The edible fungus Pleurotus ostreatus (oyster mushroom) is an industrially produced heterothallic homobasidiomycete whose mating is controlled by a bifactorial tetrapolar genetic system. Two mating loci (matA and matB) control different steps of hyphal fusion, nuclear migration, and nuclear sorting during the onset and progress of the dikaryotic growth. Previous studies have shown that the segregation of the alleles present at the matB locus differs from that expected for a single locus because (i) new nonparental B alleles appeared in the progeny and (ii) there was a distortion in the segregation of the genomic regions close to this mating locus. In this study, we pursued these observations by using a genetic approach based on the identification of molecular markers linked to the matB locus that allowed us to dissect it into two genetically linked subunits (matB␣ and matB␤) and to correlate the presence of specific matB␣ and matA alleles with differences in monokaryotic growth rate. The availability of these molecular markers and the mating type dependence of growth rate in monokaryons can be helpful for marker-assisted selection of fast-growing monokaryons to be used in the construction of dikaryons able to colonize the substrate faster than the competitors responsible for reductions in the industrial yield of this fungus.Incompatibility systems are mechanisms for the creation of variability preventing selfing. The phytopathogenic fungus Ustilago maydis and the mushrooms Coprinus cinereus and Schizophyllum commune have been used as models to study mating incompatibility in basidiomycetes. In these species, mating is controlled by two unlinked multiallelic loci whose independent segregation generates four mating specificities in the progeny of a single individual (these fungi are then called tetrapolar) (for reviews, see references 2, 7, and 11). In tetrapolar basidiomycetes, a single basidiospore produces upon germination a hypha in which all nuclei are identical (homokaryon). Two hyphae with different mating alleles at the two incompatibility loci are able to fuse and give rise to a mycelium in which the two parental nuclei do not fuse throughout vegetative growth. This kind of mycelium is called dikaryotic, and the individual mycelium is called a dikaryon. Vegetative growth is maintained until a set of environmental conditions triggers fruit body formation. Karyogamy occurs within the basidia, and it is immediately followed by meiosis producing four uninucleate spores. The monokaryotic and dikaryotic conditions can be distinguished by the presence of clamp connections in dikaryons and their lack in monokaryons. Clamp connections are hookshaped structures involved in equal nuclei sorting to the daughter cells produced by mitosis.Genetic studies carried out in C. cinereus and S. commune have shown that the A incompatibility locus codes for homeodomain-containing transcription factors (2,13,14,18,21,24,27,28). The b mating-type locus of U. maydis is homologous to the A locus and also codes for homeodomain prote...

There has been much taxonomic confusion over the identification of Prosopis species, especially where introduced. Prosopis juliflora is the most widespread species in the arid and semi-arid tropics, although it has been confused with other species, particularly the closely related Prosopis pallida. In this study, RAPDs markers were used for the first time to distinguish between these species. Eighteen primers were used in amplification reactions, which yielded an average of 120 bands per accession. A dendrogram showing genetic similarities among accessions was constructed using UP-GMA cluster analysis and the Nei and Li similarity coefficient. The genetic similarity observed between P. juliflora and P. pallida is similar to the value in sympatric Prosopis species in North America, and reconsideration of the series rank in section Algarobia is suggested. Species-specific markers confirmed that material in Burkina Faso is P. juliflora, but suggested that material collected in Brazil, Cape Verde and Senegal is P. pallida, whereas this has previously been identified as P. juliflora.

Industrial production of the edible basidiomycete Pleurotus ostreatus (oyster mushroom) is based on a solid fermentation process in which a limited number of selected strains are used. Optimization of industrial mushroom production depends on improving the culture process and breeding new strains with higher yields and productivities. Traditionally, fungal breeding has been carried out by an empirical trial and error process. In this study, we used a different approach by mapping quantitative trait loci (QTLs) controlling culture production and quality within the framework of the genetic linkage map of P. ostreatus. Ten production traits and four quality traits were studied and mapped. The production QTLs identified explain nearly one-half of the production variation. More interestingly, a single QTL mapping to the highly polymorphic chromosome VII appears to be involved in control of all the productivity traits studied. Quality QTLs appear to be scattered across the genome and to have less effect on the variation of the corresponding traits. Moreover, some of the new hybrid strains constructed in the course of our experiments had production or quality values higher than those of the parents or other commercial strains. This approach opens the possibility of marker-assisted selection and breeding of new industrial strains of this fungus.The edible mushroom production industry is more important every year for several reasons: mushrooms are an efficient low-fat protein source, they may be cultivated on a wide variety of substrates, and they have many industrial and medical applications. The oyster mushroom (Pleurotus ostreatus Jacq. ex Fr Kummer) is the second largest edible mushroom crop behind the white button mushroom, Agaricus bisporus, and it accounts for nearly one-quarter of the total worldwide mushroom production (4, 5). This fungus is also a source of enzymes and other products with industrial and medical applications (6,11,12,23), and it can be used as a decontaminating agent (3) and as an organic fertilizer (1).Industrial production of P. ostreatus is based on a two-step solid fermentation process. In the first step, the mycelium colonizes a wheat (or cereal) straw-based substrate under lightand oxygen-limited conditions at an incubation temperature of 24°C. This process takes between 1 and 2 weeks before the mycelium reaches the substrate surface. At this time, the incubation conditions are changed (12-h photoperiod, forced ventilation) to induce successive flushes of mushroom fruiting. The fruiting temperature depends on the strain and varies between 15°C (P. ostreatus var. ostreatus) and 21°C (P. ostreatus var. florida).Optimization of P. ostreatus industrial fermentation is based primarily on process improvement and strain improvement. Whereas much work has been done on process improvement (27), few systematic studies of genetic breeding of P. ostreatus strains have been reported. This is also true for other industrially cultured mushrooms.Understanding mushroom breeding systems is a major landmark ...

Agaricus bisporus is an edible basidiomycete cultivated industrially for food production. Different spawn and mushroom producers use genetically related A. bisporus strains frequently marketed as different products. In this paper we show that the use of suitable molecular markers reveals the high level of genetic homology of commercial strains of A. bisporus, and allows, at the same time, to distinguish between them. In the course of this work, a molecular marker potentially linked to the agronomic character 'mushroom weight' has been identified by bulked segregant analysis.

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