Endophytic Alternaria alternata Culture-Derived Elicitor Promotes Growth and Antibacterial Activity in Kalanchoe...

Kalanchoe spp. are valued for their antioxidant and antimicrobial properties, primarily attributed to bioactive compounds like phenolic acids. Endophytic fungi can stimulate compound production, growth, and microbial control in tissue culture. This study aims to assess the presence of selected phenolic compounds, the growth-promoting effects, and antibacterial activity of in vitro-cultivated Kalanchoe laetivirens plantlets supplemented with a powdered fungal elicitor derived from a nonliving culture. The elicitor was obtained from an antioxidant-producing endophytic fungus, previously isolated from K. laetivirens and cultured on Murashige-Skoog medium. Among 16 endophytic fungi tested via DPPH• (2,2-diphenyl-1-picrylhydrazyl) assay, Alternaria alternata (strain 16) showed the highest antioxidant activity. Identified through microscopic and ITS rDNA sequencing, this strain was cultured, powdered, and used as an elicitor in Murashige-Skoog medium for K. laetivirens explants. Extracts from elicited and nonelicited in vitro-cultivated plantlets and nonelicited in vivo-cultivated plantlets were analyzed by high-performance liquid chromatography for phenolic compounds and tested for antibacterial activity using the microdilution method. Ferulic acid was detected only in in vitro-cultivated plantlets, p-coumaric acid was present under all conditions, and other phenolic compounds were absent in all cases. Elicited in vitro plantlets showed the most potent antibacterial activity against Escherichia coli and Staphylococcus aureus. A 1:1 ratio of p-coumaric to ferulic acids resulted in the highest antibacterial efficacy, while an unbalanced 2:1 ratio reduced activity. These results suggest that in vitro elicitation improves growth and enhances the antibacterial profile of K. laetivirens, offering a strategy to enhance bioactive compound production and potentially manage systemic, especially nonculturable, phytopathogens.