use of endophytic bacteria naturally associated with cestrum nocturnum for fusarium wilt biocontrol and enhancement of tomato growth. aydi-ben abdallah, r., mejdoub-trabelsi, b., nefzi, a., jabnoun-khiareddine, h., and daami-remadi, m. (tunisia)

Three endophytic bacterial isolates, recovered from Cestrum nocturnum (night blooming jasmine) leaves and stems, were assessed for their ability to suppress tomato Fusarium wilt disease, caused by Fusarium oxysporum f. sp. lycopersici (FOL), and to improve growth of tomato plants. Isolates tested had significantly decreased disease severity by 46.6-97.7% compared to FOL-inoculated and untreated control. The isolate C4 was found to be the most effective in decreasing leaf damage by 86.6% and the vascular browning extent by 97.7% relative to control. A significant increment by 39-41.6%, compared to pathogen-inoculated and untreated control, was recorded in tomato growth parameters. Moreover, the isolate C4 had significantly enhanced plant growth by 24.5-53.3% over pathogen-free and untreated control. This isolate C4 was morphologically and biochemically characterized and identified using 16S rDNA sequencing genes as Serratia sp. (KX197201). Screened in vitro for its antifungal activity against FOL, Serratia sp. C4 led to 19.52% decrease in pathogen radial growth and to the formation of an inhibition zone of 8.62 mm in diameter. Cell-free culture filtrate of Serratia sp. C4, supplemented to PDA medium at 20% (v/v), had lowered pathogen growth by 23% as compared to 21.7 and 9.2% recorded after heating at 50 and 100°C, respectively. Chloroform and n-butanol extracts from Serratia sp. C4, applied at 5% (v/v), displayed antifungal potential against FOL expressed as growth inhibition by 54.6-66.5% compared to untreated control which was higher than that achieved using two commercial pesticides i.e. Bavistin® (50% carbendazim, chemical fungicide) and Bactospeine® (16000UI/mg, Bacillus thuringiensis-based biopesticide). Serratia sp. C4 was found to be a chitinase-, pectinase-, and protease-producing agent and was able to produce the indole-3-acetic acid and to solubilize phosphate.