Agaricus bisporus hybrids, obtaining them, and their use

Details Agaricus bisporus hybrids, obtaining them, and their use Agaricus bisporus hybrids, obtaining them, and their use

1999-10-21

2002-02-05

Poon, Peter M. (Department: 3643)

Plant husbandry

Mushroom culture

Reexamination Certificate

active

06343435

ABSTRACT:

The invention relates to novel
Agaricus bisporus
hybrids, a method of obtaining them, and their use in mushroom growing,.
It is known that growing the mushroom
Agaricus bisporus
, also called cultivated mushroom, comprises a certain number of steps, which are recalled herein-below.
A first step (composting) consists in the preparation of a substrate based on straw, horse manure and, if appropriate, nitrogen-containing additives, in order to obtain, by fermentation, a substrate (compost) which contains nutrient elements which can be used by the mycelium during the multiplication phase. The duration of this composting step is around 2 to 3 weeks. In general, the composting step is completed by a step called pasteurization, which consists in improving the quality of the compost by directed fermentation in special rooms, in general over 5 to 7 days. The following step is inoculation, which consists in seeding the culture substrate as obtained with “spawn”, that is to say mycelium multiplied on cereal grains. The inoculation rate specifies the ratio of spawn weight to compost weight. This inoculation rate is generally over 0.5% and under 1%. The next step is the incubation, during which the mycelium multiplies and progressively colonizes the culture substrate. This incubation phase is carried out either on special controlled-environment premises or in a culture cave system at a substrate temperature of around 24-26°. The average time of the incubation phase is approximately 14 days. The next operation which is carried out is called casing, which consists in covering the culture substrate with a layer of a casing material which generally, in particular in France, consists of a mixture of limestone (for example tufa) and peat. This layer has a thickness of generally around 3 to 5 cm. To enhance the formation of fruiting bodies, a thermal shock technique is used which consists in lowering the ambient temperature to around 16-17° C. with a substantial renewal of air and regular watering. This latter phase of inducing the formation of fruiting bodies is sometimes preceded, just after casing, by a phase called prefructification, which consists in maintaining an ambient temperature of around 24° C. with slight renewal of air over 8 to 10 days.
The mushrooms are harvested from successive emergences (termed “flushes”). The so-called first-flush harvest can generally be carried out three weeks after casing. In general, it is possible to harvest 4 to 5 flushes over a period of 5 to 7 weeks after the beginning of the first harvest. The total harvest yield can be expressed by weight of mushrooms per 100 kg of compost. The average yields are approximately 30%.
Thus, growing cultivated mushrooms is very restricting, in particular concerning the temperature regulation, which leads to a noteworthy consumption of energy and thus to considerable costs.
The casing step is also expensive in terms of labour and casing material.
If the formation of the cultured mushroom is to be achieved, however, the casing operation cannot be dispensed with. The same applies to the thermal shock step.
The following works on methods of growing cultivated mushrooms can be cited in particular: J. Delmas, Les champignons et leur culture [Mushrooms and their production], published by La Maison Rustique—Flammarion (Paris, France); The cultivation of Mushrooms (1988), published by Somycel; and Olivier J. M. et al., La culture des champignons [Mushroom production] (1991), published by Armand Colin. With reference to the casing step and the fact that it is required for obtaining the formation of fruiting bodies, W. A. Hayes, The Casing Layer, published by W. S. Maney and Son Ltd., Leeds (Great Britain) may also be cited.
The materials used for casing are very varied. Apart from peat and mixtures of peat and limestone rock, there may be mentioned clay, gypsum, sand and the like. The use of layers of synthetic materials or natural or synthetic polymeric materials which are capable of retaining water has also been recommended. In this matter, the patents, or patent applications, FR-2 549 346, FR-2 603 767, FR-2 676 158, FR-2 723 506 and U.S. Pat. No. 4,079,543 may be cited in particular.
It has now been found that it is possible to obtain Agaricus hybrids which can form fruiting bodies without casing and which can be grown under conditions which are less constraining as regards temperature regulation, because it has been found that certain hybrids obtained by hybridizing strains of
Agaricus bisporus
with
Agaricus bisporus
var.
burnettii
, or progeny or hybridization products of this variety, are capable of forming fruiting bodies without casing and can, moreover, form fruiting bodies without thermal shock. Moreover, the invention allows hybrids to be obtained whose mycelia are capable of multiplying on substrates at higher temperatures without losing their capability of forming fruiting bodies.
These novel hybrids can thus be grown while substantially reducing labour and energy costs.
Moreover, the invention makes it possible to grow cultivated mushrooms even in countries with a hot climate, where it was hitherto impossible to grow them profitably.
The invention relates to a hybrid mycelium of
Agaricus bisporus
having at least one of the following phenotypic, stable and genetically transmissible traits:
after multiplication on a usual culture substrate and penetration of this substrate, it is capable of forming fruiting bodies without casing;
after multiplication on a usual culture substrate and penetration of this substrate, it is capable of forming fruiting bodies at a substrate temperature of 26° C. or above;
after multiplication on a usual culture substrate and penetration of this substrate, it is capable of forming fruiting bodies at an ambient temperature of 24° C. or above;
it is capable of growing on a usual culture substrate at a substrate temperature of 30° C. or above.
The term “hybrid mycelium” designates in the present application:
a) either a mycelium which originates from at least one hybridization between two parental strains of
Agaricus bisporus
, that is to say which originates from the combination via fusion of cytoplasms (plasmogamy) of two homokaryons which themselves originate from two distinct heterokaryotic parent strains,
b) or a mycelium which originates from a spore produced by the fruiting bodies of a mycelium as defined under a) above,
c) or a mycelium which originates from a protoplast obtained from a mycelium as defined under a) and/or b) above.
Mycelia according to the invention are thus intraspecific hybrids.
When the hybrid mycelium according to the invention is capable of growing on a usual culture substrate at a temperature of, for example, 30° C. or above, it must be understood that it is capable of penetrating this substrate at this temperature, without, however, losing its capability of forming fruiting bodies, which means, in particular, that fruiting bodies are produced within normal time limits (not more than 5 to 6 weeks after inoculation), that the yield by weight (weight of harvested mushrooms per 100 kg of compost) over 5 weeks of harvest is at least equal to 10%, and that the mushrooms produced have a normal appearance (morphology, dimensions).
The usual culture substrates are well known and are described, for example, in the abovementioned works. They are generally composts based on horse manure and straw.
The invention relates in particular to a hybrid mycelium as described hereinabove which is capable of forming fruiting bodies at a substrate temperature of 28° C. or above and/or which is capable of forming fruiting bodies at an ambient temperature of 26° C. or above, in particular at 28° C. or above, and/or which is capable of multiplying on a usual culture substrate and of penetrating this substrate at a substrate temperature of 32° C. or above without losing the capability of forming fruiting bodies, and/or which is capable of forming fruiting bodies without casing with a sporophore yield of at least 10 kg per 100 kg of culture substrate over a pe

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