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

Abstract

The present study was carried out to determine the mechanisms of biological control of Fusarium oxysporum f.sp. lycopersici by Brevibacillus brevis under greenhouse conditions.  Dual culture techniques demonstrated that B. brevis 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 in vitro tests demonstrated no impacts of F. oxysporum f.sp. lycopersici metabolites on viability of B. brevis.  When live tomato roots were introduced into microcosms containing F. oxysporum f.sp. lycopersici and B. brevis, however, the fungal pathogen showed a competitive advantage over controls without B. brevis in terms of host colonisation.  The steroidal glycoalkaloid α-tomatine, extracted from tomato, inhibited conidiospore germination and growth of Fusarium oxysporum f.sp lycopersici, but had no detectable effects on viability of B. brevis. The effects of preinoculation of tomato (Lycopersicon esculentum, variety Moneymaker) roots with B. brevis in presence and absence of F. oxysporum f.sp. lycopersici 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 B. brevis 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 F. oxysporum f.sp. lycopersici. Complex interactions between the tomato plant, B. brevis and F. oxysporum f.sp. lycopersici occurred and changed with time, as indicated by variations in metabolites at different sampling times.EThOS - Electronic Theses Online ServiceGBUnited Kingdo