Mycelium

About: Mycelium is a research topic. Over the lifetime, 8923 publications have been published within this topic receiving 170993 citations.

Rock phosphate-solubilizing Actinomycetes: screening for plant growth-promoting activities

Abstract: In order to select Actinobacteria that could improve plant growth and thus agricultural yield, we assessed different plant growth promoting (PGP) abilities of eight rock phosphate (RP)-solubilizing Actinomycete isolates originating from Moroccan phosphate mines. Six of these strains were able to grow on root exudates of the wheat plant as sole nutrient sources and were efficiently releasing soluble phosphate from RP. These strains also inhibited the growth of potentially phytopathogenic fungi, bacteria (Gram +/-) or yeasts. Five of these strains pro- duced indoleacetic acid and four showed endophytic properties. When these strains were grown, in the presence of the wheat plant, in a synthetic minimum medium (SMM) containing insoluble RP as unique phosphate source or in soil experiment, the most active RP-solubi- lizing strains had the highest stimulatory effect on the production of plant biomass. The most efficient strain Streptomyces griseus-related strain (BH7), stimulated aerial growth of the plant more than 70% in test tubes and more than 30% in RP soil compared to the non-inoculated con- trol treatment. This study demonstrated that our selected Actinomycete strains could be used for the development of novel, non-polluting; farming practices by entering in the formulation of novel biofertilizer and biocontrol products constituted by spores and/or mycelium of the ad hoc Ac- tinobacteria in association with pulverized RP.

Mycelial uptake, translocation and assimilation of nitrogen from 15N-labelled ammonium by Pinus sylvestris plants infected with four different ectomycorrhizal fungi

Abstract: The uptake and assimilation of 15N-labelled ammonium was followed in Pinus sylvestris L. plants infected with four different ectomycorrhizal fungi, Rhizopogon roseolus Fr. Suillus bovinus (Fr.) O. Kuntze, Pisolithus tinctorius (Fr.) Fr. and Paxillus involutus (Mich. ex Pers.) Cohen & Couch. Plants were grown in flat perspex observation chambers or in Petri dishes containing non-sterile peat; in each case the fungal mycelium growing from a host plant was allowed to cross a barrier and to colonize an area of peat from which roots had been excluded. Labelled ammonium was fed to the mycelium, and the shoot, root and mycelial tissues analysed for total and 15N-labelled free amino acid contents after a feeding period of 72 h. High proportions of 15N-labelled glutamate/glutamine, aspartate/asparagine, and alanine were found in the fungal mycelia of all species except Pax. involutus where labelled aspartate/asparagine was not found. Lower proportions of labelled serine, threonine, tyrosine, lysine, ornithine and arginine were also found in the mycelium. The degree of 15N enrichment declined throughout the transport pathway but between 5 and 50% of the amino acids were 15N-labelled in the plant shoots. In total, at least 2-3% of the nitrogen supplied was assimilated as labelled amino acid during the 3 day feeding period, the largest amounts of labelling occurred in glutamic acid/glutamine and aspartic acid/asparagine.

Disruption of root carbon transport into forest humus stimulates fungal opportunists at the expense of mycorrhizal fungi.

Abstract: Ectomycorrhizal fungi dominate the humus layers of boreal forests. They depend on carbohydrates that are translocated through roots, via fungal mycelium to microsites in the soil, wherein they forage for nutrients. Mycorrhizal fungi are therefore sensitive to disruptive disturbances that may restrict their carbon supply. By disrupting root connections, we induced a sudden decline in mycorrhizal mycelial abundance and studied the consequent effects on growth and activity of free living, saprotrophic fungi and bacteria in pine forest humus, using molecular community analyses in combination with enzyme activity measurements. Ectomycorrhizal fungi had decreased in abundance 14 days after root severing, but the abundance of certain free-living ascomycetes was three times higher within 5 days of the disturbance compared with undisturbed controls. Root disruption also increased laccase production by an order of magnitude and cellulase production by a factor of 5. In contrast, bacterial populations seemed little affected. The results indicate that access to an external carbon source enables mycorrhizal fungi to monopolise the humus, but disturbances may induce rapid growth of opportunistic saprotrophic fungi that presumably use the dying mycorrhizal mycelium. Studies of such functional shifts in fungal communities, induced by disturbance, may shed light on mechanisms behind nutrient retention and release in boreal forests. The results also highlight the fundamental problems associated with methods that study microbial processes in soil samples that have been isolated from living roots.

The physiology of vesicular-arbuscular mycorrhizal roots

Abstract: The fungi of vesicular-arbuscular mycorrhizae colonize considerable portions of the root system and in spite of the carbon drain they impose on the host plant, their presence within the root tissues can positively influence several aspects of the host plant’s physiology In the majority of cases, improved phosphate uptake is the primary cause of growth and yield enhancements in the mycorrhizal plants Mycorrhizal roots have different phosphate absorption kinetics and lower threshold values than nonmycorrhizal roots The external hyphae developing around mycorrhizae explore a large volume of soil and absorb available phosphate beyond the depletion zone at the root surface Phosphate accumulating in the external fungal hyphae is translocated to the internal mycelium by a well-developed transport system and transferred to the host tissues mainly across the intracellular arbuscules Certain specialized enzyme activities are specifically associated with this alternative pathway of phosphate nutrition in mycorrhizal plants Improved phosphate nutrition is not always sufficient to explain the observed effects of vesicular-arbuscular mycorrhizae on the host plant’s physiology