Molecular characterization and mating type analysis of oyster mushroom (Pleurotus spp.) using single basidiospores for strain improvement

High fatty acid accumulation and coloration molecular mechanism of the elm mushroom (Pleurotus citrinopileatus)

Pleurotus citrinopileatus is a low-cholesterol, protein-rich, and high-nutrient food. The molecular mechanisms of the compounds and coloration have not been reported. Metabolome and transcriptome were used to clarify the molecular mechanisms of key compounds biosynthesis. K-means analysis identified 19 compounds in P. citrinopileatus, mainly lipids and alkaloids in class 8. In addition, 84 lipids were higher and that the different compounds were mainly enriched in linoleic acid metabolism. A total of 14 compounds detected in the linoleic acid metabolism pathway were significantly up-regulated, while 3 sterol regulatory element binding protein (SREBP) transcription factors were screened. Tryptophan metabolism and riboflavin biosynthesis pathway analysis indicated that 3 Unigenes had tryptophan decarboxylase similar elements, which belonged to tyrosine decarboxylase 1. Moreover, CL15618.Contig5_All had high homology with MFS. In conclusion, the expression of 3 SREBP, the synthesis of isobavachalcone D, and the regulation of riboflavin transport by MCH5 were the reasons for fatty acid accumulation and yellow cap formation in the P. citrinopileatus.

Development of novel rapid-growing and delicious Pleurotus djamor strains through hybridization

The development of fast-growing/short cropping period oyster mushroom (Pleurotus species) having good taste is one of the important needs of mushroom growers. Pleurotus djamor strain woody1, collected recently from the dead wood, has a short cropping period of 30 days but a moderately acceptable taste. One of the cultivated Pleurotus spp., P. djamor strain MDU1, has good taste but a long cropping period of 47 days. Thus, genetic improvement of P. djamor was carried out between these two strains by pairing monokaryons (anastomosis) to develop elite hybrid strains having a short cropping period and good taste. Monokaryons of parental strains showed variation in time required for germination; i.e., basidiospores of P. djamor strain woody1 germinated and developed monokaryotic colonies in 6 days, whereas that of P. djamor strain MDU1 developed monokaryotic colonies in 8 days of incubation. In addition, variation in the growth rate and morphology of the monokaryotic mycelia of both parental strains was noticed, and fast-growing monokaryons were selected for anastomosis. Out of 60 crosses made between mycelia of monokaryotic isolates of both parental strains, 20 crosses showed clamp connection, indicating that they were successful crosses. Out of 20 hybrids, two hybrid strains, viz., W2M4 and W4M4, exhibited higher yields than their parents. They exhibited the short cropping period trait, good taste attribute, and some specific volatile metabolites. This study showed that the developed two hybrid varieties, having desirable agronomic traits, could be used in mushroom farming to increase the mushroom grower's income.

Development of improved strain in species of Pleurotus by gamma irradiation

The oyster mushroom (Pleurotus spp.) is the second important edible mushroom in the world, with 19 per cent contribution to total mushroom production (Sharma et al., Mushroom Res 26(2):111-120, 2017). The cultivated mushrooms face the problems like loss of genetic diversity and strain degeneration (Wang et al., Curr Microbiol 65(4):424-431, 2012). Thus to enhance the productivity within short duration, three species of Pleurotus namely Pleurotus djamor, Pleurotus florida and Pleurotus ostreatus were gamma irradiated at 20 and 25 Gy at 9.779 kGy/h and performance of mutants followed by three generation of selection in paddy straw substrate were observed. Biological efficiency (BE) of P. djamor mutants irradiated at 20 Gy was increased by 9.25 per cent. The number of days taken for primordial initiation was also reduced by 1 day compared to P. djamor. P. florida irradiated at 25 Gy recorded increase in sporocarp size over P. florida. The biological efficiency of P. ostreatus irradiated at 25 Gy was improved by 12.89 per cent and there was earliness in primordial initiation by 3 days compared to P. ostreatus. The polymorphism per cent was analysed by Random Amplified Polymorphic DNA (RAPD) and revealed that P. djamor, P. florida and P. ostreatus had 16.70%, 25% and 22% polymorphism with their respective improved strains.

Cultivation and Nutritional Value of Prominent Pleurotus spp.: An Overview

Pleurotus species are commercially essential mushrooms and widely cultivated throughout the world. The production of Pleurotus mushrooms alone accounts for around 25% of that total cultivated mushrooms globally. In America and Europe, Pleurotus species are considered specialty mushrooms, whereas, in Korea, their cultivation is economically profitable, and it is one of the highly consumed species. Pleurotus species are predominantly found in tropical forests and often grow on fallen branches, dead and decaying tree stumps, and wet logs. Biographical studies have shown that the Pleurotus genus is among the more conspicuous fungi that induce wood decay in terrestrial ecosystems worldwide due to its formidable lignin-modifying enzymes, including laccase and versatile peroxidases. Pleurotus species can be grown easily due to their fast colonization nature on diversified agro-substrates and their biological efficiency 100%. Pleurotus mushrooms are rich in proteins, dietary fiber, essential amino acids, carbohydrates, water-soluble vitamins, and minerals. These mushrooms are abundant in functional bioactive molecules, though to influence health. Pleurotus mushrooms are finding unique applications as flavoring, aroma, and excellent preservation quality. Apart from its unique applications, Pleurotus mushrooms have a unique status delicacy with high nutritional and medicinal values. The present review provides an insight into the cultivation of Pleurotus spp. using different agro-waste as growth substances paying attention to their effects on the growth and chemical composition.

Genetic improvement in Pleurotus (oyster mushroom): a review

Pleurotus is an important genus comprising several edible species of great commercial significance. These species are grown all across the world. The production areas of Pleurotus mainly belong to the Asian part and are gaining wide popularity across the globe owing to their promising nutritional gains. The demand for improved strains with high productivity has also been rising. The genetic improvement in Pleurotus started with a simple selection technique, which later utilized hybridization (intraspecific, interspecific and intergeneric) and mutation breeding. The traits such as productivity, sporelessness and quality improvement are important objectives on which most of the works have been done so far. However, new generation approaches such as molecular breeding, genetic transformation and genome editing techniques also added pace to the present improvement process. Hitherto, seven species of Pleurotus have been sequenced and a sizable data has been generated that can be used in further breeding programs. This paper discusses and summarizes various research findings on genetic improvement of Pleurotus and gives an outlook for future breeding programs.

[Use of ITS and ISSR markers in the molecular characterisation of Pleurotus djamor hybrid strains]

BACKGROUND

Molecular characterisation of wild type Pleurotus species is important for germplasm conservation and its further use for genetic improvement. No molecular studies have been performed with monokaryons used for producing hybrid strains, either with the reconstituted strains obtained by pairing those monokaryons. The molecular characterisation of parental dikaryons, hybrid, and reconstituted strains as well as monokaryotic strains, is therefore of utmost importance.

AIMS

To carry out the molecular identification of Pleurotus djamor strains, i.e. dikaryotic wild type strains, hybrid strains, and the monokaryotic strains used for the hybrid formation.

METHODS

Five wild type strains of P. djamor from different states in Mexico were collected and molecularly identified by sequencing the ITS1-5.8-ITS2 region using ITS1 and ITS4 universal oligonucleotides. Four hybrid strains were obtained by pairing neohaplonts of two wild type strains selected. Six ISSR markers were used for the molecular characterisation of monokaryotic and dikaryotic strains.

RESULTS

Using the ITS markers, an amplified product of 700bp was obtained in five wild type strains, with a 99-100% similarity with P. djamor. A total of 95 fragments were obtained using the ISSR markers, with 99% of polymorphism.

CONCLUSIONS

Wild type strains were identified as P. djamor, and were clearly grouped with Mexican strains from other states of Mexico. ISSR markers allowed the generation of polymorphic bands in monokaryotic and dikaryotic strains, splitting both types of strains. The high degree of polymorphism indicates the genetic diversity of P. djamor, an advantage in mushroom production and in the improving of the species.

Investigating the Effect of Tissue Size on Mycelial Growth of Seven Mushroom Species by Using a Novel Device for Precise Tissue Isolation

Tissue isolation from mushrooms is frequently practiced by both researchers and growers to isolate new and improved strains. In the present study, we designed a simple and convenient device for precise tissue isolation and therefore investigated the effect of tissue size on mycelial growth of seven mushroom species. The developed device consists of a cutting needle and a transfer needle. The cutting needle was used to obtain circular tissue plugs having a height up to 3 mm and variable diameters (2-5 mm) from mushroom fruit bodies. The transfer needle was a stainless steel round rod (1.5 mm in diameter) with a blade-like end. It can be used for collecting mushroom tissue when the cutting needle fails to extract it. With the aid of these devices, precise tissue isolation was achieved. Plate cultures demonstrated that tissue size had little effect on mycelium extension for Lentinula edodes (the winter shiitake), Hypsizygus marmoreus, and Agrocybe aegerita, but influenced the aerobic mycelium density. For Pleurotus ostreatus, Pleurotus eryngii, and Volvariella volvacea, large tissue plugs produced faster mycelial growth and higher aerobic mycelium density compared with small ones. On the contrary, small plugs from the tissue of the flower shiitake and Agaricus bisporus favored mycelial growth. The present study revealed that the preferable tissue size for mycelial growth varies among mushroom species, and the developed device is expected to greatly facilitate the isolation of new and improved mushroom strains.

Variations and Hybridization Compatibility of Single Basidiospore Isolates of Pleurotus sajor-caju (Fr.) Sings

Pleurotus sajor-caju (Fr.) Sings, a mushroom of the family Pleurotaceae, is gaining popularity due to its high nutrient content and capability of growing on various agricultural wastes. There is a need to breed new strain of P. sajor-caju to meet the rising demands of the increasing human population. Strain improvement is achievable through selection and hybridization. Unfortunately, there is limited information regarding the genetic variations of P. sajor caju in Malaysia. Therefore, this study is of interest to document the morphological variations of single basidiospore isolates and to generate hybrids. A total of 200 single basidiospore isolates (SB) obtained from a commercialized strain of P. sajor-caju were obtained from local supermarket in Kuching, Sarawak, and cultured individually on potato dextrose agar. These 200 SBs were characterized morphologically and divided into three main groups based on colony morphology i.e. scattered, rough and smooth. Variations can still be observed in each main group. From each main group, SBs representing the variations were further categorized based on their colony diameter growth after 7 days of post inoculation (CD-7dpi), i.e. slow growing CD-7dpi (SGCD-7), medium fast growing CD-7dpi (MFGCD-7) and fast growing CD-7dpi (FGCD-7). Ten FGCD-7 and ten SGCD-7 isolates were selected for hybridization. The selected SBs were hybridized in all possible pairings without repetition. Sixteen hybridized isolates were recognized and characterized based on CD-7dpi. For all FGCD-7 pairings, SGCD-7 pairings, and between FGCD-7 and SGCD-7 pairings, hybridized isolates had higher CD-7dpi than at least one of its parents were identified. The new hybridized isolates are interesting materials for future study.