Myroides odoratimimus, a biocontrol agent from the rhizosphere of tobacco with potential to control Alternaria alternata

Bacteria from the tobacco rhizosphere were isolated and evaluated for their potential of producing volatile compounds against tobacco brown spot pathogen Alternaria alternata. Among the 82 strains of bacteria isolated from tobacco rhizosphere, 22 produced volatiles against the fungal pathogen A. alternata and showed an inhibition rate of over 50 % on A. alternata. The inhibition rate of strain T45 was the most pronounced, reaching 78.89 %. Sequence analysis of 16S rDNA of T45 identified it as Myroides odoratimimus. Scanning electron microscopy revealed that the volatile compounds it produced strongly suppressed mycelial growth, conidial germination, and sporulation, leading to mycelial fragmentation, surface crumpling, and damage to hyphae morphology. A sealed plate experiment showed volatile compounds generated from M. odoratimimus T45 exhibited inhibitory effect on the growth of eight plant pathogenic fungi (10.52-88.20 %), the inhibition was most pronounced on Valsa mali while the least pronounced inhibitory effect was on Colletotrichum orbiculare. Headspace solid-phase microextraction gas chromatography mass spectrometry analysis revealed a total of 24 compounds in the volatiles produced by M. odoratimimus. The main components of volatiles primarily included alcohols, aldehydes, acids, ketones, esters, and hydrocarbons. At a concentration of 100 A mu l per dish, isoamyl alcohol, isobutyric acid and isovaleric acid were able to completely inhibit the mycelial growth of A. alternata. This is the first report on using volatiles produced by M. odoratimimus T45 as biocontrol agents against A. alternata. The studies indicated M. odoratimimus T45 and volatile compounds isoamyl alcohol, isobutyric acid and isovaleric acid it produced could be potential biocontrol agents suitable for use against A. alternata.