The interactive effects of arbuscular mycorrhiza and plant growth-promoting rhizobacteria synergistically enhance host plant defences against pathogens

Belowground interactions between plant roots, mycorrhizal fungi and plant growth-promoting rhizobacteria (PGPR) can improve plant health via enhanced nutrient acquisition and priming of the plant immune system. Two wheat cultivars differing in their ability to form mycorrhiza were (co)inoculated with the mycorrhizal fungus Rhizophagus irregularis and the rhizobacterial strain Pseudomonas putida KT2440. The cultivar with high mycorrhizal compatibility supported higher levels of rhizobacterial colonization than the low compatibility cultivar. Those levels were augmented by mycorrhizal infection. Conversely, rhizobacterial colonization of the low compatibility cultivar was reduced by mycorrhizal arbuscule formation. Single inoculations with R. irregularis or P. putida had differential growth effects on both cultivars. Furthermore, while both cultivars developed systemic priming of chitosan-induced callose after single inoculations with R. irregularis or P. putida, only the cultivar with high mycorrhizal compatibility showed a synergistic increase in callose responsiveness following co-inoculation with both microbes. Our results show that multilateral interactions between roots, mycorrhizal fungi and PGPR can have synergistic effects on growth and systemic priming of wheat

The role of the arbuscular mycorrhiza-associated rhizobacteria in the biocontrol of soilborne phytopathogens: a review

The mutualistic symbiosis of most land plants with arbuscular mycorrhizal (AM) fungi has been shown to favor mineral and water nutrition and to increase resistance to abiotic and biotic stresses. This review reports the main mechanisms involved in the control of the disease symptoms and of the intraradical proliferation of soilborne phytopathogens by root colonization with AM fungi, with a special emphasis on the role of the rhizobacteria shown to be specifically associated with the AM extraradical network and the mycorrhizosphere (the soil zone with particular characteristics under the influence of the root/AM association). The mycorrhizosphere would constitute an environment conducive to microorganisms antagonistic to pathogen proliferation. Moreover, attempts to identify rhizobacteria from AM structures and/or the mycorrhizosphere often lead to the isolation of organisms showing strong properties of antagonism on various soilborne pathogens. The ability of AM fungi to control soilborne diseases would be strongly related to their capacity to specifically stimulate the establishment of rhizobacteria unfavorable to pathogen development within the mycorrhizosphere before root infection. Current knowledge concerning the mechanisms involved in AM/rhizobacteria interactions are also described in this review

Review. The role of the arbuscular mycorrhiza-associated rhizobacteria in the biocontrol of soilborne phytopathogens

The mutualistic symbiosis of most land plants with arbuscular mycorrhizal (AM) fungi has been shown to favor mineral and water nutrition and to increase resistance to abiotic and biotic stresses. This review reports the main mechanisms involved in the control of the disease symptoms and of the intraradical proliferation of soilborne phytopathogens by root colonization with AM fungi, with a special emphasis on the role of the rhizobacteria shown to be specifically associated with the AM extraradical network and the mycorrhizosphere (the soil zone with particular characteristics under the influence of the root/AM association). The mycorrhizosphere would constitute an environment conducive to microorganisms antagonistic to pathogen proliferation. Moreover, attempts to identify rhizobacteria from AM structures and/or the mycorrhizosphere often lead to the isolation of organisms showing strong properties of antagonism on various soilborne pathogens. The ability of AM fungi to control soilborne diseases would be strongly related to their capacity to specifically stimulate the establishment of rhizobacteria unfavorable to pathogen development within the mycorrhizosphere before root infection. Current knowledge concerning the mechanisms involved in AM/rhizobacteria interactions are also described in this reviewLa simbiosis micorriza arbuscular (MA), presente en la mayoría de las plantas terrestres, favorece la nutrición mineral, la captación de agua e incrementa la resistencia a estreses abióticos y bióticos. En esta revisión se recogen los principales mecanismos, ligados a la colonización de las raíces por hongos MA, implicados en el control de síntomas ligados a enfermedades y en el control de la proliferación intraradical de fitopatógenos del suelo. Se hace un énfasis especial en el papel de las rizobacterias asociadas específicamente a la red de micelio extraradical de los hongos MA y a la micorrizosfera (zona de suelo con características especiales debidas a la influencia de la asociación hongo/planta). La micorrizosfera constituiría un entorno propicio para el desarrollo de microorganismos antagónicos a la proliferación de patógenos. Los estudios realizados sobre rizobacterias asociadas a estructuras de hongos MA o de la micorrizosfera han conducido en muchas ocasiones al aislamiento de organismos con características antagonistas frente a patógenos del suelo. La capacidad de los hongos MA para controlar enfermedades de suelo estaría fuertemente relacionada con su capacidad para estimular específicamente el establecimiento de rizobacterias en la micorrizosfera desfavorables para el desarrollo de patógenos antes de que estos puedan infectar la raíz. En esta revisión también se describen los conocimientos actuales sobre los mecanismos implicados en las interacciones entre hongos MA y rizobacterias