Genetics and Breeding of Edible Mushrooms

A.C. Chang

• Publisher: Routledge
• Year: 2018
• ISBN:
  9781351445726
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Botany
• Index: Biological Sciences

This text not only explores the breeding problems for Agaricus bisporus, the button mushroom, but approaches the subject in the context of the large range of edible mushrooms which are currently under commercial cultivation worldwide. From the background and general objectives of culture collection and breeding to the genetic systems of edible mushrooms and the molecular biological approaches to breeding, the coverage is in-depth and current. The applications of breeding programmes for specific purposes, including provision of a food source, production of high value fungal metabolites and upgrading of lignocellulosic wastes and wastewater treatment are also discussed.

CHAPTER 1

MUSHROOM AND MUSHROOM BIOLOGY

Shu-Ting Chang

Department of Biology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.

1. INTRODUCTION

Due to its pleasant flavour and substantial protein, the mushroom is a source of human food which can help to satisfy the basic human requirement for better nutrition. The medicinal properties of mushrooms also represent a relatively untapped resource for medical applications. Furthermore, the substrates used for mushroom cultivation are derived mainly from agricultural and industrial organic waste materials. It is because of these attributes that mushroom research and industries have been gaining more and more attention in recent years.

The use of mushrooms and mushroom cultivation have a long history in human development. Mushroom science, derived from the principles of microbiology, environmental engineering and fermentation technology (Chang & Miles, 1982), has developed in modem times to form the basis both for new cottage type industries and for highly developed industrial mushroom growing complexes. Biological efficiency, i.e., the yield of fresh mushrooms, in proportion to the weight of compost at spawning, can reach 100% in experimental tests, with 40-60% as a good average value per crop.

In overall view, the world production of cultivated edible mushrooms was 2,182 thousand tons and 3,763 thousand tons in 1986 and 1989/90, respectively (Table 1). In those 3 years, mushroom production increased by 72.5% or an annual increase of 24.5% (Chang & Miles, 1991). A comparison of production between 1986 and 1989/90 reveals that all cultivated mushroom species increased during that period, ranging from 16% for Agaricus up to 438% for Pleurotus. The second largest increase was 236% for Auricularia. However, the percentage of total world production of Agaricus and Lentinus mushrooms decreased as a consequence of the increase in production of the other cultivated edible mushroom species, in particular Pleurotus species. If 88.8 cents per pound, reported as the average price received by growers in U.S.A. in 1900-1991 (NASS, 1991), is used for purposes of estimating the value of the total world mushroom crop, the figure for the 1989/90 financial year totalled US$7,485,058,500.

TABLE 1. Comparison of 1986 and 1989/90 world production of cultivated edible mushrooms.

Source: Chang & Miles (1991).

It should be noted that an upward tendency in world production of cultivated edible mushrooms is clearly indicated in Fig. 1. There is a particularly sharp increase in growth over the last five years. This tendency is expected to continue in the future due to advances both in our basic knowledge of mushroom biology and in the practical technology associated with mushroom cultivation. The significant impact of mushroom research and production can be considered globally but must be implemented according to local materials, labour and climatic conditions.

2. WHAT IS A MUSHROOM?

This is not a new question or a new issue. The word “mushroom” may mean different things to different people in various countries. Even in the literature, the term mushroom may also have different meanings (Table 2). It is my viewpoint that specialized studies, and the economic value of mushrooms have reached the point where an up-to-date definition of the term mushroom is now warranted. This will serve a useful purpose at a time when the number of cultivated mushroom species is increasing, when production of established cultivated mushrooms has also shown a steady increase (Fig. 1), and when an increasing number of countries and people are engaged in mushroom cultivation as an agricultural or industrial technology. In this chapter, “mushroom” refers to the definition given by Chang and Miles (in press). In a broader sense “the mushroom is a macrofungus with a distinctive fruiting body which can be either epigeous or hypogeous and large enough to be seen with the naked eye and to be picked by hand. Thus, mushrooms need not be Basidiomycetes, nor aerial, nor fleshy, nor edible. Mushrooms can be Ascomycetes, grow underground, have a non-fleshy texture and need not be edible”. In other words, mushrooms can be roughly divided into four categories: (1) those which are fleshy and edible fall into the edible mushroom category, e.g., Agaricus bisporus; (2) mushrooms which are considered to have medicinal applications, are referred to as medicinal mushrooms, e.g., Ganoderma lucidum; (3) those which are proven to be, or suspected of being poisonous are named as poisonous mushrooms, e.g., Amanita phalloides; (4) a miscellaneous category which includes a large number of mushrooms whose properties remain less well defined. These may tentatively be grouped together as ‘other mushrooms’. Certainly, this form of classifying mushrooms is not absolute. Many kinds of mushrooms are not only edible, but also possess tonic and medicinal qualities. In a botanical sense, mushrooms are fungi which lack chlorophyll and so cannot use solar energy to manufacture their own food as do green plants. However, mushrooms can produce a wide range of enzymes, that degrade the complex substrates on which they grow, following which they absorb the soluble substances for their own nutrition. This absorptive nutrition is a characteristic of fungi. Mushrooms can also be poetically described as: “Without leaves, without buds, without flowers: yet they form fruit. As a food, as a tonic, as a medicine: the entire creation is precious” (Chang 1990).

FIGURE 1. Annual world production of cultivated edible mushrooms.

T...