Beneficial Endophytic Bacteria-Serendipita indica Interaction for Crop Enhancement and Resistance to Phytopathogens

Abstract

Serendipita (=Piriformospora) indica is a fungal endophytic symbiont with the capabilities to enhance plant growth and confer resistance to different stresses. However, the application of this fungus in the field has led to inconsistent results, perhaps due to antagonism with other microbes. Here, we studied the impact of individual bacterial isolates from the endophytic bacterial community on the in vitro growth of S. indica. We further analyzed how combinations of bacteria and S. indica influence plant growth and protection against the phytopathogens Fusarium oxysporum and Rhizoctonia solani. Bacterial strains of the genera Bacillus, Enterobacter and Burkholderia negatively affected S. indica growth on plates, whereas Mycolicibacterium, Rhizobium, Paenibacillus strains and several other bacteria from different taxa stimulated fungal growth. To further explore the potential of bacteria positively interacting with S. indica, four of the most promising strains belonging to the genus Mycolicibacterium were selected for further experiments. Some dual inoculations of S. indica and Mycolicibacterium strains boosted the beneficial effects triggered by S. indica, further enhancing the growth of tomato plants, and alleviating the symptoms caused by the phytopathogens F. oxysporum and R. solani. However, some combinations of S. indica and bacteria were less effective than individual inoculations. By analyzing the genomes of the Mycolicibacterium strains, we revealed that these bacteria encode several genes predicted to be involved in the stimulation of S. indica growth, plant development and tolerance to abiotic and biotic stresses. Particularly, a high number of genes related to vitamin and nitrogen metabolism were detected. Taking into consideration multiple interactions on and inside plants, we showed in this study that some bacterial strains may induce beneficial effects on S. indica and could have an outstanding influence on the plant-fungus symbiosis.

Interaction between endophytic Proteobacteria strains and Serendipita indica enhances biocontrol activity against fungal pathogens

“…However, the highest degree of protection was observed when the plants were dual-inoculated with combinations of S. indica and bacteria. This synergistic effect was also observed in our previous research, in which Fusarium wilt's severity was significantly reduced by dualinoculations of S. indica with Mycolicibacterium strains P1-18 and P9-22 in comparison to single inoculations, and biocontrol of Rhizoctonia resulted most effective by combining S. indica with Mycolicibacterium P9-64 (del Barrio-Duque et al 2019). Interestingly, the endofungal bacterium of S. indica (Rhizobium radiobacter F4) was found to induce resistance responses in barley and confer resistance against different pathogens (Sharma et al 2008;Glaeser et al 2016).…”

“…Certainly, there are several reports of combinations of fungi and bacteria providing no better or, in some cases, worse plant promotion than the isolates used singly (Whipps 2001). In our previous study, combinations of S. indica with strain P9-22 or P9-64 of Mycolicibacterium negatively affected plant growth in comparison to single inoculations (del Barrio-Duque et al 2019). The same negative effect was described for co-inoculation of pseudomonad R62 and S. indica (Sarma et al 2011).…”

“…T12-10 were obtained from the AIT (Austrian Institute of Technology, Tulln, Austria) strain collection. They were isolated from tomato (T) or potato (P) roots (del Barrio-Duque et al 2019).…”

“…The growth of the beneficial fungus S. indica or the pathogens F. oxysporum and R. solani in interaction with bacteria was assessed by measuring hyphae development on agar plates as described in del Barrio-Duque et al (2019). For these experiments, bacteria were precultured for four days on Nutrient Agar No2 (NA) (Sigma-Aldrich, St. Louis, USA) and then streaked individually on 1 cm 2 in the center of a Petri dish (9 cm Ø) containing 15 ml of PDA or a mixture 1:1 of PDA + NA.…”

“…In a previous study, we detected several endophytic bacterial strains from very diverse families with the ability to stimulate S. indica growth in vitro. In that study, we focused on Mycolicibacterium strains, as this genus showed to comprise the highest number of strains having a beneficial effect on S. indica (del Barrio-Duque et al 2019). However, strains from other taxa might have similar beneficial properties on S. indica but potentially employing different mechanisms.…”