The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

The rhizosphere is a hot spot of microbial interactions as exudates released by plant roots are a main food source for microorganisms and a driving force of their population density and activities. The rhizosphere harbors many organisms that have a neutral effect on the plant, but also attracts organisms that exert deleterious or beneficial effects on the plant. Microorganisms that adversely affect plant growth and health are the pathogenic fungi, oomycetes, bacteria and nematodes. Most of the soilborne pathogens are adapted to grow and survive in the bulk soil, but the rhizosphere is the playground and infection court where the pathogen establishes a parasitic relationship with the plant. The rhizosphere is also a battlefield where the complex rhizosphere community, both microflora and microfauna, interact with pathogens and influence the outcome of pathogen infection. A wide range of microorganisms are beneficial to the plant and include nitrogen-fixing bacteria, endo- and ectomycorrhizal fungi, and plant growth-promoting bacteria and fungi. This review focuses on the population dynamics and activity of soilborne pathogens and beneficial microorganisms. Specific attention is given to mechanisms involved in the tripartite interactions between beneficial microorganisms, pathogens and the plant. We also discuss how agricultural practices affect pathogen and antagonist populations and how these practices can be adopted to promote plant growth and health

The microbiology of Lascaux Cave

Lascaux Cave (Montignac, France) contains paintings from the Upper Paleolithic period. Shortly after its discovery in 1940, the cave was seriously disturbed by major destructive interventions. In 1963, the cave was closed due to algal growth on the walls. In 2001, the ceiling, walls and sediments were colonized by the fungus Fusarium solani. Later, black stains, probably of fungal origin, appeared on the walls. Biocide treatments, including quaternary ammonium derivatives, were extensively applied for a few years, and have been in use again since January 2008. The microbial communities in Lascaux Cave were shown to be composed of human-pathogenic bacteria and entomopathogenic fungi, the former as a result of the biocide selection. The data show that fungi play an important role in the cave, and arthropods contribute to the dispersion of conidia. A careful study on the fungal ecology is needed in order to complete the cave food web and to control the black stains threatening the Paleolithic paintings. © 2010 SGM.We thank support from the Ministry of Culture and Communication, France, the Spanish project CGL2006-07424/BOS, and facilities from DRAC Aquitaine. This is a TCP CSD2007-00058 paper.Peer Reviewe

Recherches sur la résistance des sols aux maladies. X. - Comparaison de la mycoflore colonisant les racines de melons cultivés dans un sol résistant ou dans un sol sensible aux fusarioses vasculaires

International audienc

Observations sur la persistance dans le sol des microconidies de Fusarium oxysporum

International audienc

Le développement de l'embryon zygotique chez Vitis vinifera L.

The development of the zygotic embryo of Vitis vinifera L.The embryonic development of Vitis vinifera from the zygote to the mature embryo has been studied. The planes of early cell divisions are irregular, thus leading to formation of a large globular proembryo comprising about 1500 undifferentiated cells above a bulky suspensor. Organogenesis of the embryo sta rts with initiation of the cotyledons and constitution of the radicular meristem. The intercotyledonary zone, future shoot apex, is formed by about 300 cells. In this zone, cells remain undifferentiated throughout embryogenesis; its organization begins to be completed only after germination. The radicular meristem, on the other hand, is functioning from the embryonic stage. The meristem of the embryonic radicle and the meristem of the adventitious root are identical in their ('open' type) organization

Recovery of mutants impaired in pathogenicity after transposition of Impala in Fusarium oxysporum f. sp. melonis

The ability of transposon impala to inactivate genes involved in pathogenicity was tested in Fusarium oxysporum f. sp. melonis. Somatic excision of an impala copy inserted in the nitrate reductase-encoding niaD gene was positively selected through a phenotypic assay based on the restoration of nitrate reductase activity. Independent excision events were analyzed molecularly and shown to carry reinsertedimpala in more than 70% of the cases. Mapping of reinserted impala elements on large NotI-restriction fragments showed that impala transposes randomly. By screening 746 revertants on plants, a high proportion (3.5%) of mutants impaired in their pathogenic potential was recovered. According to the kinetics of wilt symptom development, the strains that were impaired in pathogenicity were clustered in three classes: class 1 grouped two strains that never induced Fusarium wilt symptoms on the host plant; class 2 and class 3 grouped 15 and 9 revertants which caused symptoms more than 50 and 30 days after inoculation, respectively. The first results demonstrate the efficiency of transposition in generating mutants affected in pathogenicity, which are usually difficult to obtain by classical mutagenesis, and open the possibility to clone the altered genes with impala as a tag