Use of microorganisms in controlling parasitic root weed Orobanche spp.

Parasitic root weed Orobanche spp. has already severely constrained the development of agriculture in many areas around the world and it is therefore urgent to develop effective control measures of Orobanche spp. As this parasitic root weed has a specific life cycle and is highly intimate to its host plants, it is difficult to develop an ideal control measure based on traditional practices. Up till now, there has been no measure to effectively control Orobanche spp. to make it completely harmless to host plants and easily applicable at large field scale. Among the control measures available, the use of micro-organisms has increased concerns. In this paper, national and global efforts to control Orobanche spp. by the use of micro-organisms and the mechanisms of the control measures are summarized. Until now, research on biocontrol of Orobanche spp. by the use of micro-organisms has focused on pathogens of Orobanche spp., such as Fusarium spp. and symbiotic bacteria (such as Rhizobium spp.) of host plants. The mechanisms of the use of micro-organisms to control Orobanche spp. have involved in two ways:one is to secrete metabolites that directly inhibited the germination and growth of Orobanche spp. or to indirectly affect the germination of Orobanche spp. by the degradation of the chemical compounds which stimulated the germination of Orobanche spp.; another way is to indirectly affect the parasitic behavior and growth of Orobanche spp. by enhancing host plant resistance against Orobanche spp. Furthermore, the possibility and research advances by the use of soil-borne antagonistic micro-organisms against soil-borne plant pathogens in controlling weedy Orobanche spp. have been discussed. Both soil-borne plant pathogens and Orobanche spp. first infected plant roots underground and then damaged normal growth of the plants. Resistances of plants to soil-borne plant diseases were similar to those of Orobanche spp. Thus, micro-organisms that isolated from soils and controlled soil-borne plant diseases may also have the potential to control parasitic root weed Orobanche spp. We screened out one actinomycete strain (Streptomyces enissocaesilis Sveshnikova) and one actinomycete strain (Streptomyces pactum Bhuyan B.K.) from soil-borne mic-organisms that against soil-borne plant diseases. These two strains effectively controlled O. cumana Wallr. and O. aegyptiaca Pers., respectively, in pot experiments. The application of S. pactum inoculum in field experiment reduced the epigaeous number of O. aegyptiaca and increased the yield of tomato, simultaneously. In conclusion, the use of micro-organisms to control parasitic root weed Orobanche spp. is an effective measure.