Unrefined corn oil was found to stimulate germination of C. truncatum spores .One method to achieve this has been to combine a bioherbicide with an herbicide to possibly produce either an additive, or synergistic effect on weed control.Use of an herbicide for possible synergistic interactions with a bioherbicide could be realized as generally occurring in two ways, i.e. , through direct action of the herbicide on its specific biochemical target site, or via secondary herbicidal effects that may weaken weed biochemical defenses against pathogen attack.However, many herbicides exhibit toxicity towards bioherbicides, caused by either the active ingredient and/or the various adjuvants, surfactants, etc. formulated in the commercial products. Combinations of glyphosate and several bioherbicides have resulted in additive or synergistic action on the control of weeds.

Synergistic interactions of the herbicide glyphosate and Myrothecium verrucaria on several weeds have been documented and C. truncatum combined with glyphosate interacted synergistically to control hemp sesbania . Glyphosate and the bioherbicide, Alternaria cassiae applied to sicklepod resulted in a synergistc interaction . Synergy of two bacterial plant pathogens with glufosinate was also demonstrated in greenhouse and field studies , but results of synergy studies of glufosinate and Pyricularia setariae were variable . Furthermore,some commercial glyphosate products are toxic to certain bioherbicides.The enzyme glutamine synthetase plays a pivotal role in nitrogen metabolism and is responsible for the condensation of ammonium ion and glutamate to produce glutamine. This metabolic reaction is vital for glutamine synthesis and for ammonia re-assimilation and detoxification in plants. Glufosinate,originally isolated from Streptomyces species as phosphinothricin, inhibits GS and causes toxic levels of ammonia to accumulate in plants.

Plant injury symptoms caused by glufosinate action develop more rapidly in light-grown plants than in dark-grown plants.In our early research with hemp sesbania seedlings treated with C. truncatum,an odor was noted during the late stages of the disease progression cycle .This was especially apparent when working with plants in small environmental cabinets, and it occurred when plants were treated under either continuous light or dark growth conditions. Because, 1) glufosinate can control hemp sesbania ,2) C. truncatum causes ammonia-like odors in hemp sesbania, and 3)bioherbicide interactions with herbicides may possibly result in beneficial additive or synergistic action for weed control, our working hypothesis for this project evolved into: “Does C. truncatum affect nitrogen metabolism in hemp sesbania through inhibition of GS ; and if so, it is possible that glufosinate and C. truncatum would act synergistically with respect to control of this weed”. Thus, our objectives were to test for these possible interactions by a series of growth, GS assay, and ammonia analysis experiments using hemp sesbania treated with C. truncatum, glufosinate, and their combination under controlled environmental conditions. C. truncatum treatment of hemp sesbania did not cause significant effects on GS activity until after 40 h, a time when hypocotyls lose their structural integrity during the initial stages of collapse .This effect has been previously described in another study .

At 64 h after treatment, the pathogen lowered GS activity by about 10%, but at 88 h, GS was inhibited by ~65%. Glufosinate and the glufosinate plus C. truncatum treatments both caused substantial inhibition of GS throughout the 16 to 88 h period.However, GS activity in the herbicide/pathogen combination treatment was slightly higher than the glufosinate alone treatment at most time points.Electrophoretic separation of the hemp sesbania proteins after the various treatments offered the chance to visually localize GS activity on the gels and to qualitatively compare the activity and mobility of GS with that of other proteins-4). Figure 4 depicts a color image of GS activity as affected by the various treatments. Activity was present in the 0-time control, the 30-hcontrol and in the C. truncatum-treated hypocotyls, 30 h after treatment. However,no activity was present in the glufosinate- or in the glufosinate plus C.truncatum-treated tissue, which indicated the enzyme was inhibited. As expected,no other proteins exhibited activity and Figure 4). These red-brown color bands that fade rapidly, were subsequently imaged, to corroborate results. Amatching gel, stained with protein stain showed the location of the GS protein , as well as the profiles of other proteins from the treatments. Generally, ammonia levels in hemp sesbania tissues under these various treatments were inversely correlated with the GS activity . The untreated control tissues contained much lower ammonia levels at 24, 64, and 88h after treatment than the C. truncatum, glufosinate or the combination of the herbicide and bioherbicide treatments. C. truncatum alone caused elevated ammonia levels only at 64 and 88 h after treatment, and this is during tissue collapse.