Integration of Trichoderma asperellum the bacteria Serratia marcescens and Sphingobacterium zeae and eucalyptus extract for the control of okra root rot caused by Rhizoctonia solani

Abstract

This study aimed to identify the causal agents of okra root rot and evaluate the efficacy of certain biocontrol agents and plant extracts in suppressing the disease caused by Rhizoctonia solani. A field survey revealed the disease's presence across all studied fields in Babylon Governorate, with an incidence rate of 17–81% and a severity of 10–44%. Ninety-eight fungal isolates were recovered; R. solani was the most frequent 72 isolates, followed by Fusarium solani 15 isolates and Macrophomina phaseolina 11 isolates, with the R. solani isolate Rs6 demonstrating the highest virulence. The bacteria Serratia marcescens and Sphingobacterium zeae were molecularly identified, showing 100% and 99.7% sequence identity, respectively. Laboratory assays showed 100% inhibition by Trichoderma asperellum and S. marcescens, and 99.67% by S. zeae, while inhibition by eucalyptus extract reached 85.22% for the aqueous extract and 85.78% for the ethanolic extract at a concentration of 4 g/100 ml.In greenhouse trials, biocontrol treatments reduced disease severity and improved plant growth compared to infected plants; the treatment combining aqueous eucalyptus extract with T. asperellum resulted in the lowest disease severity 5.24%, whereas the combination of T. asperellum and S. marcescens yielded the highest values for most growth parameters. These results confirm the potential of integrating biocontrol agents with eucalyptus extract within integrated management programs for okra root rot caused by R. solani.