Evaluation of the strawberry epiphyte Bacillus velezensis HIII11 as a biological control agent of fungal pathogens in Arabidopsis thaliana

HIRSCH, MAILÉN; BURGES, PABLO L.; MIGUELIZ, LARA; VILLARREAL, NATALIA M.; MARINA, MARÍA

Chapadmalal

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General; 2023

The strawberry (Fragaria x ananassa Duch.) is susceptible toattack by fungal pathogens such as Botrytis cinerea and Rhizopusstolonifer. The biological control (BC) of plant diseases has becomerelevant as an alternative to fungicides or other chemical substances. The BCconsists of using living microorganisms capable of reducing or eliminatingphytopathogens or the disease caused by them, providing a benefit to the host plant.The Bacillus genus comprises several strains recognized as biologicalcontrol agents (BCA). We isolated the epiphyte HIII11 from strawberry leavesand identified it as Bacillus velezensis. Previously, we observed that B.velezensis HIII11 can inhibit B. cinerea in vitro growth. In thepresent work, we evaluated the in vitro inhibition of R. stoloniferthrough confrontation between HIII11 and the fungus and by the action ofvolatile compounds. In addition, we studied whether B. velezensis HIII11exerts biocontrol of both pathogens in A. thaliana. Plants wereinoculated with the epiphyte, and the control was mock-inoculated with MgCl210 mM. Then, four to five leaves per plant were inoculated with two drops of sporesuspension. We measured the infection area at 48 and 72 h post-inoculation(hpi). We also determined the content of anthocyanins and phenolic compounds inplants previously inoculated with HIII11, and on control plants. The invitro assays showed the inhibition of R. stolonifer by HIII11. Theinhibition percentage was 40.6% when both microorganisms were co-cultivated, and10.2% when the inhibition by volatile compounds was evaluated. In the in vivo assays, we observed a significantfungal inhibition at 72 hpi for both pathogens. Interestingly, leaves were in healthiercondition in plants previously inoculated with HIII11. In addition, byTripan-Blue staining, we observed a lower amount of fungal mycelium in theinfected areas of inoculated leaves than the control ones (with pathogen but withoutbacteria). Finally, a significant increase in anthocyanins content ininoculated plants was shown, although no differences were evident in the phenoliccompounds content. The identification of BCA is complex and requires theevaluation of different aspects that comprise the BCA-plant-pathogeninteraction. Along with previous data, these results provide information aboutthe role of B. velezensis HIII11 in A. thaliana as a BCA ofpathogens responsible for significant economic losses in strawberry cultivationand encourage us to continue studying the effects of HIII11 in strawberryplants and fruits.