A Saprotrophic Fungal Isolate From Northern Sinaloa, Mexico, with Homology to Members of the Chaetomiaceae Behaves as an Antagonist of Phytopathogenic Fungi in vitro

An ascomycete was isolated from spore preparations of arbuscular mycorrhizal fungi from soil samples collected in northern Sinaloa, Mexico. This fungal isolate named CIIDIR-1, is ubiquitous in soils of this agricultural region. Only the asexual phase of CIIDIR-1 can be cultured in vitro in different culture media. DNA extracted from mycelium was used to amplify and sequence a 28S rDNA hypervariable region, which allowed its identification as related to members of the Chaetomiaceae family (Aporothielavia leptoderma and members of the genus Chaetomium). CIIDIR-1 showed a saprophytic behavior in the presence of plant roots grown in vitro. Bioassays showed that the isolate acts as an antagonist against phytopathogenic fungi. When mycelium from the isolate was placed in contact with Rhizoctonia solani and Fusarium oxysporum f. sp. lycopersici, it proliferated, surrounded them and inhibited their growth. The presence of CIIDIR-1 in all soil samples evaluated suggests an important role in the rhizosphere; also, the understanding of its interactions with plants and other rhizospheric organisms might be important for future ecological and agricultural studies. Additional keywords: Aporothielavia leptoderma, 28S rDNA hypervariable region, Rhizoctonia solani, Fusarium oxysporum f. sp. lycopersici, antagonism

Transformation of Medicago truncatula via infiltration of seedlings or flowering plants with Agrobacterium

Two rapid and simple in planta transformation methods have been developed for the model legume Medicago truncatula. The first approach is based on a method developed for transformation of Arabidopsis thaliana and involves infiltration of flowering plants with a suspension of Agrobacterium. The second method involves infiltration of young seedlings with Agrobacterium. In both cases a proportion of the progeny of the infiltrated plants is transformed. The transformation frequency ranges from 4.7 to 76% for the flower infiltration method, and from 2.9 to 27.6% for the seedling infiltration method. Both procedures resulted in a mixture of independent transformants and sibling transformants. The transformants were genetically stable, and analysis of the T 2 generation indicates that the transgenes are inherited in a Mendelian fashion. These transformation systems will increase the utility of M. truncatula as a model system and enable large-scale insertional mutagenesis. T-DNA tagging and the many adaptations of this approach provide a wide range of opportunities for the analysis of the unique aspects of legumes

Arbuscular mycorrhizal networks: process and functions. A review

International audienceAn unprecedented, rapid change in environmental conditions is being observed, which invariably overrules the adaptive capacity of land plants. These environmental changes mainly originate from anthropogenic activities, which have aggravated air and soil pollution, acid precipitation, soil degradation, salinity, contamination of natural and agro-ecosystems with heavy metals such as cadmium (Cd), lead (Pb), mercury (Hg), arsenic (As), global climate change, etc. The restoration of degraded natural habitats using sustainable, low-input cropping systems with the aim of maximizing yields of crop plants is the need of the hour. Thus, incorporation of the natural roles of beneficial microorganisms in maintaining soil fertility and plant productivity is gaining importance and may be an important approach. Symbiotic association of the majority of crop plants with arbuscular mycorrhizal (AM) fungi plays a central role in many microbiological and ecological processes. In mycorrhizal associations, the fungal partner assists its plant host in phosphorus (P) and nitrogen (N) uptake and also some of the relatively immobile trace elements such as zinc (Zn), copper (Cu) and iron (Fe). AM fungi also benefit plants by increasing water uptake, plant resistance and biocontrol of phytopathogens, adaptation to a variety of environmental stresses such as drought, heat, salinity, heavy metal contamination, production of growth hormones and certain enzymes, and even in the uptake of radioactive elements. The establishment of symbiotic association usually involves mutual recognition and a high degree of coordination at the morphological and physiological level, which requires a continuous cellular and molecular dialogue between both the partners. This has led to the identification of the genes, signal transduction pathways and the chemical structures of components relevant to symbiosis; however, scientific knowledge on the physiology and function of these fungi is still limited. This review unfolds our current knowledge on signals and mechanisms in the development of AM symbiosis; the molecular basis of nutrient exchange between AM fungi and host plants; and the role of AM fungi in water uptake, disease protection, alleviation of various abiotic soil stresses and increasing grain production