Morphological and molecular Identification of the causal agent of Fusarium wilt disease on Okra and Control it using some Trichoderma B io-agents

The study included a field survey to determine the prevalence of fusarium wilt disease on okra in different regions of Najaf, Diwaniyah, and Babylon. It was found that the infection rate in the areas under study was between 18 and 73%. Results of isolation and phenotypic characteristics of wilt-infected okra plants recorded six fungal isolates belonging to Fusarium spp. Also, three isolates of Trichoderma spp. were isolated from the soil surrounding the roots of intact okra plants. The efficiency of biological fungus isolates was studied in addition to a fourth isolate which previously identified as Trichoderma longibrachiatum against the pathogenic fungus. The isolated fungi varied in some phenotypic characteristics regarding color variation and growth rate. The results of testing the pathogenicity of the pathogenic Fusarium spp. isolates on okra in a pot experiment showed that isolate F2 (Isolate Abbasia) was the most pathogenic, used in subsequent studies. The results of the molecular diagnosis using Polymerase chain reaction (PCR) showed that the F2 isolate belongs to the fungus Fusarium solani, which was registered in the Gen Bank under the number OQ729824 Isolate T3 of the biological fungus Trichoderma spp., belonging to the fungus Trichoderma harzianum, was registered with the accession number OQ729823. The isolate T3 T. harzianum showed high antibody efficiency against F. solani on P.D.A culture media with an inhibition rate of 82.8% in the test of fungal isolates' filters. Biologically, isolate T3 gave the highest inhibition in the radial growth rate of F. solani compared to other isolates T1, T2, and T4 Trichoderma spp. In the plastic pot experiment, the isolate of the biologically resistant fungus T. harzianum T3 led to the highest growth indicators of okra plants compared to other biological isolates and worked to protect okra plants from fusarium wilt disease, as no symptoms of the disease appeared on okra plants in the treatment of this isolate compared to that. By treating the pathogenic fungus F. solani, the infection intensity reached 60%.