Isolation, identification, and activity of mycoherbicidal pathogens from juvenile broomrape plants

Although there are reports of isolation of mycoherbicidal pathogens attacki ng the widespread broom-rapes (Orobanche spp,) that parasitize legumes and vegetables, none is in use or available. This is despite there being no goo d method of controlling broomrapes in most crops other than by preplant fum igation with methyl bromide. Two highly parasitic fungi, Fusarium arthrospo rioides strain E4a (CNCM I-164) and F. oxysporum strain E1d (CNCM 1-1622), were isolated from nearly 100 organisms found on diseased, juvenile, emergi ng Orobanche flower stalks. A near-axenic polyethylene envelope system for culturing broomrape on tomato roots was used to ascertain pathogenicity of these strains. Both organisms fulfilled Koch's postulates for being primary pathogens. Their DNAs were analyzed and fingerprinted by restriction fragm ent length polymorphism and random amplified polymorphic DNA, showing that they are indeed different from each other and from many other Fusarium spp, and other formae speciales of F, oxyspomm including a strain that attacks O, cumana on sunflowers. Both strains infect O. aegyptiaca, O. cernua, and O. ramosa, but not O. cumana. They did not infect any of the vegetable and legume crops tested and thus seem specific to Orobanche. Tomato plant roots dipped into a fungal spore and mycelial suspension and planted in broomrap e-infested soil were protected for 6 weeks, as were tomato transplants in p ot experiments. About 90% control was also achieved by posttransplant soil drench with fungal suspensions in pot experiments. These pathogens may be e ffective as seed, transplant, or soil-drench treatments of high-value veget able and other crops. (C) 2001 Academic Press.