Development of high yielding strain of Pleurotus tuber- regium: fructification, nutritional and phylogenetic studies

Abstract

Mushrooms are nutritionally rich, healthy and medicinal. Pleurotus tuber-regium (Fr.) is one of the nutritious medicinal mushroom found in the tropics and subtropics, but with history of slow growth and low sclerotia yield. In this study, mutants were created by mycelia exposure to ultraviolet irradiation (at a wavelength of 254 nm and a distance of 45 cm), for 3 h and sub-cultured at 30 min interval. The DNA from the wild and mutant strains were extracted, PCR amplified and sequenced. A phylogenetic tree was constructed to show the degree of similarity and differences between the wild and the mutant strains. Fructification studies were conducted on Rhodes grass straw and sawdust to determine the viability of the mutant strains and any nutritional improvement. The wild strain of P. tuber-regium and mutant produced at 30 min (Pt30) cultivated on sawdust and Rhodes straw, yielded sclerotia with biological efficiency of 8.8 and 47.6% respectively. Proximate analysis of the sclerotium showed that the mutant, Pt30, had improved nutritional compositions compared to the wild strain with a total non-structural carbohydrate concentration of 2.41 g as against 0.93 g. Conclusively in this study, better strains of P. tuber-regium were produced with faster growth rate, higher mycelia ramification rate on lignocellulosic substrate and a higher sclerotia yield than the wild P. tuber-regium. It was also established that mutagenesis is capable of improving P. tuber-regium for a successful commercial venture in sclerotia production.

Keywords: DNA nucleotide sequence; Mushroom improvement; Mutagenesis; Proximate analysis; Sclerotium cultivation.

Fig. 1

Forty (40) days after inoculating Chloris gayana straw with aP. tuber-regium wild bP. tuber-regium mutant (Pt30) mycelia showing growth of sclerotium and good mycelia ramification cP. tuber-regium mutant (Pt60) mycelia showing thickening of the hyphal strand d Pt180 mutant showing direct Primordial formation without sclerotia showing a close semblance with the Australasian-type P. tuber-regium

Fig. 2

Scanning electron micrograph of aP. tuber-regium sclerotium with little or no food granules and non-dense biofilm b Pt30 sclerotium with no food granules but mycelia are heavily surrounded by biofilm c Pt60 sclerotium with very few spherical food granules and the mycelia enclosed in biofilm d Pt90 sclerotium having little or no food granules and EPS was obvious e Pt150 sclerotium with very few food granules and highly inter-twined hypha strands f Pt180 sclerotium with spherical food granules on the hyphae strands and an encapsulating biofilm

Fig. 3

Comparison of nucleotide sequences of ITS region of some Pleurotus species obtained from the GENBANK database (AY5-P. sajor-caju, FM-Uncultured fungus DNA isolate, AY3-P. australis, KF-Pleurotus sp and FJ-Lentinus sajor-caju), 5P (P. sajor-caju wild), 4H (P. tuber-regium hybrid), 4P (P. pulmonarius wild), 5H (P. tuber-regium hybrid) and P. tuber-regium mutants obtained at 30, 60, 90, 120, 150, 180 min and the wild strain-N) for different sites on the amplified fragments. Variations are shown in boldened letters

Fig. 4

Evolutionary relationships of some other Pleurotus taxa from GenBank database with P. tuber-regium wild (N) and mutants obtained at 30, 60, 90, 120, 150 and 180 min with their GenBank Accession numbers