Application of a Combination of Salicylic Acid and Bacillus subtilis to Control Cucumber Root and Stem Rot, Caused by Fusarium oxysporum f. sp. radicis-cucumerinum, and Evaluation of Phenylalanine Ammonia Lyase Activity

Some possible effects of exogenous application of Salicylic Acid (SA) and Bacillus subtilis on infection potential of root and stem rot disease and on induction of resistance against this pathogen were investigated in laboratory and as well under greenhouse conditions. In vitro, the effectiveness of SA concentrations (2-8mM) on growth of B. subtilis was observed as negative, while SA application completely inhibited the mycelial development of F. oxysporum f. sp. radicis-cucumerinum at concentrations exceeding 5mM. In pot experiments, application of SA (3, 5 and 7 mM) and B. subtilis post or/ and prior to inoculation with the pathogen demonestrated that disease index was reduced in cucumber plants treated by SA as a plant defense elicitor and inoculated with B. subtilis as a biocontrol agent, prior to fungal infection causing increase in some growth factors as compared with the infected control. Application of 7 mM of SA (foliar spray) and B. subtilis (soil drench), prior to fungal infection reduced the extent of fungal infection and induced plant growth as compared with control and with other treatments. An evaluation of phenylalanine ammonia lyase activity showed that, combined application of SA and B. subtilis significantly increased the activity of this enzyme as compared with SA and B. subtilis application alone and with control. Maximum level of phenylalanine ammonia lyase activity was observed on the 6th day after elicitor's application. In summary, results suggest that application of SA as a chemical elicitor and B. subtilis as a biocontrol agent plus plant growth promoter, can be a useful and promising measure for a control of such phytopathogens as F. oxysporum f. sp. radicis-cucumerinum.