Rhizospheric bacteria for use in preventing Fusarium wilt and crown root rot of tomato under natural field conditions

Biocontrol, an alternative to chemical control against plant pathogens, may also improve plant health and enhance fruit yield. Tomato production in open fields or greenhouses is constrained by the pathogens <i>Fusarium oxysporum</i> f. sp. <i>lycopersici</i> race 3 (<i>Fol</i> R3) and <i>F. oxysporum</i> f. sp. <i>radicis-lycopersici</i> (<i>Forl</i>). In this work, we studied the biocontrol effect of the antagonistic bacteria <i>Acinetobacter calcoaceticus Ac</i>DB3, <i>Bacillus thuringiensis Bt</i>MB9, <i>B. subtilis Bs</i>TA16, and <i>B. amyloliquefaciens Ba</i>MA26 in field trials with four tomato hybrids over two consecutive growing seasons (2019–2020 and 2020–2021). The effect of these bacteria on plant growth was also evaluated. The presence of <i>F. oxysporum</i> in field soil and/or infected plants was confirmed microbiologically. All four bacterial strains significantly suppressed the severity of Fusarium crown and root rot of tomato (FCRRT) and Fusarium wilt symptoms, as well as increased tomato yield under field conditions. Among the four strains, <i>B. subtilis Bs</i>TA16 showed the highest reduction in symptoms of Fusarium wilt (68%) and FCRRT (74%). To the best of our knowledge, this is the first report of biological control agents (BCAs) exerting antagonistic activity against both FCRRT caused by <i>Forl</i> and Fusarium wilt caused by <i>Fol</i> in tomato under field conditions.