Bioactive metabolites from tomato endophytic fungi with antibacterial activity against tomato bacterial spot disease

Endophytic fungi are potential antimicrobial agents that play an important role in improving plant growth. Endophytic fungi from healthy tomato plants have been evaluated for their potential antibacterial activity against Xanthomonas vesicatoria causing bacteria spot disease of tomato Thirty-eight different endophytic fungal isolates were isolated, and their extracts were screened for antibacterial activity using the well diffusion method. Three isolates showed strong antibacterial activity, which were molecularly identified as Diaporthe phaseolorum (USt1), Aspergillus fumigatus (USt2) and Aspergillus versicolor (USt3), respectively. Comparison of the components of the extracts between three isolates was made using a gas chromatography-mass spectrometry. Thirty eight compounds were found in A. fumigatus, thirty six compounds in D. phaseolorum and fourty two compounds were found in A. versicolor. The most prevalent compounds were acetol, hexanoic acid and acetic acid in all three fungi. Hexanoic acid (39.52%), acetic acid (8.95%) and acetol (8.10%), were found in A. fumigatus. However, the D. phaseolorum extract contained mainly hexanoic acid (42.35%) and acetic acid (11.89%) and acetol (9.52%), while A. versicolor contained hexanoic acid (34.44%), acetic acid (13.44%) and acetol (10.61%). Our results suggest that the three active endophytic fungi isolates provide a basis for the identification of new bioactive compounds, and for the effective biocontrol of bacterial spot of tomato.