The in vitro inhibitory effect of the essential plant oils (EPOs) of citronella, clove, neem and thyme, the fungicides Acrobat-mancozeb, Dithane M-45, Kocide 2000, Previcure-N and Ridomil-Gold-Plus and the inducer resistance elicitors (IREs), Bion (BTH), chitosan, humic acid and salicylic acid, on sporangial germination of the fungus-like Pseudoperonospora cubensis (Berk. and Curt.) Rostov, the cause of cucumber downy mildew, was investigated in vitro. The role of the tested treatments in the management of cucumber downy mildew was, also, evaluated under greenhouse conditions. In addition, the effect of the combination of the sprayed, EPO (clove), the fungicide (Previcure-N) and IRE Bion (BTH) on the management of the disease under field conditions was investigated. The inhibitory effect of the tested EPOs, fungicides and IREs on sporangial germination of P. cubensis showed that they caused a significant reduction in the germinated sporangia compared with the control treatment. In this concern, the tested fungicides were the most efficient ones followed by the EPOs and then IREs. Management of the disease showed the same trend of in vitro assessment when they sprayed on artificially inoculated cucumber plants with the sporangial inoculum of the pathogen under greenhouse conditions. When cucumber plants were praying, under field conditions the combination of the sprayed, EPO (clove), the fungicide (Previcure-N) and IRE Bion (BTH) resulted in the superior treatment for managing the disease during 2021 and 2022 growing seasons at Giza governorate compared with plants sprayed with any of the EPO (clove), Previcure-fungicide and IRC (BTH) alone or in bi- combination, as well as control treatment.
Defense-related enzymes, i.e., chitinase, phenylalanine ammonia-lyase, peroxidase and polyphenol oxidase responsible were greatly increased in the leaves of all sprayed treatments by the tested materials compared with control treatment. In addition, plants sprayed with the tested IRC (BTH) followed by the EPO (clove) recorded the highest activity of all enzymes than plants sprayed with the tested Previcure-N fungicide. |
