Specific interactions between arbuscular mycorrhizal fungi and plant growth-promoting bacteria: as revealed by different combinations

Abstract

The interactions between two plant growth-promoting rhizobacteria (PGPR, Pseudomonas fluorescens SBW25 and Paenibacillus brasilensis PB177), two arbuscular mycorrhizal (AM) fungi (Glomus mosseae and Glomus intraradices) and one pathogenic fungus (Microdochium nivale) were investigated on winter wheat (Triticum aestivum cultivar Tarso) in a greenhouse trial. PB177, but not SBW25, had strong inhibitory effects on M. nivale in dual culture plate assays. The results from the greenhouse experiment show very specific interactions; for example, the two AM fungi react differently when interacting with the same bacteria on plants. Glomus intraradices (single inoculation or together with SBW25) increased plant dry weight on M. nivale-infested plants, suggesting that the pathogenic fungus is counteracted by G. intraradices, but PB177 inhibited this positive effect. This is an example of two completely different reactions between the same AM fungus and two species of bacteria, previously known to enhance plant growth and inhibit pathogens. When searching for plant growth-promoting microorganisms, it is therefore important to test for the most suitable combination of plant, bacteria and fungi in order to achieve satisfactory plant growth benefits.

Getting the ecology into interactions between plants and the plant growth-promoting bacterium Pseudomonas fluorescens

“…P. fluorescens is mostly known as a root colonizer. Many studies have examined the effects of adding several mutualistic organisms simultaneously to soils on plant defense (e.g., Jaderlund et al, 2008; Saravanakumar et al, 2009; Senthilraja et al, 2010). A general conclusion that can be drawn from these studies is that multiple microbial introductions typically are more effective than single introductions for biocontrol (Whipps, 2001).…”

“…A general conclusion that can be drawn from these studies is that multiple microbial introductions typically are more effective than single introductions for biocontrol (Whipps, 2001). The combinations of species that have been added range from multiple Pseudomonas isolates (Saravanakumar et al, 2009; Seenivasan et al, 2012) to adding other mutualistic bacteria (Domenech et al, 2006) or mutualistic fungi (Jaderlund et al, 2008). The addition of multiple agents enhances the chance that at least one is well adapted to the local environment where the organisms are introduced.…”

Quorum sensing and fungal-bacterial interactions inCandida albicans: a communicative network regulating microbial coexistence and virulence

“…The first interactions analysed in depth concerned the plant rhizosphere where arbuscolar mycorrizal fungi and rhizobacteria act together both promoting plant growth and controlling plant pathogens (Whipps, 2001;Artursson et al, 2006;Jäderlund et al, 2008). The first interactions analysed in depth concerned the plant rhizosphere where arbuscolar mycorrizal fungi and rhizobacteria act together both promoting plant growth and controlling plant pathogens (Whipps, 2001;Artursson et al, 2006;Jäderlund et al, 2008).…”

Mycorrhizosphere: The Role of PGPR

“…A particular interest has been expected about the so-called mycorrhiza helper bacteria (MHB), a term that was coined by Garbaye (1994) and later updated by Frey-Klett et al (2007) for those bacteria which stimulate mycorrhizal mycelial growth and/or enhance mycorrhizal formation or activity. In the same way the establishment of plant growth-promoting rhizobacteria (PGPR) inoculants in the rhizosphere can also be affected by arbuscular mycorrhizal (AM) fungal coinoculation (Artursson et al 2006;Barea et al 2005b;Jaderlund et al 2008;Mallik and Williams 2008). The establishment of the AM fungus in the root cortex is known to change many key aspects of plant physiology such as the mineral nutrient composition in plant tissues, the hormonal balance and the patterns of C allocation.…”