Influence of glyphosate on amino acid composition of Egyptian broomrape [Orobanche aegyptiaca (Pers.)] and selected hosts

The parasitic plant broomrape is entirely dependent on its host for reduced carbon and nitrogen and is also susceptible to inhibition by glyphosate th at is translocated to the parasite through a host. Studies were conducted t o examine the effect of broomrape parasitism on amino acid concentrations o f two hosts: common vetch that is tolerant of low levels of glyphosate and oilseed rape that has been genetically engineered for glyphosate resistance . The influence of glyphosate on the amino acid content of broomrape and th e two hosts was also examined. Amino acid concentrations in leaves and root s of parasitized common vetch plants were generally similar to those of the corresponding tissues of nonparasitized plants, Amino acid concentrations in broomrape were lower than those of the parasitized common vetch root. Fo r common vetch, glyphosate applied at rates that selectively inhibited broo mrape growth did not alter individual amino acid concentrations in the leav es, but generally increased amino acid levels at 0.18 kg ha(-1). Glyphosate application also increased the amino acid concentrations, with the excepti on of arginine, of broomrape growing on common vetch and did not generally influence concentrations in leaves or roots of common vetch. In oilseed rap e, parasitization by broomrape generally led to higher amino acid concentra tions in leaves but lower concentrations in roots of parasitized plants. Br oomrape had higher amino acid concentrations than roots of the parasitized oilseed rape. Glyphosate applied at 0.25 and 0.5 kg ha-l generally increase d the amino acid concentrations in oilseed rape leaves, but the 0.75 kg ha( -1) application caused the amino acid concentrations to decrease compared t o those of untreated plants. In oilseed rape root the general trend was an increase in the concentration of amino acids at the two highest rates of gl yphosate. Individual amino acid concentrations in broomrape attachment-a gr owing on oilseed rape were generally increased following glyphosate applica tion of 0.25 kg ha(-1). These results indicate that law rates of glyphosate alter amino acid profiles in,both host and broomrape and raise questions a bout the regulation of amino acid metabolism in the parasite.