BACTERIAL ENDOPHYTES OF BRASSICA CROPS AS PATHOGENS ANTAGONISTS THROUGH THE PRODUCTION OF ANTIMICROBIAL COMPOUNDS

MARTIN ANDRÉS DUHALDE; LEANDRO SOLMI; FRANCO RUBÉN ROSSI; OSCAR ADOLFO RUIZ; ANDRÉS GÁRRIZ; FERNANDO MATÍAS ROMERO

La Plata

Congreso; V Congreso Argentino de Microbología Agrícola y Ambiental; 2021

Many endophytic bacteria colonize host tissues internally without causing damage, in some cases,they promote plant growth and confer protection against pathogens. One of the mechanismsinvolved in the later is the production of antimicrobial compounds. This work aimed to characterizebacterial endophytes from different brassica crops, and to analyze their antagonistic propertiesagainst phytopathogens.For the isolation of bacterial endophytes, leaves samples were taken from three brassica crops(cabagge, broccoli and Brussel sprouts) grown in horticulture farms. Leaves from these crops weresurface sterilized, homogenized and plated in rich medium. The collection obtained was screened indual cultures with important pathogens such as Pectobacterium carotovorum, Xanthomonascampestris, Sclerotinia sclerotiorum and Leptosphaeria maculans. Also, plant-growth associatedtraits were tested (phosphate solubilization, indol acetic acid and siderophore production), as wellas the production of volatile compounds with antifungal activity. Besides, whole supernatant as wellas semi-purified fractions of these isolates were tested for antimicrobial activity. Selected isolateswere identified by sequencing the 16S rRNA gene.A total of 81 endophytes were isolated from the brassica crops. Based on their ability to inhibitdifferent pathogens in dual culture assays or the activation of plant-growth promoting mechanisms,three isolates (Bru13, Bro5 and Bro11) were selected and identified. Bru13 belongs to Pantoeagenus, closely related to the species P. agglomerans. While both, Bro5 and Bro11, belongs toBacillus genus, Bro5 clustered with B. amyloliquefaciens and Bro11 with B. subtilis. The cell-freesupernatant of these isolates inhibited the growth of P. carotovorum, X. campestris, S. sclerotiorumand L. maculans. The most drastic effect was observed with the supernatant of Bro5 and Bro11showing inhibition rates ranging from 40 to 100%. To explore the nature of the antimicrobialcompounds, different semi-purifications were performed to obtain peptide, secondary metabolitesand lipopeptides fractions. Peptide fractions were the most effective, followed by the secondarymetabolites? ones. In turn, the lipopeptide fraction did not show antimicrobial activity. Peptidefractions from Bro5 was the most effective against bacteria and fungi reaching a 100% inhibition.Finally, we evaluated the antifungal activity of volatile compounds produced by these isolates. In thisway, all three isolates released volatile compounds that inhibited the growth of S. sclerotiorum andL. maculans by 50-80%.In conclusion, the isolates analyzed here exhibit a combination of beneficial traits related tobiocontrol and growth promotion activities. Moreover, their ability to release compounds withantimicrobial activity, allow their use as bio-factories to produce new compounds aiming to controlplant diseases in a more sustainable way avoiding the use of traditional agrochemicals.