Isolation, identification, and in vitro biological control of fungi causing root rot and seedling death of okra (Abelmoschus esculentus L.)

Abstract

Root rot and seedling death are among the most destructive diseases of okra (Abelmoschus esculentus L.) in central Iraq. This study isolated and identified the fungal pathogens associated with these symptoms on okra in Karbala Province and assessed their in vitro biological control using Trichoderma harzianum. Fungi were isolated from diseased roots and collapsed seedlings on PDA medium and presumptively identified by colony and microscopic morphology. Identification was confirmed by PCR amplification of the ITS1–ITS4 region of ribosomal DNA, followed by sequencing and BLAST comparison against the NCBI GenBank database. Two isolates were identified as Rhizoctonia solani and Fusarium solani and were deposited in GenBank as new Iraqi isolates under accession numbers PX850764.1 and PX850763.1, respectively. Pathogenicity tests on okra seed in Petri dishes showed that both isolates were highly virulent: seed germination was completely suppressed    (0.00 %) by R. solani and F. solani, compared with 100 % in the untreated control, and seed rot reached 100 % under inoculation with either pathogen. In dual-culture antagonism assays, T. harzianum (isolate T1) markedly inhibited the radial growth of both pathogens, with the highest inhibition rate (88.88 %) recorded against F. solani. These findings identify R. solani and F. solani as principal causal agents of root rot and seedling death of okra in Karbala Province and indicate that T. harzianum is a promising biocontrol agent against these pathogens under laboratory conditions