly white. In vertical section, the pileus and stipe are not visible. The whole structure is a knot of hyphal cells
2. Tiny button: Both the tiny button and pinhead stages are formed from interwoven hyphae. In a tiny young button, only the top of the veil is brown, while the rest is white. It is round in shape, and if a vertical cut is made through the button, the lamellae are seen as a narrow band on the lower surface of pileus
3. Button stage: This stage of paddy straw mushroom is sold while the stipe attains the maximum length The
stipe is marked with water proof drawing ink. in the market at a premium price. In this stage, the whole structure is wrapped in a coat, which is called as the universal veil. Inside the veil, closed pileus exists. As such the stipe is not visible but in longitudinal section of mushroom, it is visible.
4. Egg stage: This stage also fetches a premium price in the market, at this stage, the pileus is pushed out of the veil, and the veil remains as volva. The stipe is again not visible at this stage. The lamellae of this stage do not bear basidiospores. The size of the pileus remains very small up to this stage.
5. Elongation stage: The pileus remains close, and the size is smaller than the mature stage, while the stipe attains the maximum length. The stipe is marked with water proof drawing ink.
6. Mature stage: At mature stage, the structure is divided into three regions: (i) the pileus or cap, (ii) stipe or stalk and (iii) the volva or cup The pileus is connected in the center with a stipe and is usually 6 to 12 cm in diameter.
The fully grown pileus is circular with an entire margin and smooth surface. The surface is dark grey at center and light grey near the margin. The lower surface of the pileus bears lamellae, and their number varies from 280 to 380. The lamellae vary in size from full size to one-quarter size of the pileus.
Under the microscope, each lamella is seen to be composed of three layers of interwoven hyphae. The outermost layer is called the hymenium, and it forms the club-shaped basidia and the cystedia. The basidia bear basidiospores. Usually, one basidium bears four basidiospores. The basidiospores vary in shape; egg shaped, spherical or ellipsoidal. The colour of basidiospores again varies, and it may be of light yellow, pink or dark brown.
Another important part of the mature fruiting body is the stipe, which connects the volva and the pileus. The length of the stipe depends upon the size of the pileus, and it is usually about 3 to 8 cm in length and 0.5 to 1.5 cm in diameter. It is white, fleshy and without any annulus. At the base of stipe remains the volva, which is a thin sheet of interwoven hyphae around the bulbous base of the stipe. The volva is fleshy, white and cups shaped with irregular margins. The base of volva bears rhizomorphs, which absorb the nutrition from the substrate.
- Directorate of Mushroom Research