Bioprotection mechanisms of pea plant by Rhizobium leguminosarum against Orobanche crenata

Broomrapes are achlorophyl holoparasites of many important economic dicotyledonous crops. As weeds, they significantly decrease crop yields. Orobanche crenata is an important constraint to Mediterranean area pea (Pisum sativum L.) cultivation, as no resistant variety is available. Our previous researches showed that several Rhizobium leguminosarum strains decrease damages caused by O. crenata in pea. The aim of this work was to characterize the resistance induced by R. leguminosarum against broomrape. Higher concentrations of phenolic compounds and lignin were observed in pea roots inoculated with Rhizobia, in comparison to non inoculated. Polyphenol oxidase and peroxidase activities were significantly higher in inoculated plants  as compared to non-inoculated ones. These results suggest that the mechanisms of induced resistance by Rhizobia against O. crenata involve an elevated induction of the phenylpropanoid pathway, conferring mechanical and chemical barriers confronting the invading parasite.   Key words: Broomrape, rhizobium, biocontrol, defense related enzymes, PPO, POX, phenols, lignin. .