Evaluation of gamma irradiation effect and Pseudomonas flourescens against Penicillium expansum

Antagonistic effect of Pseudomonas fluorescens and influence of gamma irradiation on the development of Penicillium expansum, the causal agent of postharvest disease on apple fruit was studied. P. fluorescens was originally isolated from rhizosphere of the apple trees. Suspension of P. fluorescens and P. expansum were mixed in test tubes in proportions of 1:5, 2:5, 3:5 and 4:5 (V/V). The inhibitory effect depended on the proportion of the bacterium to the fungus in the mixture. The best inhibition was observed after 48 h at the ratio of 3:5. Gamma irradiation above 3 KGy completely inhibited mycelial growth, while the highest dose around 600 Gy mostly killed P. expansum spores. Our experiment demonstrates that the combination of gamma irradiation and P. fluorescens was more effective in reducing P. expansum growth, than either treatment alone and that the integration of irradiation and antagonist treatments can be more effective. The results of this study show that improved control by irradiation at labeled dose in combination with antagonist could allow direct incorporation of the biocontrol agent. Thus, the combination of the P. fluorescens with gamma irradiation showed an impressive effect on increasing applied range of irradiation for postharvest control by decreasing of dose rate.