Many different cultivation techniques and inoculum products of the plant-beneficial arbuscular mycorrhizal (AM) fungi have been developed in the last decades. Soil- and substrate-based production techniques as well as substrate-free culture techniques (hydroponics and aeroponics) and in vitro cultivation methods have all been attempted for the large-scale production of AM fungi. In this review, we describe the principal in vivo and in vitro production methods that have been developed so far. We present the parameters that are critical for optimal production, discuss the advantages and disadvantages of the methods, and highlight their most probable sectors of application.

Methods for large-scale production of AM fungi: past, present, and future

The use of tracers is relevant to study the transformations of phosphorus (P) in the soil–plant system because (a) only a small fraction of the total soil P is rapidly circulating in this system, (b) P participates in many reactions in the soil, some occurring within a few seconds, others over years, and (c) P is distributed in many pools in the soil. This review presents the use of P radioisotopes (a) to probe pools and to study P transformations in soils, (b) to trace the fate of fertilizers in soil–plant systems, and (c) to assess the foraging strategies of arbuscular mycorrhizal fungi for P. Finally, we discuss the potential of analyzing the oxygen isotopes bound to P to study soil P dynamics and the research needed to achieve this aim.

The Use of Tracers to Investigate Phosphate Cycling in Soil–Plant Systems

Mycorrhiza induced resistance in potato plantlets challenged by Phytophthora infestans

The establishment of arbuscular mycorrhizal associations causes major changes in plant roots and affects significantly the host in term of plant nutrition and resistance against biotic and abiotic stresses. As a consequence, major changes in root transcriptome, especially in plant genes related to biotic stresses, are expected. Potato microarray analysis, followed by real-time quantitative PCR, was performed to detect the wide transcriptome changes induced during the pre-, early and late stages of potato root colonization by Glomus sp. MUCL 41833. The microarray analysis revealed 526 up-regulated and 132 down-regulated genes during the pre-stage, 272 up-regulated and 109 down-regulated genes during the early stage and 734 up-regulated and 122 down-regulated genes during the late stage of root colonization. The most important class of regulated genes was associated to plant stress and in particular to the WRKY transcription factors genes during the pre-stage of root colonization. The expression profiling clearly demonstrated a wide transcriptional change during the pre-, early and late stages of root colonization. It further suggested that the WRKY transcription factor genes are involved in the mechanisms controlling the arbuscular mycorrhizal establishment by the regulation of plant defence genes.

Transcriptional regulation of defence genes and involvement of the WRKY transcription factor in arbuscular mycorrhizal potato root colonization

Symbiotic association of roots with arbuscular mycorrhizal (AM) fungi is a very widespread strategy by which plants facilitate their acquisition of mineral elements from the soil. Studies employing sophisticated methodology in the fields of in vitro culture of AM colonized roots, microscopy, isotope labeling and molecular biology have shed light into the physiology of AM fungal nutrient uptake, transport and delivery to the host plant. In addition to the direct contribution to element uptake via the symbiotic pathway, AM mycelia have also been shown to affect root morphology and functioning, as well as mycorrhizosphere soil properties. This may lead to indirect effects of the AM association on plant nutrient availability and uptake. With their thin diameter, AM hyphae might be able to access smaller soil pores, and better compete with soil microbes for nutrient resources, compared with plant roots. Alone or in collaboration with associated hyphosphere bacteria, AM mycelia might also promote chemical mobilization of nutritional elements from sparingly plant available resources. Similar with plant root systems, AM mycelia appear to differ considerably in their architecture and physiological activities depending on their genotype. Whether such inherent traits represent different strategies in nutrient acquisition in collaboration with functionally compatible host roots, still remains speculative. Not much is known about how the AM fungal symbiosis is integrated into particular plant nutrient acquisition strategies, but it can be assumed that individual symbiotic strategies are highly diverse. The AM mycelium might assist the roots in spatial and/or chemical soil nutrient resource exploitation in a complementary and/or synergistic way. Knowledge about what factors determine the extent of functional compatibility between individual plant nutrient acquisition strategies and certain AM fungal traits would contribute to our understanding of ecosystem functioning, and might assist further development of mycorrhiza technology for plant production.

Nutrient Uptake: The Arbuscular Mycorrhiza Fungal Symbiosis as a Plant Nutrient Acquisition Strategy

Actively growing extraradical hyphae extending from mycorrhizal plants are an important source of inoculum in soils which has seldom been considered in vitro to inoculate young plantlets. Seedlings of Medicago truncatula were grown in vitro in the extraradical mycelium network extending from mycorrhizal plants. After 3, 6, 9, 12, and 15 days of contact with the mycelium, half of the seedlings were harvested and analyzed for root colonization. The other half was carefully transplanted in vitro on a suitable growth medium and mycelium growth and spore production were evaluated for 4 weeks. Seedlings were readily colonized after 3 days of contact with the mycelium. Starting from 6 days of contact, the newly colonized seedlings were able to reproduce the fungal life cycle, with the production of thousands of spores within 4 weeks. The fast mycorrhization process developed here opens the door to a broad range of in vitro studies for which either homogenous highly colonized seedlings or mass-produced in vitro inoculum is necessary.

Extraradical mycelium network of arbuscular mycorrhizal fungi allows fast colonization of seedlings under in vitro conditions

The Mycelium Donor Plant system (MDP) was adapted to study the time course of the colonization of Pyrus communis by Rhizophagus irregularis under in vitro conditions. Isolated germinated spores did not colonize pear roots. Inoculum composed of R. irregularis spores/mycelium associated with chicory root fragments was used to inoculate Medicago truncatula which became thereafter the MDP of pear plantlets. Typical intraradical structures (hyphae, arbuscules, spores/vesicles) and appressoria were observed in the pear roots. During acclimatization, the pear plants formed a densely branched root system. R. irregularis colonization not only altered the root architecture but also changed the nutrient composition of the acclimatized pear plantlets.

In vitro mycorrhization of pear (Pyrus communis).

Resumen es: El experimento se realizo en el Instituto Nacional de Ciencias Agricolas (INCA), con el objetivo de caracterizar el funcionamiento micorrizico de Brachia...

/pdf/caracterizacion-del-comportamiento-micorrizico-en-brachiaria-4n76yhqgc9.pdf

Caracterización del comportamiento micorrízico en Brachiaria decumbens inoculada con Glomus hoi-like

Resumen en: Knowing the extraordinary biological and economic significance of arbuscular mycorrhizal fungi (AMF) and also due to the satisfactory results reached wit...

Reclasificación taxonómica de dos cepas de hongos micorrízicos arbusculares

Resumen es: El trabajo tuvo como objetivo definir el funcionamiento micorrizico del biofertilizante liquido LicoMic® a base del hongo micorrizico arbuscular (HMA) Gl...

http://ediciones.inca.edu.cu/index.php/ediciones/article/download/380/pdf

FUNCIONAMIENTO DE UN INOCULANTE LÍQUIDO A BASE DEL HONGO MICORRÍZICO ARBUSCULAR Glomus sp1 (INCAM-4) EN ARROZ (Oryza sativa var. J-104) EN SUELO SALINO

Kalyanne Fernández

Papers

Extraradical mycelium network of arbuscular mycorrhizal fungi allows fast colonization of seedlings under in vitro conditions

In vitro mycorrhization of pear (Pyrus communis).

Caracterización del comportamiento micorrízico en Brachiaria decumbens inoculada con Glomus hoi-like

Reclasificación taxonómica de dos cepas de hongos micorrízicos arbusculares

FUNCIONAMIENTO DE UN INOCULANTE LÍQUIDO A BASE DEL HONGO MICORRÍZICO ARBUSCULAR Glomus sp1 (INCAM-4) EN ARROZ (Oryza sativa var. J-104) EN SUELO SALINO