Biocontrol of Pythium aphanidermatum -induced damping-off disease in cucumber by the native endophytic bacterium Alcaligenes faecalis P1(1.4)

Cucumber is an important crop, cultivated in greenhouses in Oman due to the hot desert climate of the country. Damping-off disease, predominantly caused by the pathogen Pythium aphanidermatum , remains a major threat globally, drastically reducing cucumber yields and presenting significant economic challenges. Plant endophytic bacteria play a crucial role in controlling plant diseases. This study uniquely explores the novel application of a native endophytic bacterium, Alcaligenes faecalis P1(1.4), isolated from the roots of the indigenous desert tree Prosopis cineraria , as a potent biocontrol agent against cucumber damping-off. Scanning electron microscopy (SEM) indicated the presence of morphological abnormalities in the hyphae of P. aphanidermatum at the zone of inhibition in dual culture assays. Further investigation revealed that volatile organic compounds (VOCs) of A. faecalis P1(1.4) effectively suppressed the spread of P. aphanidermatum in the double-sealed base plates assay. Moreover, the bacterium exhibited significant plant growth-promoting potential, specifically in seed germination, seedling vigor, and a remarkable increase in root length. Additionally, gas chromatography mass spectrometry (GC/MS) analysis indicated a high proportion of Indole (46.32%) in the VOCs spectrum. Indole the precursor of Indole-3-acetic acid (IAA), which is indeed the main growth hormone in plants, play a crucial role in cell elongation, apical dominance, root initiation and development and tropic responses. In greenhouse trials, the bacterium effectively reduced the disease severity up to 30%. This study provided a baseline for the application of Alcaligenes faecalis in controlling damping-off disease of cucumber.