Unravelling the mechanisms of biocontrol in the tomato-fusarium oxysporum f. sp. lycopersici-Brevibacillus brevis interaction

• Main Author: Bouqellah, Nahla Alsayd
• Published: University of Aberdeen 2010
• Subjects: 579.5; Phytopathogenic microorganisms : Tomatoes
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540491

The present study was carried out to determine the mechanisms of biological control of <i>Fusarium oxysporum </i>f.sp. <i>lycopersici </i>by <i>Brevibacillus brevis </i>under greenhouse conditions.  Dual culture techniques demonstrated that <i>B. brevis </i>is capable of inhibiting the growth of fungal mycelium and germination of fungal spores due to excretion of antifungal metabolite(s) into the substrate, while reciprocal <i>in vitro </i>tests demonstrated no impacts of <i>F. oxysporum </i>f.sp. <i>lycopersici </i>metabolites on viability of <i>B. brevis.  </i>When live tomato roots were introduced into microcosms containing <i>F. oxysporum </i>f.sp. <i>lycopersici </i>and <i>B. brevis,</i> however, the fungal pathogen showed a competitive advantage over controls without <i>B. brevis </i>in terms of host colonisation.  The steroidal glycoalkaloid α-tomatine, extracted from tomato, inhibited conidiospore germination and growth of <i>Fusarium oxysporum </i>f.sp <i>lycopersici,</i> but had no detectable effects on viability of <i>B. brevis.</i> The effects of preinoculation of tomato (<i>Lycopersicon esculentum, </i>variety Moneymaker) roots with <i>B. brevis </i>in presence and absence of <i>F. oxysporum </i>f.sp. <i>lycopersici</i> on the induction of defence enzymes was examined.  Varying activities of phenylalanine ammonia lyase (PAL), peroxidases (POX) and chitinases were observed in different treatments at different time points, suggesting that the genes encoding these enzymes play a role in defence against Fusarium wilt.  Although no direct evidence of induction of these enzymes by <i>B. brevis </i>alone was observed, plants which were preinoculated with the bacterium showed enhanced induction of PAL, POX and chitinases at different time points following subsequent inoculation with <i>F. oxysporum </i>f.sp. <i>lycopersici.</i> Complex interactions between the tomato plant, <i>B. brevis </i>and <i>F. oxysporum </i>f.sp. <i>lycopersici </i>occurred and changed with time, as indicated by variations in metabolites at different sampling times.