Fungal infections cause heavy losses to plants and are usually controlled using common fungicides, which cause environmental pollution and affect health. Thus, the study aims to isolate and identify the highly active chitinolytic endophytic actinomycetes from healthy cucumber plants and evaluate their biological activity against soil-borne pathogenic fungi as alternative eco-friendly fungicides. Thirty-four actinomycetes isolates were screened for chitinase activity, antifungal activity against Fusarium solani and Rhizoctonia solani, and their ability to produce siderophores, ammonia, and hydrogen cyanide. The best performance Streptomyces isolates, ER15 and ES55, showed a reduced fungal mycelium at 88 and 86%, respectively. The most efficient isolates, ER15 and ES55, were identified using biochemical and molecular techniques. According to the 16 S rRNA gene, ER15 was identified as Streptomyces enissocaesilis, and ES55 was identified as Streptomyces rochei. Scanning electron microscopy showed that S. enissocaesilis and S. rochei degrade the fungal mycelia. A greenhouse experiment evaluated the effectiveness of endophytic strains S. enissocaesilis, and S. rochei, as plant resistance inducers against F. solani and R. solani infected cucumber. The study found that inoculating cucumber with Streptomyces strains colonized cucumber roots endophytically, increased the survival rates to 98–100%, suppressed pathogenic activities, and amplified microbial activities such as increasing chitinase by 6 fold, dehydrogenase (DHA) by 5.5 fold, peroxidase, and polyphenol oxidase compared to control. Thus, improved NPK uptake in cucumber shoots improved growth performance and yield. It can be concluded that Streptomyces enissocaesilis and S. rochei are promising biological control agents against soil-borne pathogens as eco-friendly fungicides. Also, these endophytic strains are beneficial for crop production in nutrient-poor soils. |
