Fusarium spp. suppress germination and parasitic establishment of bean and hemp broomrapes
Thirty-nine Fusarium isolates were obtained from newly emerged infected bean broomrape (Orobanche crenata) and hemp broomrape (O. ramosa) collected from infested fields of faba bean (Vicia faba) and tomato (Lycopersicon esculentum) respectively, in two governorates located south of Giza, Egypt. All Fusarium isolates were identified to species level and the effect of their culture filtrates on the germination of seeds from the two Orobanche species was tested in vitro. The inhibition of seed germination differed between the tested Fusarium isolates, depending on the plant part from which they were isolated, with isolates from the shoots of Orobanche inhibiting seed germination more than isolates from the inflorescences. The culture filtrates of Fusarium species from O. crenata were more toxic to the seeds of both Orobanche species than the Fusarium filtrates from O. ramosa. Seeds of O. crenata were more resistant to Fusarium culture filtrates than seeds of O. ramosa. The highest inhibition of Orobanche seed germination was achieved by six Fusarium isolates, one of which was identified as F. oxysporum, one as F. equiseti, whilst the other four were all F. compactum. Aqueous mixtures of mycelia and conidia of all the Fusarium isolates were directly sprayed on O. ramosa tubercles attached to the roots of tomato plants grown in transparent plastic bags, and were also used to infest soil in pots seeded with both faba bean and O. crenata. Two of the four F. compactum isolates (22 and 29) were significantly more pathogenic against O. crenata and O. ramosa, respectively, than the other Fusarium isolates tested in the pots and plastic bags. The study clearly shows the potential of biocontrol agents originating in one Orobanche sp. (e.g. O. crenata) to control another Orobanche sp. (e.g. O. ramosa), as many Fusarium isolates deriving from O. crenata were found to be more pathogenic to O. ramosa seeds than the isolates from O. ramosa themselves. This may widen the host range of these fungal pathogens, with the use of isolates from one Orobanche species effective against other species as well.
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