Effect of Three Orobanche spp. Extracts on Some Local Phytopathogens, Agrobacterium and Erwinia


Abstract: Tissues of the spikes of Orobanche spp. contain phenols and mannitol pathways, and it seems that it is very resistant, or may be immune, to bacterial infection. Therefore extracts of 3 Orobanche species, O. cernua, O. crenata, and O. egyptiaca, were evaluated for their antibacterial activity against local isolates of crown gall (Agrobacterium) and soft rot (Erwinia) phytopathogens. Extract of O. cernua showed the highest activity against both pathogens with clear inhibition zones of 8-24 mm and 12-16 mm in diameters, respectively. When the inhibitory action of 100 mg/ml concentration of the 3 Orobanche species extract on local isolates of Erwinia was compared with each other, data revealed the ability of O. cernua to exhibit more activity than the others and disability of O. egyptiaca to inhibit any of these pathogens. Dilution experiments showed that the minimum inhibitory concentration (MIC) of O. cernua extract was as follows: local isolates of Agrobacterium, No. A9_1, A201 and A20_4-12,500 µg/ml and for all Erwinia isolates-27,800 µg/ml. However, MIC of O. crenata extract was 63,000 µg/ml for all Erwinia isolates. Results showed that the MIC of 12,500 µg/ml of O. cernua is equal to the effect of Streptomycin (10 µg /ml) activity against Agrobacterium isolates No. A9_1, A20_1 and A20_4, Ofloxacin (5 µg/ml) against Agrobacterium isolates No. A9_1 and A20_1, Norfloxacin (10 µg/ml) against Agrobacterium isolate No. A20_4 and Cefotaxime (30 µg/ml) against Agrobacterium isolate No. A9_5. However, the MIC of O. cernua and O. crenata extract to inhibit all Erwinia isolates is 27,800 and 63,000 µg/ml, which is equivalent to the effect of Tobromycin (10 µg/ml). It is concluded that Orobanche tissue could be a potential source for antiphytopathogenic bacterial agents.

Keywords: Bioactivity, Orobanche, crown gall, soft rot

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