Management of Charcoal Rot (Macrophomina phaseolina) Infection in Geranium (Pelargonium graveolens L) Using Biocontrol Agents and Essential Oils

Abstract

IN a trial to control charcoal rot disease (Macrophomina phaseolina) in geranium using ecofriendly strategies, antagonistic microbes and essential oils were used. the treatments included three bacterial isolates, Bacillus polymixa, B. circulance, B. Subtilis and one fungus Tricoderma harzianum in addition to five essential oils, (Syzygium aromaticum(cloves), Ocimum basilicum L. (basil), Mentha spicata (Spearmint), Majorana hortensis Moench (Marjoram) and Mentha piperita L. (Peppermint). The in vitro antagonistic effect of microbial isolates and essential oils against M. phaseolina isolated from infected geranium was estimated in Petri plats, The essential oils were used in three concentrations 1, 3 and 5 microliter/plate. the most promising treatments were applied in an artificially infested geranium in a greenhouse experiment along two growing seasons of 2017, 2018. The in vitro screening step indicated that among the treatments, Bacillus subtilis and Trichoderma harzianum were the most promising microbes against the fungal pathogen under study using the dual culture technique. On the other hand, Peppermint oil recorded the highest reduction in radial growth of pathogen followed by Basil oil while Marjoram oil had no effect on the growth of pathogen. The green house experiment showed that, most treatments were efficient in pathogenicity reduction but the microbial treatment exhibited an advantage over essential oil where growth and yield parameters were sharply improved. The maximum enhancement was attained at T5 treatment (infested + dipping for 30 min before planting and spraying with T. harzianum after every cutting process) at all cuts during 2017 and 2018 seasons. Also, T. harzianum increased oil %, which recorded 0.45, 0.30 and 0.38% at 2017 season and 0.47, 0.31 and 0.39% at 2018 season for 1st, 2nd and 3rd cut respectively. Therefore, microbial and essential oil treatments not only reduced the fungal infection but also enhanced vegetative growth of geranium plants.