The First Report of the Fungus Rhizoctonia solani as a Causal Agent of Root Rot and Seedling Death of Indian Siris, Albizia lebbek in Karbala Governorate, Iraq and its Biological and Chemical Control

This study was conducted with the aim of isolating and diagnosing the fungus causing root rot and seedling death of Albizia lebbek (Indian siris) In the gardens of the College of Agriculture, University of Karbala, and its pathogenicity was tested under laboratory and greenhouse conditions. Four isolates were identified phenotypically: Fusarium sp. (F1, F2), Alternaria sp. (A1) and Rhizoctonia solani (R1). Isolate R1 was significantly superior to other isolates in reducing the germination rate of red radish seeds on water agar, which reached 0% (100% inhibition) compared to the control treatment where seed germination was 100%. The results of the plastic pot experiment in the greenhouse also showed that the results were consistent with the laboratory experiment, where the R1 isolate was equally superior in reducing the germination rate of A. lebbek seeds. Molecular diagnosis showed that the most pathogenic isolate R1 belongs to the fungus Rhizoctonia solani and was deposited in the American GenBank under the accession number OQ102237. The results of the laboratory experiment also showed that the effectiveness of the fungus Trichoderma koningiopsis in combating the pathogenic fungus Rhizoctonia solani with an inhibition rate of 100%. The results also showed the ability of the B. velezensis bacterium to inhibit the growth of the pathogenic fungus isolate on the PDA culture medium, and its highest effect was at concentration 10-1 on the growth of the pathogenic fungus, as the inhibition rate reached 95.2% compared to the control treatment 0%. The Beltanol fungicide treatment demonstrated superior efficacy against the pathogenic fungus, achieving infection severity rates of 20.33 and 15.66%, respectively. This was followed by the R. solani + B. velezensis treatment, which recorded 22.33 and 16.33%, respectively. The latter treatment did not show a statistically significant difference from the R. solani + T. koningiopsis treatment in reducing disease severity. However, it exhibited a significant difference in lowering both the infection percentage and severity caused by R. solani, which were recorded at 24.66 and 17.66%, respectively. All these treatments significantly reduced infection percentage and severity compared to the R. solani alone treatment, which exhibited the highest infection rates of 76.8 and 55.66%, respectively, relative to the control treatment. Keywords: Albizia lebbek, Rhizoctonia solani, ITS-rDNA region.