Aromatic Amino Acids Partially Alleviated Glyphosate Induced Effects on Metabolites and Growth in Faba Bean with a More Phytotoxicity in Orobanche crenata Parasite

The holoparasite Orobanche crenata is considered the most damaging pathogens on the faba bean grown in the Mediterranean region. Sub-lethal dose of glyphosate was used for controlling O. crenata, but it caused injury effects on faba bean growth. Glyphosate inhibits the shikimic pathway of the synthesis aromatic amino acids (AAAs), phenylalanine, tyrosine and tryptophan. Greenhouse experiment was conducted using infested pots with O. crenata to explore the possibility of coexposure AAAs with glyphosate to alleviate glyphosate effects on faba bean and determine their effects on the parasite. Moreover, changes in the metabolites related to shikimic pathway were examined in faba bean leaves, 3 and 7 days after treatments. Application of twice sprays with glyphosate at 170 or 340 g ai ha on faba bean was effective in controlling O. crenata infestation. Co-exposure AAAs (0.5 and 1 mM) with glyphosate allowed to partially mitigating the detrimental effects of the herbicide on faba bean growth. Combined treatments produced more sever effects on O. crenata parasite and completely inhibited O. crenata parasite by 120 days from sowing. Glyphosate induced differential effects on amino acids composition, endogenous free AAAs and protein content in faba bean leaves. Moreover, it increased shikimic acid content accompanied by decreases in phenolic contents and antioxidant activity. Level of these compounds was partially mitigate by co-applied glyphosate with AAAs, proposing a potential role of AAAs in increasing tolerance of the host plant by ameliorating the glyphosate induced effects on metabolites related to shikimic acid pathway.