Cultural filtrates of certain microbial isolates as an alternative to powdery mildew chemical control in cucumbers

TL;DR: This work aimed to isolate, identify, and test endophytic fungi for their antagonistic properties against the three mentioned diseases, showing that some of the pathogens were controlled in terms of disease incidence.

Abstract: The aim of this study was to assess in vitro , the antifungal activity and characterize the chemical constituents of the essential oils of Azadirachta indica (neem) and Lavandula angustifolia (lavender). The essential oils of A. indica and L. angustifolia plants were tested against several isolates of pathogenic fungal genera causing root rot disease of ginseng. Agar plate assay indicated that lavender oil at 10% exhibited the highest inhibition index of (86.0±0.7%) against Sclerotinia nivalis mycelial growth. Neem and lavender oils at 5% v/v showed inhibition index against Alternaria panax (72.9±2.1 and 45.0±1%, respectively). Lavender oil at 5% (v/v) inhibited growth of S. nivalis (83.1±0.2%) and Cylindrocarpon destructans (49.2±1%). The gas chromatography-mass spectrometry (GC-MS) analysis showed that the major constituents of neem oil were fatty acids (94.8%). However, sesquiterpenes were the dominant constituents of the lavender oil (57.6%). The antifungal indices demonstrated in this study are a clear evidence of the potentiality of neem and lavender essential oils to control plant diseases caused by phytopathogenic fungi. The aim of this work was to evaluate the effect of changing the shake flask for a stirred-tank bench bioreactor on the performance of Thevetia peruviana cultures. Maximum cell growth of 18.59 and 8.46 g DW/L for shake flask and bench bioreactor at day 14 was obtained, respectively. The end of the exponential growth phase in shake flask was correlated with total sugar consumption, while this behavior was not observed in bench bioreactor. Preferential uptake of glucose over fructose was observed in both systems. Cell morphology was similar for both systems during culture time, exhibiting individual cells with cylindrical and elongated shape at day 0 and some aggregates with rounded cells at day 14. Polyphenol production was not affected by the system configuration and scale. Intra and extracellular antioxidant activity were directly related with phenol production in both systems. Guaiacol peroxidase activity (GPX) went from 1.87 to 7.97 µM/min/mg protein in shake flask and it correlated with low reactive oxygen species (ROS) production. This is an indication of a positive enzymatic cell response for culture in shake flask mediated by GPX. In contrast, the conditions in the bench bioreactor generated a higher stress environment, increasing ROS production without activating enzymatic or non-enzymatic responses led by guaiacol and phenolic compounds, respectively. In conclusion, bench stirred-tank bioreactor scale affects biomass production and sugars uptake negatively.