Isolation and Evaluation of Indigenous Fungal and Bacterial Isolates as Potential Bioagents Against Broomrape (Orobanche cernua) in Jordan

Isolation of microorganisms antagonistic to Orobanche was attempted using Orobanche plants and rhizosphere soil of Orobanche-infected crops in Jordan. Six fungi (Cephalosporium sp., Cylindrocladium sp., Epicoccum sp., Fusarium sp., F. oxysporum and F. solani) were isolated. Of these, isolates that belonged to the Fusarium genus were the most common (more than 80% of isolates). Pathogenicity tests of these isolates on O. cernua stems indicated that Cylindrocladium sp., Fusarium sp., F. oxysporum and F. solani were most effective. These organisms caused total necrosis of inoculated stem tissues. Epicoccum sp. caused moderate damage (60% severity); while Cephalosporium sp. was least effective causing only localized necrosis. Only Cylindrocladium and Fusarium sp. isolates infected Orobanche inflorescence, causing maceration of these tissues as well as total destruction of seeds. Several bacterial isolates, including Pseudomonas and Actinomyces sp., were also recovered from soil sampled from different agricultural fields. These bacteria were found to be pathogenic in varying degrees to Orobanche stems and inflorescence. A previously isolated Streptomyces sp., R9, was also assessed in this study for its ability to inhibit O. cernua seed germination. Results showed a germination rate of 1-1.4% and 2.9-3.8% for R9 crude and lyophilized culture filtrates, respectively. In comparison, seed germination rates were 33.8-42.2% and 6.2-9.1% for water and culture medium controls, respectively. This study indicates that a wide range of microorganisms could be employed as antagonists to Orobanche. Their use as potential bioherbicides to control Orobanche appears promising.