IDENTIFICATION, MOLECULAR CHARACTERIZATION AND SUBSTRATE EFFECTS ON GROWTH OF MUSHROOMS

ABSTRACT

Mushrooms are non-timber forest products with many benefits but the availability and use are still unsustainable because of the poor traditional method of their identification as well as the assumption that substrates affect their constituents. This underscores the need for a molecular characterization of wild mushrooms and perhaps the effects of substrate on them. It is on this premise that the present study was initiated to: (i) identify and classify different types of wild mushrooms into edible and non-edible variants; (ii) determine the biochemical/nutritional constituents of the edible and non-edible mushrooms grown on different substrates; (iii) characterize  the  DNA  constituents  of  the  edible  and  non-edible  mushrooms  grown  on different substrates, and (iv) determine the growth and yield potential of wild mushrooms on a conventional substrate. Laboratory identification, growth, determination of chemical compositions and molecular characterization of the wild and grown mushrooms were carried out at the Department of Crop Science Laboratories, Centre for Energy Research, University of  Nigeria,  Nsukka  and  the  Biotechnology  Laboratory  of  the  International  Institute  of Tropical Agriculture (IITA), Ibadan. The experimental materials used were the fifteen mushrooms collected from three habitats (logs of wood, termitaria and humus soil) in five different locations in Nsukka derived savannah zone. All the experiments were laid out in completely randomized design (CRD). The genetic differences that existed among the wild mushrooms sourced from different locations were evident in the morphological, chemical parameters  measured  and  determined,  respectively  and  on  their  DNA  constituents.  The cluster analysis conducted on the quantitative traits grouped the wild mushrooms into five major clusters at 80 % similarity coefficient indicating sufficient variability to warrant selection. The study identified eight mushrooms in the order Agaricales that are edible and seven mushrooms in the order of Polporales and Russulales that are non edible. Edible mushrooms in the order Agaricales gave significantly higher levels of protein (eg. mushroom from Udenu humus gave 19.48 % protein)while non-edible mushrooms from the wild have higher pileus circumference, area, diameter and no stipe as well as moderately high levels of alkaloid, saponnin and flavonoid. For instance, the mushroom from Igboeze South log gave significantly (p<0.05) higher pileus circumference of 37.50 cm, area of 112.1 cm2 and diameter of 11.93 cm while mushroom from Nsukka humus (NLH) showed significantly (p<0.05)   lower pileus circumference of 11.94 cm. Mushroom from Igboeze humus gave moderately high levels of alkaloid (4.55 %), saponnin (3.88 %) and flavoniod (9.10 %). The detailed identification of the selected wild mushrooms by molecular characterization of the DNA showed the limitation of the traditional method in mushroom identification. Hence, the traditional method identified only nine out of the fifteen to the species level while molecular characterization identified all but one to the species level. Two out of the three spore sources grown on a conventional mushroom substrate gave higher levels of pileus circumference and five times the area of the mushrooms obtained from the wild. Substrate compositions affected the DNA constituents of the three mushrooms. The Gmelina arborea substrate maintained the DNA constituents as obtained in the mushrooms sourced from the wild while Erythrophleum suaveolens substrate modified the genetic structure, as well as their genus and species names. For instance, Pleurotus and Volvariella (genus names) in G. arborea changed to Gonaderma and Fungal endophyte respectively in E. suaveolens.

INTRODUCTION

Mushrooms are non-timber forest products that are often found as saprophytes on soil, open fields, farm lands, woods and roadsides (Stanley et al., 2011). They are primordial multicellular fungi which are typically found on or near the surface of the substrate. Mushrooms are fleshly fungi forming umbrella like fruiting body (Joseph and Oku, 2016) and are widely distributed in the temperate and tropical regions (Chang and Miles, 2004). Naturally, mushrooms growth is season dependent (Joseph and Oku, 2016). However, Volk (2001) has shown that mushroom can be grown all year round when the right factors for cultivation are in place.

In recent years, increasing attention has been given to farming of edible and medicinal mushrooms due to their special nutritional and medicinal attributes (Yan-Yan et al., 2016). Zhang et al. (2015) noted that the history of edible and medicinal mushrooms can be traced back to 4000 years, and are treasured as a healthy food because of their unique edible and medicinal values.  In Nigeria, many people in both urban and rural areas are familiar with mushrooms that are growing around them. They selectively exploit them for food and medicine (Okhuoya et al., 2010). A good number of edible mushrooms are consumed by different tribal groups in Nigeria (Gbolagade et al., 2006). Edible mushrooms are highly nutritious and can be compared with eggs, milk and meat (Oei, 2003). Studies on the nutritional values of edible mushrooms ranked them with dairy, plant and animal foods in vitamins, protein and mineral contents (Okhuoya et al., 2010). The content of the essential amino acids in mushroom is high and close to the need of the human body. Mushroom is easily digested when consumed and has no cholesterol content (Belewu and Belewu, 2005).

The growth of mushroom production industries and the use of agro-industrial based substrate as the major raw material in mushroom production may provide a solution to the nation’s waste management problems and pollution challenges, poverty alleviation and rising youth unemployment (Okhuoya et al., 2010). Mushroom production can also provide a sustainable income and can be a good source of foreign exchange through exports (Venturella, 2006).

It is therefore beyond doubt that increase in mushroom production will enhance the use in medicinal research, food supply, poverty alleviation and pollution control through proper waste management. Despite these numerous benefits of mushroom to man, mushroom production has not been fully exploited because of the over dependence on wild sources. Okhuoya et al. (2010) reported that in Nigeria, a great quantity and variety of edible mushrooms are sourced from the wild. Reliance on mushroom from the wild has made its availability unsustainable. Another challenge is the poor traditional method used in edible mushroom identification. Yan-Yan et al. (2016) stated that mushrooms are traditionally identified by morphology. Such traditional method of identification had caused death as a result of mushroom poisoning or intoxication of the consumer. Besides, it is believed that mushroom substrates do influence the growth as well as its constituents (Haas and James, 2009). This could be as a result of the fact that mushrooms secrete digestive enzymes into the substrate and absorb the dissolved nutrients (Joseph and Oku, 2016). However, no scientific research  has  proved  or  disproved  this  suspicion  about  mushroom  substrates.  Thus,  the edibility of every mushroom is always ascribed to its substrate in so many places. At present, molecular identification of mushrooms using DNA characterization has been recommended (Han et al., 2016). The application of this molecular identification technique to mushrooms from the wild has the potential of facilitating the characterization of the attributes of the edible and non-edible species.

There is therefore a need to identify and classify mushrooms using DNA method as well as grow identified ones in different substrates to determine effects of such substrates on their growth and chemical composition. The general objective of this research was to identify, do molecular characterization and study substrate effects on growth of mushrooms from the wild. The specific objectives were to:

1.   identify and classify various wild mushrooms into edible and non-edible variants;

2.   determine  the  biochemical/nutritional  constituents  of  the  edible  and  non-edible mushrooms grown on different substrates;

3.   characterize the DNA constituents of the edible and non-edible mushrooms grown on different substrates; and

4.   determine  the  growth  and  yield  potential  of  wild  mushrooms  on  conventional substrates.

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